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6 INSPECTION AND MAINTENANCE
Input Circuit Troubleshooting and Corrective Action (Continued)
Condition Cause Corrective action
Example 5
Input signal
does not
turn OFF.
• Sneak path due to the use of two power
supplies.
Input module
E
1
E
2
>
E
2
E
1
• Use only one power supply.
• Connect a sneak path prevention diode.
(Figure below)
Input module
E
1
E
2
Example 6
False input
due to
noise
Depending on short response time setting, noise
is imported as input.
Change response time setting.
Example : 10ms
20ms
<Calculation example of Example 4>
For the case with a switch with LED indicator connected to Q172LX,
causing 4 mA leakage current.
Motion CPU
module
Leakage
current 4mA
24VDC
3.6K
Q172LX
(a) The 0.18 mA OFF current of the Q172LX is not satisfied. Connect a resistor as
shown below.
Input impedance
24VDC
4mA
I
R=
3.82mA
Q172LX
Iz=0.18mA
5.6K
3.6K
(b) Calculate the connecting resistor value R as indicated below.
To satisfy the 0.18 mA OFF current of the Q172LX, the resistor R to be connected
may be the one where 3.82 mA or more will flow.
I
R:
I
Z=
Z(Input impedance): R
R Z(Input impedance)= 5.6 10 =264[ ]
3.82
0.18
I
R
I
Z
3
R<264
.
Assuming that resistor R is 220
, the power capacity W of resistor R is:
W = (Input voltage)
2
÷ R = 26.4
2
÷ 220 = 3.168 [W]
(c) The power capacity of the resistor selected is 3 to 5 times greater than the actual
current consumption. 220 [
], 10 to 15 [W] resistor may therefore be connected to
the terminal in question.
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