January 14, 2015
Pressure measurement is an important part of many applications across many industries. Processes can vary in pressure range, temperature and the media being measured. There is no ideal pressure sensor technology for all applications, so making the correct choice of sensor for your application is essential to get the best possible performance from your pressure transmitter or transducer.
Pressure sensors or pressure sensor elements are measuring elements which convert the physical quantity of pressure into an electrical quantity that is proportional to the pressure. Different physical effects and different sensor materials such as silicon, ceramic or metal are used. Each technology may have specific advantages and disadvantages. The pressure sensor design that is most suitable for an application is determined by the demands of the application, for example, the material in contact with the media and its suitability for certain media are of fundamental importance.
ESI use a range of sensor technologies;
Silicon-on-Sapphire (SoS) pressure sensors
Silicon-on-sapphire wafers are formed by depositing silicon onto the sapphire substrate at very high temperatures.
Pure sapphire crystal is grown in a controlled lab environment. The formed sapphire ingots are cut at a 60º angle, known as the R-Plane. This plane reveals the oxygen atoms in the crystal and because the spacing of these atoms is almost identical to that in a silicon crystal, the silicon can be cleanly deposited onto the surface of the sapphire wafer. Doped silicon strain gauges are etched from the layer of silicon and individual strain gauges are electrically isolated from each other by the outstanding insulating characteristics of the sapphire substrate. The ability to operate at high temperatures, chemical inertness, and virtual absence of hysteresis make the strain gauges ideal for use in pressure sensors.
Bonded foil pressure sensors
Bonded foil sensors are based on the same principle as a strain gauge. Four foil gauges, made from constantan on a flexible polyimide backing, are bonded to a stainless steel diaphragm in the form of a Wheatstone bridge circuit. The diaphragm flexes and strains in response to an applied pressure and causes an electrical resistance change in the strain gauges producing a sensitivity of 2mV/V.
Like bonded foil strain gauge sensors, thick film sensors use four resistors grouped to form a Wheatstone bridge. The resistance structures are screen printed onto a ceramic membrane diaphragm and then hermetically joined to a main ceramic body to make a robust structure. The resistance change here is due to the deformation of the membrane, resulting from the geometrical change caused by the stretching and compression of the material. Connections from the membrane are made through the body to solder points on the surface.
Isolated Silicon Sensor
An isolated silicon sensor utilizes a semiconductor (silicon) measuring diaphragm with selectively diffused structures. They use the piezoresistive effect, which is based on the change in electrical resistance in the semiconductor materials caused by the stretching and compression, which affects the mobility of the electrons under the mechanical stress. The silicon sensor is fitted onto a glass feed-through and is mounted in a 316L stainless steel housing. It is then isolated from external media behind a thin 316L stainless steel membrane which is welded to the main housing body. The housing is filled with silicon oil and sealed. Pressure acts on the membrane and is transferred through the oil to the sensor.
Piezoresistive silicon sensing element without a protective membrane. The sensor is packaged in a plastic housing for direct mounting to a printed circuit board.
ESI offers technical support to assist clients choose what type of pressure sensor best meets their needs. Contact the sales team [email protected]
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