Mitsubishi Electric Q173CPU User Manual page 194

6 INSPECTION AND MAINTENANCE
Condition
Overvoltage
applied to
load when
output turns
OFF
Load does
not turn OFF
(Triac output).
Time period
fluctuates
when load is
a CR timer
(Triac output)
(2) Output circuit troubleshooting and corrective action
This section describes troubleshooting with output circuits and their corrective
actions.
Output Circuit Troubleshooting and Corrective Action
Cause
• If load is internally half-wave rectified
(some solenoids are like this).
Output module
Load
• With polarity of power supply 1), C is charged.
With polarity 2),the C charge voltage plus the
power supply voltage is applied across D1.
Max. voltage is approx. 2.2E.
• Leakage current due to built-in surge
suppressor.
Output module
Leakage current
Output module
Leakage current
• Connect a resistor between several tens k
1)
D1
2)
• Connect a resistor across the load.
Load
• Drive a relay and use the contacts to drive
CR timer
6 - 27
Corrective action
and several hundreds k across the load.
This method causes no problems with
output terminals but lead to deterioration
or burnout of load internal diodes.
Resistor
Load
If long wiring exists between the output
card and the load, leakage currents also
arise due to wiring capacity.
Resistor
Load
the CR timer.
Be careful of example 1, as some
timers are half-wave rectified
internally.
Resistor
CR
Calculate resistor
timer
constant from load.