Relays are devices making or breaking electric circuits by their output section driven by operational signal, which is triggered by electric input signal. A simple electromagnetic relay is an adaptation of an electromagnet. Its design and operation is also not complicated .
Constitute
- A coil of wire surrounding a soft iron core.
- An iron yoke, which provides a low reluctance path for magnetic flux.
- A moveable iron armature.
- A set or sets of contacts.
Configuration
The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energised there is an air gap in the magnetic circuit. For example, relay has two sets of contacts,one is closed and the other set is open. Some relays may have more or fewer sets of contacts depending on their function. Relay has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the Printed Circuit Board (PCB) via the yoke, which is soldered to the PCB.
Operation
When an electric current is passed through the coil, the armature is attracted by the resulting magnetic field, and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. When the relay was de-energisedIf the set,then the movement opens the contacts and breaks the connection if the set of contacts was closed , and vice versa if the contacts were open.
When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
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