Mostly used as directional relays in power-system protection and high-speed switching applications.Used as protective relays in AC systems.Used as a wide range of switch configuration.Electromagnetic switches operated by a magnetic coil.They are designed to act as two SPDT relays which are actuated by a single coil. Out of these two rows are designed to change over terminals. Out of the six terminals, two of them are coil terminals.ĭouble Pole Double Throw(DPDT): The DPDT relay is the biggest of all. Thus they can act as two SPST’s which are actuated by a single coil. These terminals are further divided into two pairs. A common terminal is also included which connects to either of two others.ĭouble Pole Single Throw(DPST): The DPST relay has a total of six terminals. SPDT relay has a total of five terminals. Single Pole Double Throw(SPDT): It has three contacts. The other two terminals are needed for the coil to be connected. Out of these two terminals can be connected or disconnected. Single Pole Single Throw(SPST): The SPST is the simplest configuration that has only two configurations. If it is energized (it means the current is passed), Normally Open(NO) and Common will be connected. When the relay is not energized then the Normally Closed(NC) and Common will be connected. These can either get opened or closed when the relay is in operation. When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components.Īn electromechanical relay consists of three terminals namely common (COM), normally closed (NC) and normally opened (NO) contacts. Usually, this force is provided by a spring, but gravity is also used as commonly in industrial motor starters. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. If the set of contact was closed when the relay was de-energized, then the movement opens and breaks the connection, and vice versa if the contact were open. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact either makes or breaks a connection with a fixed contact. Other relays may have more or fewer sets of contacts depending on their function. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
![simple delay function for 8051 in c simple delay function for 8051 in c](https://i.ytimg.com/vi/71EltejZQts/maxresdefault.jpg)
It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. Working of RelaysĪ simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts. For high voltage applications, they are mainly designed to reduce a phenomenon called arcing. For low voltage applications, more preference will be given to reduce the noise of the whole circuit. One is a low voltage application and the other is high voltage. Relays are mainly used for two basic operations. Relays are also used in our day to day devices like Refrigerators, Washing Machines, Heaters, and Air Conditioning. After the invention of computers, they were also used to perform Boolean and other logical operations. They were used to switch the signal coming from one source to another destination. Relay act as an important role in switching calls in a telephone exchange. The major use of relay started during the invention of telephones. We will look into the details of relay working, types and relay Interfacing with 8051 in this article. The actuation of the relay will change the state of the contacts from open to closed or vice verses, depending on the contact configuration. When a switch can be actuated with an electrical signal, the device is then typically referred to as a relay. When the switch is opened, the circuit is open – or off. When the switch is closed, the circuit is closed – or on.
![simple delay function for 8051 in c simple delay function for 8051 in c](http://download.mikroe.com/documents/compilers/mikropascal/8051/help/img/scheme_rs232.gif)
Relays can control currents ranging from 2A – 30A. Relays operate with AC or DC at common voltages like 12V, 24V, 48V, 120V and 230V. Simply, it is used to on/off power circuits using microcontrollers. It allows digital circuits and digital microcontrollers to high power devices on and off. Because relays are the link between the low power digital electronics and high power devices. Relays are switches that open and close circuits when actuated when an electrical signal. Relay is one of the most interesting and important components.