Safe Torque Off
vacon • 92
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 69. 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 permit to achieve the
other safety capabilities
.
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 proof test interval
determined 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.
R
R
R
R
=
3
S1
G1
S2
G2
L1
L2
L3
F+
F-
U
V
W
DC+/R+
R-
DC-
SWITCH
Reinforced
POWER UNIT
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