2. Introduction
Measurements –is the determination or estimation of ratios of quantities
Instrumentation- is a collective term for measuring instruments used for
indicating, measuring and recording physical quantities.
3. Definition of Unit
Unit:- The standard of each kind of physical quantity is called a unit
Measurement implies comparison with a standard value. The magnitude of a
physical quantity can be written as:
Magnitude of a physical quantity = (Numerical ratio) x (Unit)
Numerical Ratio:- Is the number of times the unit occurs in any given amount
of the same quantity and, therefore, is called the number of measure
4. Unit cont…
For example, when it is said that the
length is 8 metres, it indicates that the
metre is the unit of length and that the
number of the units of length (i.e.
numerical ratio) is 8. So the physical
quantity, length is defined by the unit
metre. The number of measures has no
physical meaning without unit.
5. Absolute Units
A system in which the various units are all expressed in terms of a small
number of fundamental units is called an absolute Unit
The word “absolute” does not imply any special standard of accuracy; it has
been associated with relating units to units of length, mass and time.
Absolute measurements do not compare the measured quantity with
arbitrary units of the same type but are made in terms of fundamental
units
6. Fundamental and Derived Units
Experience has shown that three basic ideas or units are adequate to describe
quantitatively all the phenomena encountered in mechanical science. These are;
- Length
- Mass
- Time
And are called Fundamental units. Since these units are fundamental to most other
physical quantities beside those in mechanics, they are called Primary Fundamental
Units.
7. Fundamental and Derived Units cont…
Measures of certain physical quantities in the thermal, electrical, and illumination disciplines
are also represented by fundamental units. These units are used only when these particular
disciplines are involved and they may therefore be called as auxiliary fundamental units.
All other units which can be expressed in terms of the fundamental units are called Derived
Units.
- Every derived unit originates from some physical law or equation defining that unit.
- A derived unit is always recognized by its dimension, which can be defined as the
complete algebraic formula for the derived unit.
8. DIMENSION
The unique quality of every quantity which distinguishes it from other quantities is called
Dimension.
The dimensional symbols for fundamental units of Length, Mass, and Time are L, M and T
respectively. The various powers of the fundamental units represent the dimensions of any
derived unit.
For example the dimensional symbols for the derived units of;
- Volume = [L]3
- Speed = [LT-]
- Acceleration = [LT-2]
The dimensional formulae of the derived units are very useful for converting units from one
system to another.
9. Standards of Measurements
(Reading Assignment)
Standards of measurements are often classified as follows;
1. International Standards
2. Primary standards
3. Secondary standards
4. Working Standards
