NORD Drivesystems BU0230 - Manual (Page 38)

Functional safety with NORD SK 200E frequency inverters
38 BU 0230 GB-2712
2.4.4 Example without safe shut-down method
It is possible to implement the safety functions STO or SS1 with a digital input and a protective switching
device. With this switching version, as a maximum, Safety Category 1 as per DIN EN ISO 13849-1 can be
achieved, if in addition to the digital inputs, all other components (protective switching device, emergency stop
button, wiring) fulfil the requirements for Category 1.
This switching version should only be considered if only low requirements for functional safety need to be
fulfilled and if the risk assessment has shown that failure of the safety function can only result in slight (usually
temporary) injuries (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.
DIN1 ...
GND
Frequency inverter
DIN4 Filter
for
OSSD
optional
21
40
24
24V
Reset
Emergency stop button
Supply voltage
Reset circuit
Input circuit with
short-circuit
recognition
Safety output
24V
Shielded cable to eliminate
errors as per
DIN EN ISO 13849-2
Use of a
digital input
STO: P420[-01...-04]=10, "Disable voltage"
SS1: P420[-01...-04]=11, "Fast stop"
Note: The optional filter is only required in environments with heavy interference.
To implement the safety function STO, the digital input is parameterised to the function "Disable voltage".
With the safety function SS1 the digital input is assigned the function "Fast stop" (parameter P420[-01...-04])
and the fast stop time is set via parameter P426. It must be ensured that the drive is brought to standstill within
the parameterised fast stop time.
NOTE
As a maximum, this example achieves Safety Category 1 or Performance Level c. This circuit
version is not SIL-capable (see Section 6 ).