What Causes an SAFF (Safety Function Error) on an Altivar Process Drive and How Can It Be Troubleshot?
Resolution:
SAFF occurs when the drive detects different states between the STOA and STOB safety inputs, such as one input being ON while the other is OFF. Because these safety inputs are expected to operate consistently, the drive detects the discrepancy as a safety circuit condition and trips to prevent operation.
Possible causes include:
- Loose or incorrect wiring at the 24 VDC, STOA, or STOB terminals
- An external circuit causing different signals at STOA and STOB
- Electrical noise affecting the STO wiring
- A possible drive-related issue if the correct signals are present at both inputs but the drive does not detect them correctly
Follow the next steps to troubleshoot:
1.- Check the STO signals and wiring.
Verify the wiring between 24 VDC, STOA, and STOB. Confirm that STOA and STOB have the correct and matching signals. If one input has 24 VDC and the other does not, SAFF can be triggered.
2.- Inspect the connections.
Check the STOA and STOB terminals for loose connections or wiring issues. Also inspect the external safety circuit for anything that could cause a difference between the two signals.
3.- Check the input status in the drive.
Open the Logic Input Map: Menu 4: Display > I/O Map > Logic Input Map
Compare the STOA and STOB status displayed by the drive with voltage measurements taken between:
- COM and STOA
- COM and STOB
If the correct voltage is present at both STO inputs but the Logic Input Map does not indicate that both inputs are ON, there may be an issue with the drive.
4.- Check for electrical noise.
Electrical noise can affect the STO signals. If appropriate and safe for the application, isolate the external STO wiring and test the circuit according to the applicable installation and safety procedures. If the fault disappears after the external circuit is isolated, inspect the STO wiring and external safety circuit carefully.
Keep STO wiring separated from power wiring and use appropriate shielded cable where necessary to help reduce electrical noise.
If this article does not answer your question, check out our FAQ database that has answers to more commonly asked questions:
Frequently Asked Questions - Schneider Electric (se.com)
If this FAQ did not solve your issue, you can call us at 1-888-778-2733 Option 2 and then 4 or e-mail us atdrive.products.support@se.comto create a case with our Technical Support Team.
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