Sensors offer off-the-shelf accuracy

Written by: Paul Fanning | Published:

High-accuracy, new-generation inductive sensors are soon to be available in an off-the-shelf product. Paul Fanning reports.

A generation of inductive sensors designed to allow accurate measurement in challenging conditions will shortly be available in an off-the-shelf product.

'Precision in the extreme' is the claim of Zettlex UK, the manufacturer of the sensors in question and this principle is very much at the heart of the company's technology offering of new-generation inductive sensors. These essentially use the same principles as traditional inductive sensors, offering good, non-contact measurement performance irrespective of the operating environment. However, rather than use bulky spools of wire, Zettlex sensors use printed circuits on flexible or rigid substrates.

The technology is not new, having previously only been supplied on a bespoke basis in applications ranging from aerospace, defence and industrial to 'the world's most expensive record player', on which it provides the turntable control (because the sensor contains no bearings that might pick up on the needle).

The transition to printed windings brings with it a number of other advantages. Amongst these are a large reduction in production cost, size and weight, the eradication of sources of inaccuracy from the winding process, the ability to achieve complex measurement geometries such as curvilinear, 2D & 3D position sensing and the ability to locate multiple sensors in the same space by using multi-layer circuit boards.

Perhaps the most significant benefit, however, is the flexibility of form afforded by the technology. As Mark Howard, Zettlex's general manager puts it: "We are taking Faraday's maths and applying it in such a way that you can have any shape you want." While this ability has given Zettlex a number of what Howard calls "design wins", it has also, he feels, become something of a burden. "We've foolishly been telling customers that they can have any shape they want. That's OK, but supporting those types of project takes a lot of effort and that could limit the size of the company."

With this in mind, Zettlex is now seeking to move its technology from bespoke to off-the-shelf products. The first of these to emerge is IncOder, a high-accuracy, ring-shaped inductive encoder designed as an alternative to pancake resolvers. Intended for launch at this year's Farnborough Air Show, the encoder's unusual shape is aimed at engineers who are struggling with tight spaces or a restricted design envelope. For example, the engineer may need to pass drive shafts, bearings or cables through the space where traditional rotary encoders might sit.

Clearly, of course, there is no shortage of options when it comes to position sensors. However, says Howard: "There's a problem with pretty much all of them: potentiometers are good where you have a benign environment; with optical you need a clean environment; magnetic sensors aren't always as accurate as they could be because magnets vary from one to the next – plus they need really good mechanical alignment; capacitive sensors are too temperature- and humidity-sensitive; and strain measurement is a nightmare to set up. Inductive sensors are always chosen for large and expensive safety-critical applications and we are taking the expensive and large out of that. The market we're going after is where people want to measure accurately in difficult or dirty conditions."

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