3vacon • 15 STO AND SS1 SAFETY FUNCTIONSTel. +358 (0) 201 2121 • Fax +358 (0)201 212 2053.2 Safe Stop 1 (SS1) principleThe Safe Stop 1 (SS1) safety function initiates the motor deceleration and initiates the STO after a(user set) time delay.Figure 3. The principle of Safe Stop 1 (EN 61800-5-2, SS1 type c)The Safe Stop 1 (SS1) safety function consists of two safety related subsystems, an external timedelayed safety relay and the STO safety function. These two subsystems combined compose theSafe Stop 1 safety function as shown in Figure 4.Figure 4. Safe Stop 1 (SS1) safety functionTime0StopMotor decelerationFrequencyfactualTime delaySafe Torque Off (STO)11054.emfSafe Stop 1 (SS1)Time Delayed Safety Relay Vacon NX Safe Torque Off (STO)+Subsystem Safety Relay Subsystem STO11055.emf
