Analysis of Measured Magnetization and Pull Characteristics

Iii the design of telephone relays and similar switching apparatus, the characteristics of the electromagnet which serves as motor element may be distinguished from those of the mechanical system of contact springs and actuating members which it operates. The performance of the electromagnet is characterized statically by the mechanical work done for a given coil energization, and dynamically by the time required to actuate the mechanical load, including in this the inertia of the moving parts. Both the potential work output of the electromagnet and the energy stored in developing its field can be evaluated from its magnetization 79 80 THE BELL SYSTEM TECHNICAL JOURNAL,. JANUARY 1 9 5 4 relations. The consequent dependence of the pull and timing characteristics upon the magnetization relations makes the measurement and analysis of the latter fundamental to the understanding of performance and its relation to design. Procedures are described in this article for the evaluation from measured magnetization relations of a few parameters which suffice for the determination of the pull and of the field energy under given conditions. These parameters, the magnetic circuit constants, characterize the electromagnet to which they apply. They are used as measures of performance in comparing different structures, or in studying the effect of dimensional or material variations in a particular design. In addition to their significance as parameters summarizing measured magnetization relations, the magnetic circuit constants may be interpreted as the observed values of quantities postulated in the magnetic circuit approximation to static field theory.