PRESSURE SENSORS

Pressure

Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area.

Pressure Sensor

Measures pressure, typically of gases or liquids. Usually acts as a transducer. Generates a signal as a function of the pressure imposed.

Types of pressure sensors

Diaphragm Bourdon’s tube Pirani gauge Piezoelectric sensor Ionization gauge Bellows sensor

Diaphragm

Measure the pressure above or below the atmospheric pressure. Consisting of diaphragm, rack, pinion, pointer and calibrated scale. The fluid under pressure causes some deformation of the diaphragm With the help of some pinion arrangement, the elastic deformation of the diaphragm rotates the pointer

Bourdon’s tube

Measure the pressure above or below the atmospheric pressure Consisting of an elliptical tube, sector gear, pinion, pointer and calibrated scale The bent, tube is called bourdon’s tube Bourdon’s tube as a result of the increased pressure tends to straighten itself

With the help of simple pinion and sector arrangement, the elastic deformation of the Bourdon’s tube rotates the pointer

Pirani gauge

Measurement of the pressure in vacuum systems Invented in 1906 by Marcello Pirani. Consists of a metal filament (usually platinum) Filament is connected to an electrical circuit When the pressure of fluid is high the filament is cool and then low the temperature of filament is increase Electrical resistance of a wire varies with temperature

Piezoelectric sensor

A device that uses the piezoelectric effect to measure pressure by converting them to an electrical signal Invented by the Curie brothers in the late 19th century Naturally occurring materials such as tourmaline and quartz These materials had the ability to transform energy of a mechanical input into an electrical output

When a pressure [piezo is the Greek word for pressure] is applied to a piezoelectric material, it causes a mechanical deformation and a displacement of charges Piezoelectric sensors are electromechanical systems that react on compression

Ionization gauge

Measurement of very low pressure from about 10-3 atm to 10-13 atm Consisting a filament, grid and collector The number of ions per unit volume is dependent on the gas pressure hence the current also depends on gas pressure A filament was in the center with a grid surrounding the filament and a collector surrounding the grid

Electrons were emitted from the hot filament and attracted by a positive electrical potential toward the grid Electrons collided with gas molecules, forming positive ions The positive ions were attracted to the collector with an appropriate negative potential

Bellows sensor

Made of a sealed chamber that has multiple ridges like the pleats When pressure is applied to the chamber, the chamber will try to expand and open the pleats The travel of the bellows can be converted to linear motion so that a switch can be activated This type of sensor is used in low-pressure applications usually less than 30 psi

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