Chapter 11 Troubleshooting

11-9
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11.4 Troubleshooting Examples
Possible troubles with various circuits and their corrective actions are explained.

11.4.1 Input circuit troubles and corrective actions

The followings describe possible troubles with input circuits, as well as corrective actions.
Condition Cause Corrective Actions
Input signal
doesn’t turn off.
Leakage current of external device
(Such as a drive by non-contact switch)
Input signal
doesn’t turn off.
(Neon lamp
may be still on)
Leakage current of external device
(Drive by a limit switch with neon lamp)
y Connect an appropriate register and capacity,
which will make the voltage lower across the
terminals of the input module.
y CR values are determined by the leakage current
value.
− Recommended value C : 0.1 ~ 0.47 ㎌
R: 47 ~ 120 Ω (1/2W)
Or make up another independent display circuit.
Input signal
doesn’t turn off.
Leakage current due to line capacity of wiring cable. y Locate the power supply on the external device
side as shown below.
Input signal
doesn’t turn off.
Leakage current of external device (Drive by switch with
LED indicator)
y Connect an appropriate register, which will make
the voltage higher than the OFF voltage across the
input module terminal and common terminal.
Input signal
doesn’t turn off.
y Sneak current due to the use of two different power
supplies.
y E1 > E2, sneaked.
y Use only one power supply.
y Connect a sneak current prevention diode.
DC input
L
E1 E2
C
External device
AC input
R
Leakage current
DC in
p
ut
R
E1 DC input
L
E
External device
DC input
R
Leakage current
C
AC input
R
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AC input
External device
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External device
AC input
Leakage current
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C
External device
AC input
R
Leakage current
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