Pressure is defined as force per unit area that a fluid exerts on its surroundings. A pressure measurement can further be described by the type of measurement being performed. There are three types of pressure measurements: absolute, gauge, and differential. Absolute pressure measurement is measured relative to a vacuum. Gauge pressure is measured relative to ambient atmospheric pressure. Differential pressure is similar to gauge pressure, but instead of measuring relative to ambient atmospheric pressure, differential measurements are taken with respect to a specific reference pressure.
A pressure sensor, sometimes called a pressure transmitter, is a transducer that converts pressure into an analog electrical signal. Because of the great variety of conditions, ranges, and materials for which pressure must be measured, there are many different types of pressure sensor designs. Often pressure can be converted to some intermediate form, such as displacement. The sensor then converts this displacement into an electrical output such as voltage or current. As C. Meraz introduced in her post, the three most universal types of pressure transducers of this form are the strain gage, variable capacitance, and piezoelectric. Chunyi Wang adds other two types of sensor named resonant wire pressure sensor and Pirani gauge sensor. Besides, according to G.Carpenter’s blog, there are three types of electrical outputs available for pressure sensors: millivolt, amplified voltage, and 4-20 mA.
Figure above provides an overall orientation to the scientist or engineer who might be faced with the task of selecting a pressure detector from among the many designs available. This table shows the ranges of pressures and vacuums that various sensor types are capable of detecting and the types of internal references (vacuum or atmospheric pressure) used, if any.
Common causes of pressure sensor failure include dynamic impact that results in sensor overload, spikes that cause a hole or tear in the diaphragm, moisture ingress whereby liquid seeps in through an interface and between a cable and the sensor, extreme temperature, stress when being calibrated, and wear and tear that produces drift and failure. Advances in pressure sensors should be focus on miniaturization with integration of electronics and control capabilities into the same chip as the sensor resulting from the new, smaller form factors. By reducing the size of the sensor, pressure sensors can be used in more area.
source:
http://www.omega.com/literature/transactions/volume3/pressure.html
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