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The relay is a magnetically operated switch. A Relay opens or closes a contact or contacts when the current passes through out an electromagnetic coil (which is part of the relay).
This action is accomplished by the coil making an attraction or repulsion of an armature. This armature connects or disconnects relay terminals.
Operation of the relay:
If a current passes through the coil it pulls the armature and connects points C and D. If no current passes through the coil, the connetion is made on points D and E.
 This way we can connect one device when the coil is active, and any other kind of equipment when it is not.
It is important to know what is the resistance of the winding of the coil (which is between terminals A and B) and what the necesary voltage that activates the relay is.
The voltage tells us the necesary signal magnitude that is going to activate the relay and the resistance tells us how much current we need to supply to the relay in order to be activated
The current is obtained with the Ohm's law: I = V/R. Where:
I is the current required to activate the relay
V is the voltage to activate the relay
R is the resistance of the winding relay
Advantages of Relay
- The relay allows us to control a device a a long distance. There is no need to be close to the device to make it work.
- The relay is activated with little power, but it can trigger large machines that consume large amount of current.
- With a single control signal, we can control several relays at once.
- The relay can switch direct current or alternating current.
Related Links
- Resistor
- Inductor
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