Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 16)

Publication GMC-RM001A-EN-P — July 2001
1-6 Electrical Noise Control Overview
Electromagnetic Radiation
An example of electromagnetic radiation is radio transmission.
Industrial control wiring systems are large, wideband antenna which
radiate noise signals to the world. These signals (together with
conducted noise) are the primary target of the European regulations,
but rarely cause system malfunctions.
Solutions for Reducing
Noise Noise reduction solutions are categorized as coupling reduction and
source reduction. There are four main methods used to reduce the
coupling of noise between source and victim. However, contact
suppression is the only source reduction technique that can be
directly applied by the system builder. Refer to the table below for a
summary.
This method: In this
category: Is defined as: For more
information refer to:
HF (high frequency)
Bonding Coupling
Reduction Maintaining all metalwork at the same electrical potential. This
method is low cost and the basis for all other methods. It works by
ensuring all equipment chassis are at the same potential at all
frequencies. If different potentials exist the voltage difference is
seen as common-mode noise on all interconnecting wiring.
The chapter High
Frequency (HF)
Bonding.
Segregation Coupling
Reduction Separating sources and victims of electrical noise into zones. Noise
coupling reduces with the square of separation distance. Zoning is
zero cost (within limits). The chapter
Segregating Sources
and Victims.
Shielding Coupling
Reduction Using shielded cable and steel barriers (Faraday cage effect) to
reduce electrical noise. Because of its relatively high cost, shielding
is used with discretion. The chapter Shielding
Wires, Cables, and
Components.
Filtering Coupling
Reduction Using low-pass filters to attenuate RF noise. Relatively low cost but
impractical for every wire. The chapter Filtering
Noise.
Contact
Suppression Source
Reduction Adding contact suppression to mechanical switches to reduce noise.
Generally, the one noise source directly influenced by the system
builder. The chapter Contact
Suppression.