July 2013 3.16 Digital PLC inputs/outputs 271
Calculation example—Resistive load requires shunt resistor:
Interlocking switch directly at PLC output, data sheet specifications:
Rated control voltage U
c
:28 V DC
Rated operating current I
c
: 2.2 mA
Switching threshold "0" state U
Low
: 3.6 V
Switching threshold "1" state U
High
: 17.4 V
In "0" state of the output, the voltage drop has to be less than 3.6 V .
Calculation of the input resistance R
c
of the interlocking switch:
Calculation of the voltage drop U
Low
in "0" state at the output:
The shunt resistor at the output should be such that the voltage drop at the
output in "0" state goes clearly below the lower switching threshold, e.g. R
p
=
5 kW:
With a voltage drop of 1.79 V in "0" state, the value falls below the lower
switching threshold of the interlocking switch. If the shunt resistor of 5 kW is
used, operation directly at the PLC output is possible in this case.
Terminal X9 on PLB
62xx (FS)
R
c
Uc
Ic
---------
28 V
---------------
== =
2.2 mA
12.73 kΩ
U
Low
R
c
I
Off
⋅ 500μA⋅ == =
12.73 kΩ
6.36 V
1
R
Total
--------------------
1
R
c
--------
1
R
p
---------+=
1
R
Total
--------------------
1
------------------------
1
5 kΩ
----------------+=
12.73 kΩ
R
Total
=
U
Low
500 μA⋅ ==
3.59 kΩ
3.59 kΩ
1.79 V
Properties Socket connectors on the PLA-H
08-04-04
Connection: Socket connector with tension clamp
connection, type:
Weidmüller B2L 3.5/30 SN SW
2-row, 30-pin
Connectable conductors: Usable conductor cross sections
without wire-end sleeve:
0.08 mm
2
to 1.0 mm
2
Usable conductor cross sections with
wire-end sleeve:
0.14 mm
2
0.34 mm
2
0.5 mm
2
(only with Weidmüller PZ 6/
5 crimping pliers)
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