Measurement Technology - The Electronic Nose Artificial Olfaction Technology - page 18

The word temperature was coined to describe the degree of hotness or coolness
of a material or a body. The thermometer—a temperature measuring instrument
was first developed.
Temperature is a quantity that can be readily perceived by the human senses, by
contact with the skin or by visually by eye. The concepts ''warm'', ''cold'', ''ice
cold'' or at high temperatures ''red hot'' or ''white hot'' are known to everyone.
Human beings are relatively good at realizing temperature differences, whether
something is colder or warmer than another substance or object.
From the physical point of view, temperature can be described as a measure of
the energy inherent in a body, which results from the unordered movement of its
atoms or molecules. Temperature is a state variable, which together with quantities
such as mass, heat capacity and others, describes the energy content of a body or
system. Therefore, temperature could be measured directly in energy units.
However, the tradition of specifying the temperature in degrees had already been
introduced far earlier and was well established in physics, so that for practical
reasons it was not reasonable to discontinue the use of degrees.
Temperature plays an important role in the reproducibility of product quality,
the profitability of production processes and the operational reliability of industrial
installations and equipment. Temperature measurement methods can basically be
subdivided into contact and noncontact temperature measuring methods. In contact
temperature measuring methods, the thermometer, and in particular the part con-
taining the temperature—sensitive sensor, is brought into thermal contact with the
measured medium at the area of installation. The energy exchange between
thermometer and measured medium takes place primarily via thermal conduction.
Noncontact temperature measuring methods use the energy exchange between
measured object and thermometer by heat radiation.
Temperature sensors based on different principles have been developed. They
can be broadly classified into the following groups:
1. Liquid and gas thermometer
2. Bimetallic strip
3. Resistance thermometers (RTD and Thermistors)
4. Thermocouple
5. Junction semiconductor sensor
6. Radiation pyrometer
1.9.4 Displacement and Speed Measurement
Displacement and speed are two important parameters whose measurements are
important in many position and speed control schemes. Error free measurements of
these two parameters are required in order to accomplish good control perfor-
mance [ 5 , 6 ].
The physician and biomedical researcher are interested in measuring the size,
shape, and position of the organs and tissues of the body. Variations in these