Sensor - The Electronic Nose Artificial Olfaction Technology - page 40

Fig. 2.7 Various types of pressure sensors (diaphragm, bellows, bourdon tube)

Primary pressure sensor
Pressure measurement mainly carried out by using elastic elements: diaphragms,
bellows, and Bourdon tubes, are as shown in Fig. 2.7 . These elastic elements
change their shape with applied pressure and the change of shape can be measured
using suitable deflection [ 7 ]. Classification of pressure sensor is summarized in
Table 2.4 .

Units
1 psi (pound per square inch) = 1 lb/in. 2

= 6.9 kPa;

1Pa= 1 N/1 m 2
1 bar = 105 Pa.

Gauge pressure: Gauge Pressure is represented by defining atmospheric pressure
as zero. Pressure higher than atmospheric pressure is positive pressure, while
lower than atmospheric pressure is negative pressure. The difference between the
absolute pressure and the local atmospheric pressure is called gauge pressure.
Representation of pressure scales is shown in Fig. 2.8 .
Absolute pressure: This is the difference between the pressure of the fluid and the
absolute zero of pressure. Pressure is represented by defining absolute vacuum as
zero. Gauge pressure is generally used. Absolute pressure is used for scientific