By Dovydas Kersys · Chapter 16 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Analog inputs require identity, polarity, signal type and scaling verification. A reading that looks plausible can still be wrong by an offset, range, unit or engineering conversion.
A three-point analog check catches errors that a single “looks right” value cannot.
Why this matters during commissioning
Commissioning at only one point can hide scaling errors. A 4-20 mA signal should be checked at multiple points across the range.
Commissioning procedure
- Confirm channel type and wiring: 4-20 mA, 0-10 V, RTD, thermocouple or other.
- Verify transmitter supply and loop polarity.
- Inject or create known low, mid and high values.
- Compare actual current/voltage, PLC raw value, scaled engineering value and HMI display.
- Test underrange/overrange or broken-wire diagnostics where supported.
Common failure patterns
- 4 mA interpreted as zero raw counts when scaling expects a live zero.
- Current input wired to a voltage configuration.
- Wrong engineering units.
- Shield or grounding problem causing unstable reading.
Evidence to record
- Injected process value
- Measured signal
- PLC raw value
- Scaled value
- HMI value
- Alarm response
FIELD RULE: When an analog value is wrong, separate field signal error from scaling error by measuring the actual signal.
Appendix C. Analog Loop-Check Sheet
Print or duplicate this page as needed. Record actual measurements and references rather than relying only on check marks.
| Tag | Range | Test point | Measured signal | PLC/HMI value | Result |
|---|---|---|---|---|---|
Continue the series
- Previous chapter: Digital Output Loop Checks: Commissioning Guide
- Next chapter: Analog Output Commissioning
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Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.