Mark Buskell
Member
I am using PID'd to control chemical flow. The basic setup is fixed speed pump and we vary the flow rate with a output (4-20) to a electric solenoid (Badger Valve) and monitor the flow with a micro motion meter (4-20). This works fine and we have been doing this way for a number of years now. Flow is from 1000 to 40000 grams.
AB-ControlLogix currently.
Say the setpoint is changing from 10000 to 30000 and back.
The question is when going from a lower setpoint to a higher setpoint it takes around 10 seconds max for the loop to stablize.
But when you go from a higher setpoint down to a lower setpoint, it takes up to twice a long.
It was never an issue in the past years but due to a change in production techniques, we are now looking closely at this issue.
We thought it might be a pressure issue with the valves, but the manufacturer swears they put up to 300 psi through them and they reacted the same in both directions. (Around 6 seconds from fully closed to open and back. We operate right at 60 psi.
Right now, the solution I will be trying is when going from high to low, I will lock the valve is manual (PID Manual bit) for 4 or 5 seconds, force the output down low and then release it.
Has anyone else seen then type of problem before when working with PID's?
AB-ControlLogix currently.
Say the setpoint is changing from 10000 to 30000 and back.
The question is when going from a lower setpoint to a higher setpoint it takes around 10 seconds max for the loop to stablize.
But when you go from a higher setpoint down to a lower setpoint, it takes up to twice a long.
It was never an issue in the past years but due to a change in production techniques, we are now looking closely at this issue.
We thought it might be a pressure issue with the valves, but the manufacturer swears they put up to 300 psi through them and they reacted the same in both directions. (Around 6 seconds from fully closed to open and back. We operate right at 60 psi.
Right now, the solution I will be trying is when going from high to low, I will lock the valve is manual (PID Manual bit) for 4 or 5 seconds, force the output down low and then release it.
Has anyone else seen then type of problem before when working with PID's?