Measurement Technology - The Electronic Nose Artificial Olfaction Technology - page 17

Pressure is defined as force acting evenly over a unit area.
Pressure ¼ Force = Unit Area ¼ F = A
This force can be exerted by liquids, by gases or vapors, or by solid bodies.
Surface compression takes place at the interface between two solid bodies, but for
our purposes we can consider this additional force negligible.
Pressure can also be uttered in terms of metric (SI) units. The basic metric unit
of force is the Newton (N) and the basic unit of pressure is the Pascal (Pa).
A pressure measurement can be explained as either static or dynamic. In
conducting tests where no motion is taking place is referred to as static pressure.
Examples of static pressure include the pressure of the air inside a balloon or water
inside a basin. Often times, the motion of a fluid changes the force applied to its
surroundings. Such a pressure measurement is known as dynamic pressure mea-
surement. For example, the pressure inside a balloon or at the bottom of a water
basin would change as air is let out of the balloon or as water is poured out of the
basin.
There are three methods for measuring pressure: absolute, gage, and differen-
tial. Absolute pressure is referenced to the pressure in a vacuum, whereas gage and
differential pressures are referenced to another pressure such as the ambient
atmospheric pressure or pressure in an adjacent vessel. Pressure is measured by
converting the physical phenomenon to an intermediate form, such as displace-
ment, which can be measured by a transducer.
Diaphragms, Bourdon tube, Manometers, Bellows, Capacitive pressure sensor,
Fiber-optic pressure sensors, Resonant-wire devices, Dead-weight gage, Ther-
mocouple gage, Pirani gage, McLeod gage, and Ionization gage are types of
sensors/devices available for measuring pressure.
Pressure measurement is vital and essential in following industrial applications:
• Drilling technology utilizes pressure sensors for real-time down hole data
transfer
• Weather forecasting
• Medicine
• Aviation
• Pressure Vessels
1.9.3 Temperature Measurement
The need for reliable temperature scales as a prerequisite for clear measurement
results was already recognized in the early stages of thermometer development.
Therefore, efforts were made to calibrate the thermometers on reference points
with good reproducibility. Since it was easy to determine the freezing point and
boiling point of water at the time, these reference points were quickly used for
these purposes. In 1694, Renaldini recommended the boiling point of water as the
upper limit of the scale.