So far, we have seen a selection of input devices that can capture or "sense" various physical variables and signals, and therefore are referred to as sensors. However, there are also a variety of electrical and electronic devices that are classed as output devices and used to control or operate an external physical process. These output devices are commonly referred to as actuators.
Actuators convert an electrical signal into a corresponding physical quantity such as motion, force, sound, etc. An actuator is also considered a converter because it converts one type of physical quantity into another and is normally activated or operated by a low voltage command signal. Actuators can be classified as either binary or continuous devices depending on the number of stable states of their output.
For example, a relay is a binary actuator because it has two stable states, either tightened and locked or not tightened, and not locked while a motor is a continuous actuator because it can rotate for a full 360 ° movement. The most common types of actuators or output devices are electrical relays, lights, motors and speakers.
As we have seen before, solenoids can be used to electrically open latches, doors, open or close valves, as well as a variety of robotic and mechatronic applications, etc. We have a device called Relay that is so useful that it can be used in an infinite number of different ways. In this tutorial we will look at electrical relays.
Electrical relays may also be divided into mechanical wireline relays, referred to as "electromechanical relays", and relays using semiconductor transistors, thyristors, triacs, etc., as switching elements referred to as "solid state relays" or SSRs.
The electromechanical relay
The term relay generally refers to a device that provides an electrical connection between two or more points in response to the application of a control signal. The most common and widely used type of electrical relay is the electromechanical relay or EMR.
electrical relay circuit
An electrical relay
The most basic control of a device is the ability to turn it on and off. The easiest way to do this is to use switches to cut off power. Although switches can be used to control something, they have their drawbacks. The biggest problem is that they have to be manually (physically) turned on or off. In addition, they are relatively large, slow and switch only small electrical currents.
However, electrical relays are basically electrically operated switches that are suitable in many shapes, sizes and ratings for all types of applications. Relays can also have single or multiple contacts in a single housing, with the larger power relays used for mains voltage or high current switching applications referred to as "contactors".
This electrical relay tutorial covers only the basic operating principles of light duty electromechanical relays that we can use in motor control or robotic circuits. Such relays are used in general electrical and electronic control or switching circuits, either mounted directly on printed circuit boards or stand-alone, and in which the load currents are normally fractions of an ampere of up to 20 amps. The relay circuits are common in electronic applications.
As the name implies, electromechanical relays are electromagnetic devices that convert a magnetic flux generated by applying a low voltage electrical control signal to the relay terminals into a mechanical tensile force that actuates the electrical contacts within the relay. The most common form of electromechanical relay consists of an excitation coil, referred to as a "primary circuit", wound around a permeable iron core.
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