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I. The Operational Principle of Electromagnetic Relay
Fig. 2 shows: When a certain voltage or current is applied to both ends of the coil of an electromagnetic relay, the magnetic flux asses through the magnetic circuit composed of iron core, yoke iron, armature iron and the magnetic circuit operation air-gap. Under the influence of magnetic field, armature iron is attracted to iron-core pole-face, thus propelling normally closed contact to open and normally open contact to close, when the voltage or current at both ends of the coil is lower than a certain value and mechanical reactance is greater than electromagnetic attraction, armature iron is restored to the original state and normally open contact opens and normally closed contact connects..
II. The Components of Electromagnetic Relay
Electromagnetic relay is composed of magnetic circuit system, contact system and return mechanism. Magnetic circuit system is made up of such parts as iron core, yoke iron, armature iron and coil. Contact system is composed of such parts as static contact spring, movable contact spring and contact seat. Return mechanism is made up of return springs or draw springs.