Glossary · Stopping functions and safe states
Safe Stop 1 (SS1)
Also known as: SS1
German: Sicherer Stopp 1 (SS1)
In drive-based safety, Safe Stop 1 (SS1) is a safety function that initiates and monitors controlled deceleration of the motor, followed by Safe Torque Off (STO) or another safe condition once the motor has stopped or a limit is reached.
- Machine safety
- Risk assessment
In one sentence
Safe Stop 1 (SS1) brakes a drive under control and then removes torque, the drive-level form of a stop category 1 stop.
Example
When an operator opens a guard on a high-inertia saw, SS1 brakes the blade along a monitored ramp within two seconds and then activates STO, instead of letting it coast for twenty seconds.
How it applies
- Machine safety: SS1 is the drive function that implements a stop category 1 stop. It shortens stopping time for high-inertia loads, which can reduce the required safety distance.
- Integrated systems: IEC 61800-5-2 distinguishes variants of SS1 by how the deceleration is monitored. Specify which variant the drive uses, the ramp or time limits and what happens if deceleration is not achieved.
- Technical documentation: Describe the stop behavior users will see and the expected stopping time. Parameter changes to ramps affect safety and need change control.
- Evidence: Validation measures the actual stopping time under worst-case load and confirms the transition to Safe Torque Off.
Safe Stop 1 vs. stop category 1
Stop category 1 (IEC 60204-1) describes a stop behavior for the machine. SS1 (IEC 61800-5-2) is a drive safety function that can achieve it for one drive.