Top Five Best Free Anti-spyware Software
Ad-Aware
Ad-Aware free version is the flagship of Lavasoft and is one of the top-notch applications when it comes to spyware and adware removal. This is the anti-spyware program for you in case you don’t want to spend money on effective spyware removal. Obviously the Professional version offers an array of special features that are not available in the free version. Also another difference is that the free version only performs manual scans as and when the user chooses, but the Professional version proactively shields the computer from spyware attacks.
Spybot S & D
Spybot S & D is another excellent anti-spyware software that is as effective as Ad-Aware when it comes to spyware and adware detection and removal. Although the application ensures effective and stable protection against spyware, the fact that it is a free software implies that there will be no support provided in case of problems or doubts.
Windows Defender
Windows Defender that was earlier known as Microsoft AntiSpyware, is an anti-spyware software product from Microsoft which is specifically designed to prevent, remove and quarantine spyware in the Microsoft Windows operating system. Currently it is a part of Windows Vista and is also available as a free download for Windows XP.
McAfee
McAfee a name that is more popular for their antivirus products is undoubtedly a major player in the world of computer and network security. McAfee Anti-Spyware is quite effective with spyware types like key loggers, remote-control programs and even browser hijacks. It is effective for password security as well. Again, what lacks in this software is the mediocre performance of the real-time monitoring of spyware attacks.
Spyware Guard
This is an application by Javacool Software, which is available for free. It is sufficiently effective in real-time scanning and blockage of spyware browser-hijacks. An important feature is that it prevents download and installation of malware while surfing the net via the Internet Explorer. It provides auto-updates and log and report facilities. However in addition to the other minor disadvantages of free software, this program also unnecessarily consumes a disproportionate amount of system resources on the computer.
Tuesday, February 24, 2009
Free Antivirus Software
Best free antivirus software
Avast! Home Edition 4.7
Score - 5/5
Tests VB100%
Developer ALWIL Software
Url: www.avast.com/ eng/avast_4_home.html
Size:12 MB
Download url: http://www.avast.com/eng/download-avast-home.html
AntiVir Personal 7.00.03.02
Score 5/5
Tests VB100%
Developer Avira GmbH
Url:http://www.free-av.com/
Size:10 MB
AVG Free Edition 7.5.432
Score 5/5
Tests VB100%
Developer Grisoft
Url:free.grisoft.com
Size:17 MB
Download url: free.grisoft.com /doc/5390/lng/us/tpl/v5
BitDefender Free Edition 8.0.202
Score 3/5
Tests VB100%
Developer SOFTWIN BitDefender
Url:http://www.bitdefender.com/PRODUCT-14-en--BitDefender-8-Free-Edition.html
Size:13 MB
Download url: http://www.bitdefender.com%20/site/Download/downloadFile/340/EN/
Comodo AntiVirus 1.1
Score 4/5
Tests NO
Developer Comodo Group
Url:antivirus.comodo.com
Size:24 MB
Download url: http://www.antivirus.comodo.com/download.html
Avast! Home Edition 4.7
Score - 5/5
Tests VB100%
Developer ALWIL Software
Url: www.avast.com/ eng/avast_4_home.html
Size:12 MB
Download url: http://www.avast.com/eng/download-avast-home.html
AntiVir Personal 7.00.03.02
Score 5/5
Tests VB100%
Developer Avira GmbH
Url:http://www.free-av.com/
Size:10 MB
AVG Free Edition 7.5.432
Score 5/5
Tests VB100%
Developer Grisoft
Url:free.grisoft.com
Size:17 MB
Download url: free.grisoft.com /doc/5390/lng/us/tpl/v5
BitDefender Free Edition 8.0.202
Score 3/5
Tests VB100%
Developer SOFTWIN BitDefender
Url:http://www.bitdefender.com/PRODUCT-14-en--BitDefender-8-Free-Edition.html
Size:13 MB
Download url: http://www.bitdefender.com%20/site/Download/downloadFile/340/EN/
Comodo AntiVirus 1.1
Score 4/5
Tests NO
Developer Comodo Group
Url:antivirus.comodo.com
Size:24 MB
Download url: http://www.antivirus.comodo.com/download.html
WiFi Security
MAC Address Filtering
A common feature available with wireless access devices is the means to restrict access to only wireless devices that have their network (MAC) address configured in a filter list. Therefore, any device that tries to authenticate with a MAC address not matching the list will be rejected.
This method is not foolproof. If traffic can be decrypted then a valid MAC address could be determined and used to access the network.
Separate VLAN/DMZ for Wireless LAN
Most medium to large networks utilise virtual LAN’s (VLAN’s) to separate IP networks into logical groupings for security, performance and management reasons. Most good quality layer 3 switches provide VLAN’s that allow you to define firewall rules or access lists to restrict what resources on the network that wireless networks clients can access.
For more protection, the wireless network can be placed behind a fully featured stateful firewall rather than a VLAN alone.
WPA Wireless Clients Sample Implementation
This section shows an example of implementing WPA Enterprise with PEAP. Three components are required.
* The supplicant (the WIFI client),
* The Authenticator (the Access Point) and;
* An Authentication Server (A Radius server such as Microsoft IAS Server).
In this example the Access Point is a Cisco Aironet 1310 Series Outdoor Access Point/Bridge1 running IOS 12.3(7)JA.
In addition, since we are using PEAP, we need a suitable certificate server and we have used Microsoft Certificate Services.
Since we are using Microsoft IAS for Radius, which integrates with Active Directory, we have created 2 new Active Directory groups called "Wireless Users" and "Wireless Computers" respectively. These groups will be used to determine what computers and users are allowed access to the WIFI network. This ensures a high level of granularity for IT staff to manage access.
Configuring IAS (RADIUS)
IAS is a free component that is supplied with Win2k/Win2003 but is not installed by default. It can be installed via the Control Panel->Add/Remove Programs/Windows Components applet.
Both IAS and the authenticating access point need to be configured to perform Radius authentication. Firstly, you need to register IAS in Active Directory, so that IAS policies can be used on Active Directory users and computers to govern access.
In the left hand pane of the IAS management console, select Internet Authentication Service (Local) and right click to select the Register Server in Active Directory option.
A common feature available with wireless access devices is the means to restrict access to only wireless devices that have their network (MAC) address configured in a filter list. Therefore, any device that tries to authenticate with a MAC address not matching the list will be rejected.
This method is not foolproof. If traffic can be decrypted then a valid MAC address could be determined and used to access the network.
Separate VLAN/DMZ for Wireless LAN
Most medium to large networks utilise virtual LAN’s (VLAN’s) to separate IP networks into logical groupings for security, performance and management reasons. Most good quality layer 3 switches provide VLAN’s that allow you to define firewall rules or access lists to restrict what resources on the network that wireless networks clients can access.
For more protection, the wireless network can be placed behind a fully featured stateful firewall rather than a VLAN alone.
WPA Wireless Clients Sample Implementation
This section shows an example of implementing WPA Enterprise with PEAP. Three components are required.
* The supplicant (the WIFI client),
* The Authenticator (the Access Point) and;
* An Authentication Server (A Radius server such as Microsoft IAS Server).
In this example the Access Point is a Cisco Aironet 1310 Series Outdoor Access Point/Bridge1 running IOS 12.3(7)JA.
In addition, since we are using PEAP, we need a suitable certificate server and we have used Microsoft Certificate Services.
Since we are using Microsoft IAS for Radius, which integrates with Active Directory, we have created 2 new Active Directory groups called "Wireless Users" and "Wireless Computers" respectively. These groups will be used to determine what computers and users are allowed access to the WIFI network. This ensures a high level of granularity for IT staff to manage access.
Configuring IAS (RADIUS)
IAS is a free component that is supplied with Win2k/Win2003 but is not installed by default. It can be installed via the Control Panel->Add/Remove Programs/Windows Components applet.
Both IAS and the authenticating access point need to be configured to perform Radius authentication. Firstly, you need to register IAS in Active Directory, so that IAS policies can be used on Active Directory users and computers to govern access.
In the left hand pane of the IAS management console, select Internet Authentication Service (Local) and right click to select the Register Server in Active Directory option.
Sunday, February 15, 2009
Windows XP Dos Commands
bootcfg -View your boot loader settings, such as your default OS and selection timeout, as well as your boot entries and load options.
diskpart -Manages your disk partitions. After you type "diskpart" into your command prompt, your prompt will become "DISKPART." Type a question mark to get a list of possible arguments. Type exit to leave diskpart.
driverquery - Will get you a nice list of your drivers and their properties.
fsutil - This is a handy command. You can do everything from managing your hardlinks to querying the free space in a volume. Type "fsutil" into your command prompt, and you'll see a list of options. I choose "fsinfo" from the list, so I type "fsutil fsinfo" into the prompt. Now I get even more options, but I choose drives by typing "fsutil fsinfo drives." It's fun, it's easy, and you'll get the hang of it. Explore this utility. There are a lot of cool features and hidden twists.
getmac - This gets the MAC (Media Access Control) address.
gpresult - Get the RSoP, user settings, and computer group policy settings.
netsh - A network configuration tool. Type "netsh" to enter the tool, or "netsh /?" to learn more about it. To exit this tool, type "exit" at the "netsh>" prompt.
openfiles - Allows an administrator to display or disconnect open files in XP professional. Type "openfiles /?" for a list of possible parameters.
recover - This command attempts to recover readable information from a damaged disk. Type "recover" to get the syntax.
reg - The console registry tool. Get syntax help when you type "reg" into the prompt. You can export the registry, copy, restore, compare, and more.
schtasks - The administrator can schedule, run, change, or delete tasks on a local or remote machine. Type "schtasks /?" without the quotes for a list of options.
sfc - The system file checker scans protected system files and replaces the ones you (or your applications) hacked beyond repair with the real, official Microsoft versions. Type "sfc" into the command prompt to get a list of options. use "sfc /scannow" to run a full check of all system files.
shutdown - You can shut down or restart your own computer, or an administrator can shut down or restart a remote computer. Type "shutdown" into your command prompt to see a list of possible arguments.
systeminfo - Basic system configuration information, such as the system type, the processor type, your time zone, your virtual memory settings, and much more.
tasklist - Want to know what's going on behind the scenes? Type "tasklist" into the command prompt, and get a list of current processes.
taskkill - Now that you know what's going on behind the scenes, maybe you want to shut a few of these extraneous tasks down. That's where taskkill comes in. Type "taskkill /?" for a quick lesson in the syntax of the command, then shut down all those random processes. I just killed my MS messenger by typing "taskkill /PID 1680." I got the PID from running tasklist, above.
diskpart -Manages your disk partitions. After you type "diskpart" into your command prompt, your prompt will become "DISKPART." Type a question mark to get a list of possible arguments. Type exit to leave diskpart.
driverquery - Will get you a nice list of your drivers and their properties.
fsutil - This is a handy command. You can do everything from managing your hardlinks to querying the free space in a volume. Type "fsutil" into your command prompt, and you'll see a list of options. I choose "fsinfo" from the list, so I type "fsutil fsinfo" into the prompt. Now I get even more options, but I choose drives by typing "fsutil fsinfo drives." It's fun, it's easy, and you'll get the hang of it. Explore this utility. There are a lot of cool features and hidden twists.
getmac - This gets the MAC (Media Access Control) address.
gpresult - Get the RSoP, user settings, and computer group policy settings.
netsh - A network configuration tool. Type "netsh" to enter the tool, or "netsh /?" to learn more about it. To exit this tool, type "exit" at the "netsh>" prompt.
openfiles - Allows an administrator to display or disconnect open files in XP professional. Type "openfiles /?" for a list of possible parameters.
recover - This command attempts to recover readable information from a damaged disk. Type "recover" to get the syntax.
reg - The console registry tool. Get syntax help when you type "reg" into the prompt. You can export the registry, copy, restore, compare, and more.
schtasks - The administrator can schedule, run, change, or delete tasks on a local or remote machine. Type "schtasks /?" without the quotes for a list of options.
sfc - The system file checker scans protected system files and replaces the ones you (or your applications) hacked beyond repair with the real, official Microsoft versions. Type "sfc" into the command prompt to get a list of options. use "sfc /scannow" to run a full check of all system files.
shutdown - You can shut down or restart your own computer, or an administrator can shut down or restart a remote computer. Type "shutdown" into your command prompt to see a list of possible arguments.
systeminfo - Basic system configuration information, such as the system type, the processor type, your time zone, your virtual memory settings, and much more.
tasklist - Want to know what's going on behind the scenes? Type "tasklist" into the command prompt, and get a list of current processes.
taskkill - Now that you know what's going on behind the scenes, maybe you want to shut a few of these extraneous tasks down. That's where taskkill comes in. Type "taskkill /?" for a quick lesson in the syntax of the command, then shut down all those random processes. I just killed my MS messenger by typing "taskkill /PID 1680." I got the PID from running tasklist, above.
Useful Windows Dos Command
DIR COMMAND USAGE
CD COMMAND USAGE
Lists the contents current directory
C:\>dir
Lists Contents of absolute path
A:\documents\pictures\bitmaps>dir c:\”program files”
Switches: /w /p /s
Sorting Switches: /oe /oen /od /on /one /x
Wildcards: * ?
Wildcard usage:
C:/winnt/system32>DIR *.exe
C:/winnt/system32>DIR *.*
Changes to a directory
Folder by folder method
C:\>cd winnt
C:\winnt>cd system32
Absolute path method
C:\>cd c:\winnt\system32
Move to parent folder
C:\>cd..
Move to root folder
C:\>cd/
The parent folder is what ever folder is above your current folder
The Root folder is the top most folder
COPY/MOVE COMMAND USAGE
DEL COMMAND USAGE
This command is always used in this style
Copy “path of file” “path”
Example1:
C:\>copy Friday.doc c:\”documents and settings”
Example 2:
C:\>copy a:\weekdays\Thursday.doc c:\temp\days
Example 3:
C:\>move Friday.doc c:\”documents and settings”
Delete from current directory
C:\>Del Friday.doc
Delete From Absolute Path
C:\>Del a:\weekdays\Thursday.doc
CLS & TREE COMMAND USAGE
Clears all text from the screen
C:\>CLS
TREE Command will draw a symbolic representation of your location within the file system
FORMAT COMMAND USAGE
EDIT and TYPE COMMAND USAGE
Deletes and Prepares a floppy or hard disk to have new data written to it. When this command is preformed all data on a disk is lost.
Format First hard Drive
C:\>format c:
Format Floppy Drive
C:\>format a:
When the edit command is used on a file, DOS launches and external text editing application to edit the file.
Example 1
C:>edit c:\”documents and settings”\Thursday.txt
The Type Command displays directly on the DOS screen the contents of a file. This command only displays data and will not allow you to edit.
Example 2
C:\>type Thursday.txt
MD & RD & REN COMMAND USAGE
Makes a directory
C:\winnt>MD MYbackup
Removes a Directory
C:\winnt>RD MYbackup
Rename a File Or Folder
C:\>ren bob.txt joey.txt
C:\>ren c:\docs c:\pics
ATTRIB COMMAND
Other External Commands
ATTRIB commands will change the attributes and permissions of a file or folder.
+Adds an Attribute
- Removes an Attribute
c:\>attrib Thursday.doc +h
c:\>attrib Friday.Doc +a -h
All Switches: A R H S
Archive | Read-Only| Hidden | System
External commands are separate tools not always built into dos.
XCOPY – Copies an entire directory along with everything that directory contains.
DELTREE – Deletes an entire directory along with everything that directory contains.
QBASIC – An external application used to write and compile other dos programs from source code.
SCANDISK – Scans a drives directory structure checking for errors.
FDISK – USED to VIEW/CREATE/DELETE partitions
IPCONFIG – Network utility used to display and manage IP addresses
OTHER TIPS:
1) To launch DOS from windows you execute cmd or command from the run prompt in the start menu.
2) The SystemRoot is the directory where the operating systems core files are located Typically c:\winnt on NT based systems.
3)c:\program files\ is typically where most “user installed applications” are located.
4)c:\documents and settings\ is typically where desktop icons, documents, start menu icons and personal preferences are stored. Example: The user bob’s documents would be located in c:\documents and settings\bob\my documents
System information
TIME – Display or Change the system time
Label – Changes the label of a disk
VOL – Displays to label of a disk
VER – Displays what operations system you are using
Change to Default Windows Directory trick
C:\>CD %windir%
Common Keyboard Shortcuts
Shortcut Keys
Function
Display or hide the Start menu.
+BREAK
Display the System Properties dialog box.
+D
Minimizes all Windows and shows the Desktop
+E
Open Windows Explorer
+F
Search for a file or folder.
+F+CTRL
Search for computers.
+F1
Display Windows 2000 Help.
+L
Locks the desktop
+M
Minimize or restore all windows.
+R
Open the Run dialog box.
+TAB
Switch between open items.
+U
Open Utility Manager
ALT+- (ALT+hyphen)
Displays the Multiple Document Interface (MDI) child window's System menu.
ALT+ENTER
View properties for the selected item.
ALT+ESC
Cycle through items in the order they were opened.
ALT+F4
Close the active item, or quit the active program.
ALT+SPACEBAR
Display the System menu for the active window.
ALT+TAB
Switch between open items.
ALT+Underlined letter in a menu name
Display the corresponding menu.
BACKSPACE
View the folder one level up in My Computer or Windows Explorer.
CTRL+A
Select all.
CTRL+B
Bold
CTRL+C
Copy.
CTRL+I
Italics
CTRL+O
Open an item.
CTRL+U
Underline
CTRL+V
Paste.
CTRL+X
Cut.
CTRL+Z
Undo.
CTRL+F4
Close the active document in programs that allow you to have multiple documents open simultaneously.
CTRL while dragging an item
Copy selected item.
CTRL+SHIFT while dragging an item
Create shortcut to selected item.
CTRL+RIGHT ARROW
Move the insertion point to the beginning of the next word.
CTRL+LEFT ARROW
Move the insertion point to the beginning of the previous word.
CTRL+DOWN ARROW
Move the insertion point to the beginning of the next paragraph.
CTRL+UP ARROW
Move the insertion point to the beginning of the previous paragraph.
CTRL+SHIFT with any of the arrow keys
Highlight a block of text.
DELETE
Delete.
SHIFT+DELETE
Delete selected item permanently without placing the item in the Recycle Bin.
ESC
Cancel the current task.
F1
Displays Help
F2
Rename selected item.
F3
Search for a file or folder.
F4
Display the Address bar list in My Computer or Windows Explorer.
F5
Refresh the active window.
F6
Cycle through screen elements in a window or on the desktop.
F10
Activate the menu bar in the active program.
SHIFT+F10
Display the shortcut menu for the selected item.
CTRL+ESC
Display the Start menu.
SHIFT+CTRL+ESC
Launches Task Manager
Underlined letter in a command name on an open menu
Carry out the corresponding command.
RIGHT ARROW
Open the next menu to the right, or open a submenu.
LEFT ARROW
Open the next menu to the left, or close a submenu.
SHIFT with any of the arrow keys
Select more than one item in a window or on the desktop, or select text within a document.
SHIFT when you insert a CD into the CD-ROM drive
Prevent the CD from automatically playing.
Windows Explorer keyboard shortcuts
Shortcut Keys
Function
CTRL+PLUS
on numeric keypad (+)
Automatically resize the columns in the right hand pane
END
Display the bottom of the active window.
HOME
Display the top of the active window.
NUM LOCK+ASTERISK
on numeric keypad (*)
Display all subfolders under the selected folder.
NUM LOCK+PLUS SIGN
on numeric keypad (+)
Display the contents of the selected folder.
NUM LOCK+MINUS SIGN
on numeric keypad (-)
Collapse the selected folder.
LEFT ARROW
Collapse current selection if it's expanded, or select parent folder.
RIGHT ARROW
Display current selection if it's collapsed, or select first subfolder
CD COMMAND USAGE
Lists the contents current directory
C:\>dir
Lists Contents of absolute path
A:\documents\pictures\bitmaps>dir c:\”program files”
Switches: /w /p /s
Sorting Switches: /oe /oen /od /on /one /x
Wildcards: * ?
Wildcard usage:
C:/winnt/system32>DIR *.exe
C:/winnt/system32>DIR *.*
Changes to a directory
Folder by folder method
C:\>cd winnt
C:\winnt>cd system32
Absolute path method
C:\>cd c:\winnt\system32
Move to parent folder
C:\>cd..
Move to root folder
C:\>cd/
The parent folder is what ever folder is above your current folder
The Root folder is the top most folder
COPY/MOVE COMMAND USAGE
DEL COMMAND USAGE
This command is always used in this style
Copy “path of file” “path”
Example1:
C:\>copy Friday.doc c:\”documents and settings”
Example 2:
C:\>copy a:\weekdays\Thursday.doc c:\temp\days
Example 3:
C:\>move Friday.doc c:\”documents and settings”
Delete from current directory
C:\>Del Friday.doc
Delete From Absolute Path
C:\>Del a:\weekdays\Thursday.doc
CLS & TREE COMMAND USAGE
Clears all text from the screen
C:\>CLS
TREE Command will draw a symbolic representation of your location within the file system
FORMAT COMMAND USAGE
EDIT and TYPE COMMAND USAGE
Deletes and Prepares a floppy or hard disk to have new data written to it. When this command is preformed all data on a disk is lost.
Format First hard Drive
C:\>format c:
Format Floppy Drive
C:\>format a:
When the edit command is used on a file, DOS launches and external text editing application to edit the file.
Example 1
C:>edit c:\”documents and settings”\Thursday.txt
The Type Command displays directly on the DOS screen the contents of a file. This command only displays data and will not allow you to edit.
Example 2
C:\>type Thursday.txt
MD & RD & REN COMMAND USAGE
Makes a directory
C:\winnt>MD MYbackup
Removes a Directory
C:\winnt>RD MYbackup
Rename a File Or Folder
C:\>ren bob.txt joey.txt
C:\>ren c:\docs c:\pics
ATTRIB COMMAND
Other External Commands
ATTRIB commands will change the attributes and permissions of a file or folder.
+Adds an Attribute
- Removes an Attribute
c:\>attrib Thursday.doc +h
c:\>attrib Friday.Doc +a -h
All Switches: A R H S
Archive | Read-Only| Hidden | System
External commands are separate tools not always built into dos.
XCOPY – Copies an entire directory along with everything that directory contains.
DELTREE – Deletes an entire directory along with everything that directory contains.
QBASIC – An external application used to write and compile other dos programs from source code.
SCANDISK – Scans a drives directory structure checking for errors.
FDISK – USED to VIEW/CREATE/DELETE partitions
IPCONFIG – Network utility used to display and manage IP addresses
OTHER TIPS:
1) To launch DOS from windows you execute cmd or command from the run prompt in the start menu.
2) The SystemRoot is the directory where the operating systems core files are located Typically c:\winnt on NT based systems.
3)c:\program files\ is typically where most “user installed applications” are located.
4)c:\documents and settings\ is typically where desktop icons, documents, start menu icons and personal preferences are stored. Example: The user bob’s documents would be located in c:\documents and settings\bob\my documents
System information
TIME – Display or Change the system time
Label – Changes the label of a disk
VOL – Displays to label of a disk
VER – Displays what operations system you are using
Change to Default Windows Directory trick
C:\>CD %windir%
Common Keyboard Shortcuts
Shortcut Keys
Function
Display or hide the Start menu.
+BREAK
Display the System Properties dialog box.
+D
Minimizes all Windows and shows the Desktop
+E
Open Windows Explorer
+F
Search for a file or folder.
+F+CTRL
Search for computers.
+F1
Display Windows 2000 Help.
+L
Locks the desktop
+M
Minimize or restore all windows.
+R
Open the Run dialog box.
+TAB
Switch between open items.
+U
Open Utility Manager
ALT+- (ALT+hyphen)
Displays the Multiple Document Interface (MDI) child window's System menu.
ALT+ENTER
View properties for the selected item.
ALT+ESC
Cycle through items in the order they were opened.
ALT+F4
Close the active item, or quit the active program.
ALT+SPACEBAR
Display the System menu for the active window.
ALT+TAB
Switch between open items.
ALT+Underlined letter in a menu name
Display the corresponding menu.
BACKSPACE
View the folder one level up in My Computer or Windows Explorer.
CTRL+A
Select all.
CTRL+B
Bold
CTRL+C
Copy.
CTRL+I
Italics
CTRL+O
Open an item.
CTRL+U
Underline
CTRL+V
Paste.
CTRL+X
Cut.
CTRL+Z
Undo.
CTRL+F4
Close the active document in programs that allow you to have multiple documents open simultaneously.
CTRL while dragging an item
Copy selected item.
CTRL+SHIFT while dragging an item
Create shortcut to selected item.
CTRL+RIGHT ARROW
Move the insertion point to the beginning of the next word.
CTRL+LEFT ARROW
Move the insertion point to the beginning of the previous word.
CTRL+DOWN ARROW
Move the insertion point to the beginning of the next paragraph.
CTRL+UP ARROW
Move the insertion point to the beginning of the previous paragraph.
CTRL+SHIFT with any of the arrow keys
Highlight a block of text.
DELETE
Delete.
SHIFT+DELETE
Delete selected item permanently without placing the item in the Recycle Bin.
ESC
Cancel the current task.
F1
Displays Help
F2
Rename selected item.
F3
Search for a file or folder.
F4
Display the Address bar list in My Computer or Windows Explorer.
F5
Refresh the active window.
F6
Cycle through screen elements in a window or on the desktop.
F10
Activate the menu bar in the active program.
SHIFT+F10
Display the shortcut menu for the selected item.
CTRL+ESC
Display the Start menu.
SHIFT+CTRL+ESC
Launches Task Manager
Underlined letter in a command name on an open menu
Carry out the corresponding command.
RIGHT ARROW
Open the next menu to the right, or open a submenu.
LEFT ARROW
Open the next menu to the left, or close a submenu.
SHIFT with any of the arrow keys
Select more than one item in a window or on the desktop, or select text within a document.
SHIFT when you insert a CD into the CD-ROM drive
Prevent the CD from automatically playing.
Windows Explorer keyboard shortcuts
Shortcut Keys
Function
CTRL+PLUS
on numeric keypad (+)
Automatically resize the columns in the right hand pane
END
Display the bottom of the active window.
HOME
Display the top of the active window.
NUM LOCK+ASTERISK
on numeric keypad (*)
Display all subfolders under the selected folder.
NUM LOCK+PLUS SIGN
on numeric keypad (+)
Display the contents of the selected folder.
NUM LOCK+MINUS SIGN
on numeric keypad (-)
Collapse the selected folder.
LEFT ARROW
Collapse current selection if it's expanded, or select parent folder.
RIGHT ARROW
Display current selection if it's collapsed, or select first subfolder
Tuesday, February 10, 2009
Install Server Sensor in Cluster Environment
Installing RealSecure Server Sensor on a Microsoft Cluster is generally the same as installing RealSecure Server Sensor on any other Windows 2000 platform. There are however a number of additional points to note. - RealSecure Server Sensor is not a cluster resource but is installed locally on each cluster node. In this way RealSecure Server Sensor protects each of the component nodes of a cluster rather than just the active node. If possible perform each installation while the node is NOT active, particularly where IIS is installed. If it is necessary to install RealSecure Server Sensor on the active node you should elect to stop and restart IIS manually following the install process. - From the RealSecure Console, a cluster will appear as a number of discrete systems, and events will originate from those discrete systems rather than the cluster-name or cluster-ip-address. - By default RealSecure Server Sensor enforces Audit Policy on its host systems. If however this default is accepted, each node of the cluster will compete with the other nodes in an attempt to be the last one to re-set the Audit Policy to the preferred values. It is therefore necessary to unset Enforce Audit Policy on all but one cluster node. - The recommended way to u nset the Enforce Audit Policy setting is to do it on each cluster node as installation, and introduction to the Console, proceeds. Do NOT install RealSecure ServerSensor on all the cluster nodes and then try un-setting Enforce Audit Policy as, by this time, the competition will be well under way. - Enforce Audit Policy is set/unset from the Console: Server Sensor Properties : server_sensor_1@node > Server Sensor > Enforce Audit Policy. - If a User Defined Text Log Event is defined to watch a file on a shared resource the following behavior will be observed. - When the shared resource is visible on node A, these events will only be seen originating from Server Sensor on node A. - Following each Cluster Switch, the Server Sensor on the new active node will scan the whole file and may report events that have already been reported. Upgrading via XPU and UNinstalling - Perform any upgrades and de-installations of RealSecure Server Sensor while the node is NOT active, particularly where IIS is installed. Support - Microsoft Knowledge Base Article Q248025 describes how to "Configure Clustered IIS Virtual Servers on Windows 2000 Advanced Servers". It also states "Although it is technically possible to set up IIS by using Clustering service, Microsoft d oes not recommend that you install IIS on Microsoft Cluster server. The recommended method to provide high-availability with IIS is to use Network Load Balancing". In view of Microsoft's position, ISS does not support the use of the ISAPI (IIS) filter component of RealSecure Server Sensor on Microsoft Cluster server. If however, IIS is already installed when RealSecure Server Sensor is installed, the ISAPI Component will also be installed. When running RealSecure Server Sensor on Microsoft Cluster there are a number of additional points to note. * A 2 Node MSCS Cluster running Windows 2000 Advanced Server, as described in http://www.microsoft.com/WINDOWS2000/techinfo/planning/server/clustersteps.asp * How to Configure Clustered IIS Virtual Servers on Windows 2000 Advanced Servers (Q248025) * Using IISSYNC to Synchronize Clustered Web Sites on Windows 2000 Advanced Server (Q249603) * How to Configure SSL in a Windows 2000 IIS 5.0 Test Environment Using Certificate Server 2.0 (Q290625) * IISSYNC May Fail If SSL Is Enabled on IIS 5.0/Windows 2000 Cluster (Q288207) * How to Configure the SMTP Resource on a Windows 2000-Based Server Cluster. (Q280400)
SAFEsuite and Checkpoint
SAFEsuite and Checkpoint CommunicationsEngineering Tech Note
TERMS
SCA - Safelink Checkpoint Agent
CMM - Checkpoint Management Module
CFM - Checkpoint Firewall Module
Assumptions
All of the following scenarios assume that the SCA and the CMM are on the same subnet. If they are not, port 256 will need to be allowed to talk with any source port thru the router/firewall between subnets in addition to port 49250 for the SAFEsuite Decisions application. They also assume that Checkpoint is already installed and functioning properly.
Authenticated Connections
SCA and CMM on same solaris machine
Install SAFElink agent.
Edit the /etc/rc3.d/S98SAFElink script to include the following lines in the beginning of the script (between the last comment and the killproc function):
#this path should point to the Checkpoint installation OR
#the path to the conf directory where fwopsec.conf is contained.
FWDIR=/opt/CKPfw
export FWDIR
Restart the agentservice
/etc/rc3.d/S98SAFElink stop
/etc/rc3.d/S98SAFElink start
Copy the opsec_putkey.solarissparc to the SAFElink install directory.
Run $FWDIR/bin/fw putkey CMMIPADDRESS
Enter the secret key as prompted.
Run /opt/ISS/SAFElink/opsec_putkey.solarissparc CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA and CMM on same NT machine
Install the SAFElink agent.
Open the system control panel applet and select environment.
Select any variable in the system variables window.
Clear the text in the variable box and enter FWDIR.
Clear the text in the value box and enter c:\winnt\fw.
Click set.
NOTE: Since the firewall is already functioning on this machine, this should have already been done.
Verify that the variable has been set properly by opening a NEW command prompt and typing “echo %FWDIR%”
Restart the Agent service.
Run %FWDIR%\bin\fw putkey CMMIPADDRESS
Enter the secret key as prompted.
Run c:\program files\iss\SAFElink\opsec_putkey CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA on NT and CMM on solaris
Install the SAFElink agent.
Create a directory called conf in the agent installation directory (c:\program files\iss\safesuite decisions\agent)
Copy the fwopsec.conf file from the CMM machine to the directory created above.
Edit the file and add the following line directly below the lea_server line:
lea_server ip CMMIPADDRESS
Open the system control panel applet and select environment.
Select any variable in the system variables window.
Clear the text in the variable box and enter FWDIR.
Clear the text in the value box and enter c:\program files\iss\safesuite decisions\agent.
Click set.
Verify that the variable has been set properly by opening a NEW command prompt and typing “echo %FWDIR%”
Restart the Agent service.
On the CMM machine, type the command $FWDIR/bin/fw putkey SCAIPADDRESS
Enter the secret key as prompted.
On the SCA machine, type the command opsec_putkey CMMIPADDRESS
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA on Solaris and CMM on NT
Install SAFElink agent.
Create a directory called conf in the agent installation directory (/opt/ISS/SAFElink).
Copy the fwopsec.conf file from the CMM machine to the directory created above.
Edit the file and add the following line directly below the lea_server line:
lea_server ip CMMIPADDRESS
Edit the /etc/rc3.d/S98SAFElink script to include the following lines in the beginning of the script (between the last comment and the killproc function):
#this path should point to the Checkpoint installation OR
#the path to the conf directory where fwopsec.conf is contained.
FWDIR=/opt/ISS/SAFElink
export FWDIR
Restart the agentservice
/etc/rc3.d/S98SAFElink stop
/etc/rc3.d/S98SAFElink start
Copy the opsec_putkey.solarissparc to the SAFElink install directory.
On the CMM machine run %FWDIR%\bin\fw putkey SCAIPADDRESS
Enter the secret key as prompted.
On the SCA machine run /opt/ISS/SAFElink/opsec_putkey.solarissparc CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
Non-authenticated Connections
All steps will be the same except you may skip any steps that refer to opsec_putkey, opsec_putkey.solarissparc and fw putkey.
TERMS
SCA - Safelink Checkpoint Agent
CMM - Checkpoint Management Module
CFM - Checkpoint Firewall Module
Assumptions
All of the following scenarios assume that the SCA and the CMM are on the same subnet. If they are not, port 256 will need to be allowed to talk with any source port thru the router/firewall between subnets in addition to port 49250 for the SAFEsuite Decisions application. They also assume that Checkpoint is already installed and functioning properly.
Authenticated Connections
SCA and CMM on same solaris machine
Install SAFElink agent.
Edit the /etc/rc3.d/S98SAFElink script to include the following lines in the beginning of the script (between the last comment and the killproc function):
#this path should point to the Checkpoint installation OR
#the path to the conf directory where fwopsec.conf is contained.
FWDIR=/opt/CKPfw
export FWDIR
Restart the agentservice
/etc/rc3.d/S98SAFElink stop
/etc/rc3.d/S98SAFElink start
Copy the opsec_putkey.solarissparc to the SAFElink install directory.
Run $FWDIR/bin/fw putkey CMMIPADDRESS
Enter the secret key as prompted.
Run /opt/ISS/SAFElink/opsec_putkey.solarissparc CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA and CMM on same NT machine
Install the SAFElink agent.
Open the system control panel applet and select environment.
Select any variable in the system variables window.
Clear the text in the variable box and enter FWDIR.
Clear the text in the value box and enter c:\winnt\fw.
Click set.
NOTE: Since the firewall is already functioning on this machine, this should have already been done.
Verify that the variable has been set properly by opening a NEW command prompt and typing “echo %FWDIR%”
Restart the Agent service.
Run %FWDIR%\bin\fw putkey CMMIPADDRESS
Enter the secret key as prompted.
Run c:\program files\iss\SAFElink\opsec_putkey CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA on NT and CMM on solaris
Install the SAFElink agent.
Create a directory called conf in the agent installation directory (c:\program files\iss\safesuite decisions\agent)
Copy the fwopsec.conf file from the CMM machine to the directory created above.
Edit the file and add the following line directly below the lea_server line:
lea_server ip CMMIPADDRESS
Open the system control panel applet and select environment.
Select any variable in the system variables window.
Clear the text in the variable box and enter FWDIR.
Clear the text in the value box and enter c:\program files\iss\safesuite decisions\agent.
Click set.
Verify that the variable has been set properly by opening a NEW command prompt and typing “echo %FWDIR%”
Restart the Agent service.
On the CMM machine, type the command $FWDIR/bin/fw putkey SCAIPADDRESS
Enter the secret key as prompted.
On the SCA machine, type the command opsec_putkey CMMIPADDRESS
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
SCA on Solaris and CMM on NT
Install SAFElink agent.
Create a directory called conf in the agent installation directory (/opt/ISS/SAFElink).
Copy the fwopsec.conf file from the CMM machine to the directory created above.
Edit the file and add the following line directly below the lea_server line:
lea_server ip CMMIPADDRESS
Edit the /etc/rc3.d/S98SAFElink script to include the following lines in the beginning of the script (between the last comment and the killproc function):
#this path should point to the Checkpoint installation OR
#the path to the conf directory where fwopsec.conf is contained.
FWDIR=/opt/ISS/SAFElink
export FWDIR
Restart the agentservice
/etc/rc3.d/S98SAFElink stop
/etc/rc3.d/S98SAFElink start
Copy the opsec_putkey.solarissparc to the SAFElink install directory.
On the CMM machine run %FWDIR%\bin\fw putkey SCAIPADDRESS
Enter the secret key as prompted.
On the SCA machine run /opt/ISS/SAFElink/opsec_putkey.solarissparc CMMIPADDRESS.
Enter the same secret key entered above.
You should receive the following message:
OPSEC: Received new control security key from CMMIPADDRESS
Authentication with CMMIPADDRESS initialized
At this point you should be able to configure a new agent and job from the SAFElink console and load data.
Non-authenticated Connections
All steps will be the same except you may skip any steps that refer to opsec_putkey, opsec_putkey.solarissparc and fw putkey.
Object Access Command codes
These are the codes used in the 560 Object Access Event ID message to denote various types of object access. I do not have a full set yet.
I do not know the exact distinction yet between the high level and low level codes.
High level Generic Codes
1537 DELETE
1538 READ_CONTROL
1539 WRITE_DAC
1540 WRITE_OWNER
1541 SYNCHRONIZE
1542 ACCESS_SYS_SEC
File codes
4416 ReadData
4417 WriteData
4418 AppendData
4419 ReadEA
4420 WriteEA
4421 Execute/Traverse
4422
4423 ReadAttributes
4424 WriteAttributes
Registry Codes
4432 Query Key Value
4433 Set Key Value
4434 Create Sub Key
4435 Enumerate sub-keys
4436 Notify about changes to keys
4437 Create Link
Printer Codes
6931 Print
I do not know the exact distinction yet between the high level and low level codes.
High level Generic Codes
1537 DELETE
1538 READ_CONTROL
1539 WRITE_DAC
1540 WRITE_OWNER
1541 SYNCHRONIZE
1542 ACCESS_SYS_SEC
File codes
4416 ReadData
4417 WriteData
4418 AppendData
4419 ReadEA
4420 WriteEA
4421 Execute/Traverse
4422
4423 ReadAttributes
4424 WriteAttributes
Registry Codes
4432 Query Key Value
4433 Set Key Value
4434 Create Sub Key
4435 Enumerate sub-keys
4436 Notify about changes to keys
4437 Create Link
Printer Codes
6931 Print
Here's how to forward syslog to RealSecure agent.
Where is the Syslog File?
/etc/syslog.conf
What do I need to change or add?
1. Verify the Systems Agent Hostname and IP Exists in /etc/hosts
2. Edit syslog.conf file.add the following line
auth.notice @rshostmachine
*.info @rshostmachine
3. Restart the syslog Daemon using the following:
ps -ef | grep syslogd
kill -HUP
All Syslog messages sent to Agent in ClearText
- Certicom is not used when sending Syslog
Should only Send Info related to Signatures
- Syslog has numerous options:
*.emerg;*.alert;*.crit;*.err;*.warning;*.notice;*.info;*.debug
Syslog is not accounted for in the License Key
Credits:--Audra
/etc/syslog.conf
What do I need to change or add?
1. Verify the Systems Agent Hostname and IP Exists in /etc/hosts
2. Edit syslog.conf file.add the following line
auth.notice @rshostmachine
*.info @rshostmachine
3. Restart the syslog Daemon using the following:
ps -ef | grep syslogd
kill -HUP
All Syslog messages sent to Agent in ClearText
- Certicom is not used when sending Syslog
Should only Send Info related to Signatures
- Syslog has numerous options:
*.emerg;*.alert;*.crit;*.err;*.warning;*.notice;*.info;*.debug
Syslog is not accounted for in the License Key
Credits:--Audra
Unix Command
There are a couple of things that you need to keep in mind when using Unix. First off, everything is case sensitive in Unix. README, ReadMe, and readme are three different files that can all reside in the same directory. Second, you always use a ‘/’ not a ‘\’. This can take some getting use to if you are coming from a MS background. Also, while NT has one command shell (cmd), Unix has many. The one that you are probably going to want to use is bash. You can call this shell at any time by typing bash and hitting enter. Bash gives you some doskey like functions (like pushing up for previous commands) that you will find useful. The last side note is on the ‘|’ character. The pipe is very useful in Unix as it will let you use several small tools in conjunction to create complex tools. This doc is for Unix implementations built off of the SYSTEM V kernel (Solaris, AIX, HPUX). BSD derivatives may have different syntax.
Getting around
Commands:
ls = (dir) lists the contents of a directory
ls -al |more = this will display all files (including hidden) and there attributes. The |more will display the results one screen at a time.
pwd = displays your current directory
cd directory = change directory- it works like dos except that it requires a space between the command and first arg.
cd / = cd to root
cd .. = go up one directory
cd = cd by itself wil take you to the env defined $HOME dir
mkdir test = make directory test in the current dir
rmdir test = remove the directory test from the current dir (delete it)
rm testfile = delete the file testfile
Drives- Unix does not have logical drives (c: d: e:) it has mount points instead. I won’t go into mounting drives here, but I wanted you to know where to look for a cdrom. By default, a cdrom will be mounted in the root directory as a directory called cdrom (easy huh.) cd /cdrom should bring you to the cdrom from anywhere.
The File System and Permissions
This is the output from a ls -al |more in the root directory on a Solaris box:
# ls -al |more
total 51023
drwxr-xr-x 30 root root 1536 May 5 12:24 .
drwxr-xr-x 30 root root 1536 May 5 12:24 ..
-rw------- 1 root other 281 May 5 12:24 .Xauthority
-rw------- 1 root other 461 May 12 16:45 .bash_history
-rw-r--r-- 1 root other 231 Oct 25 1999 .bashrc
-rw------- 1 root root 1032 May 5 12:23 .cpr_config
drwxr-xr-x 13 root other 512 May 5 12:25 .dt
-rwxr-xr-x 1 root other 5111 Aug 30 1999 .dtprofile
-rw------- 1 root other 0 Apr 5 10:12 .lynx_cookies
drwxr-xr-x 11 root other 512 Nov 1 1999 .microsoft
drwxr-xr-x 2 root other 512 Sep 2 1999 .ssh
drwxr-xr-x 2 root other 512 Oct 4 1999 KeyContainer
-rw-r--r-- 1 root other 0 Feb 9 18:08 Office2000
drwxr-xr-x 2 root root 512 Aug 30 1999 TT_DB
-rw-r--r-- 1 root other 30 Apr 7 16:56 ap
lrwxrwxrwx 1 root root 9 Aug 30 1999 bin -> ./usr/bin
drwxr-xr-x 2 root nobody 512 Sep 28 1999 cdrom
-rw-r--r-- 1 root other 2506 Mar 28 12:45 common.policy
drwxrwxr-x 17 root sys 3584 May 5 12:23 dev
drwxrwxr-x 5 root sys 512 Aug 30 1999 devices
drwxr-xr-x 28 root sys 3072 May 5 12:23 etc
drwxrwxr-x 3 root sys 512 Nov 17 09:06 export
-rw-r--r-- 1 root other 1924 Apr 12 17:12 foo.cap
dr-xr-xr-x 1 root root 1 May 5 12:23 home
-rw-r--r-- 1 root other 1756 Apr 12 17:13 host
-rw-r--r-- 1 root other 189 Jan 6 14:55 iss_signing_authority_239.Pub
--More--
The first column is made up of 10 letters or -'s. The first one can be 'd' or 'l' (there are other letters that might appear here, but you shouldn't see them in your use of Unix.) 'd' means that the filename is a directory. 'l' means that the filename is a symbolic link (kind of like shortcuts in NT only better.) The other 9 places show the permissions on the file. 'r' denotes read access, 'w' denotes write access, and 'x' denotes the ability to execute a file. The first group (-rwx------) is the permissions for the owner of the file. The second (----rwx---) is for the primary group that the owner belongs to. The last set (-------rwx) is for everyone.
The third column is the owner of the file- root owns all of these files.
The fourth column is the group for which the group permissions apply.
Following this we have: file size in bytes; month, day, time last modified; and the file name.
Important notes on filenames-
anything preceded by a '.' is a hidden file (.Xauthority)
anything with a -> in it is a symbolic link. It will take the form filename -> ./dirpath/file_or_dir_pointed_to as I said before- Unix is case sensitive.
Changing Permissions
chmod oge filename = change permissions where o=owner g=group e=everyone (this isn't classic notation, but it makes more sense
Permissions on a file/dir in Unix are stored in a 24 bit variable. 8 bits are used for each of the three permission sets, so the letters above are replaced with the int value for that set (have no fear, examples will follow.) You have to dust off your binary math for this so I will make it easy for you. The possible values for these numbers range from 0 (---) to 7 (rwx). When the bits are set- r = 4, w = 2,and x = 1. You add the bit values together for the set to come up with the correct number. So, if you wanted full control for the owner/root, write/execute for the group, and read only for everyone else, you would type the following:
chmod 734 filename
The permissions would now look like this:
-rwx-wxr--
chmod 644 filename
would look like this:
-rw-r--r--
Executing commands
There are a few things about running commands in Unix that are very different from the MS world. In DOS, you know a file is executable based on it's file extension (.exe .com .bat ect.) Unix does not use file extensions to see if a file is executable- it looks at the permissions (see above.) In DOS, there are three ways to run an executable- by typing the file's name if it is in the path, by typing the full pathname to the file, or by typing the file's from the file's directory.
example (in NT):
doskey (from anywhere if c:\winnt\system32 is in your path)
c:\winnt\system32\doskey (from anywhere)
doskey (from \winnt\system32 even if it's not in the path)
Unix works a little differently. To run a command, it must be in your path or you must specify the path name(absolute or relative.)
example (Unix):
traceroute IP (from anywhere if /usr/sbin is in the path)
/usr/sbin/traceroute IP (from anywhere)
./traceroute (from /usr/sbin even if it is not in the path.)
Getting around
Commands:
ls = (dir) lists the contents of a directory
ls -al |more = this will display all files (including hidden) and there attributes. The |more will display the results one screen at a time.
pwd = displays your current directory
cd directory = change directory- it works like dos except that it requires a space between the command and first arg.
cd / = cd to root
cd .. = go up one directory
cd = cd by itself wil take you to the env defined $HOME dir
mkdir test = make directory test in the current dir
rmdir test = remove the directory test from the current dir (delete it)
rm testfile = delete the file testfile
Drives- Unix does not have logical drives (c: d: e:) it has mount points instead. I won’t go into mounting drives here, but I wanted you to know where to look for a cdrom. By default, a cdrom will be mounted in the root directory as a directory called cdrom (easy huh.) cd /cdrom should bring you to the cdrom from anywhere.
The File System and Permissions
This is the output from a ls -al |more in the root directory on a Solaris box:
# ls -al |more
total 51023
drwxr-xr-x 30 root root 1536 May 5 12:24 .
drwxr-xr-x 30 root root 1536 May 5 12:24 ..
-rw------- 1 root other 281 May 5 12:24 .Xauthority
-rw------- 1 root other 461 May 12 16:45 .bash_history
-rw-r--r-- 1 root other 231 Oct 25 1999 .bashrc
-rw------- 1 root root 1032 May 5 12:23 .cpr_config
drwxr-xr-x 13 root other 512 May 5 12:25 .dt
-rwxr-xr-x 1 root other 5111 Aug 30 1999 .dtprofile
-rw------- 1 root other 0 Apr 5 10:12 .lynx_cookies
drwxr-xr-x 11 root other 512 Nov 1 1999 .microsoft
drwxr-xr-x 2 root other 512 Sep 2 1999 .ssh
drwxr-xr-x 2 root other 512 Oct 4 1999 KeyContainer
-rw-r--r-- 1 root other 0 Feb 9 18:08 Office2000
drwxr-xr-x 2 root root 512 Aug 30 1999 TT_DB
-rw-r--r-- 1 root other 30 Apr 7 16:56 ap
lrwxrwxrwx 1 root root 9 Aug 30 1999 bin -> ./usr/bin
drwxr-xr-x 2 root nobody 512 Sep 28 1999 cdrom
-rw-r--r-- 1 root other 2506 Mar 28 12:45 common.policy
drwxrwxr-x 17 root sys 3584 May 5 12:23 dev
drwxrwxr-x 5 root sys 512 Aug 30 1999 devices
drwxr-xr-x 28 root sys 3072 May 5 12:23 etc
drwxrwxr-x 3 root sys 512 Nov 17 09:06 export
-rw-r--r-- 1 root other 1924 Apr 12 17:12 foo.cap
dr-xr-xr-x 1 root root 1 May 5 12:23 home
-rw-r--r-- 1 root other 1756 Apr 12 17:13 host
-rw-r--r-- 1 root other 189 Jan 6 14:55 iss_signing_authority_239.Pub
--More--
The first column is made up of 10 letters or -'s. The first one can be 'd' or 'l' (there are other letters that might appear here, but you shouldn't see them in your use of Unix.) 'd' means that the filename is a directory. 'l' means that the filename is a symbolic link (kind of like shortcuts in NT only better.) The other 9 places show the permissions on the file. 'r' denotes read access, 'w' denotes write access, and 'x' denotes the ability to execute a file. The first group (-rwx------) is the permissions for the owner of the file. The second (----rwx---) is for the primary group that the owner belongs to. The last set (-------rwx) is for everyone.
The third column is the owner of the file- root owns all of these files.
The fourth column is the group for which the group permissions apply.
Following this we have: file size in bytes; month, day, time last modified; and the file name.
Important notes on filenames-
anything preceded by a '.' is a hidden file (.Xauthority)
anything with a -> in it is a symbolic link. It will take the form filename -> ./dirpath/file_or_dir_pointed_to as I said before- Unix is case sensitive.
Changing Permissions
chmod oge filename = change permissions where o=owner g=group e=everyone (this isn't classic notation, but it makes more sense
Permissions on a file/dir in Unix are stored in a 24 bit variable. 8 bits are used for each of the three permission sets, so the letters above are replaced with the int value for that set (have no fear, examples will follow.) You have to dust off your binary math for this so I will make it easy for you. The possible values for these numbers range from 0 (---) to 7 (rwx). When the bits are set- r = 4, w = 2,and x = 1. You add the bit values together for the set to come up with the correct number. So, if you wanted full control for the owner/root, write/execute for the group, and read only for everyone else, you would type the following:
chmod 734 filename
The permissions would now look like this:
-rwx-wxr--
chmod 644 filename
would look like this:
-rw-r--r--
Executing commands
There are a few things about running commands in Unix that are very different from the MS world. In DOS, you know a file is executable based on it's file extension (.exe .com .bat ect.) Unix does not use file extensions to see if a file is executable- it looks at the permissions (see above.) In DOS, there are three ways to run an executable- by typing the file's name if it is in the path, by typing the full pathname to the file, or by typing the file's from the file's directory.
example (in NT):
doskey (from anywhere if c:\winnt\system32 is in your path)
c:\winnt\system32\doskey (from anywhere)
doskey (from \winnt\system32 even if it's not in the path)
Unix works a little differently. To run a command, it must be in your path or you must specify the path name(absolute or relative.)
example (Unix):
traceroute IP (from anywhere if /usr/sbin is in the path)
/usr/sbin/traceroute IP (from anywhere)
./traceroute (from /usr/sbin even if it is not in the path.)
Wednesday, February 4, 2009
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Tuesday, January 20, 2009
THERMOSTATIC EXPANSION VALVE EQUALIZERS
1. ELEMENT CHARGES
2. EQUALIZERS
3. HUNTING
The external equalizer consists of a line connecting the evaporator outlet to the area in the valve under the diaphragm.
The internal equalizer consists of a passage way in the valve from the valve outlet to the lower side of the power element.
Another way to describe the difference between the two is that the internal equalizer provides a closing force based on the pressure of the refrigerant vapor at the evaporator INLET whereas the external equalizer provides a closing force based on the refrigerant vapor at the evaporator OUTLET.
THERMOSTATIC EXPANSION VALVE CROSS CHARGES
The element charge (i.e., the fluid in the power element of a TX valve) is usually one of three types:
1. GAS CHARGE
2. LIQUID CHARGE
3. CROSS CHARGE
CROSS CHARGES use a refrigerant in the thermostatic element that is different from the refrigerant used in the refrigeration system. By using a different refrigerant, the relationship between the forces due to the evaporator pressure and suction pressure can be modified. Cross charges are often introduced so that the bulb pressure does not rise as rapidly as the pressure of the refrigerant in the system.
Cross charges have advantages similar to those of gas charges (flood-back protection during shut-down and startup), and at the same time, they are suitable for low-temperature work. Cross charges also help to reduce hunting.
THERMOSTATIC EXPANSION VALVE LIQUID CHARGES
The element charge (i.e., the fluid in the power element of a TX valve) is usually one of three types:
1. GAS CHARGE
2. LIQUID CHARGE
LIQUID CHARGES, like gas charges, use the same refrigerant in the element as is used in the refrigeration system. The difference between the liquid and gas charges is that the liquid charge has a volume such that there will always be some liquid in the bulb regardless of the amount of superheat in the suction line.
Because liquid is always present in the bulb, the thermostatic element always has control of the opening force on the valve. Therefore, unlike the gas charge, the liquid charge can contribute to flood-back during startup.
Furthermore, liquid charges tend to cause more hunting than other charges (hunting is presented later in this module). Also, liquid charges should be avoided in low-temperature systems.
THERMOSTATIC EXPANSION VALVE ADJUSTMENT CONCERNS
It is very rare that a superheat adjustment setting needs to be made in an existing system. If an adjustment is made, keep two things in mind:
1. Count the number of turns of the valve stem so that you can return the TXV valve to its original state if you don’t get the desired results.
2. After making any superheat adjustments, always observe system operation for several minutes (15-20) to insure you get the desired results.
PROPER THERMOSTATIC EXPANSION VALVE TECHNIQUES
If the superheat were too high, we could manually adjust the valve by turning the valve stem counter-clockwise (as viewed from the bottom), which would loosen the spring tension.
This would allow the bulb pressure to overcome the evaporator and spring pressure causing the valve to open, which would feed more refrigerant into the evaporator, thus lowering the superheat
CALCULATING PROPER SUPERHEAT ADJUSTMENT
Now, with less refrigerant in the evaporator, the vapor leaving the evaporator will be superheated. If, in this example, the superheated vapor leaving the evaporator rises to 50°F (10° superheat), then the temperature of the charge in the bulb will also rise to 50°F.
At a temperature of 50°F, the charge has a pressure (pushing on the diaphragm) of 47 psig.
We now see that the 10° superheat created a pressure differential between the charge and the evaporator equal to:
charge 47 psig
evaporator -37 psig
THERMOSTATIC EXPANSION VALVE POWER ELEMENT
The power element (consisting of the bulb, capillary tube, and power head) contains a charge which is usually a refrigerant - the same refrigerant as that running in the system.
The refrigerant in the bulb is a saturated vapor. Because the bulb is strapped to the suction line, the temperature of the charge is equal to the suction line temperature. As the suction line temperature increases so does the temperature of the charge.
THERMOSTATIC EXPANSION VALVE OPERATING PRESSURES
The valve meters the refrigerant by continuously increasing and decreasing the size of the orifice through which the refrigerant flows.
The orifice opening is adjusted depending on the action of three forces:
1. Force from the spring
2. Force from the evaporator pressure
3. Force from the power element on the diaphragm
The force from the spring and evaporator pressure tend to push up, closing the valve, while the thermostatic power element pushes down, tending to open the valve.
POWER ELEMENT CONSTRUCTION
Together, the bulb, capillary tube, and power head make up what is called the power element, and all three contain the charge (a fluid which is sometimes the same refrigerant running in the system) while the system is running.
CAP TUBE METERING DEVICE REQUIRES CRITICAL CHARGE
Because extreme load conditions could cause excessive flood-back, systems using cap tubes use a limited amount of charge (refrigerant). Such systems are called critical charge systems.
CAP TUBE METERING DEVICE REQUIRES CRITICAL CHARGE
Because extreme load conditions could cause excessive flood-back, systems using cap tubes use a limited amount of charge (refrigerant). Such systems are called critical charge systems.
CAP TUBE METERING DEVICE REQUIRES CRITICAL CHARGE
Because extreme load conditions could cause excessive flood-back, systems using cap tubes use a limited amount of charge (refrigerant). Such systems are called critical charge systems.
CAP TUBE METERING DEVICE OPERATION
In the reverse condition, a decrease in the load, the evaporator pressure is lowered. Although the lower evaporator pressure causes an increased liquid flow from the condenser, the cap tube greatly restricts liquid flow, effectively reducing the total amount of refrigerant flowing through the tube.
CAP TUBE METERING DEVICE CONSTRUCTION
Although the cap tube has no valve or adjustable orifice, it does provide some control of refrigerant flow to the evaporator. It should be noted, though, that this control capability is limited to a very narrow range.
An increase in the load on the evaporator causes an increase in the evaporator pressure. This in turn causes liquid to back up in the condenser where it undergoes additional sub-cooling. Because the refrigerant subsequently arrives at the evaporator at a lower temperature, it is able to absorb more of the load.
CAP TUBE METERING DEVICE FACTORS
Four factors contribute to its effective operation:
1 Tube Length
2 Inside Diameter
3 Tightness of Tube Windings
4 Temperature of Tubing
CAP TUBE METERING DEVICE OPERATION
Cap tubes operate on the principle of capillary action in which molecules of liquid are attracted to another surface. Here the other surface is the inside of the tube. Molecules of gas or vapor do not possess the same capillary action. At the same time, the small diameter tube causes a reduction in flow of the refrigerant.
Capillary action and flow resistance create a pressure and temperature drop in the refrigerant usually around the last quarter of the tube.
Saturday, January 17, 2009
Electricity
Electricity is all around us in the appliances we used in every day of our life. They are
necessities, from light bulbs to TV to Microwave, it provides us heat, cool,
entertainments and safety environment. Electricity could be dangerous if we don’t use
properly.
Two of the major electrical hazards are electrical fire and short circuit.
Some of the fires are caused by electrical system failures and appliance, but most
of the times, those fires are caused by the misuse and poor maintenance of the electrical
appliances. We should never overload the circuit, we should never plug too many
appliances into extension cords. If we are using an extension cord, we need to buy a
heavy-duty cord and make sure it is in good condition. We should never run the extension
cords under a carpet or rug. We should replace all worn, old or damaged appliance cords
immediately. Before using the electrical tools, we need to check those tools regularly for
signs of wear. We need to replace any tool if it causes overheats, smoke or sparks. If we
are using halogen lamps or electrical heaters, we should keep them at least couple feet
away from any type of combustible materials, like clothes, curtains, paper, and furniture.
Remember to turn them off if we are going to leave the room for an extended period of
time. We should never use water to extinguish an electrical fire. Water is a good
conductor of electricity. We should use a fire extinguisher rated with C for electrical
fires. When there was a fire, shut off the main switch before extinguishing the fire. We
also need to check smoke alarm periodically to make sure it is working properly.
Short Circuit is another major electrical hazard. Electricity flows easily through
water. We need to keep power tools, radios, appliances, electric lawn mowers and
other electricity devices away from swimming pools, sprinklers, garden hoses. Electricity
3
can flow through the body more easily if we are standing in the water or on the damp
floor. We should never operate any electric tools in the rain; we should never touch an
electrical appliance while standing on a wet floor; we should never operate an electric
heater, radio when we are in the bathtub or shower. If we drop hair dryers in the water,
pull the plug, don’t just grab the hair dryers. Before cleaning any appliance, we need to
disconnect the power cords. We should never force the plugs into the outlet, never try to
remove the third prong which it is the ground pin to make a three-prong plug fit a twoconductor
outlet. This is very risky practice.
What are the devices to protect us from electricity shock?
If we look around the outlets in our house, we might notice “GFCI” marked on
some of the outlets. We can find those outlets in the bathroom, kitchen, and garage.
What is “GFCI” outlet? A "GFCI" is a ground fault circuit interrupter. A ground fault
circuit interrupter is an inexpensive electrical device. If you don’t find it in your house,
please find an electrician to install it for you. The GFCI is designed to protect people
from severe or fatal electric shocks Because a GFCI detects ground faults, it can also
prevent some electrical fires and reduce the severity of others by interrupting the flow of
electric current.
All GFCIs should be tested once a month to make sure they are working properly
and are protecting us from fatal shock. GFCIs should be tested after installation to make
sure they are working properly and protecting the circuit. To test the receptacle GFCI,
first plug a nightlight or lamp into the outlet. The light should be on Then, press the
"TEST" button on the GFCI. The GFCI's "RESET" button should pop out, and the light
should go out. If the "RESET" button pops out but the light does not go out, the GFCI
4
has been improperly wired. Contact an electrician to correct the wiring errors. If the
"RESET" button does not pop out, the GFC1 is defective and should be replaced. If the
GFCI is functioning properly, and the lamp goes out, press the "RESET" button to
restore power to the outlet.
Fuses and Circuit breakers offer another layer of protection for us. A fuse is the
safety valve of the residential electrical system. A fuse is designed to burn out or blow
out when there is a short circuit. Many houses have circuit breakers instead of fuses.
Instead of blowing out, circuit breakers automatically trip to the off position when short
circuit occurs. When there is a problem, we need to find the cause, before reset the
breaker by pushing the handle to the extreme off position and then to the on position. If
we find the faulty equipments or electrical appliances, have them repaired or replaced.
For some sensitive electrical devices like TV, Computer, and entertainment
systems, we need to buy a surge protector or backup battery protector. To protect the
kids, we should leave “dummy” plugs installed in those unused outlets.
With care and respect, we can prevent fires in our home and avoid injuries from
electricity.
References
U.S. Fire Administration
http://www.usfa.dhs.gov/citizens/all_citizens/home_fire_prev/electrical.shtm
Owatonna Public Utilities: Residential: Electric Safety
http://www.owatonnautilities.com/safety/safety-e-r.php
necessities, from light bulbs to TV to Microwave, it provides us heat, cool,
entertainments and safety environment. Electricity could be dangerous if we don’t use
properly.
Two of the major electrical hazards are electrical fire and short circuit.
Some of the fires are caused by electrical system failures and appliance, but most
of the times, those fires are caused by the misuse and poor maintenance of the electrical
appliances. We should never overload the circuit, we should never plug too many
appliances into extension cords. If we are using an extension cord, we need to buy a
heavy-duty cord and make sure it is in good condition. We should never run the extension
cords under a carpet or rug. We should replace all worn, old or damaged appliance cords
immediately. Before using the electrical tools, we need to check those tools regularly for
signs of wear. We need to replace any tool if it causes overheats, smoke or sparks. If we
are using halogen lamps or electrical heaters, we should keep them at least couple feet
away from any type of combustible materials, like clothes, curtains, paper, and furniture.
Remember to turn them off if we are going to leave the room for an extended period of
time. We should never use water to extinguish an electrical fire. Water is a good
conductor of electricity. We should use a fire extinguisher rated with C for electrical
fires. When there was a fire, shut off the main switch before extinguishing the fire. We
also need to check smoke alarm periodically to make sure it is working properly.
Short Circuit is another major electrical hazard. Electricity flows easily through
water. We need to keep power tools, radios, appliances, electric lawn mowers and
other electricity devices away from swimming pools, sprinklers, garden hoses. Electricity
3
can flow through the body more easily if we are standing in the water or on the damp
floor. We should never operate any electric tools in the rain; we should never touch an
electrical appliance while standing on a wet floor; we should never operate an electric
heater, radio when we are in the bathtub or shower. If we drop hair dryers in the water,
pull the plug, don’t just grab the hair dryers. Before cleaning any appliance, we need to
disconnect the power cords. We should never force the plugs into the outlet, never try to
remove the third prong which it is the ground pin to make a three-prong plug fit a twoconductor
outlet. This is very risky practice.
What are the devices to protect us from electricity shock?
If we look around the outlets in our house, we might notice “GFCI” marked on
some of the outlets. We can find those outlets in the bathroom, kitchen, and garage.
What is “GFCI” outlet? A "GFCI" is a ground fault circuit interrupter. A ground fault
circuit interrupter is an inexpensive electrical device. If you don’t find it in your house,
please find an electrician to install it for you. The GFCI is designed to protect people
from severe or fatal electric shocks Because a GFCI detects ground faults, it can also
prevent some electrical fires and reduce the severity of others by interrupting the flow of
electric current.
All GFCIs should be tested once a month to make sure they are working properly
and are protecting us from fatal shock. GFCIs should be tested after installation to make
sure they are working properly and protecting the circuit. To test the receptacle GFCI,
first plug a nightlight or lamp into the outlet. The light should be on Then, press the
"TEST" button on the GFCI. The GFCI's "RESET" button should pop out, and the light
should go out. If the "RESET" button pops out but the light does not go out, the GFCI
4
has been improperly wired. Contact an electrician to correct the wiring errors. If the
"RESET" button does not pop out, the GFC1 is defective and should be replaced. If the
GFCI is functioning properly, and the lamp goes out, press the "RESET" button to
restore power to the outlet.
Fuses and Circuit breakers offer another layer of protection for us. A fuse is the
safety valve of the residential electrical system. A fuse is designed to burn out or blow
out when there is a short circuit. Many houses have circuit breakers instead of fuses.
Instead of blowing out, circuit breakers automatically trip to the off position when short
circuit occurs. When there is a problem, we need to find the cause, before reset the
breaker by pushing the handle to the extreme off position and then to the on position. If
we find the faulty equipments or electrical appliances, have them repaired or replaced.
For some sensitive electrical devices like TV, Computer, and entertainment
systems, we need to buy a surge protector or backup battery protector. To protect the
kids, we should leave “dummy” plugs installed in those unused outlets.
With care and respect, we can prevent fires in our home and avoid injuries from
electricity.
References
U.S. Fire Administration
http://www.usfa.dhs.gov/citizens/all_citizens/home_fire_prev/electrical.shtm
Owatonna Public Utilities: Residential: Electric Safety
http://www.owatonnautilities.com/safety/safety-e-r.php
Tuesday, January 13, 2009
PURPOSE OF THE AUTOMATIC EXPANSION VALVE:
The automatic expansion valve meters refrigerant to the evaporator based on the evaporator pressure and spring pressure. These two forces act in opposition, the evaporator pressure tending to close the valve and the spring pressure tending to open the valve.
AUTOMATIC EXPANSION VALVE OPERATION
Systems with automatic expansion valves typically have a thermostat or low pressure control to switch the compressor on and off according to suction pressure or temperature.
When the compressor stops for example, low suction temperature results, pressure in the evaporator increases resulting in the AXV driving it closed. This prevents flood-back to the compressor during the off cycle.
AUTOMATIC EXPANSION VALVE
Automatic expansion valves are designed for use in systems with constant load conditions. They are not suitable for use in systems with variable loads.
Also, the AXV capacity should equal the pump capacity as under-capacity valves will starve the evaporator and over-capacity valves will meter too much refrigerant causing sweat backs or frost backs on the suction line.
PURPOSE OF OIL SEPARATOR
Oil separators do precisely what the name implies. They separate oil from the refrigerant in a refrigeration system. Separators are installed on the discharge line (at a point after the refrigerant is discharged from the compressor) and after separating the oil from the refrigerant, return the oil to the compressor via a return line.
LUBRICATION REQUIREMENTS
Compressors require oil for lubricating pistons and bearings. If too much oil is discharged with the refrigerant, damage to the compressor and other system parts can occur, hence the purpose of the oil separator.
In addition to inadequate lubrication of the compressor, excessive amounts of oil in condensers, evaporators, and piping reduce the refrigeration capabilities simply because it takes up space that would otherwise be occupied by the refrigerant.
SEPARATING THE OIL FROM REFRIGERANT
Typical oil separators divert the flow of refrigerant and oil, thereby separating the oil. The oil is collected and returned to the compressor. As the refrigerant vapor and oil pass through the inlet line, the oil, being more dense, collects on the screen.
Because of the change in flow direction, the fact that oil atomizes into tiny droplets instead of vaporizing, and the reduction in flow velocity, the oil drips and collects at the bottom of the separator instead of flowing out the outlet with the refrigerant vapor.
OIL SEPARATOR FLOAT VALVE OPERATION
As the amount of oil collecting at the bottom increases, the float rises. When the float rises to a point where the oil is higher than the valve of the return line, the float valve opens.
Oil is forced through the return line because the discharge pressure in the separator is greater than the suction pressure in the oil return line.
The float continues to rise and fall, opening and closing the valve, as oil collects and is pumped back to the compressor.
OIL SEPARATOR LOCATION
Oil separators should always be installed in the discharge line immediately after the compressor. They need to be at a point where the refrigerant
is in a vapor state for the oil to separate.
The discharge line is the selected placement because:
1. The refrigerant is in a vapor state making the oil less miscible and easier to separate.
2. There is a pressure differential for returning oil to the compressor.
3. It is proximate to the compressor for oil return.
PURPOSE OF OIL SEPARATOR
In most refrigeration systems oil escaping from the compressor is not a major problem and oil separators are usually not necessary. This is because most systems use halocarbons as refrigerants.
Except at low temperatures, oil is quite soluble in halocarbons. As such, oil returns to the compressor with the refrigerant before significant adverse effects occur.
Systems in which oil separators are needed include:
1. Systems using ammonia as a refrigerant because ammonia and oil do not mix.
2. Systems using halocarbons at low temperatures, again because of the poor miscibility with oil.
3. Systems with flooded evaporators which can trap large quantities of oil.
4. Systems which cannot prevent the crankcase oil from absorbing the refrigerant during compressor shutdown.
5. Systems where the discharge velocity of the refrigerant is occasionally reduced, thus allowing the oil to separate instead of being carried along with the refrigerant.
OIL SEPARATOR PROBLEMS
Three potential problems exist when using an oil separator:
· The separator can become cooler than the condenser during an off cycle causing the refrigerant vapor to migrate and condense in the separator. If this occurs, on the next on cycle, refrigerant will flow through the oil return line to the compressor crankcase resulting in possible compressor damage.
· A float valve stuck open will result in the high-temperature high-pressure refrigerant vapor raising the pressure and temperature at the suction side of the compressor which could overheat the motor and reduce system capacity.
· A float valve stuck closed will result in no oil return to the compressor. Insufficient oil for lubricating the compressor can also cause compressor damage.
THE PURPOSE OF HEAT EXCHANGERS
The purpose of the heat exchanger is two fold:
1. To evaporate "slop over" (excess liquid not evaporated in the evaporator) in the suction line, thereby preventing liquid from entering the compressor.
2. To further sub-cool the liquid in the liquid line, thus improving system capacity.
Heat exchangers are designed simply by bringing the liquid line and suction line piping in contact with each other.
PRECAUTIONS IN ADDING HEAT EXCHANGERS
Heat exchangers should not be added to a refrigeration system without a thorough examination of its effects on the system. Improper application of a heat exchanger could cause damage to the compressor. In particular, two precautions should be observed above all:
1. Heat exchangers are not normally used in systems running refrigerant R-22. Condensing pressures in R-22 systems are usually quite high and an increase in the suction line superheat would raise the discharge temperature so high that the compressor could easily overheat.
2. In systems with hermetic motor compressors the motors are cooled with the suction vapor. Excessive heating of the suction gas could again overheat the compressor and cause damage.
RECEIVER PURPOSE
The receiver is a refrigeration accessory which is simply a storage tank used to accumulate liquid refrigerant from the condenser.
Ideally, the refrigeration system boils off the refrigerant in the evaporator at the same rate it condenses in the condenser resulting in a uniform rate of refrigerant flow throughout the system. In small systems, such as domestic refrigerators and room air conditioners, this can be achieved, and receivers are not needed.
However, in larger systems this is not the case, and receivers are used as temporary storage containers of liquid refrigerant. Receivers are also useful as storage tanks for the refrigerant during shut-down.
FRONT SEATED
If the valve is front seated (stem set all the way to the front), the discharge line (or suction line with the suction service valve) is closed off.
As such, the connection between the compressor and condenser is shut off with the front-seated discharge service valve and the evaporator/compressor connection is shut off with the front-seated suction service valve.
Extreme care should be taken when front seating the discharge service valve with the compressor running because excessively high pressures will build up. When the compressor is running, front seating the discharge service valve should only be performed by an experienced, well-qualified technician for closed-loop capacity checks.
With the compressor off, both service valves can be front seated to isolate the compressor from the rest of the system. The purpose of isolating the system is for maintenance or replacement of the compressor. As such, the service valves allow relatively easy replacement of compressors. The only refrigerant lost is that between the service valves and only the new compressor has to be evacuated.
MID-POSITION
The final position of the valve is mid-positioned, sometimes referred to as cracked. In this position, refrigerant is allowed to flow through the system as normal yet the service port is still opened.
The technician can connect gauges to the service port or ports (with the valve back seated) then crack the valve to monitor system operation (either or both suction line and discharge line) while the system is running.
SERVICE VALVE LOCATIONS
In general, service valves can be installed on most any line for service purposes. However, the suction service valve specifically is installed between the low side of the compressor and the suction line.
The discharge service valve is installed between the high side of the compressor and the discharge line.
Gauges are connected to the service port of either or both service valves.
PURPOSE OF CHECK VALVE
The check valve is a device used in refrigeration systems to prevent refrigerant (liquid and/or vapor) from flowing in the wrong direction. Check valves are also used to stop vapor refrigerant from migrating through the piping during off cycles.
The valve illustrated here is a spring loaded check valve. Magnetic check valves are also available.
Electricity Safety
TAGS. When any electrical equipment is to be repaired or replaced, the main supply switches or cutout switches in each circuit from which power could possibly be fed should be secured in the open position and tagged.
The tag should read, "This circuit is open for repairs". After work has been completed the technician performing the work should remove the tag(s).
SAFETY DEVICES
The covers of fuse boxes and junction boxes should be kept securely closed except while being serviced; safety devices such as interlocks, overload relays, and fuses should never be altered or disconnected except for replacements.
The interlock switch is usually wired in series with the power-line leads to the power supply unit, and is installed on the lid or door of the enclosure to break the circuit when the lid or door is opened. (See animation below.)
A true interlock switch is entirely automatic in action. Multiple interlock switches, connected in a series, may be used for increased safety.
One switch may be installed on the access door of a device, and another on the cover of the power-supply section. If panel is opened for service always use a voltmeter to check for power.
High Voltage Safety Precautions
Death can be the direct result of violating a basic safety practice and indirectly an individuals lack of equipment knowledge.
Many pieces of electrical equipment employ voltages which are dangerous and may be fatal if contacted. Practical safety precautions are incorporated into most electrical systems:
Basic Rules for High Voltage Precautions
These rules are your greatest safeguard and may prevent serious injury or even death.
Working on Energized Circuits
Repair work on energized circuits should not be undertaken whenever practicable. Only experienced personnel should do essential repairs and every safety precaution should be utilized.
The technician should be insulated from ground with some suitable non-conducting material, such as dry canvas, dry wood, rubber-soled shoes, or a rubber mat of approved construction.
The technician should use only one hand in doing repairs if possible and an assistant should be near the main switch so the equipment can be de-energized immediately in case of an emergency.
Personnel should be trained in first aid for electric shock.
Grounding of Equipment and Tools
A poor safety ground, or one that is wired incorrectly, is more dangerous than no ground at all. The poor ground is dangerous because it does not offer full protection.
The incorrectly wired ground is a hazard because if one of the line wires and the safety ground are transposed, it makes the shell of the tool "hot" the instant the plug is connected.
The old method of using a separate external grounding wire has been discontinued.
Instead, a 3-wire, standard, color-coded cord with a polarized plug and ground pin is required. In this manner, the safety ground is made a part of the connecting cord and plug.
Since the polarized plug can be connected only to a mating receptacle, the user has no choice but to use the safety ground.
All new tools, properly connected, use the green wire as the safety ground.
This wire is attached to the metal case of the tool at one end and to the polarized grounding pin in the connector at the other end. It normally carries no current, but is used only when the tool insulation fails, in which case it short circuits the electricity around the user to the ground and protects them from shock.
The green lead must never be mixed with the black or white leads that are the true current-carrying conductors.
Check the resistance of the grounding system with a low reading ohmmeter to be certain that the grounding is adequate (less than 1 ohm is acceptable).
If the resistance indicates greater than 1 ohm, use a separate ground strap. Some old installations are not equipped with receptacles that will accept the grounding plug. In this event, use one of the following methods:
1. Use an adapter fitting.
2. Use the old type plug and bring the green ground wire out separately.
3. Connect an independent safety ground line.
When using the adapter, be sure to connect the ground lead extension to a good ground. (Do not use the center screw that holds the cover plate on the receptacle.)
Where the separate safety ground leads are externally connected to a ground, be certain to first connect the ground and then plug in the tool.
Likewise, when disconnecting the tool, first remove the line plug and then disconnect the safety ground. The safety ground is always connected first and removed last.
Safety Precautions When Using Hand Tools
All tools being used should be maintained.
Any damaged or non-working tools should be repaired or discarded.
Screwdrivers, and other hand tools, should have non-conducting handles.
Portable Power Tools
All power tools should be inspected before being used, especially check cords to be sure they are free of any defects, and cords should not be run over, kinked, or patched with tape.
Electrical Hazards
Each person who works with electrical equipment must make it their responsibility to be alert to electrical hazards, be familiar with safety procedures, and identify and eliminate unsafe conditions.
How to Handle Electrical Shock and What to Do
Electric shock is a jarring, shaking sensation resulting from contact with electric circuits or lightning.
The Molecule
The molecule is the smallest particle to which a substance can be reduced and still be called the same name.
The Atom
The atom is the smallest particle that makes up the type of material called an element. The atom is broken into smaller pieces called electrons, protons, and neutrons.
Protons and neutrons are in the center of the atom with the electrons circling around the outside like planets around the sun. The orbit that the electron moves in is called a shell.
The electrical charge associated with an electron is negative and the proton is considered positive and the neutron neutral.
The element is the basic building block from which all matter is made and still retains its characteristics when subdivided into atoms.
A compound is composed of two or more elements.
Valence Shell
The outer shell of the atom is called the valence shell and the electrons are called valence electrons.
The valence electrons are very important in electronics because they can be easily freed and used to perform work. Electrons are arranged in shells and the number of shells depends on the element.
Two conditions that exist that cause an element to be a good conductor are:
How many electrons are in the valence shell, and
How far the valence shell is from the nucleus.
If an element has 8 electrons in its valence shell it is said to be stable, or a poor conductor, (an atom never contains more than 8 electron in it’s valence shell). If an element has one electron in the valence shell it is a good conductor because that electron can be easily dislodged.
Because the proton in the nucleus is positively charged and the electron is negatively charged they are attracted to each other.
Centrifugal force created by the electron moving in an orbit around the nucleus is what keeps them apart. The greater the distance between the electron and the nucleus the weaker the bond is and the easier it is to dislodge the electron.
The shell closest to the nucleus has up to two electrons.
The second shell contains up to 8 electrons, the third shell up to 18 electrons, and the fourth shell up to 32 electrons.
Elements such as copper, gold and silver each have one valence electron therefore these electrons are easily removed and considered good conductors.
Conductors
Are substances that permit the free motion of a large number of electrons.
Copper is considered a good conductor because it has many free electrons that migrate from atom to atom inside the conductor; electrical energy is transferred through conductors by the movement of the free electrons.
Some examples: Conductors
Silver
Gold
Copper
Aluminum
Zinc
Brass
Iron
Insulators
Are the poorest conductors as insulators they prevent the current from being diverted from the wires.
Insulators have five or more electrons in their valence shells.
Some examples: Insulators
Dry air
Glass
Mica
Rubber
Asbestos
Bakelite
Semi-conductor
Is neither a good conductor nor insulator made of germanium and silicon, which has four electrons in its valence shell, sometimes acts as a conductor and sometimes as an insulator.
Charged Bodies
One of the fundamental laws of electricity is that LIKE CHARGES REPEL EACH OTHER and UNLIKE CHARGES ATTRACT EACH OTHER.
A positive charge and a negative charge, since they are not alike, move toward each other.
Coulomb’s Law of Charges
CHARGED BODIES ATTRACT OR REPEL EACH OTHER WITH A FORCE THAT IS DIRECTLY PROPORTIONAL TO THE PRODUCT OF THEIR CHARGES, AND IS INVERSELY PROPORTIONAL TO THE SQUARE OF THE DISTANCE BETWEEN THEM.
The amount of attracting or repelling force which acts between two electrically charged bodies in free space depends on two things:
Their charge and
2. The distance between them.
Electric Fields
Electric fields are defined as the space between and around charged bodies.
Imaginary lines referred to as electrostatic lines of force usually represent this field.
A positive charge is always shown leaving the charge and a negative charge is shown as entering.
Magnetism
A magnet attracts substances such as iron steel, nickel, or cobalt. Magnetic poles are the points of maximum attraction.
All magnets have two poles, the north pole and the south pole.
Magnets are divided into three groups:
Natural magnets found in a mineral called magnetite.
2. Permanent magnets, which are bars of hardened steel.
3. Electromagnets are a soft iron core, which are wound by coils of insulated wire. When current flows through the coil the core becomes magnetized.
Nature of Magnetism
Weber’s theory considers the molecular alignment of the material. The theory assumes all magnetic substances are composed of molecular magnets.
A magnetized material will have most of its molecular magnets lined up so that the north pole of each molecule points in one direction and the south pole faces the opposite direction.
This theory is supported by the fact that if the magnet is split in half the pieces each has a north and south pole.
Magnetic Fields and Lines of Force
The poles of the magnet are where the attractive force is the greatest.
The magnetic lines of force are the lines in which the needle of a compass aligns itself.
A magnetic field is the space surrounding the magnet.
Characteristics of lines of force are described as follows:
1. Magnetic lines of force are continuous and always form closed loops.
2. Magnetic lines of force never cross one another.
3. Parallel magnetic lines of force traveling in the same direction repel each other. Parallel lines of force traveling in the opposite direction tend to unite and form into single lines.
4. Magnetic lines of force tend to shorten themselves.
5. Magnetic lines of force pass through all materials.
Laws of Attraction and Repulsion
1. Like magnetic poles repel each other.
2. Unlike magnetic poles attract each other.
3. The force of attraction or repulsion existing between two magnets decreases when the distance increases
Difference in Potential
As discussed earlier an atom has positively charged protons and negatively charged electrons.
If the atom has the same number of electrons as it has protons it is said to have a neutral charge-neither negative nor positive.
If an electron is removed from an atom it will have more protons (positive) than electrons (negative) and will therefore be a positively charged atom.
If an atom has more electrons than protons it will be negatively charged.
An atom will always try to be in balance (neutral), so if it is positively charged it will attract an electron from another atom. If it is negatively charged it will reject an electron to a neighboring atom.
Electrons move freely between atoms in a random fashion constantly, but when we cause them to all move in the same direction we create “current flow” or what we call “electricity”.
The force that causes free electrons to move in a conductor as an electric current are referred to as follows:
1. EMF electromotive force.
2. Voltage.
Difference in potential.
Potential difference is another name for electrical force.
The potential for producing current exists even though no current is presently flowing.
A difference in potential exists between two charged bodies that are connected by a conductor, has electrons that flow along the conductor, this flow is from the negatively charged body to the positively charged body until the two charges are equalized and the potential difference no longer exists.
The fundamental law of current electricity is the current is directly proportional to the applied voltage that is, if the voltage is increased the current is increased.
Transversely if the voltage is decreased the current is decreased.
friction
Friction - voltage produced by rubbing two materials together.
Voltage produced by friction.
The least common used. For example when you walk across a carpet and get an unpleasant shock referred to as static electricity, which can also interfere with radio communications.
The main use is for Van de Graf generators used in laboratories to produce high voltages.
Pressure
Pressure- voltage produced by squeezing crystals of certain substances together.
Voltage produced by pressure.
This is referred to as piezoelectricity. Compressing or decompressing crystals of certain substances produces voltage.
Crystals are defined as molecules arranged in an orderly and uniform manner. They are useful because of their extreme sensitivity to changes of mechanical force or change in temperature.
They are primarily used in communication equipment.
heat
Heat-voltage produced by heating the joint where two unlike metals are joined.
Voltage produced by heat.
Voltage produced by heat is referred to as thermoelectricity.
When a metal such as a copper is heated at one end, electrons move away from the hot end to the cooler end.
This is true of most metals however, in iron, the opposite takes place and electrons move toward the hot end.
The negative charges (electrons) are moving through copper away from the heat and through the iron toward the heat. They cross at the hot junction this is known as a thermocouple.
This is used in heat-sensing devices such as automatic temperature control equipment.
light
Light-voltage produced by light striking photosensitive substances.
Voltage produced by light.
In photoelectricity light strikes a surface of a substance and dislodges electrons from their orbits, this occurs because light has energy.
The photosensitive material most commonly used to produce voltage is silver oxide or copper oxide.
The cell has a curved light sensitive surface focused on the central anode. Light energy is converted to a flow of electrons and a usable current is developed.
This type of power is small but successfully used in television cameras, door openers, burglar alarms, and any photoelectric cell devices.
chemical
Chemical action- voltage produced by chemical reaction in a battery cell.
Voltage produced by chemical action.
When molecules of a substance are altered this action is referred to as chemical action.
This means the molecules have been combined with another substance or gives up atoms of its own. If atoms are added to or taken away from the molecules of a substance this chemical change will cause the substance to take on an electrical charge.
This process is used in batteries.
magnetism
Magnetism- voltage produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through a conductor in such a manner as to cut the magnetic lines of the force of the field.
Voltage produced by magnetism.
Three conditions must exist before voltage can be produced by magnetism.
1. There must be a conductor in which voltage will be produced.
There must be a magnetic field in the conductor’s vicinity.
There must be relative motion between the field and the conductor.
With these conditions present when a conductor(s) moves across a magnetic field and cuts lines of force, electrons within the conductor are impelled in one direction or another; thus, an electric force or voltage is created.
This is used to produce vast quantities of electric power from mechanical sources. The mechanical power may be provided by different power such as gasoline, diesel, water, or steam turbines.
Electric Current - electron flow
The flow of electrons through a conductor is called an electric current or electron flow.
The movement of electrons will be from a negative potential to a positive potential and is called by various terms, current, current flow, electron flow, and electron current.
There are two types of current, direct current and alternating current.
Direct current flows in the same direction whereas an alternating current periodically changes direction.
Electric Current - AMPERE
Ampere is the term used to define the unit of measurement for current the abbreviation is amp. The amp is abbreviated A.
Electric Current - COULOMB
Coulomb the unit of measurement for electrical charge.
The COULOMB is a unit quantity of electricity moved through an electric current when 1 ampere of current flows for 1 second of time, this is equivalent to 6.28 x 10 to the power of 18 electrons.
The symbol for coulomb is “ Q “. The coulomb is to electricity as the gallon is to water.
Resistance
Every material offers resistance. Good conductors offer little resistance such as copper, silver, aluminum, poor conductors are glass, wood, paper, which offer high resistance to current flow.
The size and type of material of wires are chosen to keep electrical resistance as low as possible.
The larger the diameter of the wires the lower will be their resistance (opposition) to the flow of current through them.
Resistance is expressed by the symbol “ R “ and is measured by OHMS. The Greek letter omega right side up W represents resistance.
Conductance
The term that is the opposite of resistance is conductance (G).
The symbol for conductance is the Greek letter omega upside down.
CONDUCTANCE is the ability of a material to pass electrons.
The formula is written as follows:
G (conductance) = 1/R (resistance)
Cell
A device that transforms chemical energy into electrical energy.
The cell is the fundamental unit of the battery; the simple cell consists of two strips or electrodes, placed in a container that holds the electrolyte.
Battery
A battery consists of two or more cells placed in a common container. The cells are connected in series, in parallel, or a combination of both depending on the amount of voltage required of the battery.
Batteries are used in direct current electrical energy automobiles, boats, aircraft, ships, and portable electronics equipment.
Battery Chemistry
If a conductor is connected externally to the electrodes of a cell, electrons will flow under the influence of a difference in potential across the electrodes from the zinc (negative) through the external conductor to the carbon (positive), returning within the electrolyte solution to the zinc.
After a short period of time, the zinc will begin to burn (waste away) because of the electrolyte. If zinc is surrounded by oxygen, it will burn as a fuel.
Energy is released by the zinc and is transformed into electrical energy rather than heat energy.Series connected cells
When the negative electrode of the first cell is connected to the positive electrode of the second cell, the negative electrode of the second cell is connected to the positive of the third cell this is called series connected cells.
The positive electrode of the first cell and the negative electrode of the last cell then serve as the power takeoff terminals of the battery.
Parallel connected cells
Parallel connected cells are used when more power is needed but using the same voltage.
In a parallel connection all positive connections are connected to one line and all negative are connected to one line.
Series-Parallel Connected Cells
In the graphic below a group of three cells are connected in a series. Then two series groups of three are connected in parallel.
This is used when higher voltage and increased current capacity are needed.
Simple Electric Circuit
An electric circuit is a completed conducting pathway, consisting not only of the conductor but also including the path through the voltage source.
Current flows from the positive terminal through the source and emerges at the negative terminal.
Ohm’s Law
A relationship exists between current, voltage, and resistance.
The current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance. This law is written as follows:
I=E/ R
Where:
I = current in amperes
E= potential in volts
R = resistance in ohms
An ohm is defined as a unit of electrical resistance.
(Represented by the Greek symbol omega W .)
Applying OHM’S Law
To determine the unknown quantity in an equation cover that quantity with your finger, the remaining letters will be the mathematical operation to be performed. For example to find I cover I, the uncovered letters are E divided by R.
OHMS LAW IN DIAGRAM FORM
See Image Below:
OHMS LAW IN THREE DIFFERENT EQUATIONS
I (current)= E (voltage) / R (resistance)
E= IR (I x R)
R= (E / I )
I = (E / R)
Electric Power and Energy Power
Power, whether electrical or mechanical, is the rate of work being done.
The basic unit of power is measured in watts and is equal to the voltage across a circuit multiplied by current through the circuit.
P indicates the symbol for power the basic power formula is P= E x I, E is the voltage across and I is the current through the resistor.
Forms of energy are light, heat, and motion. Work is done whenever a force causes motion.
P = I E (I x E)
I = (P / E)
E = (P / I)
P = E x I
Where E = 2 volts and I = 2 amps
P = 2 x 2
P = 4 watts
Rating of Electrical Devices by Power
Lamps, fans, and motors are electrical devices rated in watts.
The wattage rating of a device indicates the rate at which the device converts electrical energy into another energy such as light, heat and motion.
If the normal wattage rating is exceeded the equipment will overheat and may cause damage.
Rating of Electrical Devices by Power
Lamps, fans, and motors are electrical devices rated in watts.
The wattage rating of a device indicates the rate at which the device converts electrical energy into another energy such as light, heat and motion.
If the normal wattage rating is exceeded the equipment will overheat and may cause damage.
Power Capacity of Electrical Devices
Wattage rating of a device indicates the device’s operating limits; the limits are given as maximum or minimum safe voltages that a device can be subjected to.
If a device is not limited to any specific voltage its limits are given in watts.
Resistors
A resistor is defined as a circuit element whose basic characteristic is resistance, it is used to oppose the flow of current this device is used in circuits with widely different voltages
Fuses
Fuses are metal resistors with low resistance values. They are designed to blow out and open a circuit when current exceeds the fuse’s rated value.
Resistance
The total circuit resistance (Rt) is equal to the sum of the individual resistances.
For example the current in a series circuit in completing its electrical path must flow through each lamp, each lamp offers added resistance.
As an equation:
Rt = R1 + R2 + R3………Rn
Voltage
Voltage is the measure of electromotive force or EMF. Volt is the unit of measurement for electromotive force.
In a series circuit the total voltage is equal to the applied voltage.
Power
Power is the rate of doing work in an electrical circuit or rate of expending energy the symbol for power is P and measured in watts.
In a series circuit the total power is equal to the SUM of the powers dissipated by the individual resistors.
Total power is PT=p1+p2+p3+……Pn.
Rules for Series DC Circuits
Factors governing the operation of a series circuit.
The same current flows through each part of a series circuit.
The total resistance of a series circuit is equal to the sum of the individual resistors.
The total voltage across a series circuits is equal to the sum of the individual voltage.
The voltage drop across a resistor in a series circuit is proportional to the size of the resistor.
The total power dissipated in a series circuit is equal to the sum of the individual power dissipations.
Ground
The earth ground is said to be zero potential, the term GROUND is used to denote a common electrical point of zero potential.
Open Circuits
A circuit is open when a break exists in a complete conducting pathway. An open occurs any time a switch is thrown to de-energize a circuit.
Short Circuit
A short circuit is an accidental path of low resistance that would have basically the same effect, however the short will cause an increase in current and the possibility of component damage.
Parallel Circuit Characteristics
A parallel circuit is defined as one having more than one current path connected to a common voltage source.
Voltage
In a parallel circuit the same voltage is present across all the resistors of a parallel group.
Current Division
The current in a circuit is inversely proportional to the circuit resistance.
The current divides in a parallel circuit among the available paths in relation to the value of the resistors.
Parallel Resistance
The total resistance in a parallel circuit must be less than any individual resistor in the circuit.
PARALLEL RESISTANCE FORMULA
Product over sum is a convenient formula for finding the equivalent resistance of two parallel resistors.
The formula for finding the equivalent resistance of two parallel resistors is as follows: R t is circuit resistance.
R t = 1 / ( (1/R1 ) + ( 1/R2) )
Effects of Source Resistance
Every known source has resistance. Internal source resistance affects the total power dissipated and also affects the transfer of power. The presence of internal resistance results in:
Less voltage supplied to the components.
Decrease in total current.
Increase in total resistance.
Series-Parallel Circuit
The majority of circuits is a combination of series and parallel elements and is referred to as series-parallel circuits.
An electrical circuit where both series and parallel components are used the series components feel the total current for the circuit, while the parallel components feel only that current which flows through that particular branch.
Total resistance for the series-parallel circuit is determined by combining both series and the parallel methods of calculating resistance.
Specific Resistance or Resistivity
Specific resistance or resistivity is the resistance in ohms offered by unit volume of a substance to the flow of electric current.
Resistivity is the reciprocal of conductivity.
Relation Between Wire Sizes
Wires are manufactured in sizes on a table known as the American wire gage (AWG).
Wire diameters become smaller as the gage numbers become larger.
A wire gage is the instrument used to measure the diameter of wire.
Stranded Wires and Cables
A wire is a slender rod or filament of drawn metal. If a wire is covered with insulation it is called an insulated wire.
A conductor is a wire or combination of wires not insulated from one another.
A stranded conductor is a conductor composed of a group of wires these wires are usually twisted together.
A cable is either a stranded conductor or a combination of conductors insulated from one another. In general the word cable usually applies to larger conductors.
Factors governing the selection of wire size
(Allowance must be made for the influence of external heat.)
Allowable power loss in line, the loss represents electrical energy converted into heat.
Voltage drops in the line.
Current carrying ability of the line.
Current carrying capacities (in amperes) of single copper conductors at ambient temperature of below 30 ยบ C see chart below.
Conductor Insulation
Insulation is coating over the wires so that they do not come into contact with one another, other equipment, or people.
Two properties of insulation are insulation resistance and dielectric strength.
Insulation resistance
Is the resistance to current leakage through the insulation.
Dielectric strength
Is the ability of the insulator to withstand potential difference. To test this raise the voltage in a sample until the insulation breaks down.
Rubber
The most common type of insulation is rubber. The thicker the insulation the higher the voltage.
A thin coating of tin or cotton must be used between the wire and the rubber, or the rubber will become soft and gummy.
Plastic
Is another good type of insulation it has flexibility and is moisture resistant.
Varnished cambric
Is made of cotton cloth coated by varnish. It can stand much higher temperatures than rubber.
Paper
Serves as a satisfactory insulator when impregnated by high-grade mineral oil. Paper works well on high voltage cable.
Silk and Cotton
This is used in communications circuits the threads are wrapped around individual conductors, in reverse directions and coated with a special wax compound.
The tag should read, "This circuit is open for repairs". After work has been completed the technician performing the work should remove the tag(s).
SAFETY DEVICES
The covers of fuse boxes and junction boxes should be kept securely closed except while being serviced; safety devices such as interlocks, overload relays, and fuses should never be altered or disconnected except for replacements.
The interlock switch is usually wired in series with the power-line leads to the power supply unit, and is installed on the lid or door of the enclosure to break the circuit when the lid or door is opened. (See animation below.)
A true interlock switch is entirely automatic in action. Multiple interlock switches, connected in a series, may be used for increased safety.
One switch may be installed on the access door of a device, and another on the cover of the power-supply section. If panel is opened for service always use a voltmeter to check for power.
High Voltage Safety Precautions
Death can be the direct result of violating a basic safety practice and indirectly an individuals lack of equipment knowledge.
Many pieces of electrical equipment employ voltages which are dangerous and may be fatal if contacted. Practical safety precautions are incorporated into most electrical systems:
Basic Rules for High Voltage Precautions
These rules are your greatest safeguard and may prevent serious injury or even death.
Working on Energized Circuits
Repair work on energized circuits should not be undertaken whenever practicable. Only experienced personnel should do essential repairs and every safety precaution should be utilized.
The technician should be insulated from ground with some suitable non-conducting material, such as dry canvas, dry wood, rubber-soled shoes, or a rubber mat of approved construction.
The technician should use only one hand in doing repairs if possible and an assistant should be near the main switch so the equipment can be de-energized immediately in case of an emergency.
Personnel should be trained in first aid for electric shock.
Grounding of Equipment and Tools
A poor safety ground, or one that is wired incorrectly, is more dangerous than no ground at all. The poor ground is dangerous because it does not offer full protection.
The incorrectly wired ground is a hazard because if one of the line wires and the safety ground are transposed, it makes the shell of the tool "hot" the instant the plug is connected.
The old method of using a separate external grounding wire has been discontinued.
Instead, a 3-wire, standard, color-coded cord with a polarized plug and ground pin is required. In this manner, the safety ground is made a part of the connecting cord and plug.
Since the polarized plug can be connected only to a mating receptacle, the user has no choice but to use the safety ground.
All new tools, properly connected, use the green wire as the safety ground.
This wire is attached to the metal case of the tool at one end and to the polarized grounding pin in the connector at the other end. It normally carries no current, but is used only when the tool insulation fails, in which case it short circuits the electricity around the user to the ground and protects them from shock.
The green lead must never be mixed with the black or white leads that are the true current-carrying conductors.
Check the resistance of the grounding system with a low reading ohmmeter to be certain that the grounding is adequate (less than 1 ohm is acceptable).
If the resistance indicates greater than 1 ohm, use a separate ground strap. Some old installations are not equipped with receptacles that will accept the grounding plug. In this event, use one of the following methods:
1. Use an adapter fitting.
2. Use the old type plug and bring the green ground wire out separately.
3. Connect an independent safety ground line.
When using the adapter, be sure to connect the ground lead extension to a good ground. (Do not use the center screw that holds the cover plate on the receptacle.)
Where the separate safety ground leads are externally connected to a ground, be certain to first connect the ground and then plug in the tool.
Likewise, when disconnecting the tool, first remove the line plug and then disconnect the safety ground. The safety ground is always connected first and removed last.
Safety Precautions When Using Hand Tools
All tools being used should be maintained.
Any damaged or non-working tools should be repaired or discarded.
Screwdrivers, and other hand tools, should have non-conducting handles.
Portable Power Tools
All power tools should be inspected before being used, especially check cords to be sure they are free of any defects, and cords should not be run over, kinked, or patched with tape.
Electrical Hazards
Each person who works with electrical equipment must make it their responsibility to be alert to electrical hazards, be familiar with safety procedures, and identify and eliminate unsafe conditions.
How to Handle Electrical Shock and What to Do
Electric shock is a jarring, shaking sensation resulting from contact with electric circuits or lightning.
The Molecule
The molecule is the smallest particle to which a substance can be reduced and still be called the same name.
The Atom
The atom is the smallest particle that makes up the type of material called an element. The atom is broken into smaller pieces called electrons, protons, and neutrons.
Protons and neutrons are in the center of the atom with the electrons circling around the outside like planets around the sun. The orbit that the electron moves in is called a shell.
The electrical charge associated with an electron is negative and the proton is considered positive and the neutron neutral.
The element is the basic building block from which all matter is made and still retains its characteristics when subdivided into atoms.
A compound is composed of two or more elements.
Valence Shell
The outer shell of the atom is called the valence shell and the electrons are called valence electrons.
The valence electrons are very important in electronics because they can be easily freed and used to perform work. Electrons are arranged in shells and the number of shells depends on the element.
Two conditions that exist that cause an element to be a good conductor are:
How many electrons are in the valence shell, and
How far the valence shell is from the nucleus.
If an element has 8 electrons in its valence shell it is said to be stable, or a poor conductor, (an atom never contains more than 8 electron in it’s valence shell). If an element has one electron in the valence shell it is a good conductor because that electron can be easily dislodged.
Because the proton in the nucleus is positively charged and the electron is negatively charged they are attracted to each other.
Centrifugal force created by the electron moving in an orbit around the nucleus is what keeps them apart. The greater the distance between the electron and the nucleus the weaker the bond is and the easier it is to dislodge the electron.
The shell closest to the nucleus has up to two electrons.
The second shell contains up to 8 electrons, the third shell up to 18 electrons, and the fourth shell up to 32 electrons.
Elements such as copper, gold and silver each have one valence electron therefore these electrons are easily removed and considered good conductors.
Conductors
Are substances that permit the free motion of a large number of electrons.
Copper is considered a good conductor because it has many free electrons that migrate from atom to atom inside the conductor; electrical energy is transferred through conductors by the movement of the free electrons.
Some examples: Conductors
Silver
Gold
Copper
Aluminum
Zinc
Brass
Iron
Insulators
Are the poorest conductors as insulators they prevent the current from being diverted from the wires.
Insulators have five or more electrons in their valence shells.
Some examples: Insulators
Dry air
Glass
Mica
Rubber
Asbestos
Bakelite
Semi-conductor
Is neither a good conductor nor insulator made of germanium and silicon, which has four electrons in its valence shell, sometimes acts as a conductor and sometimes as an insulator.
Charged Bodies
One of the fundamental laws of electricity is that LIKE CHARGES REPEL EACH OTHER and UNLIKE CHARGES ATTRACT EACH OTHER.
A positive charge and a negative charge, since they are not alike, move toward each other.
Coulomb’s Law of Charges
CHARGED BODIES ATTRACT OR REPEL EACH OTHER WITH A FORCE THAT IS DIRECTLY PROPORTIONAL TO THE PRODUCT OF THEIR CHARGES, AND IS INVERSELY PROPORTIONAL TO THE SQUARE OF THE DISTANCE BETWEEN THEM.
The amount of attracting or repelling force which acts between two electrically charged bodies in free space depends on two things:
Their charge and
2. The distance between them.
Electric Fields
Electric fields are defined as the space between and around charged bodies.
Imaginary lines referred to as electrostatic lines of force usually represent this field.
A positive charge is always shown leaving the charge and a negative charge is shown as entering.
Magnetism
A magnet attracts substances such as iron steel, nickel, or cobalt. Magnetic poles are the points of maximum attraction.
All magnets have two poles, the north pole and the south pole.
Magnets are divided into three groups:
Natural magnets found in a mineral called magnetite.
2. Permanent magnets, which are bars of hardened steel.
3. Electromagnets are a soft iron core, which are wound by coils of insulated wire. When current flows through the coil the core becomes magnetized.
Nature of Magnetism
Weber’s theory considers the molecular alignment of the material. The theory assumes all magnetic substances are composed of molecular magnets.
A magnetized material will have most of its molecular magnets lined up so that the north pole of each molecule points in one direction and the south pole faces the opposite direction.
This theory is supported by the fact that if the magnet is split in half the pieces each has a north and south pole.
Magnetic Fields and Lines of Force
The poles of the magnet are where the attractive force is the greatest.
The magnetic lines of force are the lines in which the needle of a compass aligns itself.
A magnetic field is the space surrounding the magnet.
Characteristics of lines of force are described as follows:
1. Magnetic lines of force are continuous and always form closed loops.
2. Magnetic lines of force never cross one another.
3. Parallel magnetic lines of force traveling in the same direction repel each other. Parallel lines of force traveling in the opposite direction tend to unite and form into single lines.
4. Magnetic lines of force tend to shorten themselves.
5. Magnetic lines of force pass through all materials.
Laws of Attraction and Repulsion
1. Like magnetic poles repel each other.
2. Unlike magnetic poles attract each other.
3. The force of attraction or repulsion existing between two magnets decreases when the distance increases
Difference in Potential
As discussed earlier an atom has positively charged protons and negatively charged electrons.
If the atom has the same number of electrons as it has protons it is said to have a neutral charge-neither negative nor positive.
If an electron is removed from an atom it will have more protons (positive) than electrons (negative) and will therefore be a positively charged atom.
If an atom has more electrons than protons it will be negatively charged.
An atom will always try to be in balance (neutral), so if it is positively charged it will attract an electron from another atom. If it is negatively charged it will reject an electron to a neighboring atom.
Electrons move freely between atoms in a random fashion constantly, but when we cause them to all move in the same direction we create “current flow” or what we call “electricity”.
The force that causes free electrons to move in a conductor as an electric current are referred to as follows:
1. EMF electromotive force.
2. Voltage.
Difference in potential.
Potential difference is another name for electrical force.
The potential for producing current exists even though no current is presently flowing.
A difference in potential exists between two charged bodies that are connected by a conductor, has electrons that flow along the conductor, this flow is from the negatively charged body to the positively charged body until the two charges are equalized and the potential difference no longer exists.
The fundamental law of current electricity is the current is directly proportional to the applied voltage that is, if the voltage is increased the current is increased.
Transversely if the voltage is decreased the current is decreased.
friction
Friction - voltage produced by rubbing two materials together.
Voltage produced by friction.
The least common used. For example when you walk across a carpet and get an unpleasant shock referred to as static electricity, which can also interfere with radio communications.
The main use is for Van de Graf generators used in laboratories to produce high voltages.
Pressure
Pressure- voltage produced by squeezing crystals of certain substances together.
Voltage produced by pressure.
This is referred to as piezoelectricity. Compressing or decompressing crystals of certain substances produces voltage.
Crystals are defined as molecules arranged in an orderly and uniform manner. They are useful because of their extreme sensitivity to changes of mechanical force or change in temperature.
They are primarily used in communication equipment.
heat
Heat-voltage produced by heating the joint where two unlike metals are joined.
Voltage produced by heat.
Voltage produced by heat is referred to as thermoelectricity.
When a metal such as a copper is heated at one end, electrons move away from the hot end to the cooler end.
This is true of most metals however, in iron, the opposite takes place and electrons move toward the hot end.
The negative charges (electrons) are moving through copper away from the heat and through the iron toward the heat. They cross at the hot junction this is known as a thermocouple.
This is used in heat-sensing devices such as automatic temperature control equipment.
light
Light-voltage produced by light striking photosensitive substances.
Voltage produced by light.
In photoelectricity light strikes a surface of a substance and dislodges electrons from their orbits, this occurs because light has energy.
The photosensitive material most commonly used to produce voltage is silver oxide or copper oxide.
The cell has a curved light sensitive surface focused on the central anode. Light energy is converted to a flow of electrons and a usable current is developed.
This type of power is small but successfully used in television cameras, door openers, burglar alarms, and any photoelectric cell devices.
chemical
Chemical action- voltage produced by chemical reaction in a battery cell.
Voltage produced by chemical action.
When molecules of a substance are altered this action is referred to as chemical action.
This means the molecules have been combined with another substance or gives up atoms of its own. If atoms are added to or taken away from the molecules of a substance this chemical change will cause the substance to take on an electrical charge.
This process is used in batteries.
magnetism
Magnetism- voltage produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through a conductor in such a manner as to cut the magnetic lines of the force of the field.
Voltage produced by magnetism.
Three conditions must exist before voltage can be produced by magnetism.
1. There must be a conductor in which voltage will be produced.
There must be a magnetic field in the conductor’s vicinity.
There must be relative motion between the field and the conductor.
With these conditions present when a conductor(s) moves across a magnetic field and cuts lines of force, electrons within the conductor are impelled in one direction or another; thus, an electric force or voltage is created.
This is used to produce vast quantities of electric power from mechanical sources. The mechanical power may be provided by different power such as gasoline, diesel, water, or steam turbines.
Electric Current - electron flow
The flow of electrons through a conductor is called an electric current or electron flow.
The movement of electrons will be from a negative potential to a positive potential and is called by various terms, current, current flow, electron flow, and electron current.
There are two types of current, direct current and alternating current.
Direct current flows in the same direction whereas an alternating current periodically changes direction.
Electric Current - AMPERE
Ampere is the term used to define the unit of measurement for current the abbreviation is amp. The amp is abbreviated A.
Electric Current - COULOMB
Coulomb the unit of measurement for electrical charge.
The COULOMB is a unit quantity of electricity moved through an electric current when 1 ampere of current flows for 1 second of time, this is equivalent to 6.28 x 10 to the power of 18 electrons.
The symbol for coulomb is “ Q “. The coulomb is to electricity as the gallon is to water.
Resistance
Every material offers resistance. Good conductors offer little resistance such as copper, silver, aluminum, poor conductors are glass, wood, paper, which offer high resistance to current flow.
The size and type of material of wires are chosen to keep electrical resistance as low as possible.
The larger the diameter of the wires the lower will be their resistance (opposition) to the flow of current through them.
Resistance is expressed by the symbol “ R “ and is measured by OHMS. The Greek letter omega right side up W represents resistance.
Conductance
The term that is the opposite of resistance is conductance (G).
The symbol for conductance is the Greek letter omega upside down.
CONDUCTANCE is the ability of a material to pass electrons.
The formula is written as follows:
G (conductance) = 1/R (resistance)
Cell
A device that transforms chemical energy into electrical energy.
The cell is the fundamental unit of the battery; the simple cell consists of two strips or electrodes, placed in a container that holds the electrolyte.
Battery
A battery consists of two or more cells placed in a common container. The cells are connected in series, in parallel, or a combination of both depending on the amount of voltage required of the battery.
Batteries are used in direct current electrical energy automobiles, boats, aircraft, ships, and portable electronics equipment.
Battery Chemistry
If a conductor is connected externally to the electrodes of a cell, electrons will flow under the influence of a difference in potential across the electrodes from the zinc (negative) through the external conductor to the carbon (positive), returning within the electrolyte solution to the zinc.
After a short period of time, the zinc will begin to burn (waste away) because of the electrolyte. If zinc is surrounded by oxygen, it will burn as a fuel.
Energy is released by the zinc and is transformed into electrical energy rather than heat energy.Series connected cells
When the negative electrode of the first cell is connected to the positive electrode of the second cell, the negative electrode of the second cell is connected to the positive of the third cell this is called series connected cells.
The positive electrode of the first cell and the negative electrode of the last cell then serve as the power takeoff terminals of the battery.
Parallel connected cells
Parallel connected cells are used when more power is needed but using the same voltage.
In a parallel connection all positive connections are connected to one line and all negative are connected to one line.
Series-Parallel Connected Cells
In the graphic below a group of three cells are connected in a series. Then two series groups of three are connected in parallel.
This is used when higher voltage and increased current capacity are needed.
Simple Electric Circuit
An electric circuit is a completed conducting pathway, consisting not only of the conductor but also including the path through the voltage source.
Current flows from the positive terminal through the source and emerges at the negative terminal.
Ohm’s Law
A relationship exists between current, voltage, and resistance.
The current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance. This law is written as follows:
I=E/ R
Where:
I = current in amperes
E= potential in volts
R = resistance in ohms
An ohm is defined as a unit of electrical resistance.
(Represented by the Greek symbol omega W .)
Applying OHM’S Law
To determine the unknown quantity in an equation cover that quantity with your finger, the remaining letters will be the mathematical operation to be performed. For example to find I cover I, the uncovered letters are E divided by R.
OHMS LAW IN DIAGRAM FORM
See Image Below:
OHMS LAW IN THREE DIFFERENT EQUATIONS
I (current)= E (voltage) / R (resistance)
E= IR (I x R)
R= (E / I )
I = (E / R)
Electric Power and Energy Power
Power, whether electrical or mechanical, is the rate of work being done.
The basic unit of power is measured in watts and is equal to the voltage across a circuit multiplied by current through the circuit.
P indicates the symbol for power the basic power formula is P= E x I, E is the voltage across and I is the current through the resistor.
Forms of energy are light, heat, and motion. Work is done whenever a force causes motion.
P = I E (I x E)
I = (P / E)
E = (P / I)
P = E x I
Where E = 2 volts and I = 2 amps
P = 2 x 2
P = 4 watts
Rating of Electrical Devices by Power
Lamps, fans, and motors are electrical devices rated in watts.
The wattage rating of a device indicates the rate at which the device converts electrical energy into another energy such as light, heat and motion.
If the normal wattage rating is exceeded the equipment will overheat and may cause damage.
Rating of Electrical Devices by Power
Lamps, fans, and motors are electrical devices rated in watts.
The wattage rating of a device indicates the rate at which the device converts electrical energy into another energy such as light, heat and motion.
If the normal wattage rating is exceeded the equipment will overheat and may cause damage.
Power Capacity of Electrical Devices
Wattage rating of a device indicates the device’s operating limits; the limits are given as maximum or minimum safe voltages that a device can be subjected to.
If a device is not limited to any specific voltage its limits are given in watts.
Resistors
A resistor is defined as a circuit element whose basic characteristic is resistance, it is used to oppose the flow of current this device is used in circuits with widely different voltages
Fuses
Fuses are metal resistors with low resistance values. They are designed to blow out and open a circuit when current exceeds the fuse’s rated value.
Resistance
The total circuit resistance (Rt) is equal to the sum of the individual resistances.
For example the current in a series circuit in completing its electrical path must flow through each lamp, each lamp offers added resistance.
As an equation:
Rt = R1 + R2 + R3………Rn
Voltage
Voltage is the measure of electromotive force or EMF. Volt is the unit of measurement for electromotive force.
In a series circuit the total voltage is equal to the applied voltage.
Power
Power is the rate of doing work in an electrical circuit or rate of expending energy the symbol for power is P and measured in watts.
In a series circuit the total power is equal to the SUM of the powers dissipated by the individual resistors.
Total power is PT=p1+p2+p3+……Pn.
Rules for Series DC Circuits
Factors governing the operation of a series circuit.
The same current flows through each part of a series circuit.
The total resistance of a series circuit is equal to the sum of the individual resistors.
The total voltage across a series circuits is equal to the sum of the individual voltage.
The voltage drop across a resistor in a series circuit is proportional to the size of the resistor.
The total power dissipated in a series circuit is equal to the sum of the individual power dissipations.
Ground
The earth ground is said to be zero potential, the term GROUND is used to denote a common electrical point of zero potential.
Open Circuits
A circuit is open when a break exists in a complete conducting pathway. An open occurs any time a switch is thrown to de-energize a circuit.
Short Circuit
A short circuit is an accidental path of low resistance that would have basically the same effect, however the short will cause an increase in current and the possibility of component damage.
Parallel Circuit Characteristics
A parallel circuit is defined as one having more than one current path connected to a common voltage source.
Voltage
In a parallel circuit the same voltage is present across all the resistors of a parallel group.
Current Division
The current in a circuit is inversely proportional to the circuit resistance.
The current divides in a parallel circuit among the available paths in relation to the value of the resistors.
Parallel Resistance
The total resistance in a parallel circuit must be less than any individual resistor in the circuit.
PARALLEL RESISTANCE FORMULA
Product over sum is a convenient formula for finding the equivalent resistance of two parallel resistors.
The formula for finding the equivalent resistance of two parallel resistors is as follows: R t is circuit resistance.
R t = 1 / ( (1/R1 ) + ( 1/R2) )
Effects of Source Resistance
Every known source has resistance. Internal source resistance affects the total power dissipated and also affects the transfer of power. The presence of internal resistance results in:
Less voltage supplied to the components.
Decrease in total current.
Increase in total resistance.
Series-Parallel Circuit
The majority of circuits is a combination of series and parallel elements and is referred to as series-parallel circuits.
An electrical circuit where both series and parallel components are used the series components feel the total current for the circuit, while the parallel components feel only that current which flows through that particular branch.
Total resistance for the series-parallel circuit is determined by combining both series and the parallel methods of calculating resistance.
Specific Resistance or Resistivity
Specific resistance or resistivity is the resistance in ohms offered by unit volume of a substance to the flow of electric current.
Resistivity is the reciprocal of conductivity.
Relation Between Wire Sizes
Wires are manufactured in sizes on a table known as the American wire gage (AWG).
Wire diameters become smaller as the gage numbers become larger.
A wire gage is the instrument used to measure the diameter of wire.
Stranded Wires and Cables
A wire is a slender rod or filament of drawn metal. If a wire is covered with insulation it is called an insulated wire.
A conductor is a wire or combination of wires not insulated from one another.
A stranded conductor is a conductor composed of a group of wires these wires are usually twisted together.
A cable is either a stranded conductor or a combination of conductors insulated from one another. In general the word cable usually applies to larger conductors.
Factors governing the selection of wire size
(Allowance must be made for the influence of external heat.)
Allowable power loss in line, the loss represents electrical energy converted into heat.
Voltage drops in the line.
Current carrying ability of the line.
Current carrying capacities (in amperes) of single copper conductors at ambient temperature of below 30 ยบ C see chart below.
Conductor Insulation
Insulation is coating over the wires so that they do not come into contact with one another, other equipment, or people.
Two properties of insulation are insulation resistance and dielectric strength.
Insulation resistance
Is the resistance to current leakage through the insulation.
Dielectric strength
Is the ability of the insulator to withstand potential difference. To test this raise the voltage in a sample until the insulation breaks down.
Rubber
The most common type of insulation is rubber. The thicker the insulation the higher the voltage.
A thin coating of tin or cotton must be used between the wire and the rubber, or the rubber will become soft and gummy.
Plastic
Is another good type of insulation it has flexibility and is moisture resistant.
Varnished cambric
Is made of cotton cloth coated by varnish. It can stand much higher temperatures than rubber.
Paper
Serves as a satisfactory insulator when impregnated by high-grade mineral oil. Paper works well on high voltage cable.
Silk and Cotton
This is used in communications circuits the threads are wrapped around individual conductors, in reverse directions and coated with a special wax compound.
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