Planning Electrical Noise Rejection - Parker H Series Installation & Service Instructions Manual

Safety Guidelines for the Application, Installation and Maintenance of Solid State Control

3.4 Planning Electrical Noise Rejection

The low energy levels of solid state controls may cause
them to be vulnerable to electrical noise. This should be
considered in the planning stages.
3.4.1 Assessing Electrical Environment
Sources of noise are those pieces of equipment that have
large, fast changing voltages or currents when they are
energized or de-energized, such as motor starters, welding
equipment, SCR type, adjustable speed devices and other
inductive devices. These devices, as well as the more
common control relays and their associated wiring, all
have the capability of inducing serious current and voltage
transients on their respective power lines. It is these
transients which nearby solid state controls must withstand
and for which noise immunity should be provided.
An examination of the proposed installation site of the
solid state control should identify equipment that could
contaminate power lines. All power lines that will be
tapped by the proposed solid state control should be
examined for the presence, severity, and frequency of
noise occurrences. If found, system plans should provide
for the control of such noise.
3.4.2 Selecting Devices to Provide Noise Immunity
Installation planning is not complete without examination
of the noise immunity characteristics of the system devices
under consideration. Results of tests to determine relative
immunity to electrical noise may be requested from the
manufacturer. Two such standardized tests are the ANSI
(C37.90a-1974) Surge Withstand Capability Test and the
NEMA (ICS.1-1983) noise test referred to as The
Showering Arc Test. These are applied where direct
connection of solid state control to other electromechanical
control circuits is intended.
regulating systems or high speed logic are generally more
sensitive to electrical noise; therefore, isolation and
separation of these circuits is more critical.
Further information on electrical noise and evaluation of
the severity of noise may be found in ANSI/IEEE
Publication No. 518-1982.
Where severe power line transients are anticipated or
noted, appropriate filters such as commercially available
line filter, isolation transformers, or voltage limiting
varistors, should be considered.
All inductive components associated with the system
should be examined for the need for noise suppression.
Circuits involving analog
C.3.4.1 Assessing Electrical Environment
Noise can also occur in the form of electromagnetic
radiation, or due to improper grounding practices. Section
C.3.4.3 explains these forms of noise and precautionary
measures that should be taken for protection against them.
In many instances a system may begin to malfunction
some time after it has been installed and is working
properly. This may be due to recent installation of new
equipment capable of inducing noise into presently
operating systems. Thus, it is not sufficient to merely
evaluate a system at the time of installation. Periodic
rechecks should be made, especially as other equipment
is moved, modified, or newly installed. When installing a
solid state system, it is wise to assume various noise
sources exist and install the system to guard against
possible interference.
C.3.4.2 Selecting Devices to Provide Noise Immunity
Inductive devices are capable of generating high voltage
transients when switched off.
causing damage to solid state devices by exceeding the
semiconductor voltage rating, the high voltage transient
can be coupled to other portions of a system where it
appears as noise. Fortunately, it is fairly easy to limit the
effects of this type of noise with some form of suppression
device. When necessary, in addition to suppression
devices often provided in solid state equipment, an external
suppressor should be connected as close as possible to
the source of the transient for maximum attenuation.
NOTE: A surge suppressor increases drop-out time of an
electromechanical device.
11
E116P
In addition to possibly