Transmission error: timeout (F_WD_Time or F_WD_Time_2 elapsed)

What does 25 mean?

A transmission error due to a timeout occurred in PROFIsafe communication, meaning that the expected response was not received within the specified F_WD_Time or F_WD_Time_2 watchdog period. This can lead to a safety function interruption if communication is critical.

• Interruption or disconnection of the PROFIBUS/PROFINET cable between the safety PLC and the I/O module.
• Incorrect termination resistors at the end of a PROFIBUS segment or incorrect cable categories for PROFINET.
• The PROFIsafe watchdog time parameter (e.g., F_WD_Time) is set too short for the actual network load or latency.
• Severe electromagnetic interference (EMI) corrupting PROFIsafe telegrams, causing retransmissions and timeouts.
• Faulty PROFIBUS/PROFINET communication interface on either the safety PLC or the safety I/O module.

Click steps to track your progress.

1. 1

   1. Check the physical integrity and secure connection of the PROFIBUS/PROFINET cable at both ends of the segment.

2. 2

   2. Verify that the bus termination resistors are correctly installed and switched 'ON' at the bus segment's start and end points.

3. 3

   3. Using a network diagnostic tool, check the PROFIBUS/PROFINET network for telegram errors, retransmissions, or missing frames.

4. 4

   4. Review and potentially increase the F_WD_Time or F_WD_Time_2 watchdog parameters in the safety configuration.

5. 5

   5. Isolate the suspected faulty module (safety PLC or safety I/O) by temporarily swapping it with a known good unit (if available).