Metrology

Requirements of an Inspection Tool (Metrology)

1.10. The requirements of an ideal inspection tool are : It should be (a) accurate (b) require a minimum of operator skill (c) inspect a specific type of error (d) fast to use (e) Self checking. The degree of accuracy of calibration depends on the accuracy of the inspecting instruments. Devices which reduce dependence on […]

International System of Units (SI) (Metrology)

1.12. It is the system established in 1960 by the (CGPM) General Conference of Weights and Measures and abbreviated as SI (System International d’unites) in all languages. In India, we switched over to metric system of Weights and Measures conforming to SI units by an Act of Parliament No. 89, in 1956. This SI like […]

Role of National Physical Laboratory (NPL) in Metrology (Metrology)

1.13. NPL provides the basic backbone of organizational structure for metrology in India. NPL is the custodian of national measurement standards for physical measurement in the country. This premier national laboratory is established with the objective to strengthen and advance physics- oriented research for the overall development of science and technology in the country. NPL […]

Sources of Errors (Metrology)

1.14. In any measurement, there is always a degree of uncertainty resulting from measurement error, i.e. all measurements are inaccurate to some extent Measurement error is the difference between the indicated and actual values of the measurand. The error could be expressed either as an absolute error or on a relative scale, most commonly as […]

Errors likely to Creep in Precision Measurements—Their Care (Metrology)

1.15. 1.15.1. Effects of Environment—Temperature. Many applications specify tolerances in microns. It may be appreciated that 25 mm of steel will lengthen about 0.3 microns when its temperature is increased by 1°C. Obviously for precision measurements in terms of microns, error of 0.3 microns just by change of 1°C temperature is substantial. It should be […]

Linearity (Metrology)

1.16. The output of a measuring system may be linear or non-linear. As long as the output is repeatable, it can always be calibrated, but for a non-linear system the construction of calibration curve becomes tedious, cumbersome and time-consuming. For a liner system, a simple two or three point calibration is sufficient and recalibration is […]

Principles of High-precision Measurements (Metrology)

1.18. (i) Temperature of measurements needs to be clearly defined. An object placed at 21°C may take more than 10 hours to attain room temperature of 20°C. This is so because temperature decreases exponentially. The process can be quickened by placing the object on a large mass (say, surface place which acts as a heat […]

Rigorous definitions of accuracy and precision (Metrology)

1.17. Say it is required to measure a dimension L. With highly accurate machine, we take several measurements and obtain a distribution (normal centred around mean; strictly speaking, it is distribution which can be approximated with a normal distribution when the sample size or number of measurements is about 30 or greater). The difference 6 […]

Why Precision Measurements are required and Why Struggle for ever increasing Accuracy ? (Metrology)

1.19. The need for reliable data was recognised very early in the developmental science. Fig. 1.20 shows how the experiments have helped in establishing of theoretical postulates, and the experi- ments were possible only with the developments in precision measurements. The logical consequen- ces of preconceived views could be demonstrated by carrying out experiments. Thus […]

Establishing Calibration System (Metrology)

1.20. Market forces demand industry to ensure environment for supply of quality products to customers. Accurate measurements play a crucial role at each stage in the development and production of quality products. The aim of establishing calibration system is to develop internal metrology and calibration programmes to assure that the test and measuring instruments are […]

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