FB OPMODE Discrepancy Monitoring Error

What does FB OPMODE Bit 0 mean?

A discrepancy has been detected in the input signals monitored by the FB OPMODE function block. This usually means that dual-channel inputs (e.g., OpInX) are not switching or remaining in sync as expected, indicating a potential sensor failure, wiring issue, or timing problem. This will cause the FB to switch to an ERROR state, preventing mode selection.

• One channel of a dual-channel safety input (e.g., OpIn1A, OpIn1B from a mode selector switch) has failed open or shorted.
• Difference in switching times between the two input channels exceeding the configured 'Discrepancy Time' (e.g., P10-01 milliseconds).
• Faulty wiring or poor contact on one input channel (e.g., loose wire on terminal X1.1) of the dual-channel device.
• Mechanical failure or wear of the dual-channel switch or sensor (e.g., one contact opening before the other).

Click steps to track your progress.

1. 1

   1. Monitor the status of both input channels (e.g., OpIn1A and OpIn1B) in the TwinCAT safety editor to identify the misbehaving channel.

2. 2

   2. Measure the voltage at the input terminals of the safety I/O module (e.g., EL1957, channels 1 and 2) for both channels simultaneously.

3. 3

   3. Check the 'Discrepancy Time' parameter (e.g., P10-01) in the FB OPMODE configuration for an appropriate value.

4. 4

   4. Inspect the wiring and connections of the dual-channel safety input device for damage or loose terminals.

5. 5

   5. Actuate the dual-channel switch/sensor several times while monitoring inputs to observe consistent and synchronized operation.