Omron CP1L-EL20DR-D, Operation Manual

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85
Wiring CP1L-EL/EM CPU Units Section 3-4
Precautions when
Connecting a Two-wire DC
Sensor When using a two-wire sensor with a 24 VDC input device, check that the fol-
lowing conditions have been met. Failure to meet these conditions may result
in operating errors.
1,2,3... 1. Relation between voltage when the PLC is ON and the sensor residual
voltage:
V
ON
≤
V
CC
−
V
R
2. Relation between current when the PLC is ON and sensor control output
(load current):
I
OUT
(min)
≤
I
ON
≤
I
OUT
(max)
I
ON
= (V
CC
−
V
R
−
1.5 [PLC internal residual voltage]*)/R
IN
When I
ON
is smaller than I
OUT
(min), connect a bleeder resistor R. The
bleeder resistor constant can be calculated as follows:
R
≤
(V
CC
−
V
R
)/(I
OUT
(min)
−
I
ON
)
Power W
≥
(V
CC
−
V
R
)
2
/R
×
4 [allowable margin]
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 voltage
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.
R V
R
V
CC
R
IN
Two-wire Sensor
DC Input Unit