Troubleshooting & Maintenance of Control Systems Flashcards

When troubleshooting a smart HART transmitter, which tool is most effective for reading device diagnostics without interrupting the 4-20 mA signal?

Answer: HART communicator connected in parallel with the loop

A HART communicator superimposes FSK digital communication on the existing 4-20 mA signal, allowing diagnostics to be read without breaking the loop.

After replacing a control valve packing, the valve stem requires excessive actuator force to move. What is the most likely cause?

Answer: Packing gland over-tightened

Over-tightening the packing gland compresses the packing material excessively, dramatically increasing stem friction and the force needed to stroke the valve.

A technician finds that a PLC digital output card is not energizing a solenoid valve. The PLC ladder logic shows the output coil is energized. What should be checked next?

Answer: Check output card fuse and field wiring voltage

When PLC logic shows an output ON but the field device does not respond, the next step is checking for a blown output card fuse or missing field power.

A temperature control loop exhibits a slow, sinusoidal oscillation with a period much longer than the process time constant. Which controller parameter is most suspect?

Answer: Integral time set too short (reset rate too fast)

Long-period sinusoidal oscillation is a classic symptom of integral instability caused by an integral time that is set too short (too aggressive reset).

A pressure transmitter consistently reads 2 psi high across its entire range. This error is best described as:

Answer: Zero offset error

A constant error that shifts the entire output curve up or down uniformly across the range is a zero (bias) offset error, corrected by adjusting the zero.

Which safety practice must be followed before opening a hydraulic actuator supply line for maintenance?

Answer: Isolate and bleed pressure from the hydraulic system, then lock out the energy source

Stored hydraulic energy must be fully released and locked out/tagged out before opening any hydraulic line to prevent injection injuries or unexpected actuator movement.

A flow transmitter using a vortex flowmeter produces erratic output at low flow rates. What is the most likely cause?

Answer: The flow rate is below the meter's minimum Reynolds number requirement

Vortex flowmeters require a minimum Reynolds number (typically >10,000) to produce stable vortex shedding; below this threshold, output becomes erratic or zero.