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Pre-installation Guidelines SIMATIC 545/555/575 System Manual

2.5 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 usually enters the system through

the signal or power wiring. The noise may couple into the wiring by

electrostatic or magnetic means.

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 is

the result of 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.

Definition and

Source

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Siemens SIMATIC TI500 Especificaciones Pagina 47