Abstract :
An attempt has been made to develop the theory progressively. The relay is first considered as a simple coil. This leads to Helmholtz´s law. The inclusion of a slug, ignoring flux leakage, increases the time-constant of the relay. It is shown that time-constants add up arithmetically. This is felt to be important: it simplifies calculation. With flux leakage, the rise of flux no longer obeys Helmholtz´s law, a rough treatment giving two exponential terms in place of one. The release of slugged relays is complicated by saturation. A graphical method of dealing with this has been evolved. The impulse relay is treated at some length on account of its great practical importance and because of the interesting oscillations produced by the condenser at the dial. In order to examine the effect of flux leakage a little more thoroughly, the relay core has been viewed as a transmission line with ¿heelpiece return.¿ The slug becomes distributed inductance, and the resulting telegraph equations have been solved by Heaviside´s ¿expansion theorem.¿ In no case is the actual motion of the armature considered in this paper.
