Relay: Basics, Functions & Types
Relays are an electronic control device with a control system (that is, an input loop) and a controlled system (output loop), and are usually used in automated control circuits. The relay is actually an "automatic switch" that uses a small current to control the operation of a large current. It plays the role of conversion circuit, automatic adjustment and safety protection in the circuit.
Function of Relay
Generally speaking, when no relay is installed in the electromechanical control system, in most cases, contactors are used as electrical actuators, so that some basic automatic control actions can be realized. However, if such components are installed in a relatively complex system, the actual use requirements cannot be achieved.
In most electromechanical control systems, it is often encountered that information such as judgment and logical operations need to be transmitted according to different states of the system or changes in parameter values. The result is to control electrical actuators such as contactors, so as to achieve the purpose of automatic control. Then we need to choose and use electrical components that can be competent for accurate judgment and operation of various states and parameter values of the system, and we can call such electrical components as relays.
Types of Relay
Since the actual functions, installation, wiring and symbols are different, relays are also divided into many types. Generally speaking, the types of relays can be classified according to the reflected signal, action principle, action time, DC and AC, etc. The classification details are as follows:
- According to the reflected signal, it can be divided into: current relay, voltage relay, speed relay, pressure relay, temperature relay;
- According to the action principle, it can be divided into: electromagnetic relay, induction relay, electric relay, electronic relay;
- According to the action time, it can be divided into: instantaneous relay, delay relay;
- Electromagnetic relays can be divided into two types: DC and AC, and their main structure and working principle are basically similar to those of contactors. At the same time, AC and DC can be divided into: current, voltage, intermediate, time and other types.
