Troubleshooting & Maintenance of Instruments Flashcards
7 cards from real CCT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Troubleshooting & Maintenance of Instruments flashcards as text
A pressure transmitter consistently reads 2% higher than the reference standard across its full range. This is most likely caused by:
Answer: Zero offset error
A consistent offset across the full range indicates a zero shift, not a span or linearity problem.
During maintenance of a thermocouple installation, you notice the extension wire has been routed near a high-voltage cable. What is the primary concern?
Answer: Electromagnetic interference will corrupt the millivolt signal
Thermocouple signals are low-level millivolt signals highly susceptible to EMI from nearby high-voltage conductors.
A differential pressure flow meter shows erratic readings only when the process flow is high. The most probable cause is:
Answer: Air entrainment at high flow velocities
At high flow velocities, dissolved gases can come out of solution and cause bubble-induced signal noise in the impulse lines.
When troubleshooting a 4-20 mA loop, a technician measures 0 mA with the loop powered. The most likely fault is:
Answer: Open circuit in the loop wiring
Zero milliamps in a 4-20 mA loop indicates a broken circuit, since a functioning loop always carries at least 4 mA.
A pH electrode exhibits sluggish response during calibration, taking several minutes to stabilize. The most likely cause is:
Answer: Dehydrated or fouled glass membrane
A glass pH electrode that has dried out or is coated with process deposits will respond very slowly to changes in hydrogen ion activity.
A technician performs a five-point calibration on a level transmitter and finds that the as-found data shows a bow-shaped curve deviating from the ideal line. This indicates:
Answer: Nonlinearity
A bow or S-shaped deviation from the ideal straight line across multiple calibration points indicates a nonlinearity error.
After replacing a control valve positioner, the valve overshoots its setpoint repeatedly. The technician should first adjust:
Answer: The positioner gain or proportional band
Overshooting in a positioner is a control response issue, and adjusting the proportional gain directly controls how aggressively the positioner responds.