A Governor for Telephone Dials - Principles of Design

Machine switching telephone systems depend on the telephone dial for originating information used in completing a call. During run-down, the dial originates current pulses which operate step-by-step switching equipment or are registered for use in common-control panel or crossbar systems. For reliable functioning of dial pulse controlled switching equipment, the pulses must be closely controlled in frequency and form. Since the pulses are produced during run-down of the dial after release by the customer, the run-down speed most be constant. Friction-centrifugal governors are commonly used to provide this required control of speed. If the pulses reaching the central office were exactly like those generated by the dial, the designers of dials and central office switching apparatus and circuits would find themselves far less restricted. Unfortunately the dial pulses are distorted by the electrical characteristics of the customer's loop. To compensate for this distortion and insure accurate registration of the pulses at the central office, the dial and central office equipment must be designed to operate to close limits of performance. The designs must also be such that there is negligible change of