Measurement Underflow at AI581-S I/O Module

What does Measurement underflow at the I/O module mean?

A diagnosis message with severity level 3 reports "Measurement underflow at the I/O module" for an AI581-S input channel, even when an overcurrent condition was actually observed. The internal detection mechanism for AI581-S electronics is not always able to differentiate between over- and undercurrent because overcurrent can be followed by undercurrent effects.

• The AI581-S module's internal scaling or range configuration is incorrect for the measured input current, causing an underflow even with a valid signal.
• A hardware fault within the AI581-S module's analog-to-digital converter (ADC) or input circuitry, leading to misinterpretation of the signal.
• Ground loop or electrical noise affecting the differential measurement reference of the AI581-S module, causing an erroneous low reading.
• Software error in the module's diagnostic logic, incorrectly reporting underflow instead of overcurrent for specific input ranges.
• Incorrectly wired sensor (e.g., current loop) providing a signal outside the expected range or inverted, confusing the module's diagnostics.

Click steps to track your progress.

1. 1

   Verify the AI581-S module's input range configuration (e.g., 4-20mA, 0-10V) in the PLC programming software matches the connected sensor's output.

2. 2

   Measure the actual current or voltage at the AI581-S input terminals (e.g., AIN+, AIN-) using a calibrated multimeter to confirm the sensor output.

3. 3

   Disconnect the sensor and measure the AI581-S input terminals for residual voltage or current, checking for module internal faults.

4. 4

   Check the module's grounding and shield connections (e.g., terminal SHIELD) for proper termination and absence of ground loops.

5. 5

   Replace the AI581-S module with a new, functional unit if measurements confirm correct sensor output and configuration.