Discrepancy Time Expired

What does E3-3 mean?

For an I/O bus module, the configured discrepancy time for a specific channel has expired. This typically occurs in safety applications where redundant signals do not match within the allowed time frame, indicating a potential sensor malfunction, wiring issue, or incorrect time setting. This can lead to safety shutdowns.

• Difference in switching times or transient behavior between two redundant safety input sensors (e.g., two limit switches for a safety gate).
• One of the redundant safety input sensors (e.g., S1 or S2) is physically stuck, failed open, or failed closed, causing a permanent signal mismatch.
• High resistance or intermittent connection in the wiring of one safety channel, leading to delayed signal propagation or inconsistent readings.
• Incorrectly configured discrepancy time parameter (e.g., P30-01 'Discrepancy Delay') in the safety controller, set too short for the physical sensors.
• Noise or EMI affecting one of the safety input channels, causing momentary signal fluctuations that exceed the discrepancy window.

Click steps to track your progress.

1. 1

   1. Individually activate and deactivate each redundant safety input sensor (e.g., S1, S2) while observing their states in the safety PLC diagnostics.

2. 2

   2. Measure the voltage and continuity of the wiring for both safety channels from the sensors back to the I/O module's input terminals (e.g., X1.1 and X1.2).

3. 3

   3. Access the safety controller's configuration software and verify the 'Discrepancy Time' parameter (e.g., P30-01). Increase it slightly if typical sensor activation differences are known.

4. 4

   4. Check for and address any potential sources of electromagnetic interference (EMI) near the safety input wiring, ensuring proper shielding and grounding.

5. 5

   5. Perform a cross-check of the sensor's physical state against the observed input status on the safety I/O module to identify which sensor is causing the mismatch.