2nd YEAR (MECHANICAL)
Definition of metrology
History of measurement
Importance of measurement System
Function of inspection department
Advantages of inspection department
Tools for inspection
DEFINITION OF METROLOGY
Metrology is the science of Measurement.
Metrology is the science concerned with the establishment,
reproduction, conversion & transfer of units.
Types of Metrology
HISTORY OF MEASUREMENTS
There are mainly three quantities which are use to
measure, named as :
Length is the most necessary measurement in everyday life.
There are many units of length, for example:
The most recently and widely used unit of length is meter
It is defined as the distance between two lines on a specific platinum–
iridium bar stored under controlled conditions.
There are many units to measure a quantity named as mass.
But the most widely used unit to measure mass is gram.
Gram was originally derived from the mass of one centimeter cube of
In 1887 the unit of mass Kilo Gram (KG) is defined as the mass of a
specific platinum–iridium alloy cylinder kept at the International
Bureau of Weights and Measures at Sevres, France.
Before 1960, the standard of time was defined in terms of the mean
solar day for the year 1900.
“A solar day is the time interval between successive appearances of
the Sun at the highest point it reaches in the sky each day.”
In 1967, the second was redefined which uses the characteristic
frequency of the cesium-133 atom as the “reference clock.”
The second (s) is now defined as 9 192 631 770 times the period of
vibration of radiation from the cesium atom.
There are three standard systems which are used to measure
any quantity, named as:
The metric system, more more formally called the meter-kilogramsecond (MKS or mks) system of units, is based on three fundamental
The meter (m) that quantifies displacement.
The kilogram (kg) that quantifies mass.
The second (s or sec) that quantifies time.
The metric system is formally replaced by the very similar Standard
International System of Units ( SI ).
The centimetre–gram–second system (abbreviated CGS or cgs) is a
variant of the metric system of physical units.
It is based on:
1. Centimetre as the unit of length.
2. Gram as a unit of mass.
3. Second as a unit of time.
The sizes of many CGS units turned out to be inconvenient for
The units gram and centimetre remain useful as Prefixed units
within the SI system.
The foot–pound–second system or FPS system is a system of units
built on the three fundamental units.
Foot for length.
Pound (avoirdupois) for either mass or force.
Second for time.
It is also called British Engineering System.
FUNCTION OF INSPECTION
An inspection determines if the material or item is in
proper quantity and condition and if it conforms to the
applicable or specified requirements.
Inspection is generally divided into three categories:
1) Receiving inspection
(2) In-process inspection
(3) Final inspection
In quality control (which is guided by the principle that
"Quality cannot be inspected into a product")
The role of inspection is to verify
and validate the variance data, it does not involve
separating the good from the bad.
ADVANTAGES OF INSPECTION
Inspection are used in most of fields which shows the advantages
of inspection department. Some are as follows :
1. IN GOVERNMENT
In government and politics, an inspection is the act of a monitoring
authority administering an official review of various criteria (such as
documents, facilities, records, and any other assets) that are deemed
by the authority to be related to the inspection.
2. IN ROAD VEHICLES
A vehicle inspection, e.g., an annual inspection, is a necessary
inspection required on vehicles to conform with laws regarding
safety, emissions, or both.
3. IN ENGINEERING (MECHANICS)
Quality related inspection is an essential part of quality control.
A mechanical inspection is usually undertaken to ensure the safety or
reliability of structures or machinery.
4. IN MEDICAL
A medical inspection is the thorough and unhurried visualization
of a patient, this requires the use of the naked eye.
5. IN Real Estate
A property inspection is the examination for purposes of
evaluating a property's condition. In purchasing property,
a "whole house inspection" tries to detect defects in the
TOOLS FOR INSPECTION
There are many tools for inspection but some tools are describe as under:
There are several different types of calipers
designed to measure length, depth, internal, and
external dimensions. Calipers can also be used to
transfer dimensions from one object to another.
Take an internal diameter measurement or compare
to a pre-determined standard.
Used only to compare an object to a standard,
fixed gages can measure attributes such as angle,
length, radius, bore size, thickness, and other
These dimensional inspection hand tools
can use mechanical, digital, laser, dial,
or scale technology to precisely measure
length, depth, thickness, diameter, height,
roundness, or bore.
Measure angles with a variable protractor
or compare the angle of an object to a
standard with an angle gage.
6.Indicator and Comparator
The precision movement of a spindle or probe is amplified so the
results can be displayed digitally or on a dial or column.
7.Air metrology Instruments
Thickness, depth, diameter, roundness, taper, and bore can be
measured by calculating changes in pressure or air flow.
Typically used as a pass/fail test, ring gages
can be threaded, smooth, or tapered to test
the size of pins, threaded studs, and shafts.
Electronic or mechanical, these devices
are used to measure or compare the length
of an object.
The spacing, shape, size, and geometry of
a thread can be verified or measured with a
A measuring instrument is a device for measuring
a physical quantity.
Measuring devices are classified as:
Angular measuring devices
Linear measuring devices
1. ANGULAR MEASURING
There are a wide variety of geometric features that are
measured in angular units. These varieties include angular
separation of bounding planes, angular spacing conditions
related to circle, digression from a basic direction etc.
It has further two types :
i. Line Standard Angular Measuring Device
ii. Face Standard Angular Measuring Devices
Line Standard Angular
It is the simplest instrument for measuring angles between two faces.
It consists of two arms and an engraved circular scale.
The two arms can be set along the faces between which the angle is to
2. Universal Bevel Protractor
It is an angular measuring instrument
capable of measuring angles to within 5
The name universal refers to the
capacity of the instrument to be
adaptable to a great variety of work
configurations and angular
It consists of a base to which a vernier
scale is attached.
ii. FACE STANDARD ANGULAR
A sine bar consists of a hardened, precision ground body with two
precision ground cylinders fixed at the ends.
The axes of the two rollers are parallel to each other.
The operation of a sine bar is based on known trigonometric
relationship between the sides and the angle of a right angle
The angle is calculated by using the sine rule.
Sine block itself is not a measuring instrument. It acts as
an important link in the angle measuring process.
2. LINEAR MEASURING
Vernier Caliper can be used to
measure diameter, thickness very
Different Parts of Vernier Caliper
Micrometer is one of the most widely used precision
instruments. It is primarily used to measure external
dimensions like diameters of shafts, thickness of parts etc.