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New technologies, new transducers

12 September 2011

Pressure transducers have reached an elevated position in terms of their accuracy, repeatability and durability. However, with new sensor deposition techniques and innovative electronics design, they are set to take even higher ground, as Mike Powers describes

Pressure transducers are everywhere – from a Formula 1 car to a reactor vessel to a modern jet fighter - converting fluid pressures into electrical signals for monitoring and control. And while existing devices provide impressive service, so far as these applications go, watch this space! There is a technological trend that is seeing the performance of these components on a relentless upwards curve. And this is all down to new sensor element construction techniques and the design of the electronics packages that add so much value in terms of their output stability and accuracy.

These new methods have not only added sophisticated levels of functionality to pressure transducers, they have also enabled them to withstand particularly aggressive conditions, extremes of temperature, mechanical shock and vibration.

Combining an extremely sensitive pressure sensing mechanism with a sophisticated electronics package means these devices can respond to pressure transients of 1ms or less, offer high accuracy with almost zero drift over time and have an operating life in excess of 100 million cycles. Their resilience and sophistication is the result of some highly innovative and carefully controlled methods of construction, particularly the use of sputtered thin film and chemical vapour deposition (CVD) techniques to produce advanced strain gauge pressure sensing elements.

Indeed, CVD is highly effective in the manufacture of strain gauge sensors, which detect deflections in a pressure diaphragm to convert these tiny movements into electrical signals over a wide dynamic range. Devices manufactured via CVD are typically compact and extremely accurate with excellent hysteresis characteristics.

The sensors are produced on wafers in large batches using polysilicon deposited on a stainless steel substrate, with the strain gauge patterns being chemically milled. The results are impressive, as the product description in the panel below attests.

Sputtered thin film
Sputtered thin film technology has also been integral to the success of the latest fluid pressure transducers. Sputtering is a process whereby a solid target material is bombarded by energised particles, causing it to release atoms. Sputtered thin film deposition is a method of forming a thin film from the released atoms. The technique produces pressure transducers with a sensitive, robust diaphragm that is suitable for direct contact with almost all liquids, oils and gases.

The strength and long operating life of these transducers, combined with their strong resistance to shocks, vibration and corrosion, has widened their applications potential across many industries, from general manufacturing to transportation and medical markets. Off-highway vehicles, for example, have taken advantage of pressure transducers to assist with the measurement of their loads.

Alongside these innovations in the chemical manufacture of pressure sensors have been some equally valuable advances in electronics, which have greatly enhanced the capabilities of transducers. For example, the electronic packages that have been supplied with pressure transducers over recent years have enabled each sensor to be tuned to meet the specific customer requirements. These packages incorporate ASICs (application specific integrated circuits), which enable this level of customisation and performance enhancement.

The economic benefits of introducing ASICs into the electronic package design has been significant. Combined with improvements in volume manufacturing techniques, the ASIC has, in many instances, reduced the unit cost of transducers by a factor of ten, enabling manufacturers to sell for around £30, a sensor that offers a level of performance previously associated with units costing in the region of £300.

CVD and sputtered thin film technology, combined with ASIC electronics packaging, offer a powerful combination, which has contributed to significant advances in the accuracy and reliability of pressure transducers, and allowed their application in more challenging environments.

Mike Powers is with Gems Sensors and Controls

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