2-8
Pre-installation Guidelines
TI545/TI555 System Manual
2.5
Definition and Source of Electrical Noise
Electrical noise is defined as any unwanted electrical signal which enters
the control equipment. Noise signals cover the entire spectrum of
frequencies and may have any wave shape.
A major difficulty with noise problems is that they can occur at random
intervals. Continuous, or frequent, periodic noises generally are easy to
detect and remedy. Intermittent noise sources that produce short,
high-energy bursts at irregular and widely spaced intervals create problems
that can be harder to resolve.
The primary sources of noise in industry are those devices (and their wiring)
that produce and switch high voltage and current. Typical examples include
large motors, welders and contacts that switch heavily inductive loads such
as brakes or clutches.
Noise can enter your control equipment by several routes. It can be
conducted through signal or power wiring or can be radiated by
electromagnetic waves. Conducted noise typically is coupled with the signal
or power wiring, either electrostatically or magnetically.
Electrostatic coupling occurs through parasitic capacitance between the
noisy line and the signal/power line. This requires high voltage or high rate
of change voltages in the noisy line and high parasitic capacitance between
lines. This can occur when you have long wire runs in the same conduit.
Magnetic coupling occurs through mutual inductances between lines. This
requires high currents or high rates of change of current, as well as
significant mutual inductance.
Electromagnetically radiated noise typically is high frequency (radio waves).
The control system and its wiring may act as antennas in picking up noise
signals. This pathway is least likely to present problem levels of noise, but
its sources are common in industrial applications.
Electrical Noise
