XXIII.The primary standard of mutual inductance of the National Physical Laboratory

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.

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On the determination of the absolute unit of resistance by alternating current methods

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1912.0094 ◽

1912 ◽

Vol 87 (597) ◽

pp. 391-414 ◽

Cited By ~ 4

Keyword(s):

Lower Order ◽

Alternating Current ◽

National Physical Laboratory ◽

Mutual Inductance ◽

Electrical Circuits ◽

Physical Laboratory ◽

Absolute Measure ◽

The Absolute ◽

Set Up

1. Introductory .—Recently at the National Physical Laboratory we have constructed a standard of mutual inductance of novel type, whose value has been accurately calculated from the dimensions. This inductance has formed the basis for the determination of the unit of resistance in absolute measure by two different methods, in both of which alternating current is employed. Although there is no doubt that the accuracy attainable by these methods could be increased by greater elaboration of the apparatus used, the results already obtained seem to be of sufficient interest to warrant publication. It should be mentioned that the accuracy here aimed at was of a considerably lower order than that contemplated in the determination of the ohm by the Lorenz apparatus which is at present being carried out in the laboratory. For the experiments here described, no apparatus was specially constructed, but use was made of instruments which had already been designed and set up for the measurement of inductance and capacity. I shall first give a brief description of the standard inductance and then pass on to the methods and results. 2. Standard Mutual Inductance .—The design of the mutual inductance has already been described. The electrical circuits have the form and arrangement shown in section in fig. 1.

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The valve maintained tuning fork as a primary standard of frequency

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1934.0003 ◽

1934 ◽

Vol 143 (849) ◽

pp. 285-306 ◽

Cited By ~ 14

Keyword(s):

Radio Frequency ◽

Tuning Fork ◽

Primary Standard ◽

Frequency Standard ◽

National Physical Laboratory ◽

Continuous Operation ◽

Normal Value ◽

Rapid Advance ◽

Satisfactory Performance ◽

Physical Laboratory

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.

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On a standard of mutual inductance

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1907.0053 ◽

1907 ◽

Vol 79 (532) ◽

pp. 428-435 ◽

Cited By ~ 18

Keyword(s):

National Physical Laboratory ◽

Mutual Inductance ◽

Electrical Measurements ◽

Working Standard ◽

Standard Unit ◽

Magnetic Testing ◽

Physical Laboratory ◽

Rayleigh Method ◽

Geometrical Dimensions ◽

Commutator Method

1. Introductory .—In many electrical measurements, such as those of capacity and inductance, as well as in the magnetic testing of iron, an accurately known standard of mutual inductance is of great value. It is sometimes convenient to derive such a standard from the standard unit of resistance, and this may be done in several ways, for example, by the well-known method of the ballistic galvanometer; or by Carey Foster’s method the mutual inductions may be tested against a condenser whose capacity has been found in terms of resistance and frequency by Maxwell’s commutator method; or it may be obtained directly in similar terms by the help of an unknown inductance by the Hughes-Rayleigh method. In the National Physical Laboratory I have used both of these latter methods (with the help of a vibration galvanometer) to obtain a working standard of mutual inductance. But this procedure is somewhat illogical, seeing that the unit of resistance has been itself commonly determined by the aid of mutual inductances calculated from the dimension of the coils or other conductors used; thus for the highest accuracy it is desirable to revert to a standard whose value can be determined solely from the geometrical dimensions. Accordingly, some eighteen months ago, I took in hand the investigation of a suitable design for such a standard, and I proceed to describe the result at which I arrived.

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Establishment of air piston gauge as primary pressure standard at CSIR-National Physical Laboratory INDIA

ACTA IMEKO ◽

10.21014/acta_imeko.v9i5.994 ◽

2020 ◽

Vol 9 (5) ◽

pp. 329

Author(s):

Vikas N. Thakur ◽

Sanjay Yadav ◽

Ashok Kumar

Keyword(s):

Primary Standard ◽

Effective Area ◽

National Physical Laboratory ◽

Area Measurement ◽

Internal Diameter ◽

Piston Cylinder ◽

Piston Gauge ◽

Si Units ◽

Physical Laboratory ◽

Pressure Standard

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.

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Extending the frequency range of the National Physical Laboratory primary standard laser interferometer for hydrophone calibrations to 80 MHz

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control ◽

10.1109/58.764860 ◽

1999 ◽

Vol 46 (3) ◽

pp. 737-744 ◽

Cited By ~ 43

Author(s):

T.J. Esward ◽

S.P. Robinson

Keyword(s):

Laser Interferometer ◽

Primary Standard ◽

National Physical Laboratory ◽

Frequency Range ◽

Physical Laboratory ◽

Standard Laser

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On a method of comparing mutual inductance and resistance by the help of two-phase alternating currents

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1908.0103 ◽

1908 ◽

Vol 81 (549) ◽

pp. 450-452

Keyword(s):

National Physical Laboratory ◽

Mutual Inductance ◽

Two Phase ◽

Physical Laboratory ◽

Absolute Measure ◽

Commutator Method ◽

Capacity Of A Condenser ◽

The Ideal

A standard mutual inductance, after the design recently described by the writer, has now been constructed at the National Physical Laboratory. As the details of its construction will be published later, it is sufficient here to mention that its value calculated from the dimensions is 10.0178 millihenries. It forms an extremely accurate standard, against which both mutual and self inductances can be readily tested. In addition to this, it affords a means of obtaining values of resistance coils in absolute measure, and thus evaluating the ohm. This can be done in an indirect way by finding the capacity of a condenser in terms of resistance and time by Maxwell’s Commutator Method, and in terms of resistance and mutual inductance by Heydweiller’s modification of Carey Foster’s method. The comparison of resistance with mutual inductance can, however, be made far more simply and directly by the use of two-phase alternating currents in the method which I proceed to describe. I shall first take the ideal simple case, and afterwards notice some of the difficulties that may arise in practice. (2) Theory of the Medhod. In fig. 1 let M be the mutual inductance (a small fraction of it being adjustable) and R the resistance; and let A cos pt and B sin pt be currents in quadrature, e. g ., from a two-phase alternator or a phasesplitting device. Let G be a vibration galvanometer tuned to frequency n where p = 2 πn .

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