Two-Hand Discrepancy Error - Input Pair 2

What does FB TWOHAND Bit 1 mean?

A discrepancy has been detected within the two channels of input pair 2 for the FB TWOHAND. This means the redundant hand actuation signals are not synchronizing correctly, indicating a potential issue with the two-hand device, its wiring, or incorrect timing. This will prevent safe two-hand operation and put the machine into a safe state.

• Wiring fault on one channel of input pair 2 (e.g., broken wire to input X5.1 or X5.2 on safety PLC).
• Malfunctioning two-hand actuation button for input pair 2, causing differing actuation/release times between channels.
• Electrical interference (EMI) on the signal lines of input pair 2, leading to false switching states.
• Degraded contact within the safety pushbuttons for input pair 2, resulting in intermittent signal loss.
• Discrepancy time parameter (e.g., P_TwoHandDiscTime) set too tight, causing false positives from normal button tolerance.

Click steps to track your progress.

1. 1

   1. Power down the safety system, then use a multimeter to measure the resistance of the wiring from each button of input pair 2 to its respective safety input terminal (e.g., X5.1, X5.2).

2. 2

   2. With power restored, observe the diagnostic LEDs on the safety module for input pair 2 while actuating each button independently and simultaneously.

3. 3

   3. Replace the push button switch assembly for input pair 2 if its internal contacts show resistance instability or failure during actuation tests.

4. 4

   4. Inspect the shielded cabling for input pair 2; verify the shield is properly grounded at one end (e.g., control cabinet ground bar).

5. 5

   5. Access the safety controller's programming interface and temporarily increase the 'TwoHandDiscTime' parameter (e.g., to 500ms) to rule out overly sensitive timing.