Page 392 - Mechatronics with Experiments

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Notice that the atmospheric absolute pressure varies from the nominal value
2
(14.7lb∕in (14.7 psia)) due to variations in
1. height from sea level,
2. temperature and the resulting variations in air density

p = p +Δp(h, T) (6.154)
atm atm,0
= 14.7 +Δp(h, T) psia (6.155)

6.8.1 Displacement Based Pressure Sensors

The basic transduction principle in this type of pressure sensor is to convert the pressure
into a proportional displacement, and then convert this displacement to a proportional
electricalvoltage.Figure6.48showsvariousconceptsofpressuresensorswherethepressure
is proportional to the displacement of the sensing element (Bourdon C-tube, bellows,
diaphragm). The motion of the flexible sensing element can be translated into a proportional
voltage by various methods including position sensing, capacitance change, strain change,
and piezoelectric effects. For instance, the Bourdon tube based pressure sensor can be

Motion

p 2 p 2
p 1 p 1 p 2

p 1 Motion Motion
Bourdon tube Bellows Diaphragm

Output
Bourdon c-tube LVDT L
x
Mounting p p 1
block 2
R x E o

R L
Pressure line E i

Input

Spring
FIGURE 6.48: Various pressure sensor concepts: pressure to displacement transduction and
then displacement measurement in order to obtain pressure measurement.