Measurement underflow at the I/O module

What does 7 mean?

The input signal measurement at the I/O module has fallen below its minimum measurable range (underflow). This indicates that the sensor input is providing a value lower than the module can process, potentially leading to incorrect or invalid safety-related readings.

• The connected sensor is outputting a signal (voltage or current) that is below the minimum input range of the I/O module channel (e.g., a 0.5V signal connected to a 1-5V input).
• An open circuit in the sensor wiring or a loose connection at the I/O module terminals (e.g., AI+, AI-), leading to a near-zero or floating input.
• Malfunction of the connected sensor, causing it to output an abnormally low or zero signal even when active.
• Incorrect I/O module input type configuration in the engineering software (e.g., configured for 1-5V when a 0-10V sensor is connected that currently outputs 0V, Parameter P3-01).
• Improper scaling factor or offset parameter set in the PLC program for the analog input, causing an apparent underflow in the interpreted value.

Click steps to track your progress.

1. 1

   Using a calibrated multimeter, measure the actual analog signal (e.g., voltage across AI+, AI- or current in series) from the sensor at the I/O module terminals.

2. 2

   Compare the measured signal value with the specified minimum input range of the I/O module's analog input channel (refer to module datasheet).

3. 3

   Perform a continuity test on the signal cable from the sensor output to the I/O module terminals to detect any open circuits or high resistance.

4. 4

   Verify the I/O module's channel configuration in the PLC engineering software (e.g., Parameter P3-01 for input range) matches the connected sensor's output specifications.

5. 5

   Isolate the sensor and test its output independently to ensure it is not malfunctioning and sending an abnormally low signal.