Methods of Measurements

METHODS OF MEASUREMENTS

 

Measurement is a set of operations done with the aim of determining the value of a quantity which

can be measured by various methods of measurements depending upon the accuracy required and the amount of permissible error.The various methods of measurement are: Direct Method: This is the simplest method of measurement in which the value of the quantity to b
measured is obtained directly without any calculations, e.g., measurements by scales, vernier
calipers, micrometers etc. It involves contact or non-contact type of inspections. Human
insensitiveness can affect the accuracy of measurement.Indirect Method: The value of the quantity to be measured is obtained by measuring other
quantities, which are frequently related with the required value, e.g., angle measurement by sine
bar, density calculation by measuring mass and dimensions for calculating volume.Absolute Method: This is also called fundamental method and is based on the measurement of the
base quantities used to define a particular quantity, e.g., measuring a quantity (length) directly in
accordance with the definition of that quantity.Comparison Method: The value of a quantity to be measured is compared with a known value of
same quantity or another quantity related to it. In this method, only deviations from master gauges are noted, e.g., dial indicators or other comparators.Substitution Method: The quantity is measured by direct comparison on an indicating device by
replacing the measurable quantity with another which produces the same effect on the indicating
device.Coincidence Method: It is also called the differential method of measurement. In this, there is avery
small difference between the value of the quantity to be measured and the reference. The reference is determined by the observation of the coincidence of certain lines or signals, e.g., measurement by Vernier calipers (LC* Vernier scale reading).Transportation Method: It is the method of measurement by direct comparisons in which the value
of the quantity measured is first balanced by an initial known value P of the same quantity. Then the
value of the quantity measured is put in place of that known value and is balanced again by another
known value Q. If the position of the element indicating equilibrium is the same in both cases, the
value of the quantity to be measured is square root of PQ.

Deflection Method: The value of the quantity to be measured is directly indicated by the deflection

of a pointer on a calibrated scale, e.g., dial indicator.

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 (null).