User`s manual

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MELSEC-Q
11 I/O MODULE TROUBLESHOOTING
11.2 Output Circuit Troubleshooting
This section describes possible problems with output circuits and their corrective
actions.
Table 11.2 Output Circuit Problems and Corrective Actions
Condition Cause Corrective Action
Example 1
When the
output is
OFF,
excessive
voltage is
applied to
the load.
• Load is half-wave rectified inside (in some
cases, this is true of a solenoid).
QY22
[1]
[2]
D1
Output module
Load
• When the polarity of the power supply is as
shown in [1], C is charged. When the polarity is
as shown in [2], the voltage charged in C plus
the line voltage are applied across D1. Max.
voltage is approx. 2.2E.
(If a resistor is used in this way, it does not
pose a problem to the output element. But it
may cause the diode, which is built into the
load, to deteriorate, resulting in a fire, etc.)
• Connect a resistor several tens to hundreds of
k
across the load.
Load
Resistor
Example 2
The load is
not turned
OFF (triac
output).
• Leakage current due to built-in noise
suppression.
QY22
Output module
Leakage current
Load
• Connect C and R across the load.
(When the wiring distance from the output card
to the load is long, there may be a leakage
current due to the line capacity.)
Load
Resistor