Learning outcomes
- Explain the key principles of instrument fault finding and signal quality.
- Carry out a structured practical check or configuration task.
- Recognise common faults, risks and evidence needed for diagnosis.
Module 8 · Lesson 4
Instrument fault finding and signal quality
Diagnose noisy, drifting, frozen, saturated, intermittent and implausible process signals.
Before you begin
Trend data, calibrator, meter and loop documentation.
Safety: Use site procedures, approved test equipment and competent supervision. Never bypass a protection or interlock without formal control.
Step-by-step learning
- Compare process reality, local indication, loop current, PLC raw value and SCADA value.
- Check power, polarity, shielding, grounding and moisture ingress.
- Inspect process connections for blockage, bubbles, condensation or plugging.
- Substitute a known signal to separate field and control-system faults.
Ian's practical tips:
- Work from the process toward the display in measured steps.
- Never “calibrate out” a process-connection problem.
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.