8
EFFECTS OF ELECTRICAL NOISE
The predominant effect of noise on the system is to cause “soft” failures; that is, failures which do
not damage the system but do cause it to function improperly. Three main types of soft failures are
encountered:
1. Logic memory alteration.
2. Register alteration.
3. Momentary I/O failure.
Logic memory alteration presents the most significant potential problem in that it may, in some
cases, result in improper machine operation. Register and temporary I/O failure, normally result only
in nuisance failures such as operation in the wrong mode, machine glitches or incorrect or non-
existent error messages.
AC POWER CONSIDERATIONS
Electrical devices should not be operated at the low end of their input power voltage rating for
extended periods of time. When input voltage is low, current input is forced higher to provide the
devise with the power of needs. Additional current means additional heating. When a system is to be
installed where long brownouts are known to occur, the user is advised to supply the PLC with
power from a voltage regulating transformer. Use of this type of transformer will provide normal
voltage to the devices and keep current within normal range.
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