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Wiring
Output Wiring Precautions
Output Short-circuit
Protection
Transistor Output
Residual Voltage
Output Surge Current
R ≤ (R
× V
)/(I
IN
OFF
leak
Power W ≥ (V
– V
CC
R
Two-wire sensor
V
:
Power voltage
CC
V
:
PLC ON voltage
ON
V
:
PLC OFF voltage
OFF
I
:
PLC ON current
ON
I
:
PLC OFF current
OFF
R
:
PLC input impedance
IN
4. Precautions on Sensor Surge Current
An incorrect input may occur if a sensor is turned ON after the PLC has
started up to the point where inputs are possible. Determine the time re-
quired for sensor operation to stabilize after the sensor is turned ON and
take appropriate measures, such as inserting into the program a timer de-
lay after turning ON the sensor.
Example
In this example, the sensor's power supply voltage is used as the input to
CIO 000000 and a 100-ms timer delay (the time required for an OMRON
Proximity Sensor to stabilize) is created in the program. After the Comple-
tion Flag for the timer turns ON, the sensor input on CIO 000001 will cause
output bit CIO 000100 to turn ON.
If a load connected to the output terminals is short-circuited, output compo-
nents and the and printed circuit boards may be damaged. To guard against
this, incorporate a fuse in the external circuit. Use a fuse with a capacity of
about twice the rated output.
A TTL circuit cannot be connected directly to a transistor output because of
the transistor's residual voltage. It is necessary to connect a pull-up resistor
and a CMOS IC between the two.
When connecting a transistor or triac output to an output device having a high
surge current (such as an incandescent lamp), steps must be taken to avoid
damage to the transistor or triac. Use either of the following methods to
reduce the surge current.
× R
– V
)
IN
OFF
2
/R × 4 [allowable margin]
)
DC Input Unit
R
V
R
IN
R
V
CC
V
:
Sensor output residual current
R
I
:
Sensor control current (load current)
OUT
I
:
Sensor leakage current
leak
R:
Bleeder resistance
000000
TIM
#0001
TIM0000
000001
000100
Section 5-3
0000
255
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