INTERCONNECTION FEATURE
SELECTING THE RIGHT CONNECTOR - A FEW POINTERS
SELECTING THE RIGHT CONNECTOR
A common mistake is to leave connector selection to the last minute says David Phillips of binder UK. Choosing a connector should be made as early in the design process as possible and failure to do so can lead to being left with a compromise solution that will detract from product performance and low cost
W
hen it comes to designing-in and specifying any type of electronic
and electrical connector there are fundamental choices to be made – mainly concerning the electrical and physical features required for the application. The current, voltage and the number of contacts, together with the cable diameter, level of shielding and environmental protection required all have a direct influence on the connector choice. The physical characteristics relating to how the connector will be terminated, the method of mating and the space available both inside and outside the IEC60529 classifies the degrees of protection against access outside influences such as dust, foreign objects, moisture and water. The IP rating is split with the first number (0-6) denoting resistance to solid objects and dust and the second number (0-9K) denoting resistance to water. Typically, industrial connectors are rated IP65 and above, with many being IP67 for temporary immersion in water or the ultimate IP69K protection from high pressure water and steam cleaning. A popular misconception is that IP68 is a norm which can be compared across applications, when in fact IP68 means constant immersion in water to an agreed test between manufacturer and user.
SHIELDING, ELECTROMAGNETIC COMPATIBILITY (EMC) With increasing requirements from equipment manufacturers for shielding against electromagnetic interference (EMI), more and more applications call for shielded cable systems that require connectors with good shielding characteristics. For optimum results, 360o shielding is required and, as shielding attenuation in dB is dependent on frequency, such
anodised. A nickel plating of between eight to 10 microns offers good protection and for more demanding applications stainless steel should be considered. A significant trend now is towards low
cost, light and robust all-plastic connectors where polyamide is the preferred material, being tough, non- abrasive, and resistant to solvents and temperatures up to 120°C. For its insulating properties, excellent
connectors will have a high attenuation over a large frequency band.
CONTACTS AND TERMINATION METHODS Contact strength, spring properties, electrical conductivity and operating temperature are defined by the materials used. Quality contacts use copper-alloys for contacts, brass for pins and phosphor bronze for sockets as these ensure good strength, conductivity and temperature stability. Phosphor bronze also displays excellent spring capabilities. In addition, gold or silver plating provides high levels of conductivity and corrosion resistance and will ensure over 500 mating cycles. The method of terminating the cable
also needs careful consideration and will depend upon the application and production quantities. While solder terminations provide the most secure and best electrical joint they require skilled operators whereas crimp terminations provide a fast and simple method but require expensive crimp tools. For field wiring, screw termination provides the best solution. High quality metal connectors are
manufactured from brass for its strength and good machining ability. To reduce cost and weight, die-cast zinc or an aluminium alloy are becoming more commonly used while for corrosion resistance and aesthetics, metal parts can be nickel, chromium plated or
/ ELECTRONICS Figure 1:
Factors determining clearance and creepage distances
chemical resistance, dimensional and temperature stability up to 85ºC contact carriers and inserts should be manufactured from polybutylene terephthalate (PBT).
MATING SYSTEMS How often the connector will be mated and the IP requirements will have a major influence on the type of mating system and the chosen method will have a big impact on connector cost. Snap-in connectors provide quick and
simple mating and are generally the lowest cost solution. Recent developments mean that these can now be rated up to IP67 thus providing an economic solution with high performance while bayonet connectors offer a more secure mating although the design means they are usually restricted to IP 40. Metal push-pull connectors can be expensive. However, the trend towards plastic versions has helped to reduce cost and provides a quick mating IP67 connector with some protection against accidental un-mating. Screw connectors provide the ultimate protection against accidental un-mating and have excellent IP performance but, on the downside, they are generally the most expensive type of connector, especially in metal versions.
binder UK
www.binder-connector.co.uk T: 01442 257339
ELECTRONICS | OCTOBER 2018 19
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