What is the relay for?

Relays are usually used in automatic control circuits. In fact, they are an "automatic switch" that uses small current to control large current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.

The relay coil is represented by a long square symbol in the circuit. If the relay has two coils, draw two parallel long boxes. At the same time, the literal symbol "J" of the relay is marked in or beside the long box. There are two representations of relay contacts: one is directly drawn on one side of a long box, which is more intuitive.

Because relay consists of two parts: coil and contact group, the graphic symbol of relay in circuit diagram also includes two parts: a long box represents coil; A set of contact symbols indicates a contact combination. When the circuit with few contacts is simple, the contact group is often drawn directly on one side of the bobbin, which is called centralized representation.

Extended data:

Relay is an automatic switching element with isolation function, which is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment, and is one of the most important control elements.

Relays generally have an induction mechanism (input part), which can reflect some input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light and so on). ).

There is an actuator (output part) which can control the on-off of the controlled circuit; Between the input part and the output part of the relay, there is also an intermediate mechanism (driving part) for coupling and isolating the input quantity, processing the function and driving the output part.

There are three basic forms of relay contacts:

1, when the moving (normally open) (H type) coil is not energized, the two contacts are disconnected, and when energized, the two contacts are closed. Represented by the combined pinyin prefix "h".

2. When the dynamically disconnected (normally closed) (D-type) coil is not energized, the two contacts are closed, and when energized, the two contacts are disconnected. It is represented by the phonetic prefix "d" of hyphen.

3, conversion type (Z type) This is the contact group type. The contact group * * * has three contacts, namely the moving contact in the middle and the static contact at the top and bottom.

When the coil is not energized, the moving contact and one stationary contact are disconnected and the other is closed. After the coil is energized, the moving contact moves, so that the original disconnected contact is closed, and the original closed contact is in the disconnected state, thus achieving the purpose of conversion. Such a contact group is called a transfer contact. It is represented by the phonetic prefix "z" of the word "Zhuan".

Influencing factors of relay reliability

1 Influence of environment on relay reliability: When the relay works in GB and SF environment, the average time between failures is the highest, reaching 820,000 h, while it is only 60000h h in NU environment. ..

2 Influence of quality grade on relay reliability: When A 1 quality grade relay is selected, the average time between failures can reach 3,660,000 h, while the average time between failures of Class C relay is 1 10000, a difference of 33 times, indicating that the quality grade of relay has a great influence on its reliability.

3 Influence of contact form on relay reliability: The contact form of relay will also have an impact on its reliability. The reliability of single-throw relay is higher than that of double-throw relay with the same number of knives. With the increase of knives, the reliability gradually decreases. The mean time between failures of single-throw relay is 5.5 times that of four-throw double-throw relay.

4 Influence of structure types on relay reliability: There are 24 types of relay structures, and different types have influence on its reliability? [2]。

5 Influence of temperature on relay reliability: The working temperature range of relay is -25 ~ 70℃. With the increase of temperature, the mean time between failures of relays decreases gradually? .

References:

Baidu encyclopedia-relay