STO Self-diagnosis Error

What does E99. mean?

This error indicates an internal fault within the inverter's STO (Safe Torque Off) input terminal or its internal safety circuit. This is a critical internal diagnostic failure, signaling that the inverter's safety function itself is not operating normally. It does not depend on the GS input operation selection, implying a fundamental issue with the safety hardware.

• Short circuit or open circuit detected on the STO input terminals (e.g., S1/S2, or X3:STOA/STOB).
• Internal failure of the inverter's safety monitoring circuit components (e.g., safety relays, monitoring ICs).
• External wiring fault to the STO inputs, such as incorrect cabling to a safety relay or PLC safety output.
• Discrepancy detected between redundant STO input channels (e.g., S1 and S2 signals are not coherent).
• Transient voltage spike or electromagnetic interference (EMI) affecting the sensitive internal safety circuit.

Click steps to track your progress.

1. 1

   1. Power off the inverter, disconnect all wiring from the STO terminals (e.g., S1/S2 or X3:STOA/STOB), and re-apply power to check for internal fault.

2. 2

   2. If the fault clears with STO terminals disconnected, perform a continuity test on all external STO wiring, checking for shorts or opens.

3. 3

   3. If an external safety device is used, bypass it temporarily with a wired jumper (e.g., short S1 to SINK and S2 to SINK, referring to manual's STO wiring diagram) to isolate the external circuit.

4. 4

   4. Measure the voltage across STO input terminals (e.g., S1-SINK and S2-SINK) to ensure appropriate signal levels (e.g., 24VDC or 0VDC) from the safety source.

5. 5

   5. If the fault persists after verifying external wiring and bypassing, the inverter's internal safety circuit has failed and requires unit replacement.

6. 6

   6. Ensure proper grounding of the inverter and shielded cabling for STO inputs to mitigate EMI effects.