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7.4 I/O Connection Troubleshooti.ng
7.4.1 Input wiring troubleshooting
This section describes possible problems with the input circuit and corrective actions.
7
Condition
0
Example 1
Corrective Action
cause
Input device leakage current.
*Connect a CR network across input to drof
thevoltagebelowthe
inputmodules OF1
threshold.
-_
1
AC input signal
does not turn
off.
(Input LED
may remain
on or flicker)
AC input
I
AC input
Input unit
--I
I
Power supply
Use C = 0.1 t o 0 . 4 7 ~ Fand R = 47 to 1206
(ll2W)
Leekage current due t o contact switch
neon indicator.
:xample 2
As example 1, or.
Construct independent indicator circuit.
with
AC input
AC input signal
does not turn
I
off.
(Input LED
may remain
amor flicker)
I
Power supply
Leakage current due to line capacity of wiring
is
cable. (Linecapacityoftwistedpairwire
approx. 100 PF/m.)
Ixample 3
AC input signal
does not turn
off.
(Input LED
may remain
on or flicker)
--
0
ixample 4
DC input signal
does not turn
off.
(Input LED
may remain
on or flicker)
j
AC input
I
--
+L-dtnput
unit
I
I
AC input
IInput uni
N
Power supply
Leakage current due to contact switch
LED indicator.
--
As example 1.
*Notethatmoving
the power supply t o tht
input device end of thecable will preven.
leakage current from beinggenerated.
I
I
with
*Connect a resistor across the input andCON
to drop the voltage below the input module:
OFF threshold.
DC input (sink)
DC input (sink)
I
1
- - -Sample resistor value calculationgiven
next page.
or
Table 7.2 input Wiring Troubleshooting
c
7-14
IB INN 66132-A