PLC Fault — Analog Input Out of Range

What This Fault Means

An analog input out-of-range fault means the PLC received a signal outside the expected bounds (e.g., <4mA or >20mA on a 4-20mA input, or <1V / >5V on a voltage input). This typically indicates a field wiring or transmitter problem.

Common Causes

• Broken wire between the transmitter and the PLC analog input
• Transmitter power supply failure (no 24VDC to the loop)
• Transmitter sensor failure (RTD open, thermocouple burnout)
• Incorrect wiring (2-wire vs 4-wire loop mismatch)
• Analog input module channel configured for wrong signal type

Recommended Fix

1. Measure the signal at the PLC analog input terminal with a multimeter (mA or V).
2. If <4mA or open, trace the wiring back to the transmitter.
3. Verify 24VDC power at the transmitter.
4. Check the transmitter sensor — use the transmitter's local display or HART communicator.
5. Confirm the PLC analog module channel configuration matches the field wiring (2-wire/4-wire, mA/V).