Turn off the PID or let it Run?

BillRobinson

Member
Join Date
Oct 2006
Location
Sydney, Nova Scotia
Posts
185
I have an emergency bypass valve that I need to control around a flow using a PID loop. Just to give it a number, let's say that I need to open a valve is the flow is greater than 80; so 80 is the PID setpoint. Now lets say the flow is typically around 10-20, so if i use a PID loop it will nearly always calculate an output of 0%. This seems like a lot of unnecessary calcs for nothing.

So should I use the PID all the time or should I just turn it on when PV reaches 70? Any opinions?
 
I would leave the PID on.

There is nothing wrong doing what you are thinking about but the PID may start coming off of saturation 15 degrees from the set point. This may avoid overshoot where your arbitrary 10 degrees may not give the PID time to 'slow down'. This would be especially true if you are using the derivative gain.
 

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