NORD Drivesystems BU0230 - Manual (Page 31)

2 Description of function
BU 0230 GB-2712 31
2.1 Safe shut-down method
With the aid of a safe shut-down method the torque is now to be safely shut down. This corresponds to the
safety function STO (safe torque off).
In order to switch off the torque, the current to the motor must be interrupted. Various shut-down methods are
available according to the particular device:
"Safe pulse block" in SK 210E, SK 215E, SK 230E and SK 235E
"Switch-off of the 24V supply" in SK 205E and SK 215E
NOTE
For Size 4:
The 24V connection in Size IV SK 200E, SK 210E, SK 220E and SK 230E devices for the
supply of the control electronics cannot be used as a safe shut-down method, as the high
voltage mains unit which operates in parallel continues to supply the control unit and the
micro-controller.
NOTE
On triggering a safe shut-down method, a mechanical brake connected to terminals 79
(MB+) and 80 (MB-) is applied (only SK2x5E, see manual BU 0200 GB). If the drive unit is
not previously switched off, the brake must be designed as an operational brake.
2.1.1 Safe pulse block
Devices equipped with a "safe pulse block" have an additional DC/DC converter, which produces a 24V supply
(24V_SH, GND_SH) as either the supply voltage for the drivers or the control voltage for a mains unit which in
turn produces the supply voltage for the drivers.
If the external 24 V voltage is switched off then the DC/DC converter does not transmit any power to the
drivers. As the drivers are now no longer supplied with power, no pulses reach the semiconductor switches (T1
to T6) of the inverter. The flow of current in the semiconductor switches and the motor is interrupted. I.e. after a
certain reaction time of the electronics and the reduction time of the motor current, the motor does not develop
a driving torque.
The switch-off of the 24V supply (24V_SH, GND_SH) must be carried out by a fail-safe switching device. For
this, either the connection 24V_SH (Terminal 89) or the connection GND_SH (Terminal 88) may be
disconnected from the 24V source. For preference, the 24V_SH connection is disconnected.
GND SH
24V SH
Frequency inverter
88
89 24V
Safety output
24V
or
24V
Safety output
or
Safety output
2.1.2 Switching off the 24V supply
The 24V mains unit used to supply the control electronics can also be used as a safe shut-down method (only
with SK 205E and SK 215E Size 1 to 3).
If the 24V supply (24V, GND) is switched off, the microcontroller (µC) is disconnected from the supply voltage.
As the microcontroller is responsible for the generation of the pulse pattern to control the semiconductor
switches (T1 to T6), this method switches off all the semiconductor switches (T1 to T6). The flow of current in
the semiconductor switches and the motor is interrupted. I.e., as with the "safe pulse block" after a certain
reaction time of the electronics and the reduction time of the motor current, the motor does not develop a
driving torque.
"Switch-off of the 24V supply" (24V, GND) must also be carried out by means of a fail-safe switching device. In
this case, the connection between the voltage source and the 24V connection (Terminal 44) must be
interrupted. Switch-off via GND is not possible, as the 24V supply and the digital I/O have a common earth. If
GND was switched off, there would still be a connection to earth via the digital I/O.