Two PID To Control One Output

I am Using SLC505 Processor To Control Flow and Pressure. I am using Flow and Pressure Transmitter. I would like to use dual PID to contol one output valve. Flow control will be the primary PID once it settles it will allow pressure to control.
Any suggestions?

nsanli said:

I am Using SLC505 Processor To Control Flow and Pressure. I am using Flow and Pressure Transmitter. I would like to use dual PID to contol one output valve. Flow control will be the primary PID once it settles it will allow pressure to control.
Any suggestions?

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Did you consider cascade loop?

Can you tell me more about it?

Tell us more about what you are doing - because a cascade control might not be what you really want, and if it is then we need a lot more information to tell you about it.

Another options is to use what is know as a LOW SELECT PID control.
Check the Allen Bradley knowledgebase for a LOW SELECT PID example. Last I checked there was a problem with AB's Low Select example for the SLC500 because conditional rungs are not allowed on the PID instruction but it should give you the general idea.

Also search this forum for LOW SELECT, its been discussed lots of times.