AGL-STOV0-01SV0-05
06/12
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6.5 Two-Channel Monitoring
The STO function (Safe torque off) is realized via two channels in the frequency in-
verter (redundant design). Via two redundant monitored stop paths with no-voltage
release (STOA and STOB), the frequency inverter is switched off safely even if an
error occurs and the control voltage fails at the same time. Thus, the drive does not
generate further torque. An active movement is not stopped by the function.
Externally generated movements (such as a stroke movement by weight) must be
switched off safely by external means (for example, mechanical brake).
Triggering can be effected, for example, via a two-channel contactor control with two
release circuits and redundant disconnection of the main current or via a sensor or
emergency stop switch with two contacts and separate cable routing to the evalua-
tion unit.
Via the digital inputs STOA (X11.3) and STOB (X13.3), two DC 24 V control voltages
of a protection device are applied. If the protection device is actuated, the control
voltages are interrupted, the energy supply to the motor is switched off. Disconnec-
tion is effected at a delay according to chapter 6.2.
If the function STO i
s
triggered, the high level controller (PLC) has no more influence
on the inverter release
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in the frequency inverter. To restart, the inverter release is
enabled by the release by the user or by the superior PLC.
An error inside the STO self monitoring is identified and can then be repaired (e.g. by
replacing of a unit). Internally in the device the two stop paths are monitored cycli-
cally beginning with the terminal and ending with the power semiconductor. Both
stop paths are designed identically.
One single error will not result in a failure of the safety function.
The test required for monitoring is performed by the frequency inverter automatical-
ly. If the test results negative, the frequency inverter cannot be switched on any-
more. Starting is possible again only after the frequency inverter was completely
disconnected from voltage supplies and error has been corrected.
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If the inverter release is interrupted, a motor revolving field can no longer be generated in this state.
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