PIDE CLamp

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I have a boiler with a max steam flow. is there away to Clamp the CV value whenever the Steam output goes over 40000 PPH

My PIDe is controlling Presssure

 

[drbitboy]

yes.


change existing PIDE #1 that moves valve to control steam flow:

• PIDE #1 CV will still be the valve position.
• PIDE #1 PV will be the value from flowmeter.
• PIDE #1 SP will be output of PIDE #2 (see below)

New PIDE #2

• PIDE #2 CV will be steam flowrate cascading to PID #1 SP; max output for this CV is 40000PPH.
• PIDE #2 PV will be the value from the pressure sensor, which previously went to the PV of existing PIDE #1
• PIDE #2 SP will be the desired steam pressure.

Tuning parameters for this will be very different from the current tuning with the one PIDE, though related.


There are probably better ways to do this.

 

[Phrog30]

Many ways, one way is to set windup hi, which prevents the output from increasing.

 

[PLCMentor]

Yeah I think the easiest way may be the copy the current CV into the CVHLimit when the steam flow goes over your desired value. I'm sure there will be more to it than that, but that would be where I'd start. Releasing it when it goes below a certain value would probably be necessary.

 

[nyanpasu]

Perhaps move 40000 PPH CV into CVOverride and turn on Override mode on the PIDE?

 

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Thank you all for the great responses

 

[rupej]

I think one of the best ways is to have two PIDs- your original one that controls pressure, and a new one that controls flow. Select the one whose output is lowest to write to the actual CV.

The advantage of this method vs. clamping the CV is that this method can drive the CV lower if need be.

Sounds complicated but it's really not. Someone even just posted a Rockwell .pdf on PIDEs recently that gives an example of how to do it.