Empty 19" cases are generally in conformity with CE, because there are no technical components likely to emit perturbing radiation or to be interfered. Therefore, it is impossible to obtain a CE certificate under the legal provisions concerning electromagnetic compatibility EMC.

 

Manufacturers of mechanical components for electronic systems must nevertheless create the conditions allowing appliance manufacturers to comply with the legal provisions concerning EMC and consequently to meet the requirements for operational safety.

 

Individual electronic assemblies can be screened in different types of 19" cases, e.g. in front panel screened plug-type subassemblies, modules, subracks and in enclosing cases and cabinets.

 

However, screening of electronic assemblies may become useless if the electrical connections are not screened. In this context, it has to be noted that screening of the rear connectors to DIN 41612 used so far is impossible, since they are made of plastics.

 

For an efficient EMC screening of the electronic system, the case manufacturers propose tested screened mechanical assemblies. Fischer Elektronik produce screened plug-type subassemblies, modules and subracks meeting the EMC requirements.

 

 

EMC shielded subracks

 

The modular subrack series BGT with standard depths of 180, 240 and 300 mm offers a large number of variations. The EGT version of this modular design allows complete subracks to be screened and thus to meet the applicable EMC requirements. The high-quality EGT has a clear chromate coating, applied in special processes ensuring good electric conductivity.

 

Detachable covers with or without ventilation slots provide for shielding of the EGT subrack on the upper or on the lower side. If necessary, additional contact spring strips can be slipped onto the edges of the cover. The ventilation slots in the covers are designed to ensure a high shielding effect, even in case of free convection. Additional components suitable for retrofit, e.g. various contact springs, offer the advantage of adapting existing appliances to specific requirements. Such components can be mounted without need of subsequent mechanical work.

 

 

 

Shielded front panels

 

The product range is complemented by EMC shielded front panels, also available as hinged version. These front panels can also be used as rear panels. They are made of an anodised outer sheet and an electroconductive yellow chromated inner screening sheet. Cable screens or filters can be connected to the subrack components at low impedance and low inductance via the inner sheet.

 

 

Plug-type subassemblies

 

Partial front panels for plug-type subassemblies are available as 3 HU and 6 HU version, with grid sizes (HP) of 4 to 14. These subassemblies are connected to the subrack side panels via contact springs.

 

Special zinc diecast PC board holders allow for an assembly on both sides with a grid size of 1 HP (5.08 mm). In addition, contact springs can be mounted below the conductive PC board holders, in order to provide the electroconductive lead contact to the conductive module rails of the subrack.

 

Contact springs that can be mounted between the zinc diecast PC board holder and the electroconductive front panel are available as accessory. These contact springs serve as lead contact or for electrostatic discharge.

 

If necessary, the soldered side of the PC board can be screened by plastic covers provided with a metallic conductive outer coating.

 

 

 

Guide rails

 

In addition to the standard guide rails, new reinforced guide rails have been developed featuring a very high stability. The side faces are designed as trellis construction, thus allowing for an optimum cooling of the PC board. The rails being screw-fastened, they meet the requirement of flexibility. If necessary, contact springs for earthing or module rails of the EGT can be used. The guide rails are generally provided with spring-loaded webs which are centrally arranged on the left and on the right side.

 

 

Modules

 

Among the large variety of different module designs, the types 'I, F, V, M, HB' and the grid module 'N' as well as the heatsink insert module 'KSK' are particularly suitable for screening.

 

The type 'I' for 3HU Eurocards is provided with an aluminium shielding and a plastic conductor card cover on the soldered side of the PC board. Upon request, the PC board cover can be provided with a conductive outer coating.

 

Type 'F' for 3HU and type 'V' for 6HU cards consist of an aluminium extruded section and a cover available in different modular width dimensions.

 

 

Modules of types 'M' and 'HB' consist either of two equal sections or of two sections with a different width. They form a tube with the grid sizes 10, 12, 14, 19, 21 and 28 HP. Type 'M' is of the same design but with additional cooling fins.

 

The PC board can be easily fastened in the modules, since the slot for screw mounting is within the range of the plug-type connector (88.9 mm).

 

 

The grid module type 'N' can be extended by two different sections to 6 or 10HP and then by a multiple of 2HP, i.e. 12, 14, 16, 18 etc.. The module can be inserted in rails on the left and on the right side, in conformity with the applicable standards. The inner grid of the guide slots for 3HU Eurocards has a continuous dimension of 5.08 mm, which makes it particularly suitable for bus board wiring. Thanks to the screw-down points of the sections being arranged quite close to each other and to an electroconductive hollow tubular seal proposed as an optional extra, the electroconductive design of this module is especially suitable for EMC applications.

 

Upon request, the front panels can be equipped with aluminium or plastic handle.

 

 

Heatsink insert modules type 'KSK' with a minimum grid size of 12 HP are equipped with a heatsink (SK 421). The fluted cooling fins allow for an optimum heat dissipation. Other grid sizes (19, 20, 21 HP) are obtained by displacing the heatsink to the right, by using extension strips.

 

The tube of the insert module with front heatsink type 'EFK' is the same as used for 'KSK' modules with a grid size of 8HP. In case of this type, a heatsink section (GP 210) forms the front panel. Such a heatsink section can also be fastened to plug-type circuit boards (8HP).

 

Upon request, the front panels of the modules are supplied with anodised outside (non conductive) and chromated inside (conductive).

 

 

Fischer Elektronik GmbH & Co KG

Design / Engineering

Dipl.-Ing. Lothar Kampe

 

 

Copyright © Dipl.Ing. Lothar Kampe. All rights reserved.

This article may be reproduced with identification of source without the written permission of Fischer Elektronik.