Electromagnetic relay with precise operating point - has load and retard windings with electronic control to reduce sharp rise operating current

摘要

Relay hysteresis is eliminated by the addition of electronic components such as Zener diodes and transistors in the operating circuit and by the use of a second winding to restrain operation until the winding flux has reached a predetermined threshold so that operation is immediate. The principle of operation is to have a loud winding (L1) and a retard winding (L2) to govern the operation of a magnetic armature circuit (Rel). When a supply flows through the retard winding, a point is reached where the retard effect is overcome and an effective pulse of steep rise and short duration results. In simplest form, with a normally open relay (Rel), no current flows in the retard winding (L2) until the effective voltage of the Zener (Z) is exceeded. When the effective voltage is exceeded and current flows, retard action is initiated and the transistor (T1) is biassed to conduct, current flows in the operate winding (L1) and increases until the transistor saturates. Immediately, self-induction cuts off current through the retard winding (L2) and a full application of the source voltage (Vo) in the form of a right angled rise time pulse operates the relay.