Glossary · Stopping functions and safe states
Stopping time
In machine safety, stopping time is the elapsed time from initiation of a stop command until hazardous motion has ceased. It is part of the overall response time used to position protective devices.
- Machine safety
- Risk assessment
- Maintenance
In one sentence
Stopping time measures how long hazardous motion continues after a stop command, and it grows as brakes and clutches wear.
Example
A hydraulic press is measured with a stop-time meter at 180 ms at commissioning; the annual check shows 230 ms, so the light curtain distance is rechecked and the valve serviced.
How it applies
- Machine safety: Stopping time is a major part of T in the ISO 13855 minimum distance formula. If it increases, a protective device that was correctly placed can become too close.
- Maintenance: Brake and valve wear lengthen stopping time. Maintenance instructions should say when to measure it and what limit triggers action.
- Technical documentation: Record the measured value, the method, the load and speed during the test, and the maximum value assumed in the calculation.
- Evidence: Link each measurement to the protective device it justifies, so periodic verification results can be compared against the design value.
Stopping time vs. protective response time
Stopping time starts at the stop command. Protective response time starts earlier, at detection, and includes the sensor and logic.