MEASURING
POINT
Metrology
deals with the measurement of 3-D objects and is crucial for establishing
and maintaining quality standards, says R Ramakrishnan
Accurate
measuring equipment plays a vital role in enhancing the quality of manufacturing
products.Measurements are needed in all stages of the value chain that
a product undergoes before it is ready for the market.The complexity,
type and accuracy of a measurement is dependent on the product and the
raw materials used.
MAKING
THE RIGHT CHOICE
One
should bear in mind that the primary function of metrological instruments
is not to enhance productivity but to engender quality assurance. Investments
made for these instruments should justify the cost against the quality
achieved.The other factors that govern the selection of measuring equipment
would be – choice of equipment depending upon the size of the component,
ease of measurement and evaluation of the process of measurement. The
size and weight of the object to be measured is also an important factor
in the selection of type of measuring instrument.
Checking
of just one linear measurement like length, diameter and height can
be carried out with instruments like micrometers, verniers and height
gauges without a major cost implication. Sections of components and
co-ordinate distances to be measured may involve equipment like profile
projectors, CMM or video vision systems and involve considerable costs
before implementation.
CONTACT
OR NON-CONTACT?
Elements
like length, width and height can be measured by different means like
contact and non-contact methods.Contact measurement relates to a measurement
made by the instrument directly in contact with the object when measurements
are taken, whereas non-contact measurement is used for measuring components
which are flexible to touch. Micrometers, verniers, height gauges, ring
gauges, internal micrometers, snap gauges,CMMs, and many more equipment
of this order continue to be the most sophisticated contact measuring
instruments.
Non-contact
measuring instruments comprise systems like ultrasonic scanners, profile
projectors, video vision inspection systems and laseroperated inspection
equipment. Certain special parameters like involute profiles and helix
angle of gears can be measured more precisely and accurately with dedicated
instruments like gear testers. These dedicated inspection systems give
better reliability of measured values, compared to general inspection
equipment.
UNCERTAINTY
OF MEASUREMENT
Measuring
the diameter of a pin with the help of a profile projector would be
possible but the uncertainty of measurement by using this optical equipment
for the inspection parameter required would be higher.Measurements made
with simple micrometers yield faster and ....
.........CONTD
