AutomationDirect DL105, User Manual

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Maintenabce
and
Tr
oubleshooting
Maintenance
and
Tr
oubleshooting
8--8
Maintenance and Troubleshooting
DL105 PLC User Manual, 3rd Edition
I/O Point Troubleshooting
If you suspect an I/O error, there are several things that could be causing the
problem.
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High-Speed I/O configuration error
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A blown fuse in your machine or panel (the DL105 does not have
internal I/O fuses)
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A loose terminal block
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The auxiliary 24 VDC supply has failed
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The Input or Output Circuit has failed
When troubleshooting the DL105 Micro PLCs there are a few facts you should be
aware of. These facts may assist you in quickly correcting an I/O problem.
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HSIO configuration errors are commonly mistaken for I/O point failure
during program development. If the I/O point in question is in X0--X3, or
Y0--Y2, check all parameter locations listed in Chapter 3 that apply to
the HSIO mode you have selected.
S
The output circuits cannot detect shorted or open output points. If you
suspect one or more faulty points, measure the voltage drop from the
common to the suspect point. Remember when using a Digital Volt
Meter, leakage current from an output device such as a triac or a
transistor must be considered. A point which is off may appear to be on
if no load is connected the point.
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The I/O point status indicators are logic-side indicators. This means the
LED which indicates the on or off status reflects the status of the point
with respect to the CPU. On an output point the status indicators could
be operating normally while the actual output device (transistor, triac
etc.) could be damaged. With an input point, if the indicator LED is on
the input circuitry is probably operating properly. Verify the LED goes off
when the input signal is removed.
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Leakage current can be a problem when connecting field devices to an
I/O point. False input signals can be generated when the leakage
current of an output device is great enough to turn on the connected
input device. To correct this install a resistor in parallel with the input or
output of the circuit. The value of this resistor will depend on the amount
of leakage current and the voltage applied but usually a 10K to 20K
Ω
resistor will work. Verify the wattage rating of the resistor is correct for
your application.
S
Because of the removable terminal blocks on the DL105, the easiest
method to determine if an I/O circuit has failed is to replace the unit if
you have a spare. However, if you suspect a field device is defective,
that device may cause the same failure in the replacement PLC as well.
As a point of caution, you may want to check devices or power supplies
connected to the failed I/O circuit before replacing the unit with a spare.
Possible Causes
Some Quick Steps