CPT Advanced Diagnostics & Troubleshooting 3

Question 1

A level transmitter using a differential pressure cell reads low level when the actual level is high. Which fault is MOST likely?

Accepted Answer

High-side impulse line is plugged

Answer

A plugged high-side impulse line prevents high pressure from reaching the transmitter, causing it to report a lower level than actual.

Question 2

A reciprocating compressor shows increased vibration on every other stroke. The MOST likely cause is:

Accepted Answer

A faulty suction or discharge valve on one cylinder

Answer

A faulty valve on one cylinder causes unequal loading between cylinders, producing vibration that repeats every other stroke.

Question 3

When performing a loop check on a 4-20 mA transmitter, a technician measures 4 mA at 0% and 19.5 mA at 100%. This indicates:

Accepted Answer

Span error only

Answer

The zero (4 mA at 0%) is correct but the span is short (19.5 mA instead of 20 mA at 100%), indicating a span calibration error only.

Question 4

A process vessel pressure is rising unexpectedly with no increase in feed rate or temperature. Which cause should be investigated FIRST?

Accepted Answer

Blocked vent or relief path

Answer

An unexpected pressure rise with constant inputs most urgently points to a blocked vent or plugged relief valve preventing normal pressure release.

Question 5

During troubleshooting, a technician uses a step test by making a step change to the controller output in manual mode. The primary purpose is to:

Accepted Answer

Verify the final control element moves as expected and measure process response

Answer

A step test confirms valve stroke response and reveals the open-loop process gain, time constant, and dead time needed for tuning diagnostics.

(CPT) Certified Process Technician Practice Test