NORD Drivesystems BU0230 - Manual (Page 58)

Functional safety with NORD SK 200E frequency inverters
58 BU 0230 GB-2712
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 safety switching device with OSSD outputs
24 V -20 % +25 % (19.2 V…30 V) for the "safe pulse block"
24 V -10 % +25 % (21.6 V…30 V) for "switch-off of the 24V supply"
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”
Size 1 to 3
“Safe pulse block”
Size 4
"Switch-off of the 24V supply"
(Digital output DO1 without
load)
Continuous current
(mean value) ≤ 125 mA ≤ 40 mA ≤ 500 mA, see Section 3.6
Switch-on current ≤ 500 mA
(for t
≤ 2 ms)
≤ 250 mA
(for t
≤ 2 ms)
≤ 1 A
(for t
≤ 10 ms, delayed),
see Section 3.6
Supporting capacitance
(downstream of inverse
polarity protection) 20 µF 10 µF 200 µF
Peak current after an OSSD
test pulse (periodic) ≤ 500 mA
(for t
≤ 300 µs)
≤ 250 mA
(for t
≤ 250 µs)
≤ 4.3 A (with 21.6 V),
see Section 3.6
Please note:
Due to the supporting capacitors of the safe shut-down method, there is an increased current consumption on
switch-on and after a test pulse from an OSSD. The "safe pulse block" is equipped with an active current
limiter in order to reduce the load on safety outputs to a minimum.
On the other hand, the 24 V supply only has controlled starting characteristics and therefore a limited start-up
current. However, after an OSSD test pulse, a relatively large peak current occurs, which is only limited by the
input impedance and the source impedance. This results in the limited use of "switch-off of the 24 V supply"
with an OSSD´. => see Section 3.6