Project requirements analysis phase
Detailed understanding of process requirements: In-depth communication with mechanical engineers, process engineers and other relevant personnel of the project to obtain complete process flow and control requirements. For example, in an automated filling production line project, it is necessary to clarify details such as filling speed, accuracy, bottle specifications, material characteristics, etc. This information will directly determine the number and type (digital or analog) of I/O points in the PLC control cabinet and the required special function modules.
Determine the scope of control functions: clarify which devices require PLC control, such as motors, valves, sensors, etc., and the complexity of the control. For motors, determine whether speed regulation and forward and reverse control are required; for valves, know whether it is a switch type or a regulating valve, whether feedback signals are required, etc. This helps to determine the performance requirements of the PLC and the communication protocols that may be required.
Consider environmental factors: Evaluate the installation environment of the PLC control cabinet, such as temperature, humidity, dust, corrosive gases, electromagnetic interference, etc. If the environment is harsh, you may need to choose a cabinet with a high protection level, a PLC and accessories with strong anti-interference ability, or add additional protective equipment, such as air conditioners and filters, but these will increase costs. Therefore, under the premise of meeting environmental adaptability, try to choose economical and practical protection measures.
Plan future expansion needs: Consider whether the project has subsequent expansion plans, such as adding equipment, improving processes, etc. If so, reserve a certain number of I/O points, communication interfaces or cabinet space in the configuration list to avoid large-scale transformation in the future, but be careful not to over-reserve to avoid waste of initial investment.
Hardware configuration selection stage
PLC selection:
Performance matching: Select a suitable PLC model according to the control speed, computing power and I/O points required by the project. For small and simple control projects, such as small material handling systems, a small PLC with basic logical operation functions and an appropriate number of I/O points can meet the requirements and avoid the cost waste caused by using large, high-performance PLCs.
Brand trade-off: In brand selection, consider the quality, reliability and price of the brand comprehensively. Well-known brands usually have advantages in stability and technical support, but the price is higher; some cost-effective brands can reduce costs while meeting basic functions. For example, in situations where real-time requirements are not extremely high, some domestic PLC brands can be considered.
Special function modules: Only when the project really needs special functions (such as motion control, high-speed counting, special communication protocols, etc.), select the corresponding special function modules. For example, in a CNC machine tool project that requires precise control of motor position and speed, a PLC with a motion control function module is required, but it is not required for ordinary motor start and stop control projects.
I/O module configuration:
Accurate calculation of points: Accurately calculate the number of I/O points of each type (digital input, digital output, analog input, analog output) to avoid over-configuration. For example, determine the number of digital input points by counting the number of sensors (proximity switches, photoelectric sensors, etc.), and determine the number of digital output points according to the control requirements of actuators (motors, valves, etc.).
Module integration: Give priority to I/O modules that integrate multiple signal types to reduce the number of modules. For example, choose a hybrid module with both digital input and output interfaces. For the case of a small number of analog input and output points, choose a digital module with a small number of analog interfaces.
Distributed I/O considerations: For projects with widely distributed equipment, evaluate the feasibility of using distributed I/O. Distributed I/O can reduce a lot of cable laying costs and make the system architecture more flexible, but its communication stability and additional configuration costs should be considered.
Cabinet and accessories selection:
Cabinet material and size: Select the cabinet material according to the installation environment and protection requirements. In general indoor environments, ordinary cold-rolled steel cabinets can meet the protection requirements after spraying, and the price is relatively low; for corrosive or humid environments, stainless steel cabinets or additional protective coatings may be required. The size of the cabinet should be reasonably selected according to the layout of the internal equipment and the installation space, avoiding being too large or too small.
Accessory quality and price balance: For accessories such as switching power supplies, relays, contactors, etc., choose reasonably priced products while ensuring quality and performance. For example, by comparing the parameters of relays of different brands and models (such as contact capacity, action time, etc.), select products that can meet the project requirements and are relatively low in price. At the same time, pay attention to the compatibility and reliability of accessories to avoid system failures due to accessory failures.
Software configuration consideration stage
Programming software selection:
Function matching: If the control logic of the project is relatively simple, choosing the basic function free programming software provided by the PLC manufacturer can meet the requirements and reduce the cost of software purchase. For complex control projects, such as those involving large amounts of data processing, advanced algorithms, or the integration of multiple communication protocols, you may need to purchase fully functional genuine programming software, but you need to evaluate whether all the advanced functions are really needed.
Learning cost and technical support: Consider the learning curve and technical support of the programming software. Choosing software that is easy to learn and use can reduce the training time and cost of programmers. At the same time, good technical support can solve problems in a timely manner when they are encountered, avoiding project delays due to software problems.
Control program development strategy:
Program modular design: Using a modular programming method, the control program is divided into multiple functional modules, such as motor control module, alarm processing module, etc. This can improve the readability and maintainability of the program, and facilitate the reuse of some modules in different projects, reducing development costs.
Optimize algorithms and logic: Under the premise of meeting control requirements, try to use simple and effective control algorithms and logic. For example, for simple temperature control, using a basic PID control algorithm instead of a complex fuzzy control algorithm can reduce programming workload and debugging time.
Cost control strategy stage
Cost performance evaluation: When selecting each hardware and software component, perform a cost performance evaluation. Compare the performance and price of products of different brands and models, and calculate the price ratio per unit performance. For example, for I/O modules, calculate the price of each I/O point and select products with reasonable prices. At the same time, consider the quality and reliability of the product to avoid choosing poor quality products due to the pursuit of low prices, which will lead to increased maintenance costs in the later stage.
Bulk procurement and supplier cooperation: If the project involves multiple identical PLC control cabinets or there is a possibility of subsequent similar projects, consider bulk procurement of hardware components to obtain better price discounts. Establish long-term cooperative relationships with reliable suppliers and strive for better procurement conditions, such as discounts, priority supply, technical support, etc.
