As electronics technology continues to find applications in difficult working environments, the need to specify the right electronic connector for the job has never been more important says David Phillips of binder UK
When 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 product are also key.
The expected pollution around the connector is divided into four degrees. The first degree is where there is no conductive pollution such as may be found inside a device. The second covers non-conductive pollution and temporary condensation like that experienced by household appliances, while the third is conductive pollution that may, for example, be experienced with machine tools. The fourth degree is persistent conductive pollution caused by things like dust and water in demanding environments.
IEC60529 classifies the degrees of protection against 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.
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. 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. Crimp terminations provide a fast and simple method but require expensive crimp tools. For field wiring, screw termination provides the best solution.
While many connectors are manufactured from brass for its strength, die-cast zinc or an aluminium alloy are often used to reduce cost and weight. A trend now is towards low cost, light and robust all-plastic connectors like binder’s series 620, 720 and 770 (pictured) where polyamide is the preferred material, being tough, non-abrasive, and resistant to solvents and temperatures up to 120°C.
How often the connector will be mated and the IP requirements will have a major influence on the type of mating system.
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.
Making the best of it
Often considered as a designer’s afterthought, the connector is a vital component in any system. A connector that is the right size, has the correct electrical characteristics, uses the best method of termination and mating for the application and is protected to the required level will optimise the performance and cost-effectiveness of any system.