Control and Instrumentation Technician Interview Questions UK: 8 Real Questions and What Interviewers Want

Most Control and Instrumentation Technician interviews in the UK follow a pattern, and knowing it beats guessing. Below are eight questions from our bank of 12, each with a note on what the interviewer is really after.

Eight Control and Instrumentation Technician interview questions, and what the interviewer is thinking

1. How would you calibrate a 4-20 mA pressure transmitter, and what do you check along the way?

Why they ask: Calibration is a daily task for a C&I technician.

2. What does a control and instrumentation technician do on a typical day, and why did you choose this trade?

Why they ask: Tests understanding and motivation.

3. Explain how a thermocouple differs from an RTD, and how you would fault-find a temperature loop that reads wrongly.

Why they ask: Temperature measurement is the most common instrumentation topic.

4. What are the requirements for working in a hazardous area, and how do you identify equipment suitable for use there?

Why they ask: Hazardous areas are common in process industries.

5. How do you carry out a loop check, and what would you test on a simple level control loop?

Why they ask: Loop testing is key during commissioning.

6. You are called out because a flow transmitter is reading zero but the process operator believes there is flow. How do you start fault-finding?

Why they ask: Fault-finding is the core of the job.

7. Tell me about a time you fixed a fault that others had struggled to solve.

Why they ask: Persistence and methodical thinking matter in fault-finding.

8. What is the difference between a PLC and a DCS, and what would you check when a PLC input is not working?

Why they ask: Control system knowledge is expected from technicians.

A sample answer to question 1

How would you calibrate a 4-20 mA pressure transmitter, and what do you check along the way?

I would begin by getting the permit or isolation in place, then letting operations know I am working on that loop, as the signal feeds a control system. I would isolate the transmitter, vent it safely and connect a calibrator or pressure source, along with a precision reference gauge and a mA meter or loop calibrator. I would check zero, then apply pressure at 0, 25, 50, 75 and 100 per cent of range, and record the mA output at each point, expecting 4, 8, 12, 16 and 20 milliamps. I repeat on the way down to check hysteresis. If the readings are outside tolerance, I adjust zero and span, then repeat the check. I confirm the reading arrives correctly in the control system, with the right scaling. My calibrator must have a valid traceable certificate. I record as-found and as-left values on the calibration sheet, sign it, restore the loop, and remove my isolation, getting the operator's agreement before returning to service.

Common mistake to avoid: Adjusting without recording as-found; Using an out-of-date calibrator

Want the rest?

Full model answers, key points and common mistakes for all 12 questions are on the Control and Instrumentation Technician interview questions page. The first five are free, no sign-up needed.