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By STEVE HARPER (IMHOF)
The business of electronic package--housing electronic systems in cases or enclosures--is becoming increasingly sophisticated.
Although the basic product of the enclosure manufacturer remains--at first glance--a straightforward box, the rapid growth of electronics has radically altered the role of the enclosure. What used to be a passive box can now be a major contributor to system performance on a variety of levels. And in addition to the requirements of performance, the market has demanded that the new generation of enclosures should largely be available as standard items.
To meet this need, the portfolios of today's principal enclosure manufacturers cover a wide range of products, including 19-inch racks, sub-rack systems, many styles of cases in a variety of materials, and a huge selection of accessories vital to application suitability.
Just five years or so ago, case products generally fell into two categories: the utilitarian/functional, easy to take apart and use, but unattractive to look at; and the aesthetically pleasing, which had concealed fixings to give cleaner lines, but which incurred a penalty by being harder to use, and more difficult to assemble and take apart.
Today's standard cases strike a balance between the two. The combination of good looks with functionality has largely been achieved through the use of new materials and by finding ways to conceal fixings while still leaving the electronics easily accessible.
As with enclosures generally, much emphasis has been placed on development standard case products to fulfill particular purposes, and the need for electronics to be wall mounted in a variety of hostile environments has led to the introduction of steel, wallmounted cases sealed to IP54 and IP55 (in accordance with the procedures of British Standard 5490). To meet the need for larger enclosures in similar environments, sealed versions of free-standing racks sealed to IP66 are also available as standard.
The move of electronic systems into the front office is also reflected in the cases market, with desk top consoles, v.d.u. housings and instrument cases all a standard part of today's enclosure inventory.
Developments on the 19in. enclosure scene have been driven by two basic forces: the adoption of international standard specifications on dimensions, and customer requirement for key performance changes.
An important milestone in achieving standardization came with the adoption of specifications generated by the International Electro-Technical Commission, the British Standards Institution, and the Deutsche Industrie Normen bodies.
These specifications called for the adoption of a 600mm external width for instrument racks, and overall heights from 800mm up to a total of 2200mm in 200mm increments, and depths of 400, 600, 800 and 900mm. Despite metrication, two things remain unchanged: the 19in. panel width, and the height increment of 1 3/4in. (U). These were so firmly established that they were retained within IEC 297, BS5954, and DIN41494.
European enclosure manufacturers had been working with these dimensions since the late 1960s, but by and large British manufacturers had been slow to conform.
The introduction by Imhof in 1979 of its S80-600 range--which conforms fully to these specifications--marked the real beginning of an emphasis on standard product performance.
These developments have brought direct benefits to racking systems users: the extra space provided by the 600mm rack width provides improved facilities for cable runs: power distribution is incorporated into the rear vertical members: and the design allows for infinite adjustment of the panel mounting members within the depth of the rack, even allowing them to be flush with the front face if required.
With the gradual introduction of more IEC based racking systems, a change of emphasis has occurred: many features which had always been available as extras, such as fan trays and integral power distribution facilities, have become standard.
Many recent developments in enclosure technology are attributable to the parallel surge forward taking place in the performance of electronics systems. As developing electronics enable designers to make more powerful and sophisticated systems, they want to concentrate on the capabilities of the system rather than having to spend time considering the packaging implications.
This, in turn, means that the enclosure manufacturer has to take steps to stay ahead of new developments, assess their impact on rack requirements, and refine specifications to take them into account.
Nowhere has this discipline been more clearly demonstrated than in the area of radio frequency interference (RFI) screening. It became obvious that in environments where increasing amounts of complex circuitry were present, problems caused by uncontrolled electro-magnetic radiation in the frequency range up to 10GHz could be severe.
Technical and regulatory pressures, covering all aspects of RFI from car ignition system suppression to telecom equipment, have given rise to the availability of low cost standard RFI screened enclosures. The techniques used in manufacturing nonstandard screen products have been improved to make higher volume production possible at a realistic price.
Motek range of modular racking systems, including 19in. types, chassis and instrument cases; many to DIN standard. Eurocard rack range, designed to accommodate single and double p.c.b’s (mixed, in some versions), is available in a choice of colors and with a wide variety of accessories.
Transistek range of extruded aluminum instrument enclosures includes three models in several standard sizes; optional vented top cover.
Instrument cases in various styles, with a particular emphasis on keyboard-type enclosures for desk terminal units; Eurocard heatsink cases.
Large range of electronic enclosures, with particular emphasis in screened types for security in telecommunications and data handling. Prices for the new Imshield 60 RFI-screened modular rack series begin at just £350. Another recently-introduced product is a ruggedized card-frame, available in 19in. widths and capable of accepting all modules and accessories designed for Imhofs Inta-Euro 327 Eurocard sub-rack system. Imhof also market a range of static-protective carrying cases from Hofbauer of West Germany.
IPK (Ian P. Kinloch)
Lightweight aluminum rack-mounting cases with various depths, 1U to 3U high; no constructional fixings are visible on the front panel. Other sizes are available to special order. Prototype service.
J.D.R. Sheet metal Steel 19-in. rack-mounted cases in 1U, 2U and 3U sizes; removable rear and side panels.
A variety of metal and plastics enclosures: K range of screwed die-cast aluminum boxes for indoor and outdoor use; two ranges of glass-fiber reinforced two-part boxes in polyester or polycarbonate, with clear or transparent lids; M range of glass-filled polycarbonate boxes designed for total insulation, self-extinguishing and capable of withstanding prolonged exposures to temperatures between-40°C and +80°C; hinged boxes in mild or stainless steel; Fibox series of control boxes in impact-resistant polycarbonate, dust and water protected, with PSB slots and with a separate termination compartment; and the Piccolo series of small polycarbonate or ABS enclosures.
Linc-Ace range of aluminum enclosures based on three standard extrusions with matching endplates; suitable for p.c.b’s from 40x55mm up to 100x220. Sizes interlock with one another, enabling enclosures to be racked together. Accessories include a bracket for power semiconductors which slots into the extrusion for heat-sinking. Prices are comparable to those of die-cast aluminum boxes.
Numerous types of steel enclosure, including low-cost two-part cases, wall-mounted boxes, small 19in. rack units, drawer case units, consoles and keyboard cases. Finishes are textured acrylic or electrostatic powder epoxy. Non-standard types available by special order.
Several ranges of instrument cabinets, racks, cases, desk systems and accessories, including some special types. C65 RFI/EMI shielding cabinets are quoted as giving up to 100dB of shielding over the range 10MHz to 1GHz. A range of e.m.p.-protected cabinets gives better than 80dB of protection at 1GHz. The company offers in-house design and testing facilities.
Rider Fenn & Ridgway
Variety of 19in. racks and housings and frames, intended especially for telecommunications applications. Prototype and experimental work undertaken, including precision sheet metal work, production presswork and assembly, paint-spraying and certificated welding.
Extensive ranges of racks and consoles: Rittal claims to be the world's largest manufacturer of standard enclosure systems. The new VR series of IEC 297/2 racks, made in the company's Plymouth factory, is assembled and sprayed to order from standard components, giving short lead-times for what is almost a custom-built product. To satisfy demand from government users and high-technology concerns, Rittal have low-cost EMI/.RFI shielded rack which in tests achieved attenuation greater than 100dB. Other products include open-frame laboratory racks, the Uniset series of card-frames and a variety of instrument cases.
Wide range of standard equipment housings in cast aluminum, polyester and polycarbonate. An arc-sprayed zinc coating process now available gives RFI shielding for plastics housings; and for metal boxes, a new polyurethane sealing gasket is said to maintain protection even after repeated resealing.
Among other services offered are drilling, tapping, milling, coating and enameling.
Extensive range of steel industrial enclosures in various sizes and styles, many designed for resistance to unfavorable environments. Other series of enclosures include control desks, aluminum enclosures, 19in. racks and sub-racks. Plastics boxes are available in several styles and materials. These can also be supplied in RFI-shielded versions through an aluminum sputtering process.
Comprehensive ranges of modular housings for all types of electronics equipment: racks, sub-racks, industrial cabinets, RFI-shielded enclosures, case systems, housings for v.d.u.’s and microcomputer systems, desks and accessories.
Latest 103-page catalogue embraces a very large range of enclosures of all sorts: 19in. cases and rack systems; wall-mounted cases designed to resist adverse conditions; three types of v.d.u. housing; potting boxes; flip-top plastics cases for portable instruments; battery boxes; instrument cases with and without handles and other fittings; cases with an optional security fixing kit; molded keyboard enclosures; modem cases; drawer cases; Eurocard systems; and much more.
Company's selection of enclosures is one of the widest in the UK: the 1986-87 catalogue details a range extending from miniature nylon or metal boxes to desk and computer cases, 19in. racks and associated hardware. Materials include aluminum, steel and glass-filled plastics. Among many recent introductions are the Europack VME card-frame; the Internorm range of 19in. rack cases, which won a design award at the Hanover fair; the Combicard system for Eurocard boards in ABS; Palamos molded enclosures for portable or bench-top instruments; and various panel accessories and fittings. The company claims to have particular expertise in the design and manufacture of card-frames, with a system which has MOD approval for use in environments subject to shock and vibration.
Low-cost card-frame for 160mm and 200mm Eurocards, supplied in kit form in standard 3U and 61.1 sizes. Labracks range of floor-standing racking designed for all-round access to the installed equipment. Base units are made from 2mm steel pre-punched to allow many different configurations of racking to be added. Recent products include a range of stainless steel enclosures with seam-welded joints and electro-polished finish.
Also see: Cases and enclosures
(adapted from: Wireless World , Dec. 1986)