Connectors help reduce size, weight and power in aerospace electronics

Electronics systems are subject to vibration, varying degrees of shock and wide variations in temperature. Ensuring they operate in all required conditions is one thing; ensuring the connectors in the system are fit for duty is another. One of the biggest issues involved in such areas is fretting corrosion. With fretting, the connector's contacts rub against each other only slightly, but the effect is a rapid increase in contact resistance. This can lead to oxidisation and to open circuits. Bill Henderson, global director, commercial aviation and defence, for Smiths Connectors, said: "According to NASA, fretting corrosion is the leading problem. There are ways to overcome fretting corrosion, but the solutions add weight and cost." Scott Flower, Gecko product manager for Harwin, noted: "One of the key demands from the aerospace sector is to reduce size, weight and power. That's what we have tried to do with the Gecko range." One way of reducing fretting corrosion is to stiffen the racks holding electronic equipment and to fix the boards rigidly. "Today," said Henderson, "it's all about operating cost and reliability has to be taken for granted." Henderson suggests the ideal solution to the problem is selecting the most appropriate technology – and that, at least in his opinion, is hyperboloid connectors. It's an approach which has been offered by Smiths' subsidiary Hypertac for some years. "Whilst Hypertac's technology is mature and was patented originally in the 1950s," Henderson accepted, "it's still relevant to modern applications." Hypertac is one of three connector companies within the Smiths Connectors family, accompanied by semiconductor test specialist IDI and high speed connector developer Sabritec. "We've rebranded and restructured the organisation," Henderson noted. "We have a new sense of direction and a more focused approach to product development and markets." The global operation has six sites in the US and five in Europe. The hyperboloid connector technology offered by Hypertac was invented by French engineer FR Bonhomme. "He licensed the technology to a range of companies," Henderson said, "and there are still a couple supplying products." Hyperboloid connectors, while potentially attractive to the product designer, are less attractive to those manufacturing connectors and this explains the small number of suppliers, said Henderson. "Manufacturing cost is a barrier to entry and companies have to know how to make the devices." The hyperboloid connector cage is constructed with wires linking between two metal rings. Once wired, the rings are twisted opposite ways by a few degrees. This process narrows the gap between the wires at the mid point between the two rings, with the gap increasing hyperbolically the nearer you get to either end – hence the name hyperboloid connector. Connectivity is provided using a connector pin, which is inserted into the cage, forcing the wires slightly apart, but allowing them to encircle the connector pin. This arrangement is said to provide optimum contact reliability, even with severe vibration, and the avoidance of fretting corrosion. "Using this approach means aircraft manufacturers can take weight out of their planes and reduce manufacturing costs. And there are continuing benefits," Henderson claimed, "such as better fuel economy." Although hyperboloid connectors can be associated with use in larger applications, they do come in small sizes. "The smallest device which we offer has a pin diameter of 0.3mm," Henderson pointed out. The company also offers reverse gender options, with the pins in the connector block. Power is also an application, as well as data. "Because there are so many points of contact when you're transmitting power," said Henderson, "you can specify a smaller diameter connector. This, in turn, saves weight." Harwin's Flower pointed out that the Gecko range has been developed to meet the needs of aerospace and avionics manufacturers. "We based Gecko on the technology used in the Datamate range, but have developed a smaller package looking to help those designers who are facing size constraints." Apart from maintaining the performance characteristics of the Datamate range, Gecko connectors are smaller, light and more stable for avionics applications, Flower noted, where weight is an issue. "We've kept the power parameters as close as possible to Datamate," he continued, "but have reduced connector size by 75%." Despite the growing importance of x-by-wire in aerospace applications, there remains the need for copper cabling. Copper, of course, adds weight, so Gecko connectors are designed to support the use of smaller diameter wires. "Most of the weight in interconnect systems comes from copper cabling," Flower observed. "We have designed Gecko so that wires of 26AWG (0.4mm diameter) down to 32AWG (0.2mm) can be used – very fine diameters." Gecko connectors have a pin spacing of 1.25mm, said to be 35% smaller than high performance connectors, such as the Micro-D format. Rated to handle 2A per contact, Gecko connectors are specified to operate in temperatures ranging from -65 to 150°C and high vibration. Like Henderson, Flower noted the need for connectors to handle higher levels of vibration. "We are testing Gecko devices to much higher levels of vibration than we have previously with other parts. So we test to 20g, but have also added acceleration testing, because modern planes get up to speed more quickly." Gecko is also finding application in satellites (see box). Flower accepted the requirements for space applications don't differ greatly from those of commercial aviation, but pointed to extremes of temperature and vibration. How closely do companies such as Hypertac and Harwin have to work with aerospace designers? Henderson said: "We need to work alongside all customers, so it's important we are involved at the early stages of design. Flower agreed. "Connectors are almost always the last thing a designer thinks about. They design a board with a lot of components and then realise they don't have much space for the interconnect." Henderson concluded: "We help designers to select the best solution – and that may not be the solution they thought about initially. Selecting a connector is not just about data rate, it's also about mechanical performance." Connectors to ride in CubeSats Harwin's Gecko connectors will be used on CubeSat miniature satellites being designed by Surrey Space Centre as part of the international QB50 programme led by the von Karman Institute. The QB50 program will study the variations of a number of parameters in the lower thermosphere using a network of around 40 double CubeSats carrying identical sensors. QB50 will also measure and compare actual trajectories and orbital lifetimes during re entry against predicted data. A third part of the programme will see about 10 double or triple CubeSats used as technology demonstrators for such things as miniature sensors and the Gossamer-1 solar sail. The size of CubeSats – 10 x 10 x 20cm and weighing 2kg – means connectors have to be small, lightweight and reliable, even under extreme shock, vibration and temperature.