System Optimization & Troubleshooting Flashcards

A compressor surge is detected repeatedly despite anti-surge control. Which optimization approach would best address this?

Answer: Tighten the anti-surge controller tuning and widen the surge control line margin

Moving the surge control line further from the actual surge line and improving controller response speed provides more protective margin against surge events.

What is the purpose of filter time constant selection on a derivative (D) term in a PID controller?

Answer: To reduce amplification of high-frequency noise by the derivative action

The derivative filter limits the bandwidth of D-action, preventing the controller from reacting aggressively to measurement noise that would otherwise be amplified.

When performing a control loop audit, which metric most directly measures how well a controller maintains its setpoint against disturbances?

Answer: Disturbance rejection performance (load response)

Disturbance rejection performance measures how quickly and accurately the controller returns the process variable to setpoint after an unmeasured load disturbance.

A level controller is in automatic but the level continues to drift downward even though the outlet valve is fully closed. What is the most likely root cause?

Answer: There is an undetected leak or bypass flow path

If the valve is confirmed fully closed yet level still falls, material must be leaving through an undetected path such as a leaking valve seat, drain, or bypass.

Which ISA standard provides guidance for the management of the alarm system lifecycle in process industries?

Answer: ISA-18.2

ISA-18.2 (Management of Alarm Systems for the Process Industries) covers the full alarm lifecycle from philosophy and design through operation and continuous improvement.

In advanced process control (APC), a model predictive controller (MPC) performs poorly after a major process equipment change. The most appropriate corrective action is:

Answer: Re-identify the process model using new step-test data

MPC relies on an accurate internal model of the process; after significant equipment changes, the existing model no longer matches reality and must be re-identified.

A transmitter with a 4-20 mA output reads 3.6 mA during normal process operation. What does this most likely indicate?

Answer: The transmitter is in sensor failure or broken wire mode

NAMUR NE 43 and most transmitters use <3.8 mA to signal a sensor or internal failure, with 3.6 mA being below the valid 4-20 mA operating range.