Panasonic FPS Series User Manual page 101

Installation and Wiring
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
FPΣ
LED
1
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
FPΣ
Internal circuit
1
The formula is based on an input impedance of 5.6kΩ. 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.
5.6R
I x
5.6R + R ≤ 2.4
Therefore:
13.44R
(kΩ)
R ≤
5.6I - 2.4
The wattage W of the resistor is:
(V) 2
W =
R
V = Power supply voltage
84
4
3
COM
+
24V
2
3
4
3
2
R
COM
+
2
3
Contact
≥21.6V
Input terminal
Bleeder resistor
Input terminal
FPΣ User's Manual