By Dovydas Kersys · Chapter 31 of 58 in Machine Commissioning.

Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.

Safe Torque Off and other drive-integrated safety functions depend on correct wiring/configuration and must be tested with the drive in conditions that prove torque-producing energy is removed as intended.

Why this matters during commissioning

A drive may show “STO active” while a separate mechanical hazard remains. Safety functions must be linked to the actual hazard.

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Commissioning procedure

  1. Verify STO channel wiring and drive diagnostics.
  2. Command motion, then activate the safety function using the real initiating device.
  3. Confirm torque command is removed and motion reaches the expected state.
  4. Verify the drive cannot restart merely because STO is restored.
  5. Test diagnostics for one-channel or discrepancy faults if supported.
  6. Record drive safety parameters/signatures where applicable.

Common failure patterns

  • STO input polarity wrong.
  • Drive enable removed but STO never actually tested.
  • Brake behavior not coordinated with STO.
  • Automatic restart command remains present when STO resets.

Evidence to record

  • Measured value and test point
  • Expected value / expected state
  • Observed value / observed state
  • Pass/fail result and any deviation
  • Name/date or responsible person where required

FIELD RULE: Drive-safe status is useful evidence, but the final proof is the behavior of the hazard.

Continue the series

Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.

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