NORD Drivesystems BU0230 - Manual (Page 34)

Functional safety with NORD SK 200E frequency inverters
34 BU 0230 GB-2712
2.4 Examples / Implementation
The following illustrates several examples of solutions for the safety functions STO and SS1.
2.4.1 STO function
Normally, a protective switching device is used to implement a safety function. The safety category of the
function is determined by the component with the lowest category.
Use of
"safe pulse block"
or
Use of
"switch-off of the
24V
supply ”
24V
Reset
Emergency stop button
Supply voltage
Reset circuit
Input circuit with
short-circuit
recognition
GND
24V
Frequency inverter
40
44
GND SH
24V SH
Frequency inverter
88
89
Safety output
24V
Shielded cable to eliminate
errors as per
DIN EN ISO 13849-2
In this example, Safety Category 4 as per DIN ISO 13849-1 can be achieved. The prerequisite for this is that
the emergency stop button, the protective switching device and the wiring fulfil the requirements for Category 4.
For example, this can be achieved as follows:

Redundant protective switching device with self-monitoring

Dual-channel input circuit with short-circuit recognition (and appropriate emergency stop button)

Safety output with periodic switch-off tests (OSSD)

Elimination of errors as per DIN ISO 13849-2 for the wiring between the switching device and the input
terminals of the safe shut-down method used, by the use of a shielded cable and connection of the
shield at both ends.
NOTE If the "safe pulse block" triggers for an enabled frequency inverter, error E018 (18.0 safety
circuit) is triggered.
This can be prevented by assigning the function "Disable voltage" (P420[-04]=10) to digital
input DIN4.
For devices with "safe pulse block" (SK 210E, SK 215E, SK 230E and SK 235E), digital
input DIN4 is not implemented as a separate input, bur rather lies in parallel with the "safe
pulse block" as serves as a diagnostic path for the status of the safe pulse block at the
input terminals.
The typical reaction time can be reduced by the additional use of a digital input.
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
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.
A second safety output is required to control the digital input.