Mitsubishi A2USCPU(S1), User Manual

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11 - 24
TROUBLESHOOTING 11.
<Sample calculation for Example 4>
When a switch with LED indicator, giving leaking current of 3mA at maximum when
24VDC power is supplied to the A1SX40
(1) 1mA or less OFF current of the A1SX40 is not satisfied. Hence, connect a resistor as
shown below.
(2) Calculate the resistance value R as shown below.
To satisfy 1mA or less OFF current of the A1SX40, connect a resistor which flows
2mA or more.
I
R
:I
Z
=Z(Input impedance):R
Supposing that the resistance R is 1.5k , the power capacity W of resistor R is:
W = (Input voltage)
2
/R = 26.4
2
/1500 = 0.465 [W]
(3) Connect a resistor of 1.5(k ) and 2 to 3(W) to a terminal which may cause an error,
since the power capacity of a resistor is selected so that it will be 3 to 5 times greater
than the actual power consumption.
(4) Also, OFF voltage when resistor R is connected will be as follows.
• This satisfies 4V or less OFF voltage of A1SX40.
Table 11.2 Faults with the input circuit and the corrective actions (Continued)
Situation Cause Countermeasure
Example
5
Input signal does not
turn OFF.
• Sneak path due to the use of two power
supplies.
• Use only one power supply.
• Connect a diode to prevent the sneak path
(figure below).
DC input
Input
module
E1 E2
E1 E2
DC input
Input
module
E1
E2
A1SX40
24VDC
Leakage current 3mA
Input module
R
3mA
I
R
=2mA
24VDC
I
Z
=1mA
Input impedance
3.3k
A1SX40
R Z(Input impedance) 3.3 1.65[k ]
I
R
I
Z
2.0
1.0
3[mA] = 3.09[V]
1
1.5[k ]
1
3.3[k ]
1
+