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14/11/2008
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A new generation of circuit breakers will trip less frequently and monitor energy usage more reliably. Lou Reade reports
Miniature residual current devices (RCDs) that use digital technology to detect current surges have hit the market for the first time.
The devices – which protect people from electric shocks in the home – promise to work more efficiently than traditional devices by precisely monitoring energy usage in the circuit.
Deepstream Technologies, based in North Wales, has won a $16m (£8m) contract to incorporate its electronics technology into Moeller’s Xpole range of circuit breakers.
Jonathan Luke, chief technology officer at Deepstream, says: “Traditional analogue RCDs are threshold detectors. They must trip at 30 milliamps, but, because they are electromechanical, there will be stiction – so they often trip at 24-25mA.”
He states that Deepstream’s intelligent sensor technology will prevent these ‘nuisance trips’ – caused by a temporary overloading of the circuit – by analysing the exact conditions in the circuit.
“Digital devices don’t just look at thresholds, but measure energy in the load – so we can see if it’s resistive or capacitative,” he explains.
This, he points out, allows the system to tell whether several devices have been switched on at once – which is safe – or whether a human finger has been poked into a light socket (in which case, the system will trip).
Deepstream has developed a series of modules that fit into Moeller’s RCDs. The modules have a sensing front end – an Asic chip that measures current and voltage –plus a microcontroller and a trip system. As well as circuit design, the key to Deepstream’s success is its ability to pack these circuit elements into a small space.
“We developed the digital RCD in parallel with the 3D packaging technology,” says Luke. “You couldn’t have one without the other.”
Deepstream had to develop a new substrate technology to withstand high temperatures – and to pack everything into a smaller space. An inspiration was the design of automotive leadframes (a thin layer of metal that connects electrical terminals on the semiconductor to circuitry on larger devices such as PCBs).
By devising a way to ‘stack’ these elements, Deepstream came up with a means of shrinking the footprint.
“We create three or four layers on a flat substrate, and have a bespoke process to cut them up and stick them together,” Luke explains. “Designing 3D leadframes is a new thing.”
The way in which the layers are then interconnected lies at the heart of the company’s IP. The elements are overmoulded into an engineering polymer, such as LCP – which is able to withstand high temperatures and protect the circuit.
Deepstream claims that manufacturers of RCDs could incorporate more than 20 new features – impossible with traditional devices. Examples include energy metering, which would allow itemised billing on individual pieces of equipment, and the ability to add intelligence to various types of switching devices used in automation.
Pointers
Electronics module claims to bring digital control to low-voltage residual current devices for the first time
Moeller is the first manufacturer to use this – but other potential users are waiting in the wings
Device will allow more sophisticated analysis of energy use within a circuit
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Written by Lou Reade
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