It goes without saying that correct dimensional measurement is a key factor in business. Performing measurements with the same reference throughout all processes-from material reception to processing, assembly, inspection, and shipping-makes it possible to create products that match the design exactly and to guarantee product quality.
TO MEASURE IS: “to compute, estimate, or ascertain the extent, dimensions, or capacity of, especially by a certain rule or standard”- WEBSTER
TO MEASURE IS: “to judge or calculate the quality, importance, amount or value of something”- CAMBRIDGE
MEASUREMENT IS: “process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity”- ISO /IEC GUIDE
MEASUREMENT PROCESS IS”: set of operations to determine the value of a quantity”- ISO 10012
MEASUREMENT IS: “Acquisition of information about a state or phenomenon (object of measurement) in the world around us” -MEASUREMENT THEORY FUNDAMENTALS- Eugene Paperno
MEASUREMENT IS: “Comparison of a given unknown quantity with one of its predetermined standard values adopted as a unit”- ENGINERING METROLOGY AND MEASUREMENTS - ANNA UNIVERSITY
MEASUREMENT IS: “process of experimentally obtaining information about the magnitude of a quantity”- nternational vocabulary of basic and general terms in metrology (VIM)
METROLOGY
METROLOGY IS: “The scientific study of measurement”
METROLOGY IS mainly concerned with
§ UNIT OF MEASURMENT AND THEIR STANDARDS
§ ERRORS OF MEASUREMENT
§ UNIFORMITY OF MEASUREMENT
§ METHODS OF MEASUREMENTS
§ ESTABLISHING UNCERTAINTY OF MEASUREMENT
§ GAUGE DESIGN, MANUFACTURING AND TESTING
§ INDUSTRIAL INSPECTION
Measurement as a process
*The metrological requirements shall be determined based on customer, organization, statutory and regulatory requirements.
*The measurement processes designed to meet these specified requirements shall be documented, validated as appropriate and, if necessary, agreed to with the customer.
*For each measurement process, the relevant process elements and controls shall be identified. The choice of elements and control limits shall be commensurate with the risk of failure to comply with specified requirements. These process elements and controls shall include the effects of operators, equipment, ambient conditions, influence quantities and application methods.
*In specifying the measurement processes, it may be necessary to determine
• What measurements are necessary to ensure the quality of the product,
• The methods of measurement,
• The equipment required to execute the measurement and to define it, and the required skills and qualifications of the personnel performing the measurements.
METHODS OF MEASUREMENT
*Direct Method:
The parameter to be measured is directly compared to a primary standard or a secondary standard, its common use for measurement of basic physical quantities like length, weight and time.
*Indirect Method:
Makes use of some device witch converts quantities into analogous signal; the analogous signal is then processed by an intermediate device and displayed by the output device.
MEASUREMENT INSTRUMENTS
Measurement Instruments can be classified into several classes according to there application, mode of operation, manner of energy conversion and output format
• Deflection and null type instrument
• Analog and digital
• Active and passive
• Automatic and manual
• Absolute and secondary
• Contacting and non-contacting
• Intelligent instruments
UNITS OF MEASUREMENT
*There are a different systems of units available in a different countries like M.K.S and C.G.S,
*The General Conference of Weights and Measures (CGPM) established the “system of international units” (S.I) to assure uniformity of units
*The S.I consists of three categories of units, fundamental, supplementary and derived units
STANDARDS
-Standard is a physical representation of a unit of measurement, a known accurate measure of a physical quantity is termed as standard; these standards are used to determine a value of physical quantity by comparison method.
-Types of standards
I. International standard
II. Primary standard
III. Secondary standard
IV. Working standard
Drift: The variation of output for a giving input over a period of time
Error: The deviation of the true value from the desired value
Tolerance: The maximum allowable error in measurement
Linearity:
The degree to which bias changes with changes in the magnitude of the characteristic measured
Repeatability:
is the variation in measurements obtained
By one appraiser
with one measurement instrument
when used several times
while measuring the identical characteristic
on the same part
Reproducibility:
is the variation in the average of the measurements made
by different appraisers using the same measuring instrument when measuring the identical characteristic
on the same part.
Stability:
The dependability or consistency of the measurement process over time
References
-Encyclopedia of Measurement and Statistics - NEIL J. SALKIND
-Measurement Good Practice Guide - Stephanie Bell
-Engineering Metrology & Measurements - ANNA University
-ISO 10012
-ISO ICE17025
-International vocabulary of metrology - JCM (BIPM, IEC, IFCC,ILAC, ISO, IUPAC, IUPAP and OIML)
-Juran Quality Handbook - Joseph M. Juran
-The Expression of Uncertainty and Confidence in Measurement M3003 UKAS