Learning outcomes
- Explain the key principles of 4–20 ma loops, calibration and loop checks.
- Carry out a structured practical check or configuration task.
- Recognise common faults, risks and evidence needed for diagnosis.
Module 8 · Lesson 3
4–20 mA loops, calibration and loop checks
Wire, calibrate and commission current loops from field instrument to control-system display.
Before you begin
Loop calibrator, drawings and calibration sheet.
Safety: Use site procedures, approved test equipment and competent supervision. Never bypass a protection or interlock without formal control.
Step-by-step learning
- Verify loop supply and calculate available voltage for all loads.
- Isolate or place the loop in a safe maintenance state.
- Apply 0, 25, 50, 75 and 100 percent values and record as-found/as-left results.
- Complete an end-to-end loop check including alarms, trips and display.
Ian's practical tips:
- A loop check proves the whole chain; bench calibration proves only the instrument.
- Always restore impulse lines, manifolds and software overrides after calibration.
Fault-finding questions
- What should be happening, and what evidence proves it?
- Where is the last known correct signal, voltage, state or process condition?
- What changed immediately before the fault?
- Can the system be divided into smaller testable sections?
Practical activity
Create a one-page test record for this lesson. Include expected values, measured results, equipment used, risks controlled, defects found and the final proven condition.