National Physical Laboratory, India

The National Physical Laboratory of India, situated in New Delhi, is the measurement standards laboratory of India. It maintains of SI units in India and calibrates the national standards of weights and measures

History of measurement systems in India

One of the most ancient texts of India, "Manusmriti", describes among the duties of the king: "The king should examine the weights and balances every six months to ensure true measurements and to mark them with the royal stamp." -- "Manusmriti", 8th Chapter, Shloka 403. In the Harappan era, which is nearly 5000 years old, one finds excellent examples of town planning and architecture. The sizes of the bricks were the same all over the region. In the time of Chandragupta Maurya, some 2400 years ago, there was a well - defined system of weights and measures. The government of that time ensured that everybody used the same system. In the Indian medical system, Ayurveda, the units of mass and volume were well defined.

The measurement system during the time of the Mughal emperor, Akbar, the "gaz" was the measure of length. The "gaz" was widely used till the introduction of the metric system in India in 1956. During the British period, efforts were made to achieve uniformity in weights and measures. A compromise was reached in the system of measurements which continued till India's independence in 1947. After independence in 1947, it was realized that for fast industrial growth of the country, it would be necessary to establish a modern measurement system in the country. The Lok Sabha in April 1955 resolved : "This house is of the opinion that the Government of India should take necessary steps to introduce uniform weights and measures throughout the country based on metric system".

History of the NPL

The National Physical Laboratory is one of the earliest national laboratories set up under the Council of Scientific & Industrial Research. Jawaharlal Nehru laid the foundation stone of NPL on the 4 January 1947. Dr. K. S. Krishnan was the first Director of the laboratory. The main building of the laboratory was formally opened by Former Deputy Prime Minister Sardar Vallabhbhai Patel on 21 January 1950. Former Prime Minister Indira Gandhi, inaugurated the Silver Jubilee Celebration of the Laboratory on 23 December 1975.

NPL charter

The main aim of the laboratory is to strengthen and advance physics-based research and development for the overall development of science and technology in the country. In particular its objectives are:
*To establish, maintain and improve continuously by research, for the benefit of the nation, National Standards of Measurements and to realize the Units based on International System (Under the subordinate Legislations of Weights and Measures Act 1956, reissued in 1988 under the 1976 Act).
*To identify and conduct after due consideration, research in areas of physics which are most appropriate to the needs of the nation and for advancement of field
*To assist industries, national and other agencies in their developmental tasks by precision measurements, calibration, development of devices, processes, and other allied problems related to physics
*To keep itself informed of and study critically the status of physics.

Maintainer of standards of measurements in India

Each modernized country, including India has a National Meteorological Institute (NMI), which maintains the standards of measurements. This responsibility has been given to the National Physical Laboratory, New Delhi.

Metre

The standard unit of length, metre, is realized by employing a stabilized helium - neon laser as a source of light. Its frequency is measured experimentally. From this value of frequency and the internationally accepted value of the speed of light (299,792,458 metres/second), the wavelength is determined using the relation:

Wavelength = Velocity of light / frequency

The nominal value of wavelength, employed at NPL is 633 nanometer. By a sophisticated instrument, known as an optical interferometer, any length can be measured in terms of the wavelength of laser light.

The present level of uncertainty attained at NPL in length measurements is ± 3 × 10^-9. However in most measurements, an uncertainty of ± 1 × 10^-6 is adequate.

Kilogramme

The Indian national standard of mass, kilogramme, is copy number 57 of the international prototype kilogram supplied by the International Bureau of Weights and Measures (BIPM : French - Bureau International des Poids et Mesures), Paris. This is a platinum iridium cylinder whose mass is measured against the international prototype at BIPM. The NPL also maintains a group of transfer standard kilograms made of non - magnetic stainless steel and nickel - chromium alloy.

The uncertainty in mass measurements at NPL is ± 4.6 × 10^-9.

Second

The national standard of time interval, second as well as frequency, is maintained through four parameters, which can be measured most accurately. Therefore, attempts are made to link other physical quantities to time and frequency. The standard maintained at NPL has to be linked to different users. This process, known as dissemination, is carried out in a number of ways. For applications requiring low levels of uncertainty, there is satellite based dissemination service, which utilizes the Indian national satellite, INSAT. Time is also disseminated through TV, radio, and special telephone services. The caesium atomic clocks maintained at NPL are linked to other such instituted all over the world through a set of global positioning satellites.

Ampere

The unit of electric current, ampere, is realized at NPL by measuring Volt and Ohm separately.

The uncertainty in measurement of ampere is ± 1 × 10^-6.

Kelvin

The standard of temperature is based on the International Temperature Scale of 1990 (ITS - 90). This is based on the assigned temperatures to several fixed points. One of the most fundamental temperatures of these is the triple point of water. At this temperature, ice, water and steam are at equilibrium with each other. This temperature has been assigned the value of 273.16 kelvins. This temperature can be realized, maintained and measured in the laboratory. At present temperature standards maintained at NPL cover a range of 54 kelvins to 2473 kelvins.

The uncertainty in its measure is ± 2.5 × 10^-4.

Candela

The unit of luminous intensity, candela, is realized by using an absolute radiometer. For practical work, a group of tungsten incandescent lamps are used.

The level of uncertainty is ± 1.3 × 10^-2.

Mole

Experimental work has been initiated to realize mole, the SI unit for amount of substance.

Radiation

The NPL does not maintain standards of measurements for ionizing radiations. This is the responsibility of the Homi Bhabha Atomic Research Centre, Mumbai.

Calibrator of weights and measures

The standards maintained at NPL are periodically compared with standards maintained at other National Meteorological Institutes in the world as well as the BIPM in Paris. This exercise ensures that Indian national standards are equivalent to those of the rest of the world.

Any measurement made in a country should be directly or indirectly linked to the national standards of the country, For this purpose, a chain of laboratories are set up in different states of the country. The weights and measures used in daily life are tested in the laboratories and certified. It is the responsibility of the NPL to calibrate the measurement standards in these laboratories at different levels. In this manner, the measurements made in any part of the country are linked to the national standards and through them to the international standards.

The weights and balances used in local markets and other areas are expected to be certified by the Department of Weights and Measures of the local government. Working standards of these local departments should, in turn, be calibrated against the state level standards or any other laboratory which is entitled to do so. The state level laboratories are required to get their standards calibrated from the NPL at the national level which is equivalent to the international standards.

Research

NPL is also involved in research. One of the important research activities undertaken by NPL is to devise the chemical formula for the indelible ink which is being used in the Indian elections to prevent fraudulent voting. This ink, manufactured by the Mysore Paints and Varnish Limited is applied on the finger nail of the voter as an indicator that the voter has already cast his vote.

See also

* History of measurement systems in India