Expanded fields lead to more stable capacitive sensing

Tom Shelley reports on a development that will advance the use of non-contact capacitive sensing for difficult tasks A new range of capacitive sensors expands their sensitivities, and more importantly, their stabilities, by using novel electrode arrangements that expand their working fields combined with novel electronics. The smaller of the new "High Performance" capacitive sensors from Rechner have two rings behind each other instead of a ring and a plate as in established designs, and the larger versions have a plate arrangement that we understand, but have been asked not to describe. While the sensors are undoubtedly more sensitive, nominal sensing distances remain the same, because the vendors feel it is more important to turn down sensitivity and improve stability, working at no more than 15mm, rather than work at the maximum possible range of some 50mm. One advantage of improved stability is that the sensors are unaffected by damp. And while working at say 8mm in air is not particularly special, the same sensors respond in the same way when working through 8mm of glass, or two sheets, or a build up powder on the inside of a window. While other manufacturers state they can sense materials down with dielectric values of 1.4 or 1.5, the High Performance sensors will reliably detect products with dielectric constants down to 1.1. The sensors also continue to work if placed inside protective stainless steel cups, provided there is free access to the front surfaces. This allows the detection of product in confined spaces surrounded by stainless steel such as in pipe work or in the bottom of hoppers. Prices are from £60 to £70 each. For less exacting requirements, "Normaline" sensors are available from £40 to £50 each and for more exacting requirements, "Extreme" sensors are available for ranges up to 120mm based on Rechner's patented three electrode technology. ATEX certified units are available for areas at risk from possible gas explosions (Zone 1 and 2) and for areas at risk of dust explosions (Zone 20, 21 and 22). As well as the Namur devices, managing director Ian Frais points out that as well as the Namur devices the company has transistor output devices fully certified ATEX that can be used in all of the above zones without the need for a separate barrier. Rechner Sensors UK