Why is an electromagnetic relay used?

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electromagnetic relay

Many times it so happens that we use certain electronic or electrical equipment and gadgets but do not know the proper mechanism or technology that goes into their operation. Electromagnetic relay is used in our day to day transistors or radios but most of us do not know much about it. The functioning of electromagnet relay almost looks like the switch of electricity. Invented in 1835 except a few minor changes there has not been much change in its functioning.

 

What is an Electromagnetic relay?

Electromagnetic relay is basically a switch that can be used to turn on or off a larger electric current. They can work as switches to turn on/off larger appliances or as amplifiers to convert small currents to larger electric current.

 

 

How does an electromagnetic relay operate?

An electromagnet relay is a coil of iron that works as a magnet when electricity flows through it. It links two circuits of which on one side is the input circuit and the other is the output circuit. Electromagnetic relay has one or two sets of contacts which are attached to the armature and a coil. When voltage is introduced to the coil, current flows through it which generates magnetic field. Due to this the inner circuit turns on and activates the magnet which creates a magnetic field around it. Due to electromagnetic induction it pulls the metal bar in and closes the switch thus allowing a bigger current to flow to the outer circuit. When the voltage is stopped, the magnetic field collapses and the switch opens up and no electric current flows. A dicode is placed across the relay coil to protect the components in the relay so that they do not get damaged when the voltage is passed and the coil has no place to go. A dicode is mostly placed in case of DC loads whereas varistor is used in place of diode in case of AC loads. This varistor is connected to anode and cathode at two ends like a Zener diode.

 

What are the main features of electromagnetic relay?

Since the contacts meet physically the resistance needed is only one tenths of an ohm. Also the opening and closing of contact is solely due to the electromagnetic field and hence there is no need of any electricity between the contact and the coil. The two highlighting features of electromagnetic relay are,

  • Needs very low resistance,
  • Completely isolated physically from the control signal

What are the drawbacks of electromagnetic relay?

Some of the drawbacks of electromagnetic relay include,

  • Large size of the electromagnetic relay model
  • The coil requires large current which is around 50 to 200 mill amperes
  • The switching speed is relatively slow
  • The contacts have to maintained regularly

 

How are the transistor and relays similar?

We come in contact with electromagnetic relay quite regularly when we use a transistor, switch on the timed office lights or tested buttons. When a slow current is passed through the electromagnetic relay it produces higher current. This property is useful in alarming devices, quality control devices and other safety devices. Relays are used in telephones as well. Transistors also work like relays by turning on/off switches and as amplifiers and take much less electric current and work faster too but they work with very small currents. Therefore relays are still used in many appliances. With the advent of transistors the computer revolution started in the 20th cent 

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