Safe torque off

What does 5091 mean?

The Safe Torque Off (STO) function is active, meaning both STO signals (IN1 and IN2) are switched off or lost, causing the drive to trip. This is a critical safety function that stops the motor for safety. The drive will not start until both STO signals are restored and all faults are reset.

• Intentional activation of the STO function (e.g., emergency stop button pressed, guard door opened) causing both IN1 and IN2 to drop.
• Loss of 24VDC power supply to the external safety relay or PLC safety module driving the STO inputs.
• Complete breakage or disconnection of both STO input cables (IN1 and IN2) at the drive or safety controller.
• Faulty external safety relay or PLC safety output module failing to provide both STO signals.
• Drive internal STO circuit fault where both channels are incorrectly detected as off.

Click steps to track your progress.

1. 1

   Verify the status of the external safety circuit (e.g., emergency stop buttons, light curtains, guard door switches) to ensure they are all in a safe, closed state.

2. 2

   Measure the 24VDC supply voltage at the safety relay or PLC output module that provides the STO signals to the drive.

3. 3

   Measure voltage across both STO input terminals (e.g., X1-X3 and X2-X3) at the drive; expect 24VDC when STO is disengaged.

4. 4

   Inspect all wiring connections for both STO IN1 and IN2 at the safety controller and the drive's STO terminal block (e.g., X1, X2, X3).

5. 5

   Test the external safety relay or PLC safety module by manually engaging and disengaging its outputs, monitoring the STO signals at the drive.