Troubleshooting Examples - Mitsubishi MELESEC-ST User Manual

12 TROUBLESHOOTING

12.3.3 Troubleshooting examples

Condition
Drive by LED indicator switch.
Input signal
Example
does not
1
turn off.
Improper
Example Noise is input depending on the response time
input due
2 setting.
to noise
12 - 12
This section provides possible problems in the input circuit and output circuit and their
corrective actions.
(1) Input circuit troubleshooting
The following explains possible problems in the input circuit and their corrective
actions.
Input circuit troubleshooting
Cause
Input module
DC input (negative common)
Leakage
current
Input circuit
<Calculation for Example 1>
Leakage current
3mA
2.4 k
• The voltage V across terminal and common is calculated as follows.
TB
V =3[mA] 5.6[k ]=16.8[V] (Voltage drop across the LED is ignored.)
TB
As the OFF voltage 11[V] or less is not satisfied, the input signal does not turn
off. Therefore, connect a resistor as shown below.
2.4k
Connect a proper resistor as shown below to
make the voltage across input module terminal
and common lower than the OFF voltage.
+24V Wiring
from power
24G
distribution
module
A calculation example for selecting the resistor
to be connected is given in <Calculation for
Example 1>.
Change the response time setting.
Example: 0.5ms → 1.5ms
(When excessive noise is periodic, shorter
response time setting may have a greater
effect.) If the above action does not have any
effect, take the basic noise reduction measures
to prevent noise entry, e.g. avoid installing
power and I/O cables together, add surge
absorbers to noise source such as relays and
contactors used in the same power supply.
ST1X -DE1
Input module
+24V Wiring from power
distribution
24G
module
Input circuit
When LED indicator switch is
connected, to ST1X2-DE1,
ST1X4-DE1 or ST1X16-DE1
giving 3mA leakage current
ST1X -DE1
Input module
+24V
24G
Current I
X0
Resistor
24G
MELSEC-ST
Corrective action
Input module
DC input (negative common)
+24V
24G
Resistor
Input circuit
Wiring from
power distribution
module
Input impedance
5.6k
Wiring
from power
distribution
module
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