From Electronics Technology Handbook


Electromechanical components for electronics are those that are compatible with electronic circuitry in size, weight and ratings for mounting on circuit boards nearby in cases, cabinets or enclosures. Examples include relays, solenoids, switches, and fractional horsepower DC motors.

Electromechanical Relays

A relay is the simplest form of remote controller. The input circuits of all relays are electrically isolated from their output circuits, and their contacts can be closed remotely by passing current sufficient to actuate the relay coils through wires controlled by a manual switch or another relay. Relays are classed as electromechanical (EM) and solid-state relays (SSRs). Solid-state relays are discussed in Sec. 5, "Fundamental Electronic Circuits."

All electromechanical relays are identified by:

  • Output current rating

  • Number of poles

  • Composition of output contacts

  • Packaging style and form factor

  • Application

The general classifications for electromechanical relays are:

  • General-purpose relays

  • Power relays

  • Sensitive relays

  • Telephone-type relays

  • Reed-switch relays

General-Purpose Electromechanical Relays

A general-purpose electromechanical relay used in electronics applications is a modern version of the traditional relays invented more than a century ago and manufactured primarily for use in electrical power and lighting, telegraph, and telephone systems. A conventional coil-and-contact relay, as shown in Fig. 3-1, consists of an electromagnetic coil, movable spring-loaded armature, and electrically isolated input and output circuits. When the coil is energized, the electromagnet attracts the hinged and spring-loaded armature against the tension of the return spring, causing the upper normally closed (NC) contacts to break and the lower normally open (NO) contacts...

Products & Services
Solid State Relays
Solid state relays (SSR) or semiconductor relays are semiconductor devices that can be used in place of mechanical relays to switch electricity to a load in many applications.
Safety Relays
Safety relays and control modules differ from conventional relays in that they have force-guided or positive-driven contacts.
Reed Relays
Reed relays are electrically-operated switching devices that consist of two thin, magnetic strips (reeds) encapsulated in a glass envelope. They are used to switch industrial components such as solenoids, contactors and starter motors.
High Voltage Relays
High voltage relays are used to transfer power for high voltage and high frequency applications. They are heavily insulated and consist of strong materials to increase contact life.

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