FPΣ User's Manual 
 
6.4 Input and Output Wiring 
85 
In the actual selection, use a value that is 3 to 5 times the value of W. 
Precaution when using an LED-equipped limit switch 
If the input of the PLC does not turn off because of the leakage current from the LED-
equipped limit switch, the use of a bleeder resistor is recommended, as shown below. 
COM
1
2
3
4
R
r
 
A 
LED-equipped limit switch 
3
 
Bleeder resistor 
B 
FPΣ 
4
 
Input terminal 
1
 
Internal circuit 
r 
Internal resistor of limit switch (kΩ) 
2
 
Power supply for input 
R 
Bleeder resistor (kΩ) 
The OFF voltage of the input is 2.4V. Therefore, when the power supply is 24V, select the 
bleeder resistor R so that the current will be greater than the result of this formula: 
I =  
24 - 2.4
r
 
The resistance R of the bleeder resistor is: 
(kΩ)  
13.44R
5.6I - 2.4
R ≤ 
 
The wattage W of the resistor is: 
(V)
2
R
W = 
 
V = Power supply voltage 
In the actual selection, use a value that is 3 to 5 times the value of W. 
 
6.4.2 Output Wiring 
Do not connect a load that exceeds the maximum switching ability of the output terminal. 
To prevent the output circuits from being damaged by a short-circuit or other electrical 
problems on the output side, transistors with short-circuit protection are provided (except for 
Y0, Y1, Y3, and Y4 of the FPΣ CPU and FP0 expansion units).