We have a control valve in steam line, which receives a command from temperature controller (sanup advanced SDX4). the control valve not operating when it receives a command from it, but it works well when connected with mA source. command given in cable connected at the temperature controller output.

I have calibrated it with mA source and valve responds good, but when controller comes in to line its response is very slow. like it takes at least a minute to open and closes immediate (similar to valve hunting).

Control valve positioner is electr-pneumatic (Spiraxsarco EP 500)

Can anyone please guide to what else to check, possibilities to resolve the issue.

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Put the controller in manual mode, then
- go to 0% output and check the valve response
- go to 50% output and check the valve response
- go to 100% output and check the valve response

I suspect that you will get a fast response and that the valve/positioner response will mimic what you saw with the mA source, proving that the controller can, in fact, cycle the valve from closed to open.

If that's the case, then something in the controller is causing sluggish output. It could be PID tuning, or it could be an issue with the input sensing, or it could be a setup parameter that rate limits the upscale output changes but not downscale output changes.

 

It is probably tuned that way on purpose.

--
Bob
http://ilbob.blogspot.com/

 

Take the control valve in manual mode & try the following operations.

gives the command to control valve at 0, 25, 50, 75, 100%, then see the response of control valve.

if responds okay then problem with PID tuning, go for PID tuning.

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As advised by another member also, suggest to put the controller in manual mode and then vary the controller output from 0 to 100%. If the control valve moves accordingly, then there is no problem with the hardwire connection between the positioner and the controller. Then you need to look into the controller settings and input sensing.

Keeping the controller in manual mode pl. vary the input sensor values. If the controller indicates correct reading of the input value then definitely the problem will be with the controller setting. You may reset the controller tuning and check again.

If at the 1st place controller output changes in manual mode is not moving the valve accordingly, then there is problem in hardwire connection between the controller and the positioner. May be cable resistance and positioner resistance together is more than the controller load driving capability of 600 ohm or there may be grounding problem.