Glossary · Stopping functions and safe states
Safely-Limited Speed (SLS)
Also known as: SLS, safely limited speed
German: Sicher begrenzte Geschwindigkeit (SLS)
In drive-based safety, Safely-Limited Speed (SLS) is a safety function that prevents motor speed from exceeding a specified limit. If the limit is exceeded, the drive initiates a defined fault reaction.
- Machine safety
- Risk assessment
In one sentence
Safely-Limited Speed (SLS) caps motor speed at a monitored limit, so people can work near moving parts in setup or teach modes.
Example
During setup of a printing press with the guard open, SLS limits the cylinders to crawl speed; exceeding the limit triggers Safe Stop 1.
How it applies
- Machine safety: SLS is typically combined with hold-to-run control or an enabling device in special operating modes. The speed limit itself must come from the risk assessment, for example what a person can react to.
- Integrated systems: Document the speed limit, the reaction when it is exceeded and the operating modes in which SLS is active. The limit refers to the drive; check that gear ratios translate it into the intended speed at the hazard.
- Technical documentation: Instructions for setup mode state the reduced speed, the protective devices still in effect and the residual risks that remain at limited speed.
- Evidence: Validation shows that exceeding the limit triggers the reaction within the assumed time.
Safely-Limited Speed vs. reduced speed
A speed reduced by the standard control is a setting. SLS is a monitored safety function with a defined reaction and a required performance.