Mitsubishi A1SJH(S8) User Manual page 167

11. TROUBLESHOOTING
Table 11.2 Faults with the input circuit and the corrective actions (Continued)
Situation
Example Input signal does not
5 turn OFF.
<Calculation Example for Example 4>
Consider a switch with LED indicator connected to the A1SX40, giving a leakage current
of 3mA when a 24VDC power is tuTorned on.
(1)
(2)
(3)
(4)
Cause
• Sneak path due to the use of two power
supplies.
E1
E2
E1 E2
Leakage current 3mA
The 1.7mA OFF current of the A1SX40 is not satisfied. Hence,connect a resistor as
shown below.
I =2mA
R
24VDC
Calculate the resistor value R as indicated below.
To satisfy the 1.7mA OFF current of the A1SX40, the resistor R to be connected may
be the one where 0.63mA or more will fiow.
I :I =Z(Input impedance):R
R Z
I
Z
R Z(Input impedance)
I
R
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 resistor is seiected so that will be 3 to 5 times
greater than the actual power consumption.
Also, OFF voltage when resistor R is conned will be as follows.
1
1 1
+
1.5[k ] 3.3[k ]
• This satisfies 6V or less OFF voltage of A1SX40.
• Use only one power supply.
• Connect a diode to prevent the sneak path
DC input
Input
module
A1SX40
Input module
24VDC
A1SX40
3mA
I =1mA
Z
Input impedance
R
3.3k
1.0
3.3 1.65[k ]
2.0
3[mA] = 3.09[V]
11 - 18
Countermeasure
(figure below).
E1
E2
DC input
Input
module