In automation industries,relay is a common device used for control application.Basic operation of electrical relay is a device that changes the state of a circuit in response to it being energized or de-energized by that or another circuit.
It function to open or close the circuit or contact and respond depend on signal that we gave it to the magnetic coil.It have normally open and normally close contact that we can choose when design the control circuit for our application.
For generally understanding,relay also may consider as a amplifier and controller.It only a small device in automation circuit but it have important roles to make our system running accordingly.
Types and Features of Relay
For this post,i want share some information about electromechanical and electrothermal relay types.Actually we can found them in variety of form and concept but the basic characteristics that are described here are common to all of them.
Basic application of relay is to control the flow of electric current by means of contacts, which may be open or closed. When these contacts are open, they create a very high resistance and when they are closed, their resistance is low.
They may have multiple contacts. As many as eight SPDT contact assemblies are available on relays that are in stock. Each contact assembly is electrically isolated from all the others, and the contacts are actuated in some definite sequence.
For each of the various mechanical relay,structures has certain advantages and limitations that we must consider before selected. Some relay designed to respond rapidly in less than 1 ms but it cannot safely handle large amounts of power.In others type of relay it can handle large amounts of power but it respond at a slower speed.
Normally relays forms can be obtained with open contacts, can be enclosed in dust covers, or can be hermeticallysealed in glass tubes or in vacuum-degassed plastic.
Some of relay designed in the glass tubes are evacuated for handling extremely high voltages. Some have contact assemblies suited for handling radio frequency voltages and to protect against capacitive cross-coupling.
Other type of relay that common application is a solid state which use transistors, SCRs, triacs, and similar components as current-control elements.
In these devices the controlled circuit is usually isolated from the controlling circuit by a transformer (DC only),by an optical element, or perhaps by an electromechanical relay.