5
vacon • 22 STO and SS1 safety functions
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5.2 Safe Stop 1 (SS1) Principle
After a safe stop command the motor starts decelerating and SS1 safety function initiates the STO
after a user set time delay.
Figure 8. 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 time
delayed safety relay and the STO safety function. These two subsystems combined compose the
Safe Stop 1 safety function as shown in Figure 9.
Figure 9. Safe Stop 1 (SS1) safety function
Time
0
Stop
Motor
deceleration
Frequency
f
actual
Time delay
Safe Torque Off (STO)
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