Types of Relays
Electrical relays are used in many areas of our lives and in a wide variety of devices. They are a very common part of the electrical systems in cars and trucks for example where they control the equipment that turns on your headlights when you press the switch on your car dashboard. They are also used in our refrigerators, traffic lights and even automatic garage doors. Relays are used when a switch needs to handle a high amount of current that exceeds the capacity of the wiring and switch itself. This is where the amplification function of the relay comes into play.
The concept behind a relay is relatively simple. A magnet in a coil of wire creates an electromagnetic field which activates the armature, making or breaking (depending on construction) a contact with a fixed set of contacts. When the coil current is switched off, a force that is about half as strong as the magnetic field (or electric) causes the armature to be returned by the yoke or spring to its initial position.
Relays are available in a number of different sizes and capacities depending on the application and voltage required, but they all work in basically the same way. They use one circuit to power another without the need for high-amperage switching or wiring, reducing the size and cost of the device they are being used in.
Some of the different types of relays include:
Electromechanical relays – a very basic type of relay. The design consists of few mechanical parts including an electromagnet, movable armature, contacts and yoke. They are normally open and can be energized by either AC or DC current. Electromechanical relays need to be rated for the voltage of the load that they are switching and should have good quality contacts to avoid any problems like short circuits.
Solid-state relays – very similar to electromechanical relays except that they use semiconductor devices instead of mechanical parts. They are typically faster and have a longer life span than electromechanical relays.
Reed relays – they are a very basic and inexpensive type of relay that uses a magnet in the middle of a coil of wire to make or break a contact. They are very easy to test with a multimeter by ensuring that there is a connection between the yoke or spring and the armature, and that it is closed when energized and open when de-energized.
There are other types of relays that have special applications such as ground fault detectors. They detect any electricity that is flowing outside of its intended path and are able to differentiate between single or double-phase systems. If a problem is detected, they are able to shut down the system to prevent further damage from occurring. This is accomplished by analyzing whether the current is higher or lower than it should be in certain areas of the circuit by using the continuity function on your multimeter to check for a circuit-to-ground connection. 중계