Tuning of PID Loop


Thread Starter

Abrar Ahmad

Dear All

I have to fine tune of the FIC Control loop. This loop contains Magnetic Flowmeter and Variable Speed motor. Now The variable speed motor is replaced with constant speed motor. The problem is that this constant speed motor is tripped after 1 second whenever the loop is controlled on Auto mode. We are just running the loop on manual mode.

Kindly suggest.
What is your problem? Why in the world did you replace the Variable Speed motor?

Did you install a control valve? Is your constant speed motor powerful enough to overcome the pressure drop across the control valve?

Please give a more complete description of your control loop.

Dick Caro
Richard H. Caro, Certified Automation Professional, CEO, CMC Associates,
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david mertens

Unless your motor is seriously over sized, you can not start a DOL motor connected to a centrifugal pump in an open line. the pump will not be able to build up pressure and the resistance will increase exponentially. You need a closed outlet valve downstream of the pump, a soft starter, or a variable speed drive. Without at least a control valve or a VSD drive in your loop, you will never be able to control the flow. A control valve will waste most of the energy your pump provides, so in most applications a variable speed drive is the way to go.