The word metrology has a long tradition and is derived from the Greek word for measure. It is well-known saying that the knowledge about anything is complete only when it can be expressed in numbers and something is known about it. Thus for every kind of quantity measured, there must be a unit to measure it and express it in numbers of that unit. Further, in order that this unit is followed by all and not one who is taking the measurements, there must be a universal standard and the various units for various parameters of importance must be standardised.In metrology, which literally is the science of measurements we have to go one step ahead and bother ourselves about the correctness of measurement also.
Principle of measurement. It is the physical phenomenon utilised in the measurement.
Method of measurement. It is the way the measuring principles and measuring means are used.
Nominal size (Basic Size). It is the size on which the limits of size are based and which is assigned to a part in accordance with its function.
True size. It is the theoretical size of a dimension, which is free from any errors of measurement.
Actual Size. It is the value of size obtained through measurement with the permissible measuring error.
Exact size. It is the value of size obtained with the highest metrological accuracy attainable in practice.
Approximate Size. It is the value of size obtained with an error exceeding the permissible error of measurement and requiring refinement.
Error of measurement. It is the difference between the true value of the size being measured and the value found by measurement. Error pertains to a measurement and not to an
instrument.
Correction. It is the amount which should be algebraically added to the indicated value to
obtain the actual value of the size being measured. The correction is numerically equal to the error,
but opposite in sign.
Correctness of measurement. It is quantitative characteristic showing how close to zero
are the systematic errors of measurement results.
Reliability of measurement. It is a qualitative characteristic which implies confidence in
the measured results depending on whether or not the frequency distribution characteristics of
their deviations from the true values of the corresponding quantities are known.
Verification. It is the process of testing an instrument for the purpose of assessing the
indication errors and determining whether setting standards or measuring instruments meet the
prescribed specifications.
Calibration. It is the process of determining the values of the quantity being measured
corresponding to a pre-established arbitrary scale.
Method of measurement. It is the way the measuring principles and measuring means are used.
Nominal size (Basic Size). It is the size on which the limits of size are based and which is assigned to a part in accordance with its function.
True size. It is the theoretical size of a dimension, which is free from any errors of measurement.
Actual Size. It is the value of size obtained through measurement with the permissible measuring error.
Exact size. It is the value of size obtained with the highest metrological accuracy attainable in practice.
Approximate Size. It is the value of size obtained with an error exceeding the permissible error of measurement and requiring refinement.
Error of measurement. It is the difference between the true value of the size being measured and the value found by measurement. Error pertains to a measurement and not to an
instrument.
Correction. It is the amount which should be algebraically added to the indicated value to
obtain the actual value of the size being measured. The correction is numerically equal to the error,
but opposite in sign.
Correctness of measurement. It is quantitative characteristic showing how close to zero
are the systematic errors of measurement results.
Reliability of measurement. It is a qualitative characteristic which implies confidence in
the measured results depending on whether or not the frequency distribution characteristics of
their deviations from the true values of the corresponding quantities are known.
Verification. It is the process of testing an instrument for the purpose of assessing the
indication errors and determining whether setting standards or measuring instruments meet the
prescribed specifications.
Calibration. It is the process of determining the values of the quantity being measured
corresponding to a pre-established arbitrary scale.
No comments:
Post a Comment