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These are the methods of comparison used in measurement process. In precision measurement various methods of measurement are adopted depending upon the accuracy required and the amount of permissible error.

**METHODS OF MEASUREMENTS **

These are the methods of comparison used
in measurement process. In precision measurement various methods of measurement
are adopted depending upon the accuracy required and the amount of permissible
error.

The
methods of measurement can be classified as:

l. Direct
method

2. Indirect
method

3. Absolute
or Fundamental method

4. Comparative
method

5. Transposition
method

6. Coincidence
method

7. Deflection
method

8. Complementary
method

9. Contact
method

10.
Contact less method

**1. ****Direct
method of measurement: **

This is a simple method of measurement,
in which the value of the quantity to be measured is obtained directly without
any calculations. For example, measurements by using scales, vernier callipers,
micrometers, bevel protector etc. This method is most widely used in
production. This method is not very accurate because it depends on human
insensitiveness in making judgment.

**2.
Indirect method of measurement:**

In indirect method the value of quantity
to be measured is obtained by measuring other quantities which are functionally
related to the required value. E.g. Angle measurement by sine bar, measurement
of screw pitch diameter by three wire method etc.

**3.
Absolute or Fundamental method:**

It is based on the measurement of the
base quantities used to define the quantity. For example, measuring a quantity
directly in accordance with the definition of that quantity, or measuring a
quantity indirectly by direct measurement of the quantities linked with the
definition of the quantity to be measured.

**4.
Comparative method:**

In this method the value of the quantity
to be measured is compared with known value of the same quantity or other
quantity practically related to it. So, in this method only the deviations from
a master gauge are determined, e.g., dial indicators, or other comparators.

**5.
Transposition method:**

It is a method of measurement by direct
comparison in which the value of the quantity measured is first balanced by an
initial known value A of the same quantity, and then the value of the quantity
measured is put in place of this known value and is balanced again by another
known value B. If the position of the element indicating equilibrium is the
same in both cases, the value of the quantity to be measured is AB. For
example, determination of amass by means of a balance and known weights, using
the Gauss double weighing.

**6.
Coincidence method:**

It is a differential method of
measurement in which a very small difference between the value of the quantity
to be measured and the reference is determined by the observation of the
coincidence of certain lines or signals. For example, measurement by vernier
calliper micrometer.

**7.
Deflection method:**

In this method the value of the quantity
to be measured is directly indicated by a deflection of a pointer on a
calibrated scale.

**8.
Complementary method:**

In this method the value of the quantity
to be measured is combined with a known value of the same quantity. The
combination is so adjusted that the sum of these two values is equal to
predetermined comparison value. For example, determination of the volume of a
solid by liquid displacement.

**9.
Method of measurement by substitution:**

It is a method of direct comparison in
which the value of a quantity to be measured is replaced by a known value of
the same quantity, so selected that the effects produced in the indicating
device by these two values are the same.

**10.
Method of null measurement:**

It is a method of differential
measurement. In this method the difference between the value of the quantity to
be measured and the known value of the same quantity with which it is compared
is brought to zero.

Tags : Mechanical - Metrology and Measurements - Concepts of Measurement

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