2 PIDs

I have 2 PID blocks running at the same time and they seem to be giving identical outputs and SV and PV are different on each. Any ideas why this is happening and what I could do to fix it.

Data:
PLC = Delta DVP 32EH2
Analog Module= DVP 06XA 4 in 2 out set on 4ma - 20ma.

Both PIDs run on the same parameters in registers D100 - D109

1st PID Information
SV = D2103
PV = D16
Output = D150

2nd PID Information:
SV = D2099
PV = D18
Output = D151

I have attached a screenshot showing the HLT heater running. It didn't start until the BK Heater cut on. The HLT was already above set point so heater shouldn't have been running. Any help solving this one would greatly appreciated. I kind of think this is something that started recently. I don't think this problem has been going on since I started testing.

Thanks,

David

First, I would ask why you think you need to "fix" these two PID loops? I'm not really familiar with Delta PLCs, but I find it odd that a program that has been operating normally would suddenly create a problem.

So what if the two PIDs are operating on the same configuration parameters? They may be for twin processes. Is it possible that they are different PIDs for a single process, and that there is logic in the program to select which loop is active under certain conditions?

A heater "starting" and running when it shouldn't run doesn't sound like a PID issue. If you have concerns regarding an interlock issue, then the PID controls might not be where the problem lies. Did you write these PID loops? Did they work properly until recently?

Bit_Bucket_07 said:

First, I would ask why you think you need to "fix" these two PID loops? I'm not really familiar with Delta PLCs, but I find it odd that a program that has been operating normally would suddenly create a problem.

So what if the two PIDs are operating on the same configuration parameters? They may be for twin processes. Is it possible that they are different PIDs for a single process, and that there is logic in the program to select which loop is active under certain conditions?

A heater "starting" and running when it shouldn't run doesn't sound like a PID issue. If you have concerns regarding an interlock issue, then the PID controls might not be where the problem lies. Did you write these PID loops? Did they work properly until recently?

Click to expand...

I wrote the loops. This may have been going on all along as I have had a lot of bugs and logic issues throughout my first automation project. The problem may be the parameters are not able to be used by multiple PID. I'm reading something in the manual under the PID instruction that says: there is no limitation on times using PID instruction but the register # holding the parameters can't be repeated. Does that sound like I need to create a new set of parameters for each PID instruction?

Thanks,

David

Cowboy12 said:

I wrote the loops. This may have been going on all along as I have had a lot of bugs and logic issues throughout my first automation project. The problem may be the parameters are not able to be used by multiple PID. I'm reading something in the manual under the PID instruction that says: there is no limitation on times using PID instruction but the register # holding the parameters can't be repeated. Does that sound like I need to create a new set of parameters for each PID instruction?

Thanks,

David

Click to expand...

Yes, it does.

Bit_Bucket_07 said:

First, I would ask why you think you need to "fix" these two PID loops? I'm not really familiar with Delta PLCs, but I find it odd that a program that has been operating normally would suddenly create a problem.

So what if the two PIDs are operating on the same configuration parameters? They may be for twin processes. Is it possible that they are different PIDs for a single process, and that there is logic in the program to select which loop is active under certain conditions?

A heater "starting" and running when it shouldn't run doesn't sound like a PID issue. If you have concerns regarding an interlock issue, then the PID controls might not be where the problem lies. Did you write these PID loops? Did they work properly until recently?

Click to expand...

Bit_Bucket_07 said:

Yes, it does.

Click to expand...

Do you think it would only apply if I'm running 2 different heaters at the same time or for every PID instruction?

Every PID instruction needs its own unique registers.
You can't just reuse them.

rdrast said:

Every PID instruction needs its own unique registers.
You can't just reuse them.

Click to expand...

Thanks, was just conserving space and trying to keep it tidy. I have 11 PID instructions in the program and each take 20 registers. I have not tested it yet to make sure my problem is solved but will check it tonight.