User`s manual

Troubleshooting I/O circuit troubleshooting
11 – 100
11.4.2 Output circuit troubleshooting
Exam-
ple
Condition Cause Corrective action
1 When the external
power supply turns
on, the load is turned
on for a moment.
Erroneous output due to the stray capacitance (C)
between collector and emitter of photocoupler.
(An erroneous output may occur at high sensitivity load
(such as solid state relay).
If the external power supply is turned on precipitously, I
C
current flows to the next stage of transistor Tr1 gate and Y0
output turns on by 100 µs.
When turning on or off the external
power, check that the external power
supply rising edge is 10 ms or more,
and switch S to the primary side of
external power supply.
If the external power supply should be
switched on the secondary side, the rise
time of the voltage should be extended
by RC-circuit to minimum 10 ms.
Calculation of the components:
R1: Several tens of Ohms;
Power capacity
= (external power supply current)
2
x R1 x (3 to 5)
C1:
Several hundreds of microfarads, 50 V
Example: R1= 40
Ω , C1 = 300 µF
Use the below expression to calculate a
time constant:
T= C1 x R1 = 300 x 10
-6
x 40
= 12 x 10
-3
= 12 ms
Measures will not be effective to the
Output module QY81P due to the char-
acterictic of external power supply cir-
cuit.
Tab. 11-1: Output circuit troubleshooting
Photocoupler
Constant
voltage cir-
cuit
Output module, Combined module
Switch S ON
(External power supply at
On)
울 10 ms
Output Y0
approx. 100 µs
External power
supply
Primary side
S
Secondary side
To PLC
Sink output
Load
Source output
Load