NORD Drivesystems BU0230 - Manual (Page 32)

Functional safety with NORD SK 200E frequency inverters
32 BU 0230 GB-2712
GND SH
24V SH
Frequency inverter
40
44 24V
Safety output
24V
or
24V
Safety output
or
Safety output
NOTE For devices with an AS interface (SK 225E und SK 235E) the 24V can and may not be used
as a safe shut-down method "Switch-off of the 24V supply".
For the devices SK 200E, SK 210E, SK 220E and SK 230E the control unit is powered via
a link circuit which is supplied from a mains unit. Here, the „"Shut-down of the 24V supply"
is not available as a safe shut-down method. This also applies to Size 4 devices, although
these have a 24V input.
The devices SK 200E, SK 220E and SK 225E therefore do not provide a safe shut-down
method.
2.2 Digital inputs
In order to implement a safety function, the digital inputs can be used as auxiliary inputs, e.g. for the triggering
of a braking process. It should be noted that the digital inputs only fulfil minimum safety requirements. A safe
shut-down method is always required!
The digital inputs, other I/Os and the 24V supply have a common earth. This means that a digital input may
only be switched off by disconnecting the associated connection (21 for DIN1 to 24 for DIN 4). Switch-off via
GND is not possible!
DIN1 ...
GND
DIN4
Frequency inverter
Filter
for
OSSD
optional
21
40
24V
Safety output
Safety output
24V 24
Safety output
24V
When operating with an OSSD a filter is only required for environments with strong interference.
If only low levels of functional safety are required, the safety function can also be implemented with the digital
inputs. It is recommended that this is only considered if the risk assessment has shown that slight (normally
temporary) injuries could result on failure of the safety function (see also Section 6). In case of doubt, a safe
shut-down method, "safe pulse block" or "switch-off of the 24V supply" should always be used.
2.3 Safety functions
A stop function can be executed by means of a safe shut-down method. As this has priority over other control
functions this stop-function is suitable for stopping in emergencies. This ensures that the torque is shut down
by means of a safe shut-down method. This function is known as "safe torque off" or STO.
It is also possible to first stop the motor in a controlled manner and then to switch off the torque. This function
is referred to as "safe stop 1" or SS1.
2.3.1 Safe torque off, STO
With the STO function the drive torque is switched off as quickly as possible (see Technical Data  Reaction
Time) and the drive until (motor and machine) run down to a standstill. This behaviour corresponds to Stop
Category 0 (uncontrolled braking) as per EN 60204-1. A certain time therefore elapses until the drive unit does
not perform any further dangerous movements and a safe state is achieved. Monitoring of whether or when the
drive unit has achieved a safe state is not integrated into the frequency inverter.
According to the switching equipment used and with the use of a safe shut-down method, an STO function with
Safety Category 4 as per DIN EN ISO 13849-1 can be implemented.
NOTE Control of a mechanical brake by means of the inverter is not fail-safe!
A mechanical brake connected to terminals 79 (MB+) and 80 (MB-) is applied by the triggering
of the STO function. This means that in this case, the brake must be designed as an operating
brake, as the drive unit and all of its rotating mass is stopped by the mechanical brake.
Slippage of lifting gear when triggering the STO function must be prevented by suitable brakes
where necessary!