25-07-2012, 04:47 PM
ENGINEERING METROLOGY AND MEASUREMENTS
54569565-NOTES-ON-Engineering-Metrology-and-Measurements.pdf (Size: 3.55 MB / Downloads: 220)
Introduction to Metrology:
Metrology word is derived from two Greek words such as metro
which means measurement and logy which means science. Metrology is
the science of precision measurement. The engineer can say it is the
science of measurement of lengths and angles and all related quantities
like width, depth, diameter and straightness with high accuracy.
Metrology demands pure knowledge of certain basic mathematical and
physical principles. The development of the industry largely depends on
the engineering metrology. Metrology is concerned with the
establishment, reproduction and conservation and transfer of units of
measurements and their standards. Irrespective of the branch of
engineering, all engineers should know about various instruments and
techniques.
Introduction to Measurement:
Measurement is defined as the process of numerical evaluation of a
dimension or the process of comparison with standard measuring
instruments. The elements of measuring system include the
instrumentation, calibration standards, environmental influence, human
operator limitations and features of the work-piece. The basic aim of
measurement in industries is to check whether a component has been
manufactured to the requirement of a specification or not.
Types of Metrology:
Legal Metrology. 'Legal metrology' is that part of metrology which
treats units of measurements, methods of measurements and the
measuring instruments, in relation to the technical and legal
requirements.
The activities of the service of 'Legal Metrology' are:
(i) Control of measuring instruments;
(ii) Testing of prototypes/models of measuring instruments;
(iii) Examination of a measuring instrument to verify its
conformity to the statutory requirements etc.
1.3.2 Dynamic Metrology. 'Dynamic metrology' is the technique of
measuring small variations of a continuous nature. The technique has
proved very valuable, and a record of continuous measurement, over a
surface, for instance, has obvious advantages over individual
measurements of an isolated character.
Deterministic metrology. Deterministic metrology is a new
philosophy in which part measurement is replaced by process
measurement. The new techniques such as 3D error compensation by
CNC (Computer Numerical Control) systems and expert systems are
applied, leading to fully adaptive control. This technology is used for
very high precision manufacturing machinery and control systems to
achieve micro technology and nanotechnology accuracies.
1.4 Objectives of Metrology:
Although the basic objective of a measurement is to provide the
required accuracy at a minimum cost, metrology has further objectives in
a modern engineering plant with different shapes which are:
1. Complete evaluation of newly developed products.
2. Determination of the process capabilities and ensure that these are
better than the relevant component tolerances.
3. Determination of the measuring instrument capabilities and
ensure that they are quite sufficient for their respective
measurements.
4. Minimizing the cost of inspection by effective and efficient use of
available facilities.
5. Reducing the cost of rejects and rework through application of
Statistical Quality Control Techniques.
6. To standardize the measuring methods:
7. To maintain the accuracies of measurement.
8. To prepare designs for all gauges and special inspection fixtures.
Necessity and Importance of Metrology:
1 The importance of the science of measurement as a tool for
scientific research (by which accurate and reliable information
can be obtained) was emphasized by Ga1ileo and Gvethe. This is
essential for solving almost all technical problems in the field of
engineering in general, and in production engineering and
experimental design in particular. The design engineer should not
only check his design from the point of view of strength or
economical production, but he should also keep in mind how the
dimensions specified can be checked or measured. Unfortunately,
a considerable amount of engineering work is still being executed
without realizing the importance of inspection and quality control
for improving the function of product and achieving the
economical production.