How the relay works

Update:29-06-2019
Summary:

We will explain the working principle of the relay acco […]

We will explain the working principle of the relay according to the example. The following figure is a diagram of a relay control bulb. The relay has a normally open contact and a normally closed contact. The movable contact is a common terminal. This is a smart home relay, that is, when the relay coil passes DC power (the battery is powered on the figure). ), the coil with the iron core will output the corresponding magnetic field, the armature will be attracted, and the moving contact will run from the normally closed contact side to the normally open contact side, which is equivalent to the normally open contact. . From the figure, the start/stop button, the battery, and the relay coil form a control loop. As long as this loop is engaged, the coil will have current passing through it and generate a magnetic field.
The normally open contact, the bulb, and the control power supply of another bulb (the other battery on the figure) form a loop. When the normally open contact is closed, the loop is closed and the current will be from the control power supply. The positive end, flowing through the bulb, passes through the closed normally open contact and then back to the negative pole so that the bulb will illuminate.
When the start/stop button is disconnected, the coil will lose current, so that the armature has no magnetic attraction and will be reset by the spring, so that the other end of the moving contact will return from the normally open contact side to the normally closed contact. Here, the energized circuit of the bulb is forcibly disconnected, and the bulb has no current, and naturally it will be dark.
Therefore, the relay is also called "magnetism" by some old electricians. It uses the function of the electromagnet to control the pull-in or disconnection of another circuit. Inside the electromagnetic relay, coils, iron cores and springs are needed. It is composed of key accessories such as contacts. The contacts generally have normally open contacts and normally closed contacts. The two often have a common end. When the coil is not energized, the normally closed contact and the common end are shorted, and the normally open contact and the common end are open. After the coil is energized, the normally open contact and the common end are shorted, and the normally closed contact and the common end are open, just reversed, so that the voltage (current) of the coil can be controlled, and the circuit of the contact series can be controlled. Already working.