NORD Drivesystems BU0530 - Manual (Page 44)

Functional safety with NORD SK 500E frequency inverters
44 BU 0530 GB-3712
5 Protective switching devices
The safety switching device used for the intended purpose, as well as all additional components required to
implement a safety function, must fulfil the requirements of the special application in accordance to the risk
analysis.
The switching device outputs must fulfil the following basic conditions:
5.1 Output voltage

Mechanical protective switching device: 24V± 25% (18V…30V)

Electronic protective switching devices with OSSD
5
outputs: 24V-20%+ 25% (19.2V…30V)
The stated voltages should be available at the input terminals of the inverter. I.e. the line drop in the cable
used may need to be taken into account.
5.2 Switching capacity and current load
The safety outputs of the switching devices used must be able to withstand the following loads:
Load per connected frequency inverter “Safe pulse block”
Continuous current (mean value) ≤ 50 - 140 mA, according to size
Switch-on current ≤ 400 mA (for t ≤ 2 ms)
Supporting capacitance (downstream of inverse polarity protection) max. 30 µF
Peak current after an OSSD
4
test pulse (periodic) ≤ 400 mA (for t ≤ 300 ms)
Please note:
Due to the supporting capacitors of the safe shut-down method, there is an increased current consumption for
a short time on switch-on and after a test pulse from an OSSD
4
. The "safe pulse block" is equipped with an
active current limiter in order to reduce the load on safety outputs to a minimum.
5.3 OSSD
8
outputs, test pulse

t
off
≤ 0.5ms (width of test pulse)
Maximum time for which the output of the safety switching device is switched off for test purposes.

D ≥ 90% (Duty)
The supply voltage is applied for at least 90% of the time. I.e. for a test pulse of t
off
=0.5 ms the supply
voltage is subsequently applied for at least t
on
=4.5 ms.

Double pulses are permitted when the two pulses are at least 1ms apart and the condition for D is
observed.
The following sequence results at maximum pulse width: First test pulse, where t
off
= 0.5 ms, the supply
voltage is then connected for 0.5 ms, followed by the second test pulse where t
off
= 0.5 ms, and then the
supply voltage is connected for at least 8.5 ms!
8
Output Signal Switching Device
Permissible test pulses for an OSSD
0
1
-1 0 1 2 3 4 5 6 7 8 9 10 11
Time in ms