Technical Information - Elma Electronic - (Version JPG) - Page n° 19 - PDF Catalogue | Technical Documentation

Untitled



	Dimensions and Technical Information

Enclosure openings Ideal shielding can be achieved by placing the electronic components in a metal enclosure welded all round. This is only very rarely possible, however, in practical applications. Openings are required for operation and indications, for cable entries, for ventilation and for the mount-ing and removal of components. The individual parts of the enclosure must be electrically conductive with good continuity across the joints in order to prevent a reduction of the shielding effectiveness. Without conductive gasket or contacts with closely situ-ated contact points (e.g. screws) gaps are produced, which produce antenna effects owing to their length. Gaps lengths less than ¹/₂₀ of the wavelength only have a negligible effect on enclosure shielding effectiveness. In units subject to strong radiation, the gap length should be kept shorter than ¹/₅₀ of the wavelength. EMC gaskets The primary function of an EMC gasket is the reduction of the interface resistance across a joint of the enclo-sure. The lower the interface resistance, the better the seal. The interface resistance depends on the surface resistance of the enclosure parts, the conformability of the seal, the contact pressure and the conductivity of the seal. Elma enclosures are provided with copper-beryllium contact strips and a plastic foam seal, sheated with a conductive metal. These seals ensure low interface resistance. The effectiveness of the EMC gasket under extreme environmental conditions, e.g. humid heat, is extremely important.			Cable entries Careful consideration should be paid to the cable entries in the enclosure. Errors in cable runs can result in the required shielding effectiveness being almost entirely lost. The following possibilities are available for correct execution of cable entries and exits.
			Decoupling capacitors
			1^st possibility Decoupling capacitors. Decouple all cable wires with a capacitor of low value (10 nF) and very short connections to the enclosure.
			Shield contact all round
			Shielded cable Metallic
			connector body
			2^nd possibility: Shielded cables. The shield contacts the enclosure all round via a cable fitting or a metallic connector body.

Filter

3^rd possibility: Filter. The filter must be screwed to a good conducting surface of the enclosure.

www.elma.com		Elmaset		G \| 15

Technical Information - Elma Electronic - #19

Encoder, Knob, Backplane connector, Tester, Cabinet