What is a Relay?

A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But rather than a homemade operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit.

Relays can be of different types like electromechanical, and solid state. Electromechanical relays are constantly used. Let us see the internal corridor of this relay before knowing about it working. Although numerous different types of relay were present, their working is the same.

Every electromechanical relay consists of an

  1. Electromagnet
  2. Mechanically portable contact
  3. Switching points and
  4. Spring

Electromagnet is constructed by wounding a bobby coil on an essence core. The two ends of the coil are connected to two legs of the relay as shown. These two are used as DC force legs. Generally, two further connections will be present, called switching points to connect high-ampere cargo. Another contact called common contact is present in order to connect the switching points.

These connections are named typically open( NO), typically closed( NC), and common( COM) connections.

We can use a Relay either in an AC circuit or a DC Circuit. In the case of AC relays, for every current zero position, the relay coil gets demagnetized and hence there would be a chance of continuous breaking of the circuit.

So, AC relays are constructed with a special medium similar to non-stop captivation is handed in order to avoid the above problem. similar mechanisms include electronic circuit arrangement or shadowed coil medium.

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We use relays for a wide range of operations similar as home robotization, buses and bikes( motorcars), artificial operations, DIY systems, test and dimension outfit, and numerous further. But what’s Relay? How a Relay workshop? What are the operations of Relays? Let us explore further about relays in this companion.

How a Relay work?

  The following vitality shows a simplified working of a relay.

  • Relay works on the principle of electromagnetic induction.
  • When the electromagnet is applied with some current, it induces a glamorous field around it.
  • A switch is used to apply DC current to the load.
  • In the relay, Bobby coil and the iron core acts as electromagnet.
  • When the coil is applied with DC current, it starts attracting the contact as shown. This is called amping of relay.
  • When the force is removed it retrieves back to the original position. This is called De amping of relay.

There are also similar relays, whose connections are originally closed and opened when there’s force i.e. exactly to contrary to the below shown relay.

Solid state relays will have seeing element to sense the input voltage and switches the affair using opto- coupling.


Relay Contact Types

As we’ve seen that relay is a switch. The language “ Poles and throws ” is also applicable for relay. Depending on the number of connections and a number of circuits it switches relays can be classified. Before we know about this bracket of connections we’ve to know the poles and throws of a relay switch.

Poles and Throws

Relays can switch one or further circuits. Each switch in relay is appertained as pole. Number of circuits a relay connects is indicated by throws.

Depending on the poles and throws, relays are classified into

  • Single Pole Single Throw
  • Single Pole Double Throw
  • Double Pole Single Throw
  • Double Pole Double Throw
Single Pole Single Throw

A single pole single gamble relay can control one circuit and can be connected to one affair. It’s used for the operations which bear only ON or OFF state.

Single Pole Double Throw

A single pole double gamble relay connects one input circuit to one of the two labors. This relay is also called as transfiguration relay.

Though the SPDT has two affair positions, it may correspond of further than two throws depends on the configuration and demand of the operation.

Double pole single Throw

A double pole single gamble relay has two poles and single gamble and it can be used to connect two outstations of a single circuit at a time. For illustration, this relay is used for connecting both phase and neutral outstations to the cargo at a time.

Double pole double Throw

A DPDT( double pole double gamble) relay has two poles and two throws for each pole. In motor direction control, these are used for phase or opposition reversal.

The switching action between connections for all these relays is performed when the coil get amped .

Relay Applications

Relays are used to cover the electrical system and to minimize the damage to the outfit connected in the system due to over currents voltages. The relay is used for the purpose of protection of the outfit connected with it.

These are used to control the high voltage circuit with low voltage signal in operations audio amplifiers and some types of modems.

These are used to control a high current circuit by a low current signal in the operations like starter solenoid in machine. These can descry and insulate the faults that passed in power transmission and distribution system. Typical operation areas of the relays include

  • Lighting control systems
  • Telecommunication
  • Industrial process controllers
  • Traffic control
  • Motor drives control
  • Protection systems of electrical power system
  • Computer interfaces
  • Automotive
  • Home appliances
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