Siemens SINUMERIK 840D Description Of Functions page 444

8 Application examples
8.1 Conventional brake control (single-channel from the PLC)
The application examples listed below are intended to provide support when
engineering and using Safety Integrated. It involves recommended solutions for
applications that are frequently encountered in the field and for which there is
no clear or trivial solution. The examples are intended purely as an aid to
configuration and should not be interpreted as configuration instructions, i.e.
equally suitable alternative solutions may exist.
8.1 Conventional brake control (single-channel from the PLC)
Many brake actuation systems still use a PLC output that switches an additional
hardware relay. The reason for this is that a standard S7 output can only supply
0.5 A and a current of this magnitude is usually insufficient to be able to actuate
a brake.
This circuit has the following disadvantages:
Firstly, control via the PLC does not comply with the safety requirements (in the
worst case, the PLC can crash without resetting the outputs, i.e. the axis could
fall). Secondly, the application time of the holding brake is increased because
the hardware relay has to be controlled and it also has an associated switching
time.
In order to keep the switching time of the contactor as short as possible, neither
an interference suppression diode (6 to 10-fold increase in the switching time)
nor a diode combination (2 to 6-fold increase in the switching time) may be
used for interference suppression of the contactor. The only practical solution in
this case is a varistor (increase of approximately 2–5 ms).
It is better to use an optocoupler or an S7 module, both of which provide an
output current of 2 A.
Holding/service break actuation
Current source/sink version
Holding brake
Fig. 8-1 Single-channel brake control, P-switching (single-channel from the PLC)
If this type of brake control is used with Safety Integrated, the STOP A/B active
signal (DB3x.DBX 111.4) is available to be logically combined with further
criteria to control the brake (for SI with SPL, a significantly more sophisticated
brake control function can be implemented, that is described further below).
8-444
SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
Auxiliary relay
Holding
brake
© Siemens AG 2003 All Rights Reserved
11.03