Safe Torque Off (STO)
Instruction handbook b maXX BM4400, BM4600, BM4700
Document No.: 5.12008.07 Baumüller Nürnberg GmbH
332
of 358
C.2
n Control of the positively driven NC contact.
n Using an external circuit or switching device, which is adequate for two-channel monitoring
(for example safety switching device or safe control).
m The faultless functioning of the relay must be checked at least once a year. The relays must
be de-energized. The closing function of the NC contacts must be monitored.
m The faultless functioning of the second path „Pulse enable“ must be checked at least once a
year. The pulse enable (X3-5/3: IF + and IF -) must be de-energized. The motor must be
torque-free.
m Prior to switching on the drive for the first time (with a safety device), the state of the NC con-
tacts must be monitored on its closing function.
m An abrupt stop of the drive or an irregular running can be caused by an error in the safety
chain. The drive must be switched off, if this error occurs.
m The STO function separates the drive from its torque, but not from its voltage. For the safe
isolation of the supply, other measures must be executed (for example the use of a main
switch).
m A temporal excitation occurs, if the internal driver (IGBT) or a control element (also in STO
state) fails. The motor can generate a magnetic field for a moment, if the DC link is „short-
circuited“ via a motor winding.
If an asynchronous motor is used, then the occurring DC field cannot cause a jerk of the rotor.
At a permanent-field synchronous motor the rotor rotates into a notch position. The angular
movement covered, in this case depends on the rotor position and the number of pole pairs
of the motor. It amounts to a maximum of 180°/number of pole pairs.
m The safety function STO may not be used at drives, where an external application of force
occurs.
m A plausibility monitoring must be executed between the request signals for STO and the feed-
back signals by the external control.
m Installation space must be protection class of IP 54, at least.
m Cabling must be done, that no cross-circuits or short-circuits are possible.
m The incoming application must comply with the requirements of the requested minimizing risk
(PL-d,/SIL2 or PL-e/SIL3).
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