scholarly journals The valve maintained tuning fork as a primary standard of frequency

In 1922 an investigation was carried out at the National Physical Laboratory to determine the constancy of frequency that could be expected from a valve maintained tuning fork. It was found that the fork was capable of operating with a degree of steadiness of frequency which was greater than was then necessary for most purposes. The investigation resulted in the design of a 1000 cycles per second fork which served as the Laboratory frequency standard until 1931. For precision work it was necessary to measure the frequency of the fork during the observations by comparison with a standard Shortt clock ; but if the accuracy required was less than 2 parts in 10 5 it was sufficient to apply a correction for temperature to the nominal value of the fork frequency. With the rapid advance in radio frequency technique and the ever-increasing number of wireless transmitting stations the problem of frequency standardization became increasingly important; and it was decided to instal a standard, which should be in continuous operation at a frequency within I part in 10 6 of its normal value. As the most suitable frequency for use in conjunction with the existing equipment for the measurement of radio frequencies was 1000 cycles per second, and as the tuning fork had hitherto given a satisfactory performance, it was decided to continue the investigation on the fork to determine whether it could form a frequency standard of the desired degree of accuracy.

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 329
Author(s):  
Vikas N. Thakur ◽  
Sanjay Yadav ◽  
Ashok Kumar

The air piston gauge (APG) was established at CSIR-National Physical Laboratory, India (NPLI) since 2000. Later the same piston- cylinder(p-c) assembly was calibrated in NIST USA; however, it was never published for metrology communities. As per international protocol, the establishment of the APG as a primary standard, the effective area of p-c assembly, and masses must be directly traceable to SI units. The first time we have calculated the effective area and associated uncertainty of p-c assembly using dimension and mass metrology, traceability to the SI units, i.e., meter and kilogram. To realize the APG as primary pressure standards, we have calculated the effective area of p-c assembly of APG directly from dimension metrology, which is further supported by various other methods. The effective area values obtained in the pressure range of 6.5 – 360 kPa lie in the range of 3.356729 – 3.357248 cm² due to uncertainty limitation in the measurement of dimension of internal diameter of cylinder. The expected values of the effective area which are also measured from cross-float technique against ultrasonic interferometer manometer (UIM), primary pressure standards. The accuracy in effective area measurement is possible only when the resolution in the internal radius of the cylinder should at least be up to 5th decimal order and the uncertainty is 80 nm. The expanded uncertainty was measured nearly 11 ppm at <em>k</em> = 2 by considering the uncertainty in internal radii of cylinder and radii of piston around 80 nm.


Author(s):  
A. Cook

Fellows of The Royal Society have been concerned with the definition and measurement of time from the first days of the Society. John Flamsteed, F.R.S., ‘Royal Astronomer’, showed that the rotation of the Earth was isochronous and that the length of the solar day varied with the season because the path of the Earth about the Sun was an ellipse inclined to the Equator of the Earth. In the 20th century, D.W. Dye, F.R.S., made quartz oscillators that replaced mechanical clocks, and L. Essen, F.R.S., brought into use at the National Physical Laboratory the first caesium beam frequency standard and advocated that atomic time should replace astronomical time as the standard. The Society supported the development of chronometers for use at sea to determine longitude, and Fellows used the electric telegraph to find longitude in India. Edmond Halley, F.R.S., estimated the age of the Earth from the saltiness of lakes and seas; Lord Kelvin, F.R.S., estimated the rate at which energy was being radiated from the Sun; and Lord Rutherford, F.R.S., showed how the ages of rocks and of the Earth could be found from decay of radioactive minerals in them.


The standard mutual inductance devised and designed by Mr. A. Campbell and constructed in 1907-8 at the National Physical Laboratory has been one of the foundations of our alternating current measurements since that date. It will be sufficient here to note that the special feature in the design of the Campbell type of mutual inductance consists in a primary single-layer winding, so proportioned that the field due to it is practically zero over the region occupied by the secondary coil. By this means the dimensions of the secondary coil are rendered relatively unimportant, so that it may be an overwound many-layer winding, whereby a suitably large value of mutual inductance may be obtained.


The Bureau of Standards, Washington, U. S. A., emits from its station at Beltsville, WWV, a few miles from Washington, a standard frequency of reference by which other organizations and individuals can measure the frequency of their own apparatus. The frequency is 5 million cycles per second, and its departure from the nominal value is not expected to exceed 1 cycle per second. The frequency of emission is compared continuously with that of the standard equipment at the Bureau and is monitored so as not to differ from that frequency by more than 1 part in 10 8 . The value of the frequency has been determined at the National Physical Laboratory, Teddington, on a number of occasions. The observations have afforded information as to the agreement of standards of frequency in the two countries, and show with what accuracy the frequencies of two different standards can be compared by the use of emissions at a radio frequency. Some information is also obtained concerning the effect of the intervening medium on the propagation of an emission at this frequency.


MAPAN ◽  
2021 ◽  
Author(s):  
Sanjay Yadav ◽  
Goutam Mandal ◽  
V. K. Jaiswal ◽  
D. D. Shivagan ◽  
D. K. Aswal

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