Metrology Notes for the GATE Exam 2024
Metrology Definition
What do you understand by Metrology?
- It is basically the science of measurement.
- The purpose of this discipline is to establish means of determining physical quantities.
Important Metrology Terminologies
Nominal Size
This is used for general identification purposes and the size of any part is defined during its drawing.
Basic Size
The size of a part to which all limits of variation are applied. It is a theoretical concept.
Actual Size
It is the actually measured dimension of a part.
Note: The difference between basic and actual size should not exceed certain limits otherwise it will interfere with the interchangeability of the mating parts.
- More Notes: GATE Mechanical Engineering
Upper or High or Maximum Limits
It is the largest permissible size for a dimension, out of the two extreme permissible sizes for a dimension.
Lower Limit
It is the lowest permissible size for a dimension.
Tolerance
This is the difference between the upper limit and the lower limit. This is also the maximum permissible variation in a dimension.
Zero Line
A straight line corresponding to the basic size and the deviations are measured from this line.
Deviation
It is an algebraic difference between a size (actual, maximum) and the corresponding basic size.
Actual Deviation
It is the algebraic difference between the actual size and the corresponding basic size.
Upper Deviation
The algebraic difference between the actual size and the corresponding basic size.
Lower Deviation
It is the algebraic difference between the minimum size and the corresponding basic size.
Mean Deviation
It is the arithmetical mean of lower and upper deviations.
Fundamental Deviation
This is the deviation, either the upper or the lower deviation, which is the nearest one to the zero line for either a hole or a shaft.
Unilateral and Bilateral Limits
Unilateral limits occur when both the maximum limit or minimum limit is either above or below the basic size, but in the case of Bilateral limits maximum limit is above and the minimum limit is below the basic size.
- Read Also: Gear Terminology and Basic Definition
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