There is a problem somewhere in this liquid flow control system. The controller is in automatic mode, with a setpoint of 65%, yet the flow indicator and the flow controller both register 0.3%: (nearly) zero flow. A P&ID of the loop appears here:
Explain how you would begin troubleshooting this system, and what possible faults could account for the controller not being able to maintain liquid flow at setpoint.
More Question
- Explain how you could divide this control system into distinct areas or zones which you may then begin to refer to when “dividing and conquering” the problem.
Answer :
One possible fault has to do with the control valve: perhaps something has happened to make it fail closed (loss of air supply, signal, etc.). Other possible problems include the following:
- Pump not running (no source of fluid power to motivate flow)
- Very poor controller tuning
- Wrong controller action
- Valve failed closed (loss of air supply, signal, etc.)
- Transmitter failed, showing no flow when in fact there is
A good “first test” for troubleshooting the loop is to check the controller output: is it trying to open up the valve?
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