Safe torque off 1

What does FA81 mean?

An asymmetric loss of one of the Safe Torque Off (STO) signals has occurred (e.g., IN1 lost while IN2 is present). This is interpreted as a malfunction in the safety circuit and causes the drive to trip. The drive will not start until both STO signals are restored and all related faults are reset.

Complete Troubleshooting Guide

1. 1

   Verify the integrity and continuity of all safety circuit connections to the STO input terminals.

2. 2

   Confirm that the external safety device (e.g., safety relay, PLC) is correctly supplying the STO signals for both channels.

3. 3

   Check the value of parameter 95.04 (Control board supply) to ensure stable power to the control board.

4. 4

   After resolving the cause, reset the drive from an appropriate source (e.g., control panel, digital input).