NORD Drivesystems BU0230 - Manual (Page 36)

Functional safety with NORD SK 200E frequency inverters
36 BU 0230 GB-2712
2.4.2 SS1 Function
A digital input is always required for the implementation of the SS1 function in order to initiate a braking
process performed by the inverter. For this, the digital input used is set to the function "fast stop" [11].
Filter
for
OSSD
optional
DIN1
GND
GND SH
24V SH
Frequency inverter
21
40
88
89
Use of
"safe pulse block"
or
DIN1
GND
GND
24V
Frequency inverter
21
40
40
44
24V
Reset
Emergency stop button
Supply voltage
Reset circuit
Input circuit with
short-circuit
recognition
Safety output 1
24V
Safety output 2
24V
delayed
Shielded cable to eliminate
errors as per
DIN EN ISO 13849-2
Use of
"switch-off of the
24V
supply ”
Note: The optional filter on the digital input is only required in environments with heavy interference.
When the safety function is requested, a controlled stopping procedure is first triggered via the digital input
(here DIN1). Here it must be ensured that the drive is brought to standstill within the parameterised fast stop
time (P426). After the elapse of a delay time which is controlled by the switching device, the safe shut-down
method is triggered. The delay time must be dimensioned so that the delay is longer than the fast stop time
plus the DC follow-up time (P559). The delay time must be selected so as to be fail-safe.
Here it should be noted that controlled braking can fulfil the requirements for Safety Category 1. Safety
Category 4 as per DIN EN ISO 13849-1 can be achieved with final switch-off by the triggering of a safe shut-
down method "safe pulse block" or "switch-off of the 24V supply". For this, the same conditions as described in
the examples for the STO function apply. If controlled braking fails then the device switches over to STO (after
the set delay).
NOTE
A separate shielded cable must be used for the "safe pulse block" or "switch-off of the 24V
supply". When using a protective switching device with short-circuit monitored OSSD-outputs,
the safety outputs can be combined in a single shielded cable.
NOTE
Only the safe shut-down methods "safe pulse block" and "switch-off of the 24V supply" are
able to fulfil the requirements for Safety Category 4 /Performance Level e. Safety Category 1
(and PL c) can be achieved for the digital inputs and therefore for controlled braking.