an inductance coil used in electrical measurements and in testing and calibrating measuring devices. Inductance standards are characterized by constant inductance; by the nondependence of inductance on amplitude or frequency of the current and minimal dependence on temperature, humidity, and time; and by minimal effective resistance.
A distinction is made among constant-value, or single-value, standards (single inductance coils); sets of inductance standards; and standards with variable value (inductance variometers). Inductance standards are used in AC circuits with frequencies up to 1,500 hertz (Hz). They are made exclusively in the form of coils of constant inductance, which are used as quality factor meters in the frequency range from 0.5 to 50 MHz.
An inductance coil is an insulated copper wire wound on a frame made of a dielectric. To provide independence from temperature and time, inductance coils are made on the basis of ceramic toroids, with a winding deposited by the galvanic method; the inductance of the coil is determined by the number of turns and the geometric dimensions of the winding. Standard coils are made with an inductance of fractions of a millihenry to 1 henry.
As a rule, inductance sets consist of several tapped coils. Such sets may provide smooth or stepped regulation of inductance and may have switching provisions for combining inductances. Variometers are used mainly for smooth adjustment of inductance.