×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

analog differential or single ended inputs

analog differential or single ended inputs

analog differential or single ended inputs

(OP)
I am wiring four 4-20 mA inputs to a control logix 1759 AI8 module, via IFM module. All four inputs are from 4 wire transmitters, supplying their own power. I have two options,
1. Wire the card as differential analog inputs giving me no spare inputs.
2. Wire the card as single ended inputs, giving me 50% spare capacity.
I am leaning towards option 2, my uncertainty is having the commons all tied together (single ended input). Is this a problem if all the 4-20 transmitters are isolated? I think not but am a little unsure. Thank's for any response. Steve

RE: analog differential or single ended inputs

Well since 4-20 makes no direct sense to differential are you really converting the 4-20 with a resistor across it?

If yes. I'd go with single ended. Just don't do anything that would prevent you from going to double ended if some hitch comes up.

With your isolated 4-20 I think you're good.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: analog differential or single ended inputs

If the four 4-20 lines are insulated from any potential, including gnd, AND have separate power supplies AND are not used for any other purposes where they may also be connected to gnd or some other potential, then you can use single ended connection to your IFM module.

What you describe seems to be exactly such a system, so just do it.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: analog differential or single ended inputs

Good morning Keith! Yes, of course, a resistor is needed.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: analog differential or single ended inputs

(OP)
Thanks Keith,

The analog current input card has internal 249ohm resisors, so the card does the conversion to 1-5 Volts.

Steve

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources