Beginner PIDE Question

I'm working with the PIDE block for the first time and want to make sure I'm not doing something wrong.

The process is a simple resistive heater used to heat trace a tube, with thermocouple input for PV.

The output of the PIDE is used by a SRTP block to cycle the heater relay on/off.

In order to get this to perform reasonably well, I'm finding I need a proportional gain of over 100, and an integral term of over 50/min.

Does this sound OK or am I doing something wrong? I am using the independent equation, and the block is in a periodic task executing every 1000 mS.

Thanks for any advice,

Rob

Thought I'd bump this and ask again. Can anyone think of a configuration error that would cause the necessary gains to be so large (bearing in mind I do have this in a 1000 mS periodic task)?

Greetings Rob ...

you really need to post your entire program code (ACD file) ... you'll need to zip it first (forum rule) ... if it's still too big, do a File Save As operation and save it as an Import/Export type file (L5K) ... then zip and post that ...

the problem is that the PIDE instruction has at least 167 settable parameters – and that's before you even start looking at the inputs and outputs and external controls that are involved ...

so ...

we really need to take a look at what you've got in order to give you meaningful answers ...

but ...

just based on what you've posted so far, the Proportional gain that you mentioned looks to be really high ...

scaling issues? ...

Assuming RSlogix 5000?

Is your SRTP set to the default heat/cool split of 50/50? this would mean the system will do nothing until your CV reaches 50percent.

Check your PV range. How tight are you trying to control it? if your transmitter is say 0-100, and you expect the heater to come on at full roar when the temperature changes by 1 degree, then I would expect such high values.

Thanks for the replies, I will post the file first thing in the morning (and take another look at the scaling and SRTP settings)

Thanks again,

Rob

I've attached the file. The PIDE that I've "tuned" is called Lead_1_PIDE_Controller. If anyone has the time to look and can see where I've gone wrong, I sure would appreciate the help.

Thanks again,

Rob

You've got a max and min for your PV of -210 to 1200. The PIDE converts this to a percentage before putting it into the PID equation. You would therefore expect your tuning values to be 10 times larger than someone who had a -21 to 120deg span.

Also, having your SRTP in the 1000ms task, means it only has 3 speeds: 0sec, 1sec or 2sec duty. "Place the SRTP instruction in a faster, higher priority task," as per the example in the help file.

OK Ian, that makes sense to me as far as the gain.

I do have the SRTP in my continuous task though, I think that should be OK.

Thanks so much for your time,

Rob