115
Wiring CP1L CPU Units Section 3-4
3. Relation between current when the PLC is OFF and sensor leakage cur-
rent:
I
OFF
≥ I
leak
Connect a bleeder resistor if I
leak
is greater than I
OFF
. Use the following
equation to calculate the bleeder resistance constant.
R ≤ R
IN
× V
OFF
/(I
leak
× R
IN
− V
OFF
)
Power W ≥ (V
CC
− V
R
)
2
/R × 4 (allowable margin)
Vcc: Power voltage Vr: Sensor output residual current
Von: PLC ON voltage Iout: Sensor control output (load current)
Voff: PLC OFF voltage
Ion: PLC ON current Ileak: Sensor leakage current
Ioff: PLC OFF current R: Bleeder resistance
Rin: PLC input impedance
4. Precautions on Sensor Inrush Current
An incorrect input may occur due to sensor inrush current if a sensor is
turned ON after the PLC has started up to the point where inputs are pos-
sible. Determine the time required for sensor operation to stabilize after the
sensor is turned ON and take appropriate measures, such as inserting into
the program a timer delay after turning ON the sensor.
Program Example
In this example, the sensor's power supply voltage is provided to input bit CIO
0.00 and a 100-ms timer delay (the time required for an OMRON Proximity
Sensor to stabilize) is created in the program. After the Completion Flag for
the timer turns ON, the sensor input on input bit CIO 0.01 will cause output bit
CIO 100.00 to turn ON.
Output Wiring Precautions
Output Short-circuit
Protection
If a load connected to the output terminals is short-circuited, output compo-
nents and the 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.
Connecting to a TTL
Circuit
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.
Inrush Current
Considerations
When connecting a transistor or triac output to a load having a high inrush
current (such as an incandescent lamp), steps must be taken to avoid dam-
age to the transistor or triac. Use either of the following methods to reduce the
inrush current.
RVR
VCC
RIN
Two-wire Sensor
DC Input Unit
TIM
100
#0001
0.00
100.00
0.01T100
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