2. PRESSURE SENSORS

3.  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.

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

5.  Diaphragm  Bourdon’s tube  Pirani gauge  Piezoelectric sensor  Ionization gauge  Bellows sensor

6.  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

8.  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

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

11.  Measurement of the pressure in vacuum systems  Invented in 1906 by Marcello Pirani.Marcello Pirani  Consists of a metal filament (usually platinum)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

13.  A device that uses the piezoelectric effect to measure pressure by converting them to an electrical signalpiezoelectric effectpressure electrical  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

14.  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

16.  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

17.  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

19.  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