RSLogix 500 PID

iMalinko · Apr 1, 2016

Hi, all.

I am new to AB PLCs, and I've been a shadow on these forums looking for information. I've been wanting to set up a PID loop, and I wanted a little help of help, or at least confirmation in terms of concept of what I'm doing.

I am attempting to control a power controller that utilizes a 0 - 5 VDC signal, so 0 - 16380.

I have a feed source of water, which varies but bounces around 1,800 to 2,400 uS. I want the desired product (from the component) to be 300 uS. The component will utilize the power controller signal to increase/decrease the power required to get the 300 uS output. Ideally, I'd want to have this 300 value be a number that I key in from my HMI (which I have already set up).

So, how would I set this up?

I know that I need 23 blocks to use a PID controller. I know the Process Variable needs to be the feed, and I know the control variable needs to be 300, or whatever I enter it on the HMI.

Would I use E = SP - PV?

Output min and max would be 0 - 100%
Setpoint min and max would be 0 - 16380

I guess I don't know what to make setpoint SP or process variable PV in the PID setup.

Any help, or guidance to articles would be appreciated. I've been looking at examples/other posts in terms of their application.

FactoryTalktotheHand · Apr 1, 2016

iMalinko said:
Hi, all.

I am new to AB PLCs, and I've been a shadow on these forums looking for information. I've been wanting to set up a PID loop, and I wanted a little help of help, or at least confirmation in terms of concept of what I'm doing.

I am attempting to control a power controller that utilizes a 0 - 5 VDC signal, so 0 - 16380.

I have a feed source of water, which varies but bounces around 1,800 to 2,400 uS. I want the desired product (from the component) to be 300 uS. The component will utilize the power controller signal to increase/decrease the power required to get the 300 uS output. Ideally, I'd want to have this 300 value be a number that I key in from my HMI (which I have already set up).

So, how would I set this up?

I know that I need 23 blocks to use a PID controller. I know the Process Variable needs to be the feed, and I know the control variable needs to be 300, or whatever I enter it on the HMI.

Would I use E = SP - PV?

Output min and max would be 0 - 100%
Setpoint min and max would be 0 - 16380

I guess I don't know what to make setpoint SP or process variable PV in the PID setup.

Any help, or guidance to articles would be appreciated. I've been looking at examples/other posts in terms of their application.

Your process variable is the analog input from the measuring device. You do not set this. The Setpoint is what you would LIKE the Process Variable to be.

Whether you're using E=SP-PV or E=PV-SP depends on how your controller works. E=SP-PV means that if the PV is lower than the SP, the output will INCREASE. If your controller increases flow with a higher signal voltage, then that is what you want to use. If your controller decreases flow as the signal increases, then you'll want to use the Direct-Acting, or E=PV-SP.

EDIT: I've attached the most helpful files I've found to date for this. I've used the Micrologix Tuning example before and got a near-perfect tuning for a heating setup with it.

iMalinko · Apr 1, 2016

Thanks for the attachments. I'll review, and see what I can learn.

So this process is interesting. The input will always be higher than the set point. Ideally, I want the power controller to increase and decrease the power applied so we can get the outlet as close to 300 as possible.

For example, the more power I have, the lower the outlet would be. The less power I have, the higher the outlet would be.

I am assuming I have to use E=SP-PV

bright676 · Apr 1, 2016

Doesn't 0-5 VDC = 0 - 16384? Not 0-16380?

Mickey · Apr 1, 2016

bright676 said:
Doesn't 0-5 VDC = 0 - 16384? Not 0-16380?

Values to get 0-5vdc out would depend on the analog card and how it is configured. The OP needs to tell us more. What controller, what analog input card, what analog output card.

iMalinko · Apr 6, 2016

All,

I've reviewed the material, and looked at examples, and I still have a few questions.

For the PID instruction (under File/Misc); I see the fields:
PID File
Process Variable
Control Variable

What is PID File?

Also,

I have two sensors -- a feed sensor (which measures a number between 500 - 2000 and varies). In my PLC, it is F8:0

I have a product sensor -- this is what the actual output is (going through my component). This is F8:3.

I have a keypad input on my HMI. N7:36. This is what I want my set point to be.

Do I have enough for these fields? I guess I just don't know where I can put my set point value into.

RSLogix 500 PID

iMalinko

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FactoryTalktotheHand

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iMalinko

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bright676

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Mickey

Lifetime Supporting Member

iMalinko

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