![]() When the contacts are closed the contact resistance should be zero, a short circuit, but this is not always the case. ![]() When the contacts are open the resistance between the contacts is very high in the Mega-Ohms, producing an open circuit condition and no circuit current flows. The relays contacts are electrically conductive pieces of metal which touch together completing a circuit and allow the circuit current to flow, just like a switch. Connected between the yoke and armature is normally a spring (or springs) for the return stroke to “reset” the contacts back to their initial rest position when the relay coil is in the “de-energized” condition, i.e. The armature is hinged or pivoted allowing it to freely move within the generated magnetic field closing the electrical contacts that are attached to it. This iron core has both a fixed portion called the yoke, and a moveable spring loaded part called the armature, that completes the magnetic field circuit by closing the air gap between the fixed electrical coil and the moveable armature. The most common form of electromechanical relay consist of an energizing coil called the “primary circuit” wound around a permeable iron core. The relay circuit are common in Electronics applications.Īs their name implies, electromechanical relays are electro-magnetic devices that convert a magnetic flux generated by the application of a low voltage electrical control signal either AC or DC across the relay terminals, into a pulling mechanical force which operates the electrical contacts within the relay. Such relays are used in general electrical and electronic control or switching circuits either mounted directly onto PCB boards or connected free standing and in which the load currents are normally fractions of an ampere up to 20+ amperes. In this tutorial about electrical relays we are just concerned with the fundamental operating principles of “light duty” electromechanical relays we can use in motor control or robotic circuits. Relays can also have single or multiple contacts within a single package with the larger power relays used for mains voltage or high current switching applications being called “Contactors”. Also, they are relatively large, slow and only switch small electrical currents.Įlectrical Relays however, are basically electrically operated switches that come in many shapes, sizes and power ratings suitable for all types of applications. The biggest one is that they have to be manually (physically) turned “ON” or “OFF”. Although switches can be used to control something, they have their disadvantages. The easiest way to do this is using switches to interrupt the electrical supply. The most fundamental control of any equipment is the ability to turn it “ON” and “OFF”. However, if the solenoid plunger is used to operate one or more sets of electrical contacts, we have a device called a relay that is so useful it can be used in an infinite number of different ways and in this tutorial we will look at Electrical Relays. We saw previously that solenoids can be used to electrically open latches, doors, open or close valves, and in a variety of robotic and mechatronic applications, etc. The most common types of actuators or output devices are Electrical Relays, Lights, Motors and Loudspeakers. Actuators can be classed as either binary or continuous devices based upon the number of stable states their output has.įor example, a relay is a binary actuator as it has two stable states, either energised and latched or de-energised and unlatched, while a motor is a continuous actuator because it can rotate through a full 360 o motion. An actuator is also classed as a transducer because it changes one type of physical quantity into another and is usually activated or operated by a low voltage command signal. These output devices including the electrical relay are commonly classed as: Actuators.Īctuators convert an electrical signal into a corresponding physical quantity such as movement, force, sound etc. But there are also a variety of electrical and electronic devices which are classed as Output devices used to control or operate some external physical process. Thus far we have seen a selection of Input devices that can be used to detect or “sense” a variety of physical variables and signals and are therefore called Sensors. ![]()
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