Mitsubishi A1SJH User Manual

11. TROUBLESHOOTING
11 - 17
MELSEC-
A
Table 11.2 Input circuit problems and corrective action
Condition Cause Corrective action
Example
5
Input signal
does not turn
OFF
•
Sneak path due to the use of two power supplies.
E1
E2
E1 > E2
Input module
•
Use only one power supply.
•
Connect a sneak path prevention diode.
(Figure below)
E1
E2
Input module
<Example 4s Calculation Example>
Leakage current 3mA
24VDC
Input
module
A1SX40
4.7k
If a switch with an LED display is
connected to A1SX40 and a leak
current of 3 mA is observed
•
Voltage V
TB
across the terminal and common base is:
V
TB
= 3 [mA]
×
3.3 [k ] = 9.9 [V] (Ignore the voltage drop caused by the LED.)
Because the condition for the OFF voltage (
4 [V]) is not satisfied, the input does not turn
off. To correct this, connect a resistor as shown below.
A1SX40
Current I
4.7k
24VDC
Input
impedance
3.3k
R
•
Calculation of resistance of connected resistor R
The voltage of A1SX40 across the terminals must be reduced to within 4 [V]. The current
for reducing the voltage across the terminals to within 4 [V] is:
(24
4 [V]
÷
4.7 [k ] = 4.26 mA)
Therefore resistor R for flowing current I of 4.26 [mA] must be connected.
•
Resistance of the connected resistor R is obtained in the following equations.
4 [V]
÷
R > 4.26
1.21 [mA] 4 [V]
÷
Input impedance 3.3 [k ]
4 [V]
÷
3.05 [mA] > R
1.31 [k
] > R
Suppose that the resistance R is 1.2 [k
].
The power capacity W of the resistor when the switch turned on is:
W = (Applied voltage)
2
/R
W = (26.4 [V])
2
/ 1.2 [k ] = 0.58 [W]
•
Because the resistance is selected so that the power capacity is three to five times the
actual power consumption, 2 to 3 [W] should be selected.
From the above, the resistor to be connected across the terminal in question and COM is
1.2 [k
] 2 to 3 [W].

Mitsubishi A1SJH Specifications

General

Brand	Mitsubishi
Model	A1SJH
Category	Controller
Language	English