III. Telephone-type relays

THE TIME INTERVAL required for the closing or opening of a relay contact after the current is applied or removed, is dependent upon the balance of mechanical forces acting on the mass of the armature. These balanced forces are the spring load force, the magnetic operating force, the frictional force, and the force of acceleration. Because changes in the magnetic forces occur when the armature is unoperated, while it is moving through its stroke, and also after it is operated, it is necessary to show the relationship of the magnetic forces as a function of armature stroke at constant ampere-turn values and the magnetic forces as a function of ampere turns at various armature stroke positions. The curve of Figure 8 shows these relationships in a typical telephone-type relay structure carrying an operating load of 12 make-contacts and operating with zero residual. air gap.