Releasing times of telephone relays

This is a study of the factors determining the time which elapses between the cessation of current in a relay winding and the return of the contacts to their normal condition, particularly in relays fitted with a copper slug to produce a slow release. The author obtains an expression showing that the releasing time for a given relay and slug depends mainly upon the logarithm of the ratio of the initial excitation to the current at which the relay releases, and shows by experimental results that the release time can be predicted and can for any given relay be kept within any desired limits by controlling the excitation and release current. Curves are also given showing how the release time varies with duration of excitation.