Industrial Electronics Game changer
Nicolas Roche looks at how Honeywell has been re-writing the rules in sensor design as it works to combine the mechanical and electronic worlds into a single device
F
or many years, engineers have been battling with two seemingly impossible – and competing – ideals: how to bring together the best of the 'mechanical' and 'electronic' worlds into a sensor environment, and into a single device. Manufacturers too have long-since
recognised that if a sensor could be developed that combined the highest levels of sensitivity with the lowest levels of power consumption, they would be able to transform – and maybe even revolutionise – the manufacturing process. It is against this context that the
Research and Development teams at Honeywell Sensing and Control have been working over the last two years to attempt to come up with the a 'mechanical' and 'electronic' combination, a forced marriage that has often created considerable headaches due to difficulties related to size
has developed a way of bringing its Anisotropic Magneto-Resistive (AMR) structures on top of a BiCMOS die to create an extremely low power miniaturised magnetic sensor – the SM350LT Series of nanopower magneto- resistive Sensor ICs.
These sensors, it believes, are changing the rules: they have higher sensitivity, are omnipolar and sense in parallel planes. The new sensors consume so little current that users may even be forced to reinvest in a new device if they are not capable to scale in nanoampere current regions!
Flexibility in design The nanopower magnetoresistive sensors give engineers more flexibility and possibilities in terms of design. With very high sensitivity (7G (0,7mT) max. 11G), it means that engineers can use large tolerances to activate the sensor with a magnet. In addition, the new nanopower sensors provide more space, giving engineers the option of choosing a smaller magnet thus potentially saving considerable cost. The applications are endless. Where designers have previously been obliged to use mechanical switches or reed contacts, the new generation of nanopower magnetoresistive sensors is allowing them to think again. Medical applications include phone
frequency switches for hearing aids, emergency stop switches for exercise equipment, cartridge detection for infusion units, drawer positioning for drug/pharmaceutical carts, and the automatic positioning/movement control of hospital beds.
Industrial applications are equally The new Series of nanopower
magnetoresistive Sensor ICs are supplied in the sub-miniature SOT-23 surface mount package – small enough to fit on your fingertip
or manufacturing.
Honeywell's designers have created a new device that they believe will be a true 'game changer', a ground-breaking technology that will re-write the way that engineers and manufacturers view the sensor of the future. And it's all down to a combination of nanopower and magnetoresistive technology. Using its experience of working with magnetoresistive technology, the company
34 September 2014
numerous: counter mechanisms and anti- tamper sensors on water and gas meters; door and window security closures; alarm test sensors for homes and buildings; selection and battery positioning sensors on power tools; lid and door closure fittings on white goods and consumer electronics. Any wireless-based system with wireless peripherals where battery life is an issue has the potential to be transformed. The possibilities are limited only by imagination, and the benefits are universal: a dramatic re-evaluation of the design and cost benefits of a multitude of products.
Magnetic agnostic Foremost behind the thinking of the new research work is that the new sensors meet stringent production and quality control criteria. Being omnipolar, or 'magnetic agnostic' as has been described, the sensors have the same characteristics
Components in Electronics
regardless of whether they are activated by the south or north pole and will be thermally balanced so that they are stable over the entire temperature range of -40C to +85C.
The SM350LT Series is available in two magnetic sensitivities: for applications requiring ultra-high sensitivity (7G typical; 11G maximum), the SM351LT has a very low current draw (360nA typical); for applications requiring very high magnetic sensitivity (14G typical; 20G maximum) and a very low current draw (310nA typical) there is the SM353LT. Both are supplied in the sub-miniature SOT-23 surface mount package on tape and reel (3000 units per reel) for use in automated pick and place component installation.
So how does this new nanopower sensor family compare to other devices, and notably Reed switches and Hall Effect sensors?
Favourable comparisons The SM351LT compares directly with Reed switches, and has the ability to replace a Reed switch in a range of battery-operated applications thanks to its size, durability, and extremely lower power consumption. Similarly priced, the SM351LT AMR device out-performs Reed switches in areas such as reliability - as magnetic features are more stable over time and temperature; durability - as solid state technology does not wear out over time; and quality - as a plastic molded housing provides greater product integrity. One of the principal objections over the use of Reed switches is their fragility and the instability of the magnetic characteristics over the longer term.
The SM353LT, meanwhile, is directly comparable with a high sensitivity Hall- Effect sensor. These would typically be in the 30 Gauss range where the SM353LT is proven to deliver twice the level of
The new Series of nanopower
magnetoresistive Sensor ICs is already being specified for use in the counting mechanism on water meters, where the sensing element has to detect through a 6mm thick shock-proof glass wall
sensitivity over its Hall-Effect equivalent. In addition to the higher Gauss sensitivity, the SM353LT senses in the parallel plane which offers new possibilities in terms of design options compared to more commonly used Hall-Effect sensors which sense a magnetic field in a perpendicular plane. Giving more ultra-low power options to design engineers provides those not currently leveraging active magnetic sensing technology with far greater choice. They can benefit either from the savings in battery life (the SM353LT uses at least 10 times less power than its Hall Effect equivalent), or through the ability to add further devices 'at the edge'. To expand on one of the applications
already highlighted, the SM353LT is already being specified, for example, for use in the counting mechanism on water meters: sometimes, the sensing element has to detect through a 6mm thick shock-proof glass wall, with the magnet immersed into an anti-frost glycol solution. The information is then sent wirelessly to a remote control unit. On water meters, and indeed other similar installations, an additional sensor can be used as an anti- tamper switch to detect the absence/presence of an external magnetic field. Often, that same sensor is also used as a configuration switch to set the time at which the meter reading needs to be sent to the remote control unit.
This new way of thinking, and new way of getting 'traditional' technologies to work together in a wholly 'untraditional' way, has the potential to deliver products of the future that are better designed, more reliable, less costly to manufacture, and use less power, with all of the additional benefits that brings. But if you want all of those benefits, then you might just have to invest in a new ampere meter!
Honeywell |
www.honeywell.com
The sub-miniature SOT-23 surface mount package is standard across all of the variants within the new nanopower magnetoresistive Sensor ICs range
Nicolas Roche is EMEA Product Leader for Magnetic and Optical Sensors, Honeywell Sensing and Control
www.cieonline.co.uk
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