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CHAPTER 8 TROUBLESHOOTING
8
8.1 Troubleshooting for Input Circuit
Calculation
example
The resistance value of a connected resistor is calculated by the following formula.
A switch with LED indicator that generates a current leakage of 2.82mA when 24VDC is supplied is connected to the LX40C6.
Check the following with the specifications of the module.
• Off current: 2.0mA
• Input resistance. 3.8k
To hold the current leakage through the LX40C6 equal to or lower than the off current (2.0mA), connect a resistor so that 0.82mA or more
current flows to the resistor. Calculate the resistance value (R) of the connected resistor as follows.
The resistance value R < 9.27k must be met.
<Checking a connected resistor by calculating the power capacity.>
When the resistor (R) is 8.2k, for example, the power capacity (W) of the resistor (R) is calculated as follows.
Since the resistor requires the power capacity of 3 to 5 times as large as the actual power consumption, the resistor connected to the
terminal should be 8.2k and 1/3 to 1/2 W.
Off voltage when the resistance (R) is connected is calculated as follows.
This meets the condition: less than or equal to the off voltage of the LX40C6, 8V.
Case
Ex.
I(Leakage current)=IZ(Off current of the LX40C6)+IR(Current flowing to connected resistor)
I
R=I-IZ=2.82-2.0=0.82[mA]
IR: IZ=Z(Input impedance): R
R
I
Z
IR
Z(Input impedance)
<
=
2.0
0.82
3.8=9.27[k ]
W= =
(Input voltage)
2
28.8
2
8200
=0.101[W]
R
2.82[mA]=7.32[V]
1
3.8[k ]
1
8.2[k ]
1
+