Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Stopping functions and safe states

Protective response time

Also known as: reaction time

In machine safety, protective response time is the time from detection of a protective demand to achievement of the required protective state. It covers the whole chain of sensor, logic and actuator, including the stopping of the machine.

  • Machine safety
  • Risk assessment

In one sentence

Protective response time sums up every delay from sensing a demand to reaching the protective state, and it drives safety distances.

Example

For a light curtain on a press brake, the protective response time adds the light curtain response time, the safety relay delay, valve switching and the press stopping time; the total sets the mounting distance.

How it applies

  • Machine safety: In ISO 13855 the overall stopping performance T enters the minimum distance formula S = (K × T) + C. Underestimating any link in the chain puts the protective device too close to the hazard.
  • Integrated systems: Networked safety adds bus cycle times, latency and watchdog times. Every element of the reaction chain needs a documented worst-case value, not a typical one.
  • Technical documentation: Record the values and their sources (data sheet, measurement, calculation) and state that changes to parameters, valves or brakes require the response time to be rechecked.
  • Evidence: Measured stopping times at commissioning and in periodic checks show that the assumed value still holds.

Protective response time vs. stopping time

Stopping time covers only the machine, from the stop command to standstill. Protective response time also includes detection and signal processing before the stop command.

By knowledge.aitechdoc.world · Published September 25, 2026 · Last reviewed

Source: AI TechDoc Knowledge editorial definition, based on ISO 13855, Safety of machinery — Positioning of safeguards with respect to the approach of the human body

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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