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Chapter 10 PLC Installation, Mounting, Wiring
10-5
(5) Wiring to the input terminals
DC input AC input
3] 4] 6] C1
0 V C0 5] 7]
24 V DC
0]
24+
2]
1]
Current output type
Proximity switch
Example of 14-point type
③④⑥ C1
C0 ⑤⑦
0
②
①
Example of 14-point type
Figure 10.5 Input wiring
(a) DC input
1] When all input terminals (X0, X1, ...) and the common terminal (C) are loaded with 24 VDC, the input
becomes ON status, and approximately 7.5 mA of current flows to the external input contacts.
2] For sensors such as a proximity switch or photoelectric switch, current output type (transistor open
collector) can be connected directly. For voltage-output-type sensors, connect them to the input terminal
after first going through the transistor.
3] Take measures to prevent faulty contact in a strong electric contact.
C
3 W
560
Ω
24 V DC
1]
Strong electric
contact
Approx. 50 mA
DC input module
The current that flows to a contact when external contacts
are closed is approximately 7.5 mA. If a strong electric
contact must be used, add resistance as shown in the diagram
at left and supply sufficient current to the contact to prevent
a faulty contact.
4] Limit the wiring length within 30 m.
5] Multiple number of common terminals located at each input section are not connected internally. Make
the connections externally as needed.
6] There are no RUN and STOP switches for the 10-point type. Connect with the RUN input terminal
according to the above connection procedure so that RUN and STOP can be performed. Operation cannot
be performed unless this connection is done.
(b) AC input
In case of AC input module, input voltage may exist if input wiring is long although no device drives. This
phenomenon is caused from leakage current due to floating capacitance between lines.
External
device
AC input
module
The countermeasures are [1] or [2] as follows. This voltage due to electrostatic coupling must be half of max.
OFF voltage or less.
[1] To install dummy resistor in parallel so that impedance of input module is lower.
[2] To replace power supply at drive (external device) side.
External
device
AC input
module
Dummy resistor