Safety reaction time (system reaction time)
The worst-case time from a safety-related event, or a fault, until the system is in its safe state.
The network analogy
An end-to-end worst-case latency budget summed hop by hop from sensor to actuator, where the network is one of the hops.
Why it matters for wireless
Network connection limits are terms in the sum. Any longer connection limit chosen to survive roaming shows up directly in the safety reaction time, and from there in the required safety distance.
One vendor defines system reaction time as the worst-case time from a safety-related event as input to the system or as a fault within the system, until the system is in the safe state, summed from sensor, controller, and actuator reaction times. Its worked light curtain example includes a network term, an input connection delay of 4 x RPI1, beside an assumed machine stop time of 900 ms. IEC 61784-3 uses the related term safety function response time.
The network term is often small next to the machine’s own stopping time. It is still the term the wireless design controls, and the machine builder’s calculation, not the network team, decides how large it may be.
About this page
Built from 4 sources: 1 standards body or lab and 3 vendor documents. Researched and drafted with AI assistance, then reviewed and approved by Ben Rutter on . How pages are made
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Cite this page
Plain
Ben Rutter. "Safety reaction time (system reaction time)." OT Wireless, published October 5, 2026. https://otwireless.com/glossary/safety-reaction-time/
APA 7
Rutter, B. (2026, October 5). Safety reaction time (system reaction time). OT Wireless. https://otwireless.com/glossary/safety-reaction-time/
BibTeX
@misc{rutter2026safetyreactiontime,
author = {Rutter, Ben},
title = {{Safety reaction time (system reaction time)}},
year = {2026},
howpublished = {\url{https://otwireless.com/glossary/safety-reaction-time/}},
organization = {OT Wireless},
}