The measurement of the self-inductance of variable air condensers
W H Ward · Journal of Scientific Instruments · 1936
Three methods are described by which the self-inductance of variable air condensers may be measured. In the first, a rectangular coil is connected to the condenser, and the total inductance of the circuit is found when the coil is short-circuited at a number of points along its length. The self-inductance of the condenser is found by extrapolating to zero length of the coil. The necessary correction to allow for the capacitance of the coil is discussed, and a method of finding it is described. The second method consists in short-circuiting the terminals of the condenser under test, and finding the frequency of resonance of the circuit so formed. The inductance of the air condenser can then be calculated from the capacitance and the frequency of resonance. In the third method, the effective capacitance of the condenser under test is compared at two frequencies, one low and the other high, with the effective capacitance of a special air condenser of negligible inductance. From the change of effective capacitance with frequency the self-inductance may be deduced. The results obtained by the three methods are shown to be in good agreement. The effect of various sizes of wire as short-circuiting link in the second method is shown, and some results are given on the variation of self-inductance with setting of variable air condensers.