Mitsubishi Electric A173UHCPU User Manual page 130

5. INSPECTION AND MAINTENANCE
Symptom
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)
(b) Troubleshooting output circuits
Table 5.8 describes problems and corrective actions for output circuits.
Table 5.8 Troubleshooting Output Circuits
Cause
• If load is internally half-wave rectified
(some solenoids are like this)
A1SY22
Output module
Load
• With polarity (1), C is charged. With polarity (2),
the C charge voltage plus the power supply
voltage is applied across D1. Max. voltage is
approx. 2.2V.
• Leak current due to internal surge suppresor.
A1SY22
Output module
Leak current
A1SY22
Output module
• Connect a resistor between several tens k
and several hundreds k
(This method causes no problems with output
[1]
D1
terminals but can lead to deterioration or burn-
out of load internal diodes.)
[2]
• Connect a resistor across the load.
(If long wiring exists between the output card
and the load, leak currents also arise due to
Load
wiring capacity.)
• Drive a relay and use the relay contacts to drive
the CR timer.
(See note attached to Example 1, as some
timers are half-wave rectified internally.)
CR timer
Leak current
5 − 19
Corrective Action
across the load.
Resistor
Load
Resistor
Load
Resistor
Calculate resistor
CR timer
constant from load.