Omron SYSMAC CS Series Operation Manual page 369

Wiring
Precautions when
Connecting a Two-wire DC
Sensor
1,2,3...
Note When using a reed switch as the input contact for an AC Input Unit, use a
switch with an allowable current of 1 A or greater. If Reed switches with
smaller allowable currents are used, the contacts may fuse due to surge cur-
rents.
When using a two-wire sensor with a 12-V DC or 24-V DC input device, check
that the following conditions have been met. Failure to meet these conditions
may result in operating errors.
1. Relation between voltage when the PLC is ON and the sensor residual
voltage:
≤ V
V – V
ON CC
2. Relation between voltage when the PLC is ON and sensor control output
(load current):
(min) ≤ I
I
OUT
I = (V – V
ON CC
When I is smaller than I
ON
bleeder resistor constant can be calculated as follows:
R ≤ (V
– V
CC
Power W ≥ (V
Note The residual voltage in the PLC is 4.0 V for the following Units:
C200H-ID211/ID212/IM211/IM212/INT01
The residual voltage is 1.5 V for all other Units.
3. Relation between current when the PLC is OFF and sensor leakage cur-
rent:
≥ I
I
OFF leak
If I is larger than I
leak
constant can be calculated as follows:
R ≤ R × V
IN OFF
Power W ≥ (V
Two-wire sensor
V : Power voltage
CC
V : PLC ON voltage
ON
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.
R
≤ I
(max.)
ON OUT
– 1.5 [PLC internal residual voltage])/R
R
(min), connect a bleeder resistor R. The
OUT
)/(I (min.) – I )
R OUT ON
2
/R × 4 [allowable margin]
– V )
CC R
, connect a breeder resistor. The breeder resistor
OFF
× R
/(I – V )
leak IN OFF
2
/R × 4 [allowable margin]
– V )
CC R
R
V R
R
V
CC
V : Sensor output residual current
R
I : Sensor control current (load current)
OUT
I : Sensor leakage current
leak
R: Bleeder resistance
Section 5-3
IN
DC Input Unit
IN
331