What is Relay?

Relay is an electrically operated switch that opens and closes the circuit by receiving electrical signal from the outside source

Relay Type:

Ø Relay technology is divided into two categories

1. Movable Contacts

2. No-Movable Contacts

Mechanical Relay

Solid State Relay

Relay Types:

Mechanical Relay

Ø This relay has contacts that are mechanically actuated to open/close by a magnetic force

Ø This magnetic force is produced by a coil which is excited by the electric current

Ø Due to movable part it creates noise during operation

Solid-State Relay

Ø This relay does not have mechanical contacts to control outputs

Ø There are electrical switching elements such as Triac and MOSFET

Ø Since no movable part is there so no noise it creates

Mechanical Relay- Advantages

Ø It provides physical isolation between input and output

Ø It can withstand higher voltages

Ø These relays can tolerate short-term overload condition

Ø Transients do not affect output of the relay significantly

Mechanical Relay- Disadvantages

Ø Due to mechanical contacts its switching speed is slow

Ø It has limited life span due to mechanical parts

Ø These relays create contact-bounces which cause arcing

Solid State Relay - Advantages

Ø It also provides physical isolation between input and output

Ø Switching time is less as compared to the mechanical relay

Ø Life expectancy is higher

Ø These Relays offer greater reliability

Ø No contact-bounce problems

Solid State Relay – Disadvantages

Ø Resistance in the output circuit is normally higher as compared to an Electromechanical relay

Ø It is not resilient to transient spikes and other overload conditions, like a mechanical relay, unless it is protected

Ø A transient above the limits of the output device could destroy the solid state relay

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