Omron CJ2 CPU UNIT - AC Input Units; Precautions When Connecting a Two-Wire DC Sensor

5 Installation
5-36
CJ2 CPU Unit Hardware User’s Manual
z AC Input Units
Precautions for Safe Use
When using a reed switch as the input contact for an AC Input Unit, use a switch with an allow-
able current of 1 A or greater. If reed switches with smaller allowable currents are used, the con-
tacts may fuse due to surge currents.
z Precautions when Connecting a Two-wire DC Sensor
When using a two-wire sensor with a 12-VDC or 24-VDC input device, check that the following con-
ditions have been met. Failure to meet these conditions may result in operating errors.
• Relation between voltage when the PLC is ON and the sensor residual voltage:
V
ON ≤ VCC − VR
• Relation between voltage when the PLC is ON and sensor control output (load current):
I
OUT (min) ≤ ION ≤ IOUT (max.)
I
ON = (VCC − VR − 1.5 [PLC internal residual voltage])/RIN
When ION is smaller than IOUT (min), connect a bleeder resistor R. The bleeder resistor constant
can be calculated as follows:
R ≤ (V
CC − VR)/(IOUT (min.) − ION)
Power W ≥ (V
CC − VR)
2
/R × 4 [allowable margin]
V
CC: Power voltage
V
R: Sensor output residual current
I
ON: PLC ON current
I
OUT: Sensor control current (load current)
R
IN: PLC input impedance
COM
IN
AC Input Unit
Contact output
AC Switching
Proximity
switch
main
circuit
COM
IN
AC Input Unit