Electro Mechanical Relay

8/13/2019 Electro Mechanical Relay

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FROM-

RONAK JAISWAL - 05

DARSHIL VAGHANI - 44 MANANK SHASTRI - 62

AKSHAY PATEL- 63

GUIDE TEACHER- KRISHNA CHAUHAN


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Objectives

Upon completion of this presentation, we will be ableto:

Construct an experimental relay Describe how a relay works

Observe basic relay functions


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A relay is defined as an electrically controlled devicethat opens and closes electrical contacts, or activatesand deactivates operation of other devices in the sameor another electrical circuit. Two types of relaytechnology are available:-

1. Mechanical

2. Solid State.


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A relay may also be called an electromagnetic switch

Relays use a low amperage circuit to control a high

amperage circuit The low amperage circuit controls an electromagnetic

device

The electromagnetic device closes/opens the high

amperage circuit


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Latching Relay

Reed Relay

Mercury-wetted Relay

Mercury Relay PolarizedRelay

Machine Tool Relay

Ratchet Relay

Vacuum Relays

Coaxial Relay

Contactor Solid-stateRelay

Solid State ContactorRelay

Buchholz Relay

Forced-guided Contacts

Relay Overload Protection

Relay


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It is a reed switch enclosed in a solenoid. The switch has a set ofcontacts inside an evacuated or inert gas-filled glass tube whichprotects the contacts against atmospheric corrosion; the contactsare made of magnetic material that makes them move under theinfluence of the field of the enclosing solenoid or an externalmagnet.

Reed relays can switch faster than larger relays and require verylittle power from the control circuit. However, they haverelatively low switching current and voltage ratings. Though rare,the reeds can become magnetized over time, which makes themstick 'on' even when no current is present; changing the

orientation of the reeds with respect to the solenoid's magneticfield can resolve this problem. Sealed contacts with mercury-wetted contacts have longer

operating lives and less contact chatter than any other kind ofrelay.


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It is a form of reed relay in which the contacts arewetted with mercury. Such relays are used to switchlow-voltage signals (one volt or less) where themercury reduces the contact resistance and associated

voltage drop, for low-current signals where surfacecontamination may make for a poor contact, or forhigh-speed applications where the mercury eliminatescontact bounce.

Mercury wetted relays are position-sensitive and mustbe mounted vertically to work properly. Because of thetoxicity and expense of liquid mercury, these relays arenow rarely used.


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A machine tool relayis a type standardized for industrialcontrol of machine tools, transfer machines, and othersequential control.

They are characterized by a large number of contacts

(sometimes extendable in the field) which are easilyconverted from normally-open to normally-closed status,easily replaceable coils, and a form factor that allowscompactly installing many relays in a control panel.

Although such relays once were the backbone of

automation in such industries as automobile assembly,the programmable logic controller (PLC) mostly displacedthe machine tool relay from sequential controlapplications.


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A relay allows circuits to be switched by electricalequipment: for example, a timer circuit with a relay

could switch power at a preset time. For many years relays were the standard method of

controlling industrial electronic systems. A number ofrelays could be used together to carry out complex

functions (relay logic). The principle of relay logic is based on relays which

energize and de-energize associated contacts. Relaylogic is the predecessor of ladder logic, which iscommonly used in programmable logic controllers.


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Separation of AC and DC circuits

Interface between electronic control circuits and

power circuits


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A relay is an electromechanical device that uses smallelectrical currents and voltages to control largerelectrical currents and voltages. Relays have unlimitedpossibilities, ranging from industrial applications to

consumer electronics, such as microwave ovens andtelevision sets.


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Relay Symbol

Normally closed

(NC) contact

CR1-1 CR1-2

Normally open

(NO) contact

CR1

Coil

Contacts are open whenno current flows through

the coil but close as soon

as the coil is energized.

Contacts are closed whenno current flows through

the coil but open as soon

as the coil is energized.


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Coil Voltage Voltage required for switching

Contact Rating How much current the relay can

handle

Normally Open (NO) or Normally Closed (NC)


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Electromagnetic Relay Operation

An electromagnetic relay is a magnetic switch. It uses

electromagnetism to switch contacts.

A relay will usuallyhave only one coil

but may have any

number of different

contacts.


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Electromagnetic Relay Operation

With no current flow

through the coil(coil de-energized),

the armature is held

away from the core

by spring tension.

When the coil is energized,

the electromagnetic field

moves the armature

causing the contact points

of the relay to open or

close.


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In a microwave oven, the push of a few tiny buttons onthe keypad gives commands to a microcontroller,

which can produce only very small output voltages.Those small voltages turn on a relay, which is capableof controlling the large voltages and currents requiredto produce the heating effect that takes place.

In a television, the tiny impulses from the hand-heldremote unit control a relay in the power supply.

Examples of Electromechanical Relays


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A relay is basically a switch that is controlled by anelectromagnet.

A relay is used when a large current needs to beturned on or off by a small current.

Relays are used in many industrial applications aswell as devices such as televisions, stereo systemsetc.

Manufactured Relay

Homemade Relay

Examples of Electromechanical Relays

All electromechanical relays have three basic parts:


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A relay is basically a switch that is controlled by anelectromagnet.

A relay is used when a large current needs to beturned on or off by a small current.

Relays are used in many industrial applications aswell as devices such as televisions, stereo systemsetc.

Electromagnet

Switching

contacts

Switching

contacts

Electromagnet

All electromechanical relays have three basic parts:

1. Electromagnetconsists of an iron core wrapped with turns of insulated wir

2. Armaturethis is the moving part of the relay.

3. Switching contactsat least one must be stationary and one fastened to

the armature. This is known as a single-pole single-throw arrangement.

Armature

Armature

Note: In the manufactured relay, the switching

contacts are insulated from the armature. Our

experimental relay uses the metal armature and

a 8d common nail as the switching contacts.


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This diagram shows the

basic parts of an

electromechanical relay: a

spring, moveable armature,

electromagnet, moveable

contact, and stationary

contact. The spring keeps

the two contacts separated

until the electromagnet is

energized, pulling the two

contacts together.

Moveable Armature

Moveable Contact

ElectromagnetSpring

Stationary Contact


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Spring

To Control Circuit

Moveable Armature Moveable Contact

Load

Power Supply

Electromagnet

This diagram shows how to wire

an electromechanical relay.

When the control circuit turns the

electromagnet on, the moveablearmature is drawn towards the

electromagnet and connects the

moveable contact and the

stationary contact. This

completes the circuit and delivers

power to the load.

Stationary Contact


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Relays are used for:

Amplifying a digital signal, switching a large amount ofpower with a small operating power. Some special cases are: A telegraph relay, repeating a weak signal received at the end

of a long wire Controlling a high-voltage circuit with a low-voltage signal, as

in some types of modems or audio amplifiers,

Controlling a high-current circuit with a low-current signal,

as in the starter solenoid of an automobile, Detecting and isolating faults on transmission and

distribution lines by opening and closing circuitbreakers (protection relays),


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Suppose, there is a need to control a solenoid valve for a waterdrain application. Control is to be accomplished with amicrocontroller. The solenoid valve requires 120 VAC to open.Assuming that a 120 VAC power supply is available, how cancontrol of the solenoid valve be accomplished using a

microcontroller that can only supply 5 VDC?

This problem is easily solved using a relay. There are many relaysthat are turned on and off with a 5 VDC coil. The relay providesthe interface between the microcontroller and the 120 VAC power

supply that is needed to open and close the valve.


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120 VAC

Ground

To Microcontroller

Solenoid Valve

Relay

Coil

Circuit for Control of a 120 VAC Solenoid Valve


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Contacts can switch AC or DC

Low initial cost

Very low contact voltage drop, thus no heat sink is

required High resistance to voltage transients

No Off-State leakage current through open contacts


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The contacts wear and thus have limited lifedepending on loads

Short contact life when used for rapid switchingapplications or high loads

Poor performance when switching high inrushcurrents

Package Size


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Electromechanical relays are an excellent solutionto separate electronic control circuitry and powercircuitry. Electromechanical relays are not the

best choice in high frequency switchingapplications and do have a limited life due to wearon the contacts inside the relay. When used in thea proper application, the electromechanical relay

provides safe and reliable integration betweenpower circuits and control circuits.

Electro Mechanical Relay

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