An introduction to subrack systems
RFI protection, Shock and vibration protection, ESD protection and Fire
enclosure safety to name but a few. Let’s examine a number of the functional aspects of the subrack and look at the alternative solutions available
THE SUBRACK PRINCIPLE
Why would you choose to use an extrusion based subrack ? In a word, accuracy. The need to provide a precise framework in which PCBs are supported and guided into
connector positions is most efficiently achieved using accurate extrusion technology and hard-tooled end plate design. The subrack function now extends far beyond the pure support role and covers such areas as
RFI PROTECTION
This is achieved by the use of covers, EMC contact fingers and conductively finished mating parts. The Faraday cage achieved with subracks can give very high levels of signal attenuation across a wide band of frequencies. The nature of the construction also allows the user to define a balance between EMC and ventilation. Selective RFI protection is another option, with the use of plug in screened modules.
There are a couple of alternatives, either the problem can be designed out at board level ( there is some doubt, however, that susceptibility problems can be designed out through tracking and layout changes), or the problem areas can be ‘canned’, but again there are some doubts regarding susceptibility.
SUBRACKS SHOCK AND VIBRATION
The KM6 subrack range; KM6-II, KM6-RF and KM6-HD167, is recognised worldwide as one of the leading products in its field having evolved around a number of international standards and in response to a number of trends. Principal among these trends are increased component densities, higher speed bus systems, greater
connector contact counts, a greater range of operating environments, EMC and electrical safety regulations and, of course, economic pressures. This is achieved with the use of secure card guides (screwed in), two point extrusion to endplate fixing and additional mounting at the rear of the frame. It should be remembered that the effectiveness of the mounting is only as good as the
rack/system into which the frame is mounted.
There are only custom solutions for securely mounting PCBs without using a subrack and these are normally loosely based around the subrack principle.
ESD PROTECTION
This is achieved using grounding clips in the card guide system to discharge Electrostatic build up from the PCB either during insertion or during the course of normal operation in situ. Additional grounding at the front panel is now seen as good ESD practise and this is achieved either with the use of metal inserts or through the grounding pin in IEEE1101.10 Injector/Ejector mechanisms.
Alternative methods of ESD are hard to define. Some claim that good production methods ie .operators fitted with discharge clips and product storage in anti-static packaging are helpful. Others claim sufficient discharge through an allocated pin(s) in the
connector.
VERSATILITY
S Extrusion based subrack The Subrack concept allows the user to configure the usable space to suit the application, thus removing the necessity to ‘tool’ each configuration as a custom solution.
Divider kits for the front and rear allow a variety of heights, widths and depths within a single envelope size. Even the orientation of the PCBs can be readily changed from vertical to horizontal, or indeed a combination of the two within the same frame.
The alternative to this is to produce a custom based solution, which may well produce a high tooling investment requirement. Verotec have made a significant investment in tooling to produce good quality, versatile subrack products.
Our manufacturing facilities have long been at the forefront of technological development, and their commitment to the providing of the most fit-for-
purpose products is demonstrated by the fact that we currently manufacture some of the most advanced packaging systems and
enclosures available. Verotec’s facilities are fully equipped with the latest electronic design and manufacturing systems, enabling customers to access a “virtual” factory for the procurement of product. We have long experience in the design, manufacture and supply of subracks and
enclosures in both standard and custom forms and, as a result, we have expertise in solving a wide range of problems encountered by the electronics industry when housing or ‘packaging’ components and systems. This publication reflects both that experience and expertise. Verotecs is dedicated to being a world-class provider of a comprehensive range of standard and custom product, borne from the integrated design, manufacturing and service capabilities, enabling it to provide OEMs with rapid deliveries at competitive prices. We believe that every customer is a priority, and contact is maintained by means of our own dedicated sales forces and via our technical sales and marketing specialists, who are able to draw upon global resource. T RFI protected subrack
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Tel: +44 (0)2380-246900 sales@verotec.co.uk
