User`s manual

I/O circuit troubleshooting Troubleshooting
MELSEC System Q, Hardware 11 – 97
11.4 I/O circuit troubleshooting
11.4.1 Input circuit troubleshooting
Exam-
ple
Condition Cause Corrective action
1 Input signal is not
turned off.
Leakage current of input switch
(e.g. drive by non-contact switch).
Connect an appropriate CR so that the
voltage across the terminals of the input
module becomes lower than the off volt-
age.
It is recommended to use 0.1 to 47
μ F
+47 to 120
Ω (1/2 W) for the CR con-
stant.
2 Input signal is not
turned off.
Drive by a limit switch with neon lamp.
 Same as Example 1 or
 Provide an independent display cir-
cuit separately.
3 Input signal is not
turned off.
Leakage current due to line capacity
of wiring cable.
(Line capacity C of twisted pair wire is
approx. 100 pF/m).
Same as Example 1.
(However, leakage current is not gener-
ated when the power supply is located
in the input equipment side as shown
below.)
4 Input signal is not
turned off.
Drive by a switch with LED display.
Connect an appropriate resistor so that
the current across the input module
becomes lower than the off current.
* A calculation example of the resist-
ance to be connected is shown on the
following page.
Tab. 11-1: Input circuit troubleshooting
AC input
Input
module
Power supply
Leakage current
C
Input
module
AC input
Leakage current
AC input
Input
module
Power supply
Leakage
current
AC input
Input
module
Power supply
AC input
Input
module
Power supply
Leakage current
DC input
Input
module
DC input
Input
module
R