A brief discussion on the circuit diagram of electrical control

How to read an electrical control circuit diagram? How to read an electrical control circuit diagram? How to read an electrical control circuit diagram? For beginners of electrical engineering, how to understand a circuit diagram?

How to read an electrical control circuit diagram? How to read an electrical control circuit diagram? How to read an electrical control circuit diagram?

For beginners in electrical engineering, how to understand circuit diagrams and the general method of looking at electrical control circuit diagrams is to first look at the main circuit, then look at the auxiliary circuit, and use the loop of the auxiliary circuit to study the control program of the main circuit.

1. Look at the steps of the main circuit

Step one: See clearly the electrical equipment in the main circuit. Electrical equipment refers to electrical appliances or electrical equipment that consume electrical energy. When looking at the picture, you must first clearly see how many electrical appliances there are, their categories, uses, wiring methods, and some different requirements.

Step 2: Find out what electrical components are used to control the electrical equipment. There are many ways to control electrical equipment, some are directly controlled by switches, some are controlled by various starters, and some are controlled by contactors.

Step 3: Understand the control electrical appliances and protective electrical appliances used in the main circuit. The former refers to other control components other than conventional contactors, such as power switches (transfer switches and air circuit breakers) and universal transfer switches. The latter refers to short-circuit protection devices and overload protection devices, such as the specifications of electromagnetic releases and thermal overload releases in air circuit breakers, and the uses and specifications of components such as fuses, thermal relays and overcurrent relays. Generally speaking, after analyzing the main circuit as mentioned above, you can analyze the auxiliary circuit

Step 4: Check the power supply. You need to know the power supply voltage level, whether it is 380V or 220V, whether it is powered from the busbar or distribution panel, or from the generator set.

2. Look at the steps of the auxiliary circuit

Auxiliary circuits include control circuits, signal circuits and lighting circuits.

Analyze the control circuit. According to the control requirements of each motor and executive appliance in the main circuit, find out other control links in the control circuit one by one, "break the control circuit into parts", and divide it into several local control circuits according to different functions for analysis. If the control circuit is complex, you can first exclude lighting, display and other circuits that are not closely related to the control so that you can concentrate on analysis.

Step one: Check the power supply. First, check the type of power supply. Is it AC or DC. Secondly, you must see clearly where the power supply of the auxiliary circuit is received from and its voltage level. The power supply is generally connected from the two phase lines of the main circuit, and its voltage is 380V. It can also be connected from one phase line and one neutral line of the main circuit, and the voltage is single-phase 220V; in addition, it can also be connected from a special isolation power transformer, with voltages of 140, 127, 36, 6.3V, etc. When the auxiliary circuit is DC, the DC power supply can be connected from the rectifier, generator set or amplifier, and its voltage is generally 24, 12, 6, 4.5, 3V, etc. The coil rated voltage of all electrical components in the auxiliary circuit must be consistent with the auxiliary circuit power supply voltage. Otherwise, the circuit components will not operate when the voltage is low; when the voltage is high, the coils of the electrical components will be burned out.

Step 2: Understand the uses of various relays and contactors used in the control circuit. If some relays with special structures are used, you should also understand their operating principles.

Step 3: Study the operation of the main circuit based on the auxiliary circuit.

After analyzing the above content and combining it with the requirements in the main circuit, the action process of the auxiliary circuit can be analyzed.

The control circuit is always drawn between two horizontal power lines or two vertical power lines according to the sequence of actions. Therefore, analysis can be done from left to right or from top to bottom. For complex auxiliary circuits, the entire auxiliary circuit in the circuit forms a large loop, and this large loop is divided into several independent small loops. Each small loop controls an electrical appliance or an action. When a small circuit forms a closed loop and current flows, the electrical components (contactors or relays) in the loop act to connect electrical equipment to people or cut off the power supply. In auxiliary circuits, buttons or switches are generally used to connect the circuit. The analysis of the control circuit must be carried out in conjunction with the action requirements of the main circuit at any time. Only after a comprehensive understanding of the main circuit's requirements for the control circuit can we truly grasp the action principle of the control circuit. The action principles of each part cannot be viewed in isolation, but attention should be paid to Are there any mutual constraints between various actions? For example, there should be interlocking between forward and reverse rotation of the motor.

Step 4: Study the interrelationships between electrical components. All electrical components in the circuit do not exist in isolation but are interconnected and restrictive. This mutual control relationship is sometimes manifested in one loop, and sometimes in several loops.

Step 5: Research other electrical equipment and electrical components. Such as rectifier equipment, lighting, etc.

To sum up, the key points of the line checking method of electrical control circuit diagrams are:

(1) Analyze the main circuit. Starting from the main circuit, we analyze the control content of each motor and actuator according to the control requirements of each motor and actuator, such as motor starting, steering control, braking and other basic control links.

(2) Analyze the auxiliary circuit. Look at the power supply of the auxiliary circuit and understand the functions of each electrical component in the auxiliary circuit and their mutual constraints.

(3) Analyze interlocking and protection links. Production machinery has high requirements for safety and reliability. To achieve these requirements, in addition to rational selection of drag and control schemes, a series of electrical protections and necessary electrical interlocks are also set up in the control circuits.

(4) Analyze special control links. In some control circuits, there are also some special links that are not closely related to the main circuit and the control circuit and are relatively independent. Such as product counting devices, automatic detection systems, thyristor trigger circuits, automatic temperature adjustment devices, etc. (http://www.diangon.com/Copyright) These parts often form a small system of their own. The method of reading and analyzing pictures can refer to the above analysis process, and flexibly use the electronic technology, communication technology, and automatic control system that have been learned. , detection and conversion knowledge are analyzed one by one.

(5) Overall inspection. After "breaking the whole into parts" and gradually analyzing the working principle of each local circuit and the control relationship between each part, the entire control circuit must be checked to see if there are any omissions using the "breaking into parts" method. Finally, we need to further examine and understand the connection between each control link from an overall perspective, so as to clearly understand the role, working process and main parameters of each electrical component in the circuit diagram.

1. First, you must know how this equipment operates, uses, and works;

2. Look at the circuit block diagram of this equipment, clarify the connections, relationships, and interactions between the block diagrams, and use your understanding of the "operation, use, and work of the equipment" to understand and analyze the block diagram;

3. Enter the specific circuits of each block diagram. Find the power supply terminal, signal input and output terminals of the block diagram,...

4. Open the actual circuit of the device, first find the corresponding part of the circuit corresponding to the block diagram, and divide the actual circuit into several parts according to the block diagram;

5. Enter each partial circuit, compare the circuit diagram, find the location of the corresponding components, and constantly understand and memorize the functions, operations, and possible fault manifestations of each main component in the actual circuit;

6. Finally realize the understanding of circuit diagrams and actual circuits and troubleshooting!