Biomedical Engineering Reference
In-Depth Information
into different species to make it easier to understand and in order to identify
common features. Classification also allows us to draw general conclusions and
rules about the various classes [ 4 ].
A measurement provides a means of describing various phenomena in quan-
titative terms. It has been quoted ''whatever exists, it has to be exists in some
amount''. The determination of the amount is measurement all about. There are
innumerable things in nature which have amounts. The determination of their
amounts constitutes the subject of mechanical measurements. The measurements
are not necessarily carried out by purely mechanical means. Quantities like
pressure, temperature, displacement, fluid flow and associated parameters,
acoustics and related parameters, and fundamental quantities like mass, length, and
time are typical of those which are within the scope of mechanical measurements.
However, in many situations, these quantities are not measured by purely
mechanical means, but more often are measured by electrical means by trans-
ducing them into an analogous electrical quantity [ 4 ].
Classification of measurement allows general rules and conclusions to be drawn
about measurement systems in terms of their accuracy, ease of use, and suitability
for various types of application.
Methods of measurements:
The methods of measurements may be broadly classified into two categories:
1. Direct method
2. Indirect method
Direct method:
In these methods, the unknown quality (also called the measurand) is directly
compared against a standard. The result is expressed as a numerical number and a
unit. The standard in fact is a physical embodiment of a unit. In simple words
''Measurements are directly obtained''. All the physical dimensions are generally
measured directly. In the direct measurement, the meaning of measurement and
the purpose of the processing operation are identical.
Example: Vernier calipers (as shown in Fig. 1.2 ), Micrometer etc.
Fig. 1.2
Vernier calipers
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