A relay is a switch that uses an electromagnet to mechanically operate a circuit. It can be used to control circuits with high amperage and in applications where there is a need for electrical isolation between the two circuits. There are different types of relays, but they all function in the same way by using one circuit to power another. Relays are commonly found in electrical devices like refrigerators, thermostats, traffic lights and many more.
There are several factors that influence the performance of a relay, such as its size, capacity and operating voltage. However, the most crucial element that determines reliability is the contact material and the type of current it interrupts. Choosing the right contact material is important because it will ensure that there is minimal contact resistance and less wear on the contacts.
Joseph Henry created the first electrical relay in 1835 and it was largely used in telegraphy. The relay is considered to be a useful invention because it can reduce the need for high-amperage switches and wiring, thereby saving on costs, time and space. It also makes it possible to fit more functionality into a small case.
Relays have four kinds of terminals – coil, common, normally open (NO) and normally closed (NC). The control input is connected to the coil through a low-power source and the output is connected to a device that needs to be controlled. The NO and NC terminals allow you to connect the device in such a way that it will be on when the relay is active and off when it is not.
The core of the relay has copper wire windings on it which form a coil and is surrounded by a movable armature. The armature is a simple metal piece balanced on a pivot or stand that makes or breaks the connection with the contact points when the coil is energized. Some relays have a spring connected to one end of the armature to push it back into place if the coil is not energized.
The armature is also attached to a yoke which attracts and holds the movable arm when the coil is energized. The yoke is usually made from a plastic or PVC stand-like structure but it can be replaced with other materials like brass, copper, etc. Some relays have a yoke that is adjustable in length and position which gives them more versatility and flexibility. Contacts are placed on either side of the armature and can be triggered by the yoke or the coil when it is energized. The contacts are rated for AC or DC voltage and should be chosen to match the load. The contacts are usually sealed with an epoxy resin to make sure they do not come in contact with water or other liquids that could cause corrosion. They are also insulated from the rest of the assembly to prevent shock and fire hazards. Contacts are also referred to as switching points and can be switched on or off by pressing the appropriate button. 중계