Hello all, I am new to 5000 and am trying to set up a PID block. I need to control fan speed VFD using a temp indication. I have the temp coming in as my PV and my speed control AO set up as the CV. No matter what set point I give it the output stays at 100% and I do have it in auto.
Rs5000 pid
- Thread starter grider75
- Start date
Mickey
Lifetime Supporting Member
I am not a RSLogix5000 user but for those that are can help you if you can post your program. Zip it first.
dginbuffalo
Member
Yes- zip and attach if you can?
Is your process way under setpoint?
Do you have the control action set correctly? SP-PV or PV-SP?
Is your process way under setpoint?
Do you have the control action set correctly? SP-PV or PV-SP?
I cant attach the file. My company wouldn't like that. It is a new program that I am working on so I can play around with it and not effect anything. I am pulling in the PV through a message block from a PLC5 if that makes a difference.
just the cowboy
Member
Just zip the PID part
If you just zip the PID part there should not be an problem.
And yes PV from can be a problem depends on how fast your loop is updating, it may not see the change if traffic is heavy on data highway.
Does the blower have to change that fast you need a PID?
If you just zip the PID part there should not be an problem.
And yes PV from can be a problem depends on how fast your loop is updating, it may not see the change if traffic is heavy on data highway.
Does the blower have to change that fast you need a PID?
Last edited:
Well, just messing around I deleted my PID tag and started from scratch. Now it seems to be working fine. No, it actually does not have to change speeds that fast. What are you suggesting? Oh, I do have a timer on the rung to control the speed of the scan too.
widelto
Member
Aye you using PID or PIDE.
Ken Roach
Lifetime Supporting Member + Moderator
The first question should be whether you are using the PID instruction or the PIDE instruction.
Then you should explain if you've followed the basic rules about executing the instruction in a periodic task or using a timed subroutine.
Only then can you begin to describe the inputs, outputs, and gains and get advice on performance.
So start at the beginning.
Then you should explain if you've followed the basic rules about executing the instruction in a periodic task or using a timed subroutine.
Only then can you begin to describe the inputs, outputs, and gains and get advice on performance.
So start at the beginning.
widelto
Member
The first thing you have to do is verify that your drive is capable of changing temperature as you desire when you change motor speed. So try changing motor speed manually with your PID(PIDE) and measuring temperature with your changing speed.
just the cowboy
Member
back to basics
If it does not need to be that fast of a change go back to basics.
If temp need increase of large amount move a output value.
as temp gets closer reduce value. I had a blower system that response time from blower would not let PID run stable. Built logic to do it no problems.
If it does not need to be that fast of a change go back to basics.
If temp need increase of large amount move a output value.
as temp gets closer reduce value. I had a blower system that response time from blower would not let PID run stable. Built logic to do it no problems.
Thanks for all the input. I am getting the hang of this. I will probably put these in a periodic task. That makes sense. We are currently controlling the older 1336plus VFD's in a PLC 5 using a PID block, so will probably start with those parameters and tune from there. This is on a huge 10 cell cooling tower, so its not needing to be too accurate really. I could possibly do this with logic like cowboy said, because from what I have noticed they are usually only running two different speeds depending on the time of year.
Mickey
Lifetime Supporting Member
I would never do anything like that. Relying on a message instruction and a communication link for control. No matter how reliable it seems to be there are always hiccups. IMHO
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