You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old December 17th, 2006, 09:15 PM   #1
flyers
Member
Singapore

flyers is offline
 
Join Date: Sep 2006
Location: Amk
Posts: 295
Difference between Isolated & Non-Isolated

Dear all,

I'm looking at the Flex IO analog input, 1794-IE8 & 1794-IF4I, what is the different between the isolated & non-isolated?

The 1794-IE8 should be using a 1794-TB3 or TB3S? I'm mixed up with the manuals as per attached. Referring to the table.

Thank you.

Last edited by flyers; December 17th, 2006 at 09:28 PM.
  Reply With Quote
Old December 18th, 2006, 01:26 AM   #2
Singapore_Mats
Member
Singapore

Singapore_Mats is offline
 
Singapore_Mats's Avatar
 
Join Date: Nov 2006
Location: Singapore
Posts: 159
for me, isolated should be that signal ground is not connected to power ground.
  Reply With Quote
Old December 18th, 2006, 09:38 AM   #3
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 5,287
I'm not familiar with the Flex I/O stuff, but in general isolated in this context refers to analog I/O that does not have the power supply "-" tied to gether on all transmitters or all points on the I/O card. If you are using multiple loop powered transmitters on a single power supply, they are not isolated.

In many cases you have to look carefully at the I/O card as well. Many analog inputs are inherrently non-isolated, since they have all of the "-" terminals on the card internally connected.
  Reply With Quote
Old December 18th, 2006, 07:27 PM   #4
flyers
Member
Singapore

flyers is offline
 
Join Date: Sep 2006
Location: Amk
Posts: 295
Thanks for the replies.

If I understand correctly, isolated means the '-' signal is individual among all the channels, while non-isolated then '-' signal are connected with each other.

So the advantage of isolated is, when there is a short circuit at a particular channel, only that particular channel will be affected, the rest will still be okie? Am i right?
  Reply With Quote
Old December 18th, 2006, 07:41 PM   #5
Black Jack
Member
United States

Black Jack is offline
 
Join Date: Dec 2006
Location: Northwest
Posts: 30
Typically on analog input modules, isolated means separate analog to digital converters for every channel and every channel can be sourced from a different power source. Non-isolated inputs share a common converter and are referenced to the same common voltage.
  Reply With Quote
Old December 18th, 2006, 07:43 PM   #6
Singapore_Mats
Member
Singapore

Singapore_Mats is offline
 
Singapore_Mats's Avatar
 
Join Date: Nov 2006
Location: Singapore
Posts: 159
yes, and sometimes you want to measure temperatures in different buildings and dont want any current to leak, or in my case where a ship can have DC24V, AC115V and AC230V, all used at the same time.
  Reply With Quote
Old December 18th, 2006, 07:57 PM   #7
flyers
Member
Singapore

flyers is offline
 
Join Date: Sep 2006
Location: Amk
Posts: 295
Quote:
Originally Posted by Singapore_Mats
yes, and sometimes you want to measure temperatures in different buildings and dont want any current to leak, or in my case where a ship can have DC24V, AC115V and AC230V, all used at the same time.
Hi,

This means different operating voltage of the analog devices can be connected to the same analog input module?

But, I taught analog module can accept 4-20mA (of course can accept voltage like 0 -5 VDC...etc..), no matter what is the operating voltage for the devices as long as the analog device is giving 4-20mA I can connect them into the analog module? NO?
  Reply With Quote
Old December 18th, 2006, 08:17 PM   #8
Singapore_Mats
Member
Singapore

Singapore_Mats is offline
 
Singapore_Mats's Avatar
 
Join Date: Nov 2006
Location: Singapore
Posts: 159
yes, you can connect all of them into one analog module, but if you have one analog coming from an office and one from workshop next to a welding-machine or big motor... then its a good idea to have them isolated.
  Reply With Quote
Old December 18th, 2006, 10:24 PM   #9
rPraveenkum
Member
India

rPraveenkum is offline
 
rPraveenkum's Avatar
 
Join Date: Aug 2006
Location: Chennai
Posts: 876
If the common of the all analog inputs shorted is Non-Isolated & the no connection between the one analog input channel to the other then it is called isolated Input
__________________
.................................................. .................................................. ..........................................
.................................................. .................................................. ..........................................
PRAVEEN KUMAR
http://www.praveen.envy.nu
Life is like butterfly, handle with care - Praveen
  Reply With Quote
Old December 19th, 2006, 04:59 AM   #10
Ken Moore
Member
United States

Ken Moore is offline
 
Ken Moore's Avatar
 
Join Date: May 2004
Location: Upstate South Carolina
Posts: 2,325
Isolated inputs are needed if you have any 4-wire instruments. Each 4-wire will usually supply it's own power, so they don't share a common.
__________________
"To give real service you must add something that cannot be bought or measured with money; and that is sincerity and integrity."
- Donald A. Adams

  Reply With Quote
Old December 19th, 2006, 09:56 AM   #11
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 5,287
"Isolated inputs are needed if you have any 4-wire instruments. Each 4-wire will usually supply it's own power, so they don't share a common."


Actually, Ken, that isn't necessary. We have often mixed 2-wire (such as a pressure transmitter) and self powered transmitters (such as a 120 VAC powered analytic instrument) on the same analog card without problems.

If there is a return wire for the signal it all works out OK. That's because a loop powered device is like a current sinking device, constantly changing it's internal impedence so the current through it is proportional to the measured parameter. It isn't necessary for the output current to the PLC card to be returned to the transmitter to have it function.

A self powered device is current like a current sourcing device, where it actually modulates the output current directly to make it proportional to the measured parameter. It isn't necessary to have the signal current through the PLC card actually return to the device for proper function.

Last edited by Tom Jenkins; December 19th, 2006 at 09:58 AM.
  Reply With Quote
Old December 19th, 2006, 10:30 PM   #12
flyers
Member
Singapore

flyers is offline
 
Join Date: Sep 2006
Location: Amk
Posts: 295
Thank you for all the replies, appreciate that.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
1771-IFE/C REV Difference or program e27978 LIVE PLC Questions And Answers 6 September 16th, 2006 05:45 PM
what difference between Continuous updating and Mass I/O copying? steven37 LIVE PLC Questions And Answers 2 June 16th, 2006 10:03 PM
Difference between Reversing and regular starter anks LIVE PLC Questions And Answers 3 June 8th, 2006 09:41 PM
DCS..HMI..SCADA whats the difference?? Preeya LIVE PLC Questions And Answers 4 August 20th, 2004 05:56 AM
Difference of PLC with motion control and PLC without motion control tanwillie LIVE PLC Questions And Answers 6 May 9th, 2003 09:51 AM


All times are GMT -5. The time now is 03:27 AM.


.