Relays are an electronic component that can implement switching logic.A relay is a switching device for isolating or shifting the state of an electrical circuit from one state to another. These devices are economical, easy to replace and allow a wide range of switch configurations, some of the important types of relays:
Electromagnetic Relays:
These relays are electromagnetic switching devices, General purpose relays operate with AC or DC current, at common voltages such as 12V, 24V, 48V, 120V and 230V, and they can control currents ranging from 2A-30A. Electromagnetic relays are low cost and available in wide range of switching configurations.
There are different types of electromagnetic relays based on the power type used and the mechanism used:
AC or DC relays:
Relays works in both AC and DC but they differ in how they employed. DC relays are used with a freewheeling diode to de-energize the coil and the AC relays use laminated cores to reduce current losses.
For AC supply the path of current varies for every half cycle. This makes the relay continuously make and break the circuit. So additional circuit is needed to make the relay continuously in action.
Machine Control Relays:
A magnetic coil also powers device command relays. They are heavy-duty relays that are used to power starters and other components of industry. While they are more costly than relays for general purposes, they are usually more reliable.
The greatest advantage this relay over general purpose relays is Machine Control Relays ’ expandable versatility by incorporating accessories.
Reed Relays:
Reed Relays are a lightweight, compact, fast switch model with a single contact, NO. Reed Relays are hermetically sealed in a glass container, making contacts unaffected by pollutants, gases or moisture, allowing stable switching, and having a higher life expectancy for contacts.
Reed relays can toggle industrial components like solenoids, contactors and starter motors. Reed relays are made of two reeds.
When a magnetic force, such as an electromagnet or coil, is applied, this creates a magnetic field where the end of the reeds assumes opposite polarity. The irresistible strength of the opposite poles, when the magnetic field is strong enough, overcomes the rigidity of the reeds and pulls them together.
On releasing the magnetic force the reeds spring come back to the open position. These relays work very quickly because of the short distance between the reeds.
Hybrid relays:
These relays consist of electrical relays and components of electronics. The input component usually includes the electrical circuitry conducting rectification and other control functions, and the output portion includes electromagnetic relay.
Solid State Relays:
No moving parts are employed in the working of solid state relay. For this relay, only low power is needed to operate, comparing electromagnetic relays.
There are different types of solid-state relays, reed relay coupled SSR, transformer-coupled SSR, photo-coupled SSR, and so on. The above-shown figure is of photo coupled SSR.