Panasonic FP0R User Manual page 84

Precaution when using an LED-equipped Reed switch
When an LED is connected in series to an input contact such as an LED-equipped Reed
switch, make sure that the ON voltage applied to the PLC input terminal is greater than 21.6V
DC. In particular, take care when connecting a number of switches in series.
1
2
A
LED-equipped Reed switch
B
FP0R
1 LED
Precaution when using a two-wire type sensor
If the input of the PLC does not turn off because of leakage current from the two-wire type
sensor (photoelectric sensor or proximity sensor), the use of a bleeder resistor is
recommended, as shown below.
1
A
Two-wire type sensor
B
FP0R
1 Internal circuit
The formula is based on an input impedance of 9.1k. The input impedance varies depending
on the input terminal number.
The off voltage of the input is 2.4V. Therefore, select a bleeder resistor value R so that the
voltage between the COM terminal and the input terminal will be less than 2.4V.
9.1R
I x
9.1R + R ≤ 2.4
Therefore:
21.84R
(kΩ)
R ≤
9.1I - 2.4
The wattage W of the resistor is:
2
(V)
W =
R
V = Power supply voltage
4
3
COM
+
24V
2 Contact
21.6V
3
4 Input terminal
3
2
R
COM
+
2 Bleeder resistor
3
Input terminal
Installation and Wiring
83