Discrepancy time expired

What does 3 mean?

The configured discrepancy time for redundant inputs has elapsed, meaning that the states of redundant channels did not synchronize within the expected timeframe. This indicates a fault in the sensors, wiring, or configuration, preventing valid safety signal evaluation.

• One of the redundant input sensors (e.g., safety gate switch S1 vs S2) has a significantly slower response time or actuation delay than the other.
• Intermittent signal loss or delay on one of the redundant input channels due to wiring issues (e.g., a loose connection at terminal X2.5 delaying signal transmission).
• The configured discrepancy time (e.g., Parameter S2-01) in the safety controller is set too short for the normal operational differences between the redundant sensors or the application's physical response.
• A physical obstruction or mechanical issue preventing one sensor from actuating or de-actuating in sync with its redundant counterpart.
• One of the redundant sensors is intermittently sticking or failing to change state reliably, leading to timing mismatches.

Click steps to track your progress.

1. 1

   Actuate and de-actuate the safety function (e.g., opening and closing a guard door) while monitoring the status of both redundant inputs in the PLC's diagnostic view, observing their transition times.

2. 2

   Using an oscilloscope or logic analyzer, measure the actual signal transition times of both redundant inputs directly at the I/O module terminals to identify delays.

3. 3

   Verify the configured discrepancy time (e.g., Parameter S2-01) in the safety controller's programming matches the expected operational delays and adjust it if necessary (with careful safety assessment).

4. 4

   Perform a continuity test on the wiring for both redundant channels to rule out intermittent open circuits or high resistance that could cause signal delays.

5. 5

   If one sensor consistently responds slower or fails to transition, isolate and test that specific sensor for mechanical or electrical faults; replace if confirmed faulty.