The Measurement of Choke Coil Inductance

The investigation described has emphasized the facts that: (1) The inductance of the choke coil depends upon the degree to which its core is magnetically saturated because of direct current flowing through its winding. (2) With a given direct current flowing through the winding of a choke coil, the inductance varies to a marked extent with the magnitude of the alternating current flowing through the winding. Methods of measurement which do not take into account or measure the magnitude of the alternating current are, therefore, unreliable. (3) The inductance for given conditions may be determined from the saturation curve of the coil. It is determined by the average slope of the saturation curve over the range within which the current varies. Three modifications of the ammeter-voltmeter method of measuring inductance are presented: (1) The circuit used in thefirst modification of this method is applicable where only a few approximate measurements are to be made and where simplicity of connection is of the greatest importance. (2) The second modification of the method involves simplicity of connection and permits of greater accuracy of measurement than does the first modification, but where a large number of measurements are to be made, it involves inconvenience of manipulation. (3) The third modification of the ammeter-voltmeter method of measuring the inductance of choke coils involves the use of apparatus not always available, but permits of accuracy of measurement and convenience of manipulation.