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 technician is troubleshooting a level transmitter on a condensable vapor service that has been reading high. The impulse lines are not heat-traced. The most likely cause is:
Answer: Condensate accumulation in the low-pressure impulse line
On condensable vapor service, liquid can accumulate in the low-pressure leg, adding a false head pressure that makes the transmitter read higher than actual level.
During a loop check, the control room reads 25% on a 4-20 mA transmitter while a calibrator at the field device reads 8 mA. What is indicated?
Answer: The control room input card is malfunctioning
8 mA corresponds to 25% of the 4-20 mA span, so both readings are consistent and indicate normal transmitter operation.
A flow control loop is stable but the process variable consistently lags the setpoint changes by several minutes. What tuning parameter most directly addresses this?
Answer: Increase integral (reset) rate
Increasing the integral rate causes the controller to eliminate offset more quickly, reducing the time it takes for the PV to reach setpoint after a change.
A technician notices a digital HART transmitter shows a good primary variable but has a fixed output of 4 mA regardless of process changes. The most likely cause is:
Answer: The transmitter is in multidrop mode
HART multidrop mode fixes the analog output at 4 mA and communicates process data digitally only, which can be mistaken for a failed analog output.
When performing maintenance on a turbine flowmeter, inspection reveals worn or chipped rotor blades. What is the expected effect on meter performance?
Answer: Pulse output frequency will decrease, causing the meter to underread
Damaged turbine blades reduce the rotor's rotational efficiency, causing fewer pulses per unit volume and an under-reading of actual flow.
A technician is calibrating a pressure switch and finds the switch actuates 5 psi higher on increasing pressure than it releases on decreasing pressure. This difference is called:
Answer: Deadband or differential
The difference between the actuation point on increasing pressure and the release point on decreasing pressure is the switch deadband or differential.
What is the primary reason for performing a 'as-found' calibration check before making any adjustments to an instrument?
Answer: To document the instrument's condition before intervention and support traceability
As-found data documents the instrument's pre-adjustment condition for traceability, quality records, and assessing whether the instrument has drifted outside tolerance.