3
■
Power System Wiring
(See Diagram 5)
1
The power supply for the PLC and I/O devices should be separate, and a
noise filter should be installed to the PLC power supply.
2
Noise between the PLC and the ground can be greatly reduced by adding an isolating
transformer. In such an event, do not ground the secondary coil of the transformer.
3
Keep the wiring between the transformer and the PLC as short as possible, twist the
wires well, and keep the wiring separate from high-voltage and power lines.
■
Wiring External I/O Signal Lines
1
To absorb reverse electromotive force when an inductive load is connected
to an output signal, connect a surge protector near the inductive load in an
AC circuit, and connect a diode near the inductive load in a DC circuit.
(See
Diagram 6 and 7)
2
The output signal line should not be near or parallel with high current or
power lines.When nearby, they should be separated by a duct, and an
alternative wiring pipe should be established. In this event, the duct and
wiring pipe must be grounded.
(See Figure 8)
3
Connect the shield to the ground terminal at the PLC, and leave it
unconnected at the input device.
4
Wire the lines so that common impedance does not occur. Such
wiring will increase the number of wires, so use common return
circuits. Use thick wires with sufficient allowance for the return
circuits, and bundle them with lines of the same signal level.
5
For long I/O lines, wire the input and output signal lines separately.
6
Use twisted-pair wires for pilot lamps (and particularly lamps with
filaments).
7
Using a CR surge absorber or diode etc is effective in reducing
noice sources from input devices or output load devices.
■
External Wiring
The wiring method can have a large impact on creating a system that
is strong against noise and a system that can operate with a high
degree of reliability. Wiring, and noise countermeasures in particular,
are based on experience, and it is necessary to closely manage wiring
based on experience and information in the manuals.
●
Preventing Faulty Wiring
1
By attaching marker bands to cables showing their direction, faulty
wiring can be prevented, and wiring checks and maintenance can
be facilitated.
2
Use different colors during wiring.
3
Place wires that transmit the same kind of signal into the same
ducts, and separate them into groups.
●
General Precautions
1
Do not join wires between terminals.
2
Support and fix the power line so that its end does not pull at the
ends of multi-conductor cable.
3
Use flexible wires for the movable places such as doors etc. Install
them one part on the panel body and the other on the door so that
they may not be damaged by the movement of a door.
4
Connect crimp terminals to the end of the wire and use a tor
q
ue
driver for connection to the terminal, and screw in at an appropriate
pressure. For terminal connection to an AC power unit, a round-
type crimp terminal should be used instead of a U shaped terminal,
for safety purposes.
5
The dust protection cover attached to the PLC unit should be kept
in place until the wiring is completed to prevent dust from the wiring
from entering. Further, as the internal temperature will increase
greatly when the unit is in operation, the dust protection cover
should be removed once wiring is completed to prevent loss in
functionality.
6
All wiring for the power circuit should be twisted.
7
The primary or secondary noise filter should not be bundled, as this
reduces its effectiveness.
Di
a
gr
a
m 5. Power
Su
pply
S
y
s
tem Di
a
gr
a
m
Power Circ
u
it
Noi
s
e
Filter
Power
su
pply for gener
a
l oper
a
tion
s
circ
u
it
s
PLC Inp
u
t Circ
u
it
Power
Su
pply
PLC O
u
tp
u
t Circ
u
it
Power
Su
pply
PLC Power
Su
pply
Electric
S
ocket
(For peripher
a
l device
s
)
Di
a
gr
a
m 6. Inp
u
t
S
ign
a
l Noi
s
e Co
u
nterme
asu
re
s
PLC
DC Inp
u
t
Unit
Ind
u
ctive Lo
a
d
Diode
s
Connect
a
diode in
a
DC circ
u
it
Di
a
gr
a
m 7. O
u
tp
u
t
S
ign
a
l Noi
s
e Co
u
nterme
asu
re
s
PLC
O
u
tp
u
t
Unit
PLC
O
u
tp
u
t
Unit
Affix diode
s
for DC circ
u
it
s
Affix
su
rge protector for AC circ
u
it
s
Ind
u
ctive
Lo
a
d
Ind
u
ctive
Lo
a
d
Fig
u
re
8
. I/O C
ab
le Wiring
Floor D
u
ct Type
Piping Type
Sus
pended D
u
ct
I/O C
ab
le
I/O C
ab
le
Power Line
Power Line
I/O C
ab
le
Power Line
