The Temperature Coefficient of Inductances for Use in a Valve Generator

This paper discusses the relative importance of skin effect on the temperature coefficient of inductance. It starts with a definition of inductance which includes explicitly the effect of magnetic field within the wire and analyzes inductance into an internal and external component. It is the internal inductance which has a temperature coefficient which can make the total coefficient greater than that of linear expansion. Its ability to affect the total coefficient obviously depends on the ratio of internal to total inductance. This ratio is assessed for various typical coils of round, solid wire, and found to be seldom less than about 5 per cent. It is also assessed for tubular and flat-strip conductors. The dependence of internal inductance on frequency is explored in general terms, and it is suggested that the product of high-frequency resistance and internal inductance tends to be constant for all conductors. An expression is derived for the ratio of the total temperature coefficient of a typical coil to that of linear expansion; it is shown that this ratio may well be four or five but that it need never exceed unity appreciably if the radius of the wire is chosen suitably with respect to the frequency. Some general rules are given for this choice. Finally three methods of constructing coils on a ceramic former are compared in relation to the temperature coefficient.