Electro-Mechanical Relays – Technical Information

A relay is an automatic switch. When provided with an input signal of electric, magnetic, light or heat energy, it will control the output circuit automatically (for the purpose of this application guide, we'll consider only electromagnetic relays.) When the input is removed (or reduced to a certain level), the relay will revert to its initial state and the output circuit will correspondingly revert to its initial state (see Fig. 1). Regardless of the relay's operating principle and structure, the function can be segmented as: induction (receiving input signal), comparison (provide changeover point), and performance (control of output circuit). The relay is a four-terminal component, with its input and output circuits electrically isolated. The operating principle is shown in Fig. 1 and Fig. 2 below (where X is the input to the system and Y is the output).

Current flowing through the coil of an electro-mechanical relay creates an electromagnetic field. A magnetic circuit is formed by the core, yoke, armature, and air gap. When the coil current is increased beyond a certain level, a magnetic force is set up sufficient to draw the armature to the core surface, causing a transfer of the contacts. When the coil current is reduced to another level, the magnetic field collapses and the armature reverts to its initial state as a result of the armature restoring spring, thereby completing a full cycle of the load circuit transfer.

There are several relay applications. Among these are:
•Multiplicity of Switching Functions
•Separation of Control and Power Loads (isolation)
•Signal Amplification (small control signal, large load)
•AC Load Switching with DC signals (computer interface, etc.)
•Creating Hard Logic (i.e. ON/OFF signals)
•Remote Control

For a representative listing of Stetron's Industrial Control Relay product line, please request our Industrial Control Relay Catalog.

For technical assistance and customer service, please contact either of our North American Offices.

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	Electro-Mechanical Relays – Technical Information A relay is an automatic switch. When provided with an input signal of electric, magnetic, light or heat energy, it will control the output circuit automatically (for the purpose of this application guide, we'll consider only electromagnetic relays.) When the input is removed (or reduced to a certain level), the relay will revert to its initial state and the output circuit will correspondingly revert to its initial state (see Fig. 1). Regardless of the relay's operating principle and structure, the function can be segmented as: induction (receiving input signal), comparison (provide changeover point), and performance (control of output circuit). The relay is a four-terminal component, with its input and output circuits electrically isolated. The operating principle is shown in Fig. 1 and Fig. 2 below (where X is the input to the system and Y is the output). Current flowing through the coil of an electro-mechanical relay creates an electromagnetic field. A magnetic circuit is formed by the core, yoke, armature, and air gap. When the coil current is increased beyond a certain level, a magnetic force is set up sufficient to draw the armature to the core surface, causing a transfer of the contacts. When the coil current is reduced to another level, the magnetic field collapses and the armature reverts to its initial state as a result of the armature restoring spring, thereby completing a full cycle of the load circuit transfer. There are several relay applications. Among these are: •Multiplicity of Switching Functions •Separation of Control and Power Loads (isolation) •Signal Amplification (small control signal, large load) •AC Load Switching with DC signals (computer interface, etc.) •Creating Hard Logic (i.e. ON/OFF signals) •Remote Control For a representative listing of Stetron's Industrial Control Relay product line, please request our Industrial Control Relay Catalog. For technical assistance and customer service, please contact either of our North American Offices.