Engineering Metrology
DR: Eman Khtab
Introduction
• Metrology is a science of measurement.
• Metrology is a lso concerned with the
industrial inspection and its various
techniques.
• Measurement is a process of comparing
inputs with predefined standard and
giving the output.
• For every kind of quantity measured,
there must be a unit to measure it.
Definitions
• The word metrology is derived from two Greek words
Metro=measurement and Logy=science
• Thus metrology is the science of measurement
• Metrology is the field of knowledge concerned with
measurement and includes both theoretical and
practical problems with reference to measurement.
• Metrology is the science of weights and measures
• Metrology is the process of making precise
measurements of the relative positions and
orientations of different optical and mechanical
components
• Metrology is the science concerned with the
establishment, reproduction, conversion and transfer
of units of measurement and their standards
Need For Measurement
• To convert physical parameters into meaningful numbers.
• To determine the true dimensions of apart.
• To increase our knowledge and understanding of the
world.
• Needed for ensuring public health and human safety.
• To test if the elements that constitute the system function
as per the design.
• For evaluating the performance of a system.
• To ensure interchangeability with a view to promoting
mass production.
• To establish the validity of design and for finding new data
and new designs
Need of Inspection
• To ensure the material, parts and components conform
to the established standards
• To meet the interchangeability of manufacture
• To provide the means of finding the problem area for
meeting the established standards
• To produce the parts having acceptable quality levels
with reduced scrap and wastage
• To purchase good quality of raw materials, tools and
equipment that govern the quality of finished products
• To take necessary efforts to measure and reduce the
rejection percentage
• To judge the possibility of rework of defective parts
Elements of Metrology
Standard
• The most basic element of measurement is standard
without which no measurement is possible.
• Standard is a physical representation of unit of
measurement.
• Different standards have been developed for various units
including fundamental units as well as derived units.
Workpiece
• Workpiece is the object to be measured/measured part
• Variations in geometry and surface finish of the measured
part directly affect measuring system’s repeatability
• Compressible materials like plastic or nylons pose a
different type of problem that any gauge pressure will
distort the material. This can be avoided by fixing of
gauging pressure as suggested by the industry so that
everyone will get uniform results
Elements of Metrology
Instruments
• Instrument is a device with the help of which the
measurement can be done
• The instrument must be selected based on the
tolerance of the parts to be measured, the type of
environment and the skill level of operators
• It should be remembered that what type of
instruments the customer prefer to measure.
Person
• There must be some person or mechanism to carryout
the measurement
• Modern gauges are increasingly easy to use but the
failure to adequately train the operating personnel will
lead a poor performance
Elements of Metrology
Environment
• The measurement should be performed under
standard environment
• Temperature, dirt, humidity and vibration are
the four environmental factors that influence
measurement.
• Vernier scale division of vernier caliper always
changes when the measurement process is
carried for ‘n’ number of times for the same
dimension. The environment is indirectly related
to temperature, humidity, conditioning etc.,
Types Of Metrology
• Industrial Metrology-Industrial metrology’s
purpose is to ensure that instruments, used in a
wide variety of industries, are functioning
properly.
• Scientific Metrology-This form of metrology deals
with the organization and development of
measurement standards and with their
maintenance.
• Legal Metrology-Concerned with the
measurements that influence economic
transactions, legal metrology is a very refined
type of metrology.
Objectives of Metrology
• Complete evaluation of newly developed
products.
• Determination of the process capabilities
• Minimizing the cost of inspection by effective and
efficient use of available facilities.
• Reducing the cost of rejects and rework through
application of Statistical Quality Control
Techniques.
• To standardize the measuring methods
• To maintain the accuracies of measurement.
• To prepare designs for all gauges and special
inspection fixtures
Generalized Measuring System
Components of Generalized
Measurement System
A generalized measurement system consists of
the following components:
• Primary Sensing Element
• Variable Conversion Element
• Variable Manipulation Element
• Data Processing Element
• Data Transmission System
• Data Presentation Element
Components of Generalized
Measurement System
Components of Generalized
Measurement System
Components of Generalized
Measurement System
Components of Generalized
Measurement System
The liquid or gas filled temperature bulb acts as primary
sensing element and variable conversion element. It
senses the input quantity(temperature) and converts it
into a pressure built up within the bulb. This pressure is
transmitted through the capillary tube (which acts as
data transmission element) to a spiral bourdon type
pressure gauge. Bourdon tube acts as a variable
conversion element which converts the pressure into
displacement. The displacement is manipulated as a
variable manipulation element. The pointer and scale
indicate the temperature, thus serving as data
presentation elements.