Basic principles and classification of relays


The relay is an electrical control device, which can make the output circuit perform predetermined switching actions according to the change of the input circuit. The relay can realize the isolation and control of strong and weak electricity, and can also realize the simultaneous control of multiple circuits.

There are many ways to classify relays, the common ones are as follows:

  • According to the different input volume, it can be divided into voltage relay , current relay , Time Relay , speed relay , pressure switch wait. These relays can control the output circuit according to the input quantity, direction, frequency, time and other parameters 2 .
  • According to different working principles, it can be divided into Electromagnetic relay , Inductive relay , Rectifier relay , static relay wait. These relays use different physical effects to switch between input and output.
  • According to different uses, it can be divided into control relay , protection relay wait. These relays can be used to implement different control or protection functions.

Of these, the most common are Electromagnetic relay , which uses the magnetic field generated by the input coil to attract or release the movable armature, thereby driving the opening and closing of the contacts. According to the structure, the electromagnetic relay can be divided into solenoid coil type, attracting armature type and rotating tongue type, etc. .

When a certain amount of DC or AC current is applied to the coil, the iron core generates a magnetic field to attract the movable armature to overcome the spring force and friction force to make the contacts close or open. When the coil is disconnected, the reactive spring force resets the movable armature and restores the original state of the contacts .