Estimation and Control of the Operate Time of Relays: Part I - Theory

The operate and release times of most telephone relays lie in the range from 1 to 100 millisecs. (0.001 to 0.100 sees.). To use these relays in telephone switching, involving complex patterns of sequential switch 109 110 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1 9 5 - 1 and relay operation, it is necessary: (1) to be able to estimate the operate and release times of any relay for which this information is needed in circuit studies, and (2) to develop relays capable of meeting specific timing requirements, both fast and slow. The essential basis for such design and estimation is a dynamic theory of the operation of electromagnets, of sufficient accuracy for engineering use. The theory presented here is applicable to electromagnets in general, although the applications discussed are those relating to relays. The theory presented is approximate, partly because of the difficulty of providing a more exact, treatment, and partly because simplicity and generality are more important for engineering purposes than accuracy in estimation, which is in any case subject to correction by measured results. The theoretical relations are used alone only in preliminary estimation and in the initial stages of development, as discussed in Part I of this article. In advanced development and in the modification and application of existing structures, as discussed in Part II, the theory is used as a guide in the correlation and extrapolation of observed performance. The dynamics of electromagnets involve the concurrent and interrelated phenomena of field development and armature motion, and are accordingly governed by the two differential force equations respectively applying, each containing a coupling term expressing their reaction on each other.