110
11 TROUBLESHOOTING
11.4 Examples of Troubles with the I/O Module
Troubleshooting for output circuit
A load momentarily turns on when the external power supply is powered on
■Cause
An incorrect output occurs due to the stray capacitance (C) between collector and emitter of a photocoupler.
There is no problem with the normal load. When a high sensitivity load (such as solid state relay) is used, however, this
incorrect output may occur.
When the external power supply is powered on rapidly, the current (Ic) flows due to the stray capacitance (C) between
collector and emitter of a photocoupler.
The current (Ic) flows to the gate of the transistor (Tr1) of the next stage and the output Y0 turns on for approximately 100s.
Y0
C
SW
Ic
Tr1
COM-
CTL+
24VDC
Output module
Photocoupler
Constant-
voltage circuit
Load
SW: External power supply
(24VDC) at ON
10ms or less
Output Y0
Approx.100µs
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