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What is the purpose of the relay and how to use it?

What is the purpose of the relay and how to use it?

Issue Time:2021-03-02
A relay is an electrical component used in a circuit with a lower voltage or a smaller bai current to turn on or off a circuit with a higher voltage and larger current. It may be said that it is used to control a higher voltage or Electric switch of larger power circuit: Give a control current to the working coil of the relay, the relay will be closed, and the corresponding contact will be turned on or off. In the power supply circuit, the relay is also called a contactor. According to the power requirements of the drive relay (operating voltage of the drive line package), the general relay is divided into AC relay and DC relay, which are used for AC circuit and DC circuit respectively. In addition, according to the level of its working voltage, there are 6, 9, 12 , 24, 36, 110, 220, 380 and other different working voltages are used in different control circuits. Another distinguishing point of the relay is its contacts (to switch on or off the controlled circuit). There are differences between normally open, normally closed, and conversion. In addition, there are differences in the number of contacts and how much work can be controlled. The difference between voltage and current (that is, the power that the contact allows to control) is for different purposes; in addition, there are special contacts with self-locking (even if the control voltage disappears after the action, the contact itself maintains the state when it loses control), with delay Time pull-in or delayed release function, etc., for use in special situations. To distinguish from the appearance of the relay, there are differences between sealed, small, and miniature. Sometimes, for example, a control circuit starts with button control and ends with the relay that controls the load. Other relays are used because these relays only control the work of other relays. The contact load does not need to be large. The relays in these parts are often called intermediate relays. For example, the use of three buttons, relays (AC contactors) and thermal protection, etc. can form a positive, flip and stop circuit for controlling a three-phase motor. In the washing machine, the relay is under the control of the microcomputer. It is the task of the relay to connect and disconnect the control motor to make the pulsator forward and reverse. Because the output of the microcomputer cannot directly drive the washing machine motor, a "relay" is used. Circuits detected by various sensors are used to detect different physical quantities such as temperature, pressure, and time, and the detected output is connected to a relay to form a so-called voltage relay, pressure relay, and so on. This type of relay is actually an electronic device including a relay, not an independent relay. Some special relays are supplemented. These relays do not need other circuits and can respond differently to different signals (connecting different contacts): Step relay: In the past, automatic telephone exchanges were used a lot, and the relay itself could control the coil according to the input. The number of pulses automatically moves the moving contact to the corresponding position. For example, if 6 pulses are input, the moving contact will connect to the fixed contact No. 6, and if 9 pulses are input, it will be connected to the No. 9 contact. The phone is automatically switched to the required line according to the dial pulse number; Resonant relay: The relay itself has multiple moving contacts of different lengths, thicknesses, such as reeds, and the resonant frequency of each contact itself is different and reasonably distributed. When input When the current frequency of the relay coil is exactly the same as the resonant frequency of a certain reed contact, due to resonance, the reed produces a large vibration, thus closing with the corresponding fixed contact. When another frequency signal is input, another contact can be made. Point action, which is equivalent to translating signals of different frequencies into corresponding circuit connection actions, which is completely different from current electronic decoding and is realized through mechanical principles. In addition, there are proportional relays, which can distinguish the duty cycle of the pulse signal of the input line package driving the relay, and automatically adjust the output (connect different contacts); and so on. At present, the switching circuit composed of thyristor components is independently packaged and called solid-state relay (non-contact relay). The upper part of the use can replace the traditional relay, but it also has its shortcomings. Therefore, ordinary relays are still widely used.

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