Noise Troubleshooting

Noise Troubleshooting
9–17
Maintenance and Troubleshooting
Noise Troubleshooting
Reducing
Electrical Noise
While electrical noise cannot be eliminated it can be reduced to a level that will not
affect the system.
S Most noise problems result from improper grounding of the system. A
good earth ground can be the single most effective way to correct noise
problems. If a ground is not available, install a ground rod as close to
the system as possible. Insure all ground wires are single point grounds
and are not daisy chained from one device to another. Ground metal
enclosures around the system. A loose wire is no more than a large
antenna waiting to introduce noise into the system; therefore, you
should tighten all connections in your system. Loose ground wires are
more susceptible to noise than the other wires in your system. Review
Chapter 2 Installation, Wiring, and Specifications if you have questions
regarding how to ground your system.
S Electrical noise can enter the system through the power source for the
CPU and I/O. Installing a isolation transformer for all AC sources can
correct this problem. DC sources should be well grounded good quality
supplies. Switching DC power supplies commonly generate more noise
than linear supplies.
S Separate input wiring from output wiring. Never run I/O wiring close to
high voltage wiring.
Maintenance
and Troubleshooting
Noise is one of the most difficult problems to diagnose. Electrical noise can enter a
system in many different ways and falls into one of two categories, conducted or
radiated. It may be difficult to determine how the noise is entering the system but the
corrective actions for either of the types of noise problems are similar.
S Conducted noise is when the electrical interference is introduced into
the system by way of an attached wire, panel connection ,etc. It may
enter through an I/O module, a power supply connection, the
communication ground connection, or the chassis ground connection.
S Radiated noise is when the electrical interference is introduced into the
system without a direct electrical connection, much in the same manner
as radio waves.
Maintenance
and Troubleshooting
Electrical Noise
Problems
DL205 User Manual, 3rd Ed., Rev. A, 08/03
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