ControlLogix PID: MINO and Integral Accumulation

[kutuz]

Hi there,

I have a PID which I limit at MINO = 25% and MAXO = 100%.

When the PID runs for the first time it takes time to start reacting at 25+% output. It seats at 25% for quite a bit even though error is positive. At that time I can see .DATA[0] (Integral Accumulation) is below 25% but increasing. When Integral Accumulation comes close to 25% I can see PID output starts reacting.

On the other way when output decreasing I don't see this behavior anymore.

Is this know behavior and if there is any workaround?

Thank you.

 

[defcon.klaxon]

Do you have this PID block in a periodic task?

What's with all the MOV blocks in front of the PID block?

 

[kutuz]

The PID block is in a periodic task.
The MOV blocks allow me to change attributes and see feedback on the same page. As you might noticed it is a Test PID.

Regarding Integral Accumulation: i have a PID that controls VFD pumps and operating limit is 15-100% Speed. I limit .MINO at 15% and MAXO at 100%. Every time pump starts in Auto, its speed is set at 15% but it takes time before PID starts reacting (until Integral Accumulation reaches 15% or so). How to eliminate that delay?

 

[defcon.klaxon]

The PID block is in a periodic task.

Excellent. This is the biggest thing to make sure you do, because otherwise things are just not going to work right.

The MOV blocks allow me to change attributes and see feedback on the same page. As you might noticed it is a Test PID.

What's odd to me is that your source and destination are the same. So I'm not following how this allows you to make changes to configuration for testing. Can you walk me through what you're trying to do? I think I see what you're getting at, but I would have expected you to create "test tags" that are moved into those various values, not moving the values into themselves.

Regarding Integral Accumulation: i have a PID that controls VFD pumps and operating limit is 15-100% Speed. I limit .MINO at 15% and MAXO at 100%. Every time pump starts in Auto, its speed is set at 15% but it takes time before PID starts reacting (until Integral Accumulation reaches 15% or so). How to eliminate that delay?

That's a question I'm not sure how to answer. I've seen similar behavior. It's as though the output is limited to 15% but not *scaled* to 15% so until the error integrates to anything over 15%, it's just going to sit there. Maybe someone with more AB experience can chime in?