Monitoring Discrepancy Error - Input Group 1

What does FB MON Bit 0 mean?

A discrepancy has been detected between the channels of input group 1 in the FB MON function block. This means the redundant inputs are not switching in sync or are reporting different states, indicating a potential sensor fault, wiring issue, or incorrect timing that could compromise the monitoring function, leading to a safety stop.

• One channel of a monitored redundant safety input device (e.g., safety gate switch S1-S2) is stuck open or closed.
• Broken conductor or loose terminal connection on one channel (e.g., input MonIn_CH1) of the monitored safety device.
• Asynchronous switching of the redundant contacts within a safety device due to mechanical wear or sticky contacts.
• Electrical noise or transient voltage spikes on one input channel causing a momentary discrepancy.
• Input synchronization time parameter (e.g., P_MON_DISC_TIME_G1) set too short for the specific safety device's characteristics.

Click steps to track your progress.

1. 1

   Actuate the monitored safety device (e.g., open/close safety gate) and observe the corresponding input LEDs (e.g., IN_G1_A, IN_G1_B) on the safety controller for synchronized state changes.

2. 2

   Measure continuity across both redundant output contacts of the safety device (e.g., between terminals 3 and 4, and 5 and 6 of a safety interlock switch) in both states.

3. 3

   Check resistance of individual wire runs from the safety device output terminals to the safety controller input terminals (e.g., from safety switch 3 to controller MonIn_CH1).

4. 4

   Increase the discrepancy time parameter (e.g., P_MON_DISCREPANCY_DELAY_G1) in the safety controller configuration if inputs are switching asynchronously but within acceptable limits.

5. 5

   Verify that the monitored device (e.g., safety light curtain OSSD outputs) has stable power supply and is not experiencing internal faults.