Safe Torque Off vacon • 120
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9
9.5.4 Safety Capability Cat. 1 / PL c / SIL 1
Without any automatic monitoring of STO output feedback, the safety capability is reduced to Cat. 1
/ PL c / SIL 1. The STO inputs (which can be connected in parallel) must be supplied by a safety push
button or a safety relay.
The picture below shows an example of connection for the STO function. A switch (a safety push but-
ton or a safety relay) may be connected with 2 wires to the drive.
When the contacts of the switch are opened, the STO is demanded, the drive indicates F30 (="Safe
Torque Off") and the motor stops by coasting.
Figure 95. STO example without automatic monitoring of the feedback and STO inputs connect-
ed in parallel.
The choice of using the STO inputs (without the automatic monitoring of the output
feedback) does not allow
other safety capabilities to be achieved.
The standards for functional safety require that functional proof tests are performed
on the equipment at user-defined intervals. Therefore,
this safety capability can be
achieved, as long as the STO function is manually monitored at the frequency deter-
mined by the specific application
(once a month can be acceptable).
This safety capability can be achieved by connecting in parallel the STO inputs exter-
nally and by ignoring the use of the STO output feedback.
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