PIDCONL

Hello Experts

I need to program PID as follow kindly suggest solution.

1) Discharge Density---- PID1

2) Discharge Flow ------- PID2

Conditions :- 

1) If discharge density is more than set point then density control PID loop will work and pump speed will be controlled accordingly . Flow Control will be Off.

2) If discharge flow is less than set point then flow control loop will work and pump speed will be controlled accordingly . Density control will be off.

There is comman pump(VFD) for above two loops. 

Also transfer between two PID should be bumpless.

We are using PCS7 V8.1 SP1

Thanks

Ravi

Hi Autoguy,

Please take a look at the APL v8.1 library template-> "OverrideControl". It is based on two PIDConL controllers which share a common actuator.

You may adjust it to you needs.

Just quick thinking: You also can use the "ER" output of the PIDConL to determine the amount of difference between PV en SP. Then you can compare this with a parameter and activate the PIDConL (MV_TrkOn=0) and interlock the second PIDConL.

Thanks for your reply. But in my case one PID is with negative gain(-1.0) and one is with Netural gain(1.0). In this case what modifications are necessary in override control template.

Thanks

Ravi

You have to set variable "NegGain" for the controller with negative gain.

The error by the way (ER) is calculated as follows: SP - PV_Out.

Hi Oreca

Yes setting the parameter NegGain will reverse the output.

I mean to ask wheather there will be any problem with bumpless transfer switching between PID1 & PID2 due to negative gain.

How about using the program mode for one of the PID.

Thanks

Ravi

Well, you have to arrange the system in such a way, that taking over by the controllers is smoothly.

I have a good document with an example, also override control, which has a flow and pressure controller, where the pressure controller has a negative gain: Flow controller-> Positive gain because when valve opens, flow increases, Pressure controller-> Negative gain because when opening the valve, the pressure drops.

So I suggest you read the document, I think it's much clearer to you if you have the pictures and explanations rather then me talking here