As an electrical maintenance technician, being able to read circuit diagrams is an essential skill. Circuit diagrams provided by different manufacturers may vary, and the arrangement of the diagrams will also differ depending on the complexity of the equipment. Some simple equipment, such as traditional drilling machines or lathes, can be represented by just a few pages, while complex automated equipment or production lines may require dozens or even thousands of pages of diagrams.
Understanding circuit diagrams hinges on grasping their underlying principles. Each diagram is arranged according to specific patterns; we need to locate the relevant points and components based on the circuit's operating principle. Here are the basic methods for reading circuit diagrams:
1. Schematic diagrams are usually drawn in parts such as power supply circuit, main circuit, control circuit, signal protection circuit, and lighting circuit.
2. The positions of electrical contacts in the schematic diagram are drawn according to their normal positions when the circuit is not energized and not subjected to external force. When analyzing the principle, you should start from the normal positions of the contacts.
3. Electrical components in the schematic diagram are not drawn with actual physical shapes, but are drawn using the unified national standard symbols prescribed by the state, in accordance with the GB4728 standard.
4. In the schematic diagram, although the electrical components are not drawn together according to their actual positions, their actions are related and must be labeled with the same text symbols.
5. In the schematic diagram, cross wire connection points with direct electrical connection should be represented by small black dots, while cross wire connection points without direct electrical connection should not be drawn with small black dots.
Once you've grasped these basic principles, you can try writing the circuit's operation flowchart. Most modern equipment is automatically controlled, and the PLC's input and output points are also shown in the circuit diagram. Only by clearly understanding the circuit diagram can you have a clear path to follow during repairs; otherwise, you'll be at a loss.
In factories, we often encounter imported equipment whose circuit diagrams are designed according to the practices of foreign manufacturers, such as Siemens, ABB, and Mitsubishi. Before reading these circuit diagrams, it's essential to understand their unique patterns. In future articles, I will continue to share some circuit diagram reading techniques from foreign manufacturers to help everyone better master circuit diagram reading methods.
I. The Importance of Circuit Schematic Design
Circuit schematics are one of the core documents in electronic circuit design. They graphically illustrate the connections between various electronic components and the flow of signals within a circuit. Through circuit schematics, engineers can clearly understand the working principle of a circuit, enabling circuit analysis, fault diagnosis, and design optimization. Simultaneously, circuit schematics serve as an important basis in the electronic manufacturing process, providing guidance for PCB (printed circuit board) design, component selection, and assembly and debugging.
II. Basic Steps in Circuit Schematic Design
Define design requirements
Before starting to design a circuit schematic, it is essential to clearly define the design requirements and objectives. This includes considerations such as the circuit's function, performance specifications, input/output requirements, and operating environment. Only by clearly defining the design requirements can the circuit be designed in a targeted manner, ensuring that the designed circuit meets the requirements of the actual application.
Selecting electronic components
Selecting appropriate electronic components based on design requirements is a crucial step in circuit schematic design. When selecting components, factors such as performance parameters, reliability, cost, and package type must be considered. Additionally, the component datasheet should be consulted to understand its usage and precautions.
Draw circuit schematic
After selecting the electronic components, you can begin drawing the circuit schematic. When drawing the schematic, certain specifications and standards must be followed to ensure clarity, legibility, and accuracy. Generally, a circuit schematic should include power supplies, input/output ports, electronic components, wiring, and labels. During the drawing process, professional circuit schematic design software such as Altium Designer, Eagle, and KiCad can be used. These software programs offer rich component libraries and drawing tools, which can greatly improve design efficiency. After drawing the circuit schematic, it needs to be analyzed and optimized. Circuit analysis helps engineers verify whether the circuit's functionality and performance meet design requirements and identify potential problems and risks. Common circuit analysis methods include DC analysis, AC analysis, and transient analysis. Based on the analysis, the circuit can be optimized, such as adjusting component parameters and changing the circuit structure, to improve the circuit's performance and reliability. After completing the circuit schematic design, design documents need to be generated, including the circuit schematic, component list, and design specifications. These documents will serve as important bases in the electronic manufacturing process, ensuring that the manufactured electronic products meet design requirements.
III. Techniques and Precautions for Circuit Schematic Design
When drawing circuit schematics, components should be arranged logically to ensure clarity and readability. Functionally related components can be grouped together, arranged according to signal flow. At the same time, pay attention to the size and shape of components to avoid overlap and crowding. In the circuit schematic, the names, parameters, and signal names and directions of components must be correctly labeled. Labels should be clear, accurate, and easy to understand and communicate. Consistency and standardization of labeling are also important to avoid confusion and errors.
In high-speed digital circuit design, attention must be paid to signal integrity issues, such as signal reflection, crosstalk, and timing. Several measures can be taken to improve signal integrity, such as using impedance matching, terminating resistors, and proper wiring. After completing the circuit schematic design, an electrical rule check should be performed to ensure that there are no electrical errors in the schematic, such as short circuits, open circuits, or floating pins. Professional circuit schematic design software can be used for electrical rule checks to improve the reliability of the design. When designing circuit schematics, it is beneficial to refer to excellent design examples and learn from the design experience and techniques of others. Relevant design examples can be searched online, or professional e-books and magazines can be consulted.
