×
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

Can i get two 4-20ma output signals from one PTx
5

Can i get two 4-20ma output signals from one PTx

Can i get two 4-20ma output signals from one PTx

(OP)
Hi All
      I have project where i need i require to take two 4-20ma signals.

1. 4-20ma to contorl valves
2. to connect to the PLC .
The transmitter is yokogawa pressure transmitter , loop -powered .

As i need one 4-20ma signal to control the exisiting control valves.
And if possible second 4-20ma signal DCS via PLC in order to alarm .
Thank You
 

RE: Can i get two 4-20ma output signals from one PTx

2
Can you get two 4-20mA signals proportional to temperature from a single pressure transmitter?  No.

Can you take the voltage from a dropping resistor across the input of the PLC and use the voltage?  Yes.

Can you wire the 4-20mA in series with the PLC and the DCS?  In all probability, yes.

Can you buy a signal multiplier, one 4-20mA in, two 4-20mA out and use it for getting a separate 4-20mA signal to the PLC and the DCS?  yes.

something like Phoenix Contacts' MCR-FL-C-UI-2UI-DCI-NC
2814867
http://rd.phoenixcon.com/products/interface/db/datasheets/MCR-2UI.pdf

RE: Can i get two 4-20ma output signals from one PTx

You can also use just a signal isolator either loop powered or line powered, use the original signal where you need the best reliability and the isolated signal for the second.
Roy

RE: Can i get two 4-20ma output signals from one PTx

2
The lowest cost option is to wire the control valve and the PLC in series with the transmitter 4-20mA loop

There are two issues to watch out for:-
1. That the total loop resistance remains less than 600 Ohms.(which shouldn't be difficult)
2. Wire the PLC in the loop after the valve positioner. (PLC's often ground the negative terminal,this can cause issues if there is more than one mA input on the PLC). Placing the PLC last in the loop should over come this.

I trust this helps,
Mlv
http://www.coulton.com

RE: Can i get two 4-20ma output signals from one PTx

Hey, there's something missing in this loop. Where is the controller?
Roy

RE: Can i get two 4-20ma output signals from one PTx

Standingback, So you put the PLC on the wrong side of controller just to see if I was paying attention.
I have often used a 1-5V PLC input across the controller 250 Ohm, that works as well.
BTW, I was refering to the original post, not your's, INSDE08 doesn't mention the controller, I think he has 2 (to) valves as well.
Regards
Roy

RE: Can i get two 4-20ma output signals from one PTx

You will need some type of controller for the valve and a loop isolater should work fine.

RE: Can i get two 4-20ma output signals from one PTx

(OP)
Thank You All
           I have redesigned using your advises and ideas.

Cheers

RE: Can i get two 4-20ma output signals from one PTx

Do you want to send the process variable or the valve position to the PLC??
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

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