With the steam age came the demand for pressure measuring
instruments. Bourdon tubes or bellows, where mechanical
displacements were transferred to an indicating pointer were
the first pressure instruments, and are still inuse today.
Pressure metrology is the technology of transducing pressure
into an electrical quantity. Normally, a diaphragm construction
is used with strain gauges either bonded to , or diffused into it,
acting as resistive elements. Under the pressure-induced strain,
the resistive values change.
of a capacitor that changes its value under pressure-induced
displacement.
Pressure sensing using diaphragm technology measures the
difference in pressure of the two sides of the diaphragm.
Depending upon the relevant pressure, we use the terms
ABSOLUTE, where the reference is vacuum (1st picture),
GAUGE, where the reference is atmospheric pressure
(2nd picture), or DIFFERENTIAL, where the sensor has two
ports for the measure of two different pressure.
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