E-Stop Discrepancy Error - Group 1 (Safe Inputs Active)
Beckhoff · TwinSAFE Logic FB
What does FB ESTOP Bit 8 mean?
This fault indicates a discrepancy in E-Stop input group 1, similar to 'FB ESTOP Bit 0', but specifically when the 'Safe Inputs after Disc Error' option is activated. This means that even after a discrepancy, the FB attempts to maintain a safe state for the inputs, but a persistent or critical discrepancy has occurred, preventing normal operation and requiring intervention.
Common Causes
- One channel (e.g., S_IN1_G1) of the E-Stop input group remains active while the other (S_IN2_G1) becomes inactive, or vice versa, during operation.
- Intermittent connection loss or momentary short to ground on one E-Stop input wire for Group 1 while the system is enabled.
- Degraded E-Stop button contacts that cause one channel to open faster or slower than the other when actuated.
- Electrical noise or transient voltage spikes on an active input line (e.g., X7.1) causing an apparent discrepancy.
- Safety controller's internal monitoring logic incorrectly detects a discrepancy during 'Safe Inputs Active' mode.
Repair Steps & Checklist
Click steps to track your progress.
- 1
Monitor the real-time status of both E-Stop input channels for Group 1 (e.g., diagnostic LEDs G1_A, G1_B) during system operation and E-Stop actuation.
- 2
Measure the voltage level on both E-Stop input terminals (e.g., X7.1 and X7.2) relative to common ground while the 'Safe Inputs Active' condition is present.
- 3
Perform an insulation resistance test on the E-Stop cable conductors for Group 1 to detect any hidden damage.
- 4
Increase the E-Stop input debounce time (e.g., P_ESTOP_DISC_TIME_G1_ACTIVE) in the safety controller configuration if transient discrepancies are observed.
- 5
Temporarily disconnect the E-Stop button and apply external test signals to the controller inputs (e.g., 24VDC) to verify controller functionality.