×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Convert a 0-200 Microamp Signal for use in PLC?

Convert a 0-200 Microamp Signal for use in PLC?

Convert a 0-200 Microamp Signal for use in PLC?

(OP)
I have an old turbine control system that uses black boxes for temperature and speed control. I'm trying to get the speed (passive Mag pick-up) and temperature signals (Type K Thermocouple) in to a PLC for monitoring. I think piggy backing off the Mag pick and taking the signal into a high speed counter card at the PLC should be straightforward.

The temperature signal is more complicated. There's only one Type K signal (wire) going straight to the black box. I'd rather not molest/piggyback the thermocouple signal (splitter has delays, drift, etc) so am looking at a 0-200 MICROamp output signal that is available off of the temp control black box (proportional to the input t/c signal) that I could use for monitoring. How in the world can I convert or get a 0-200 microamp signal in to a PLC?

RE: Convert a 0-200 Microamp Signal for use in PLC?

(OP)
Accuracy isn't too critical. 0.5% - 1.0% or better preferred. The 0-200 microamp signal is just for monitoring, not precise control.

RE: Convert a 0-200 Microamp Signal for use in PLC?

Parallel the Type K thermocouple with a length Type K wire from the input on the black box into a commercial temperature transmitter which will give you a 4-20mA output that any PLC can handle. Transmitters are typically "2-wire, loop powered", meaning you also have to provide a 24Vdc power supply to power the transmitter, but that power runs over the 2 wires going to the transmitter.

I suggest isolated inputs on temperature transmitters, because many commercial thermocouple junctions are grounded and grounding can produce ground loop problems; an isolated transmitter input avoids that issue.

There are two categories of temperature transmitters - dumb and smart. The dumb transmitter is factory configured for some input range, say, 0-500 Deg F. with a corresponding proportional 4-20mA output.

The smart transmitter's input can be configured zero/span for the 4-20mA output. Problem is, unless you're in an industry where the software/modem or handheld programming communicator is readily available, then you're stuck buying and learning whatever gear is needed to set the range.

A dumb transmitter should be pre-ranged; my recommendation for a smart transmitter one is to find a vendor who will configure the range for you so you don't have deal with the configuration end.

It pays to physically label a field transmitter with its configured input range so the next guy knows what the 4-20mA output signal represents.

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! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close