Mitsubishi MELESEC-ST User Manual page 139

12 TROUBLESHOOTING
Condition
Erroneous output due to the stray capacitance (C) between
collector and emitter of photocoupler.
Photocoupler
If the external power supply is turned on precipitously, Ic
current flows due to the stray capacitance (C) between
collector and emitter of photocoupler.
When the current Ic flows, the potential difference is
When the
generated between the source and gate of transistor Tr1,
external
which turns ON the output of Y0 for 100 s.
power
supply
Example
turns on
1
the load
turns on
for a
moment
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(2) Output circuit troubleshooting
The following explains possible problems in the output circuit and their corrective
actions.
Output circuit troubleshooting
Cause
There is no erroneous output at normal load.
An erroneous output may occur at high sensitivity load
(such as solid state relay).
Output module
Tr1
C
Ic
Constant
voltage
circuit
SW: External power
supply (24V)
at On
Output Y0
Base module
Y0
24G
Shield
SW -
+
+24V
24V
Connection from power
distribution module
24G
10ms or less
Approx.100 s
MELSEC-ST
Corrective action
When external power supply turns
ON/OFF, check that the external power
supply rising edge must be 10ms or
more, and switch the SW1 to the
primary side of external power supply.
Primary side
External power
supply
SW1
L
When switching to the secondary side
of the external power supply is
required, the external power supply
rising edge connected a condenser
must be slow, and measured 10ms or
more.
Base module
Y0
24G
Shield
+24V
Connection from power
distribution module
24G
R1: Several tens of ohms
Power capacity
(external power current*
resistance value
C1: Several hundreds of microfarads
50V
*1 Refer to consumption current of the
external power supply for modules
used in this manual.
*2 Select the power capacity of
resistance to be 3 to 5 times lager
than the actual power consumption.
(Example)
R1 = 40 , C1=300 F
Use the below expression to
calculated a time constant
C1 R1 = 300 10
-3
= 12 10
= 12ms
Secondary side
PLC
L
SW -
+
R1
24V
C1
1 2
)
2
(3 to 5)*
-6
40
s
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