Cannot get output from my Eurotherm controller

[divine7]

I am using a Eurotherm 3504 controller to controll a valve based on input pressure.

See details:
PV – Pressure transmitter input (0-5 bar), 4-20mA (i/p to controller)
Module 1 – Remote setpoint (0-5 bar), 4-20mA (i/p to controller)
Module 2 – Analogue output of valve actuators position to control room (0-100%), 4-20mA (o/p from controller)
Module 3- Analogue output to valve actuators (0-100%), 4-20mA (o/p from controller).

---Proportional action with gain of 40%/bar

(I interprete this to mean ...a 1 bar change in pressure results in 40% valve movement when proportional acts on its own. This gives a gain of 2 and PB of 50% I believe).

---Integral action time – 300 secs
---No derivate

Problem: I do not get any response in the output. Modules 2&3 are both reading their lowest vales – 4mA as output, which corresponds to 0% open in the actuators.

I am using a set point of 2.5 bar (midway of the 0-5bar pressure transmitter scale). When I vary the i/p current I am using to simulate the PV, (4-20mA), I do not get get any output in the valves.

Have I got my interpretation of the PB wrong?

I wish I could post screen captures here.

 

[IRstuff]

"I wish I could post screen captures here."

You can; the button below does that

TTFN
faq731-376

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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
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[danw2]

Output driven in one direction off scale is a symptom of the wrong control action.

Is the existing control action reverse or direct? Have you tried changing to the opposite control action?

 

[divine7]

Hello,

I have been able to get the valves to move, thanks to the explanation below

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Proportional Band: The amount of change in the controlled variable, expressed in engineering units, required to move the actuator from one end of its stroke to the other.

%PB: Percent proportional band is the proportional band expressed as a percentage of the sensor span.



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I had previously set the PB as 2.5%, instead of 2.5 eng units.

All is fine now.

Thanks a lot.