Understanding Stop Time Measurement

A key element of Machine Safety

In any environment where machinery and people work side by side, safety systems play a crucial role in preventing accidents and protecting operators. Among the many safety practices used in industrial settings, Stop Time Measurement (STM) stands out as one of the important ones - yet least understood.

Stop Time Measurement focuses on one essential question: How long does a machine take to stop once a safety device is triggered?

The answer determines whether safety devices are placed correctly and whether machine operators are fully protected during machine operation.

Stop Time Measurement is a process that measures the duration between the activation of a safety device - such as a light curtain, laser scanner, or emergency stop - and the moment the hazardous movement comes to a complete stop.

This measurement is used to calculate the minimum safe distance required between the protective device and the point of danger. That distance ensures that if someone enters a hazardous zone, the machine has enough time to stop before they reach the danger point.

Why Stop Time Measurement Matters?

Ensures Accurate Placement of Safety Devices
Safety devices such as light curtains, laser scanners, and pressure‑sensitive mats must be installed based on real stopping performance - not assumptions. Stop Time Measurement (STM) provides precise data that determines the exact distance required between the protective device and the hazardous point of operation.

Accurate stop‑time data helps prevent:

• Safety devices mounted too far away, resulting in unnecessary loss of valuable floor space
• Safety devices mounted too close, which may not allow enough time for the machine to stop before a person reaches the danger point

Supports Compliance With Safety Standards
Machine safety standards require that the minimum safe distance be calculated using verified stop‑time measurements. Key regulations such as ISO 13855 and the EU Machinery Regulation (2023/1230) specify the need for measured data - not theoretical values.

Through STM, organisations can ensure that:

• Safety distances comply with internationally recognised standards
• Risk‑reduction measures are backed by proper validation
• Clear, traceable documentation is available for audits, inspections, or certification processes

Identifies Mechanical Wear Before It Becomes a Risk
A machine’s stopping performance changes over time. Without monitoring, these changes can go unnoticed—leading to unsafe operating conditions.

Stopping distance can increase due to:

• Brake wear
• Mechanical degradation
• Changes in tooling, load, or speed
• Faults in the control system

STM acts as an early‑warning system. By regularly measuring stopping time, any decline in braking performance is detected early. This helps prevent unsafe conditions, unexpected downtime, and costly repairs. It also ensures that safety devices remain positioned correctly even as the machine ages.

Stop Time Measurement Service Scope