One of the most important . measures to achieve good EMC characteristics is to bond all metallic (conducting) structures together with many wide connections. Connect metal to metal by as large area as possible, with good surface conductivity. These joined parts form a conductive equipotential structure, that act as a reference plane or ground for all electrical and electronic circuit in its vicinity. In practice, the apparatus body and the metal casing, forms this reference plane. In most cases, the ground planes in PCBs must also be connected to the reference plane to achieve the desired EMC properties.
Most designers . and installers of electrical equipment agree that shielded cables are a good way to achieve EMC. But many times I have seen big money thrown ”down the drain” because of overconfidence to the cable shield effects and ignorance of its proper use and design.
EYE ON . It is relatively easy to achieve good attenuation (> 80 – 100 dB) of electromagnetic fields using a compact metal shield. In most practical cases, the shield is not complete, there are almost always openings, i.e. slots, windows and apertures. It is mainly these imperfections in the shield that determines the overall shielding effectiveness of the box.
EYE ON . Shielding is one of the concepts associated with EMC. Often, for example, mechanical engineers are tasked to build a shielding box, without further specification of ie operating frequencies or desired attenuation.
How much attenuation is reasonable to expect?
EYE ON . One fundamental concept in EMC design is zoning. Zoning is easy to understand. It is used in the most varied contexts and situations. Situations covering everything from old communist dictatorships, such as for example the former East Germany (DDR), to city planners and the European Union. Zones are used in order to achieve various properties in demarcated geographic areas, or within volumes. Zoning with application in electronic engineering are also known as the Controlled Electromagnetic Topology.
EYE ON . EMC is a complex topic. To achieve the desired EMC characteristics of a product, in an efficient way, often requires collaboration between different professional groups. In addition to electronics designers, all parties involved should have the understanding and basic knowledge of the subject. The most concerned may be: mechanical designers, project managers, machine builders, installers, and others.