Siemens SIMATIC ET 200pro - Page 154

Setting functions
8.8 Safe Torque Off (STO) safety function
SIMATIC ET 200pro FC-2 converter
154 Operating Instructions, 04/2015, FW V4.7.3, A5E34257324B AB
Table 8- 19 The principle of operation of STO
Safe Torque Off (STO)
Standard converter functions linked with STO
1. The converter detects via the F0 rail that STO
has been selected.
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2. The converter prevents energy from being fed
to the motor. When STO is active, the motor
does not generate any torque.
If you use a motor holding brake, the converter
closes the brake.
3.
The converter signals "STO is active".
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Figure 8-23 Principle of operation of STO when the motor is stationary and when the motor is rotating
If the motor is still rotating when STO is selected, then it coasts down to standstill.
The STO safety function is standardized
The STO function is defined in IEC/EN 61800-5-2:
"[…] [The converter] does not supply any energy to the motor which can generate a torque
(or for a linear motor, a force)."
The STO converter function complies with what is defined in the standard.
The distinction between Emergency Off and Emergency Stop
"Emergency Off" and "Emergency Stop" are commands that minimize different risks in the
machine or plant.