Channel stuck-at error

What does 25 (Channel Stuck-at) mean?

An I/O channel is detected to be 'stuck' in a specific state, meaning its input signal is not changing as expected when it should. This indicates a potential wiring fault, sensor failure, or an internal issue with the I/O module. Such a condition compromises the reliability of the safety input and can lead to incorrect safety evaluations.

• A short circuit in the wiring (e.g., between the signal line and 24VDC or GND) is forcing the input channel into a permanent ON or OFF state.
• An open circuit in the input wiring (e.g., a broken wire to terminal X1.1) is causing the input to float or remain at a fixed state (e.g., always OFF for a pull-down input).
• The connected sensor itself has failed in a fixed ON or OFF state (e.g., a proximity sensor output transistor shorted or open).
• Internal hardware failure within the I/O module's input circuitry, preventing it from detecting changes in the external signal.
• Constant external voltage or current being applied to the input terminal, regardless of the intended signal source.

Click steps to track your progress.

1. 1

   Disconnect the sensor from the affected I/O module input terminal (e.g., X1.1) and use a multimeter to measure the voltage directly at the I/O module terminal.

2. 2

   Actuate the sensor independently and measure its output voltage/current to verify it is changing state correctly according to its specifications.

3. 3

   Perform a continuity test on the wiring from the sensor to the I/O module terminals to identify any short or open circuits.

4. 4

   With the sensor disconnected, manually force the input state (e.g., by momentarily connecting the terminal to 24VDC or GND) and observe if the I/O module's diagnostic LED (e.g., input status LED) changes.

5. 5

   If the module's input status LED remains stuck even with the sensor disconnected and manual forcing, the I/O module may be internally faulty and require replacement.