Standard, Magnetic

a standard (etalon) that is used to reproduce and preserve the legal value of a unit of a magnetic quantity, that is, the value established by a state standard (gosudarstvennyi standart), or GOST. Magnetic standards ensure the uniformity of magnetic measurements.

The fundamental characteristics of a magnetic field or a magnetic material are magnetic flux, magnetic flux density, and magnetic moment. The units of the three magnetic quantities are reproduced by national standards (gosudarstvennye etalony).

The unit of magnetic flux in the International System of Units (SI) is the weber (Wb). The standard for the unit is a coil with two windings on a quartz core. When a current is passed through the primary winding, a magnetic field is generated in that winding; the field permeates the plane of the turns of the secondary winding. The magnetic flux linkage between the secondary and primary windings when the current in the primary winding is equal to 1 ampere (A) gives the value of the magnetic flux in the standard. The system used with the magnetic flux standard includes equipment for transferring the size of the unit to secondary and working standards. The constant of the standard’s coil is determined as the ratio of the magnetic flux to the current that generates the flux in the primary winding; the rated value of the constant is equal to 0.0100176 Wb/A. The error in determining the constant is not higher than 0.001 percent. The error in transferring the size of the unit of magnetic flux does not exceed 0.01 percent.

The SI unit of magnetic flux density is the tesla (T). The standard for the unit consists of three solenoids on a quartz core. The magnetic flux density induced in the central part of each solenoid is equal to 7.5 × 10^–4, 1.15 × 10^–4, and 0.57 × 10^–4 T, respectively. The effect of the earth’s magnetic field is neutralized by a special system of coils. The error in reproducing the unit does not exceed 0.0004 percent. The size of the unit of magnetic flux density is transferred to secondary and working standards with an error of not higher than 0.0005 percent.

The SI unit of magnetic moment is the ampere meter squared (Aηm²). The standard for the unit comprises nine permanent magnets in the shape of ellipsoids of revolution. The magnetic moments of the magnets are determined by means of a standard magnetometer; they range from 0.14 to 1.7 Aηm². The error in reproducing the unit of magnetic moment does not exceed 0.1 percent.

Research is in progress on the development of a single magnetic standard that could reproduce all three fundamental magnetic units.