The relays are widely used not only in industry, but also in everyday life. These devices are designed to switch electrical networks and control various electrical appliances. If you understand their design features, the principle of operation, as well as the relay circuit, you will be able to independently solve various practical problems.
Content
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Operating principle
- Magnetic device
- Electronic device
- Connection features
Operating principle
Relays are classified according to various criteria. In accordance with the principle of operation, devices can be electromagnetic, electronic, thermal, etc. Since the devices of the first two types are most often used in everyday life, they should be considered in more detail.
Magnetic device
Relays of this type have a fairly simple design and an attractive cost. When current is applied to the coil, an EMF is created in its winding. This leads to the appearance in the core of a magnetic field that attracts the armature. This structural element is connected to moving contacts, which close the fixed ones. If the current falls to a certain value, the spring returns the armature to its initial position and the circuit opens.
To ensure higher accuracy of operation, resistors are often introduced into the design of an electromagnetic device. Also, these devices are equipped with protection against voltage surges and sparking.
The tasks can be solved with the help of capacitors. Among the advantages of electromagnetic relays are low cost, resistance to interference, as well as the ability to switch electrical circuits with large loads, while having compact dimensions.
However, the device also has some disadvantages:
- Relatively low response speed. This significantly limits the scope of application of the relay as a protective device.
- Contact surfaces are susceptible to oxidation and deformation by sparks. As a result, the service life of the device is reduced.
- Interference occurs during operation. To protect the electronic components, the relays have to be shielded.
Electronic device
The use of semiconductors in the manufacture of relays allows you to get rid of many disadvantages.characteristic of electromagnetic models. The transistor is the element that is able to perfectly cope with the role of the switch. When a voltage with certain characteristics is applied to the base-emitter junction, an electric current will begin to flow through the collector-emitter circuit.
Its nominal value will be significantly higher compared to the base chain. It is this property of transistors that is used to amplify signals. Comparing electromagnetic and electronic relays, then the latter have the following advantages:
- Semiconductor junctions do not lose performance over time.
- They have small dimensions and weight.
- High response speed.
- Even with hundreds of thousands of switchings per second, electronic devices do not fail.
Unfortunately, there are also some drawbacks here. Among them, the main one is the instability to electromagnetic interference. Some devices can be damaged by static electricity.
In addition, during the operation of the device, a large amount of thermal energy is released, which must be removed.
Connection features
There are many types of relays. You can study the relay connection diagram using the example of an intermediate device. It has found wide application in various automation and control systems. You can connect the device to the electrical circuit in parallel or in series. Most often, devices are equipped with several pairs of contacts. It should be remembered that they can be of two types:
- Normally open. They are designated by letters NO.
- Normally closed. Marked with the letters NC.
The absence of a signal on the winding is taken as the normal state of the device. Since the coils do not have a specific polarity, the contacts can be connected in any order. The device is installed between the actuator or device and the source of the task. However, it can also be used as a contactor.
This device is equipped with four contact groups. Three of them are used to control the load, and one is needed to hold the current on the winding. You can also connect a relay to a motion sensor to automatically control the room lighting system. The scheme of such a connection is quite simple:
- The coil of the device is connected to the sensor.
- The power contact is connected to the light source system.
It should be remembered that there is no universal recommendation for connecting devices. Connection diagrams are selected in accordance with the tasks to be solved. They are similar in many ways, and if you deal with one of them, there should be no problems when using the others.
