Interconnection
A waterproof connector, but not as we know it
David Phillips describes a new waterproof connector that retains protection while unmated and sets new standards in its class
T
o experienced connector designers the eternal problem of making connectors waterproof is well
understood. The degree of protection is defined in EN 60529 and is commonly referred to as the IP rating. It is defined by two numbers: the first determining protection against foreign objects 'dust' (rated 0-6) and the second defines protection against water with '0' indicating no protection and IP69k indicating resistance to high-pressure water and steam cleaning.
unmated due to servicing or cleaning or if, in normal usage, it is only mated when an optional accessory is fitted. Often the user is blissfully unaware that the IP rating is not being maintained and that dirt, water or other liquids can enter the connector and cause faults and interference. In the worst-case scenario, this can lead to serious consequential costs of total system failure and expensive repair.
Conventional solutions Conventional systems used to protect unmated sockets usually carry some disadvantage. The most common method is to use a protective cap that is inserted and locked when the socket is not in use and is retained to the socket by means of a wire, strap or chain when the connector is in use. If the additional cost and assembly time can be tolerated this is fine, but what good is a protective cap if, as is often the case, the operator does not use it?
A less common Connector manufacturers usually quote
the degree of protection based on a mated and locked pair of connectors, for example a bulkhead socket and cable plug, and default for connectors in the industrial environment is IP67, dust and waterproof to a depth of 1m for 30 minutes. For constant immersion in water, IP68 is the norm although, despite the popular misconception, this is not a standard across all manufacturers but is subject to agreement between the manufacturer and user and can vary widely. Protection is achieved with the socket sealed to the bulkhead via a polymeric seal and clamped with a back-nut or with a flange fixing. The cable entry at the rear of the mating cable connector is also protected via another seal compressed by a pressing screw or the connector may be moulded directly to the cable. The interface between the connector and the socket is protected by a further seal when mated and locked.
But when unmated? In many applications, particularly in instrumentation and test equipment, a real problem arises when a connector is
20 October 2014
alternative is a hinged cap, usually sprung, that closes after removal of the connector. However, in addition to the extra cost, this increases the footprint and is more cumbersome in that it requires two hands to open and mate the connector. Another popular alternative is to dispense with a protection cap and pot the rear of the socket with a resin that provides a waterproof and aesthetic solution albeit an expensive one. The contacts though do remain exposed and are susceptible to pollution and, in extreme cases, corrosion. In addition, temperature fluctuations and differing coefficients of expansion can lead to failure of the potting.
An alternative solution With the newly developed Binder series 770 NCC (not connected and closed) connector the disadvantages of these conventional solutions are eliminated as a unique design completely closes the contact interface when the connector is unmated. The secret is hidden inside of
Components in Electronics
what, at first sight, may not appear to be an electrical connector because the contacts in the socket are obscured by an integral sprung cover that closes as the connector is unmated and completely secures the contacts against the ingress of water, dirt and other foreign bodies and any type of environmental or physical stress.
This is achieved by the combination of special contoured sprung contacts that are mounted inside the wall of the socket and by the depression of the cover. As the central spigot of the mating cable connector depresses the cover, the contacts in the socket close on the annular contacts of the cable connector providing a secure electrical connection. When the cable connector is unmated the cover slides forward and opens the contacts before closing the contact area again.
A material difference
The major challenge and key to the success of this concept was the selection of the materials used. After much research a tough, non-abrasive, solvent-resistant polyamide was the material of choice while the profiling of the individual components was achieved by drawing on experience from successful designs in the medical industry. Apart from
retaining IP ratings while disconnected this new design
brings a number of other advantages. The unique sprung nature of the gold-plated bronze socket contacts protects the gold- plated brass contacts in the connector from wear and in so doing guarantees over 5000 mating cycles, an exceptional life compared with the 500 cycles typically achieved for industrial applications with traditional pin and socket contacts. The all-plastic socket also offers excellent resistance against vibration and shock and
in a field where there is an on-going demand for miniaturisation.
The mating all-plastic cable connector at only 20mm in diameter has a highly tactile feel and provides an attractive design while a bayonet locking ring and pronounced coding provide easy location and positive locking with a simple but secure three point quarter turn bayonet action. This offers a significant advantage where quick connection is required and access to or the visibility of the interface is poor. The gold- plated brass solder contacts are rated to 2A and 175V, with a contact resistance of 15m or less and are mounted in an easily accessible arrangement and the option of three cable outlets means cables with a diameter of 2.5 to 8mm can be accommodated. The simple design and low component count allow for quick and easy assembly.
Engineering in action
The NCC connector with its unique closure system provides a worthy alternative to protection caps and other unmated protection methods and is ideal for applications where waterproof characteristics are required such as measurement technology and hand-held and portable equipment. It is a perfect example of an engineering project that has solved one problem and, rather than creating another, has set an improved overall standard for that class of interconnection.
Binder UK |
www.binder-connector.co.uk
David Phillips is Managing Director of Binder UK
www.cieonline.co.uk
is ideal for demanding applications while the compact profile with a diameter of only 18mm housing eight solder or dip solder contacts provides significant benefits
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