1. Introduction The precision machining of the wing alignment points of a certain Chinese aircraft model is a crucial step in wing manufacturing. To ensure the quality of this machining, an electrical measurement system is used to measure the horizontal measurement points of the wing. This system allows for real-time monitoring and recording of the horizontal measurements taken before and during wing precision machining to ensure that the wing's installation dimensions meet design requirements. According to a survey conducted by an aircraft company, previous horizontal measurement and control systems for various aircraft models used a general-purpose computer language-based human-machine interface and a microcontroller control system. However, these systems revealed several shortcomings: measurement accuracy (0.1%) did not meet testing requirements, system upgrades were difficult, and there was a lack of safety fault detection functionality. While these microcontroller-based control systems have low hardware costs, their development costs are high, and their versatility is generally limited. Based on the summary of previous systems, this paper uses an industrial control computer (IPC) as the host computer, and then installs configuration software as the program development platform on the IPC as the hardware platform to complete the display of industrial processes and control parameters, and realize production monitoring and management functions. The slave computer uses a programmable logic controller (PLC) and a data acquisition module as field-level control devices for data acquisition, status judgment and output control, forming a simple and practical wing processing level measurement and control system. 2 Composition of the measurement and control system (see Figure 1) 2.1 Hardware configuration of the measurement and control system 2.1.1 Execution system As shown in Figure 2, it is equipped with an air filter (1) air pressure reducing valve; (2) pressure sensor; (3) solenoid valve manifold; (4) two-position five-way solenoid valve; (5) speed control valve; (6) cylinder; (7) and turntable lifting mechanism, etc. It is used to adjust the measurement position and the action speed of the cylinder. The displacement sensor changes the measurement displacement under the drive of the cylinder. 2.1.2 Monitoring System To meet the above process requirements, this system uses a SIMATIC S7-200 series PLC as the field control device because this series of PLCs offers high cost-effectiveness and powerful network communication capabilities. An industrial PC (IPC) is used for network monitoring, and text displays are provided on-site for monitoring and input. Both are connected to the PLC's RS-485 communication interface. The measurement and control system has 17 analog inputs and 16 digital outputs. Simultaneously, the PLC control system should have at least two RS-485 communication interfaces. The CPU226 has two RS-485 communication interfaces, 14 digital inputs, and 10 digital outputs; two EM235 expansion modules with 8-bit digital inputs and 8-bit digital outputs are also included for future expansion. Displacement sensors, pressure sensors, sensor signal detection modules, and a 20-bit A/D conversion module are also configured. The displacement sensor is an LVDT type with an accuracy of 0.05%. Considering factors such as on-site interference and a wide temperature range, the sensor is powered by a constant current source and temperature compensated. 2.2 Configuration Software for Measurement and Control System 2.2.1 Configuration Software Previously, measurement systems lacked monitoring software; instead, human-machine interfaces (HMIs) were typically developed using general-purpose computer languages. However, these interfaces often lacked robust monitoring capabilities and had poor program scalability. Professional monitoring configuration software is a software platform tool oriented towards monitoring and data acquisition, primarily including HMIs, real-time databases, real-time control, SCADA (Supervisory Control and Data Acquisition), communication and networking, open data interfaces, and extensive support for I/O devices. Therefore, selecting professional industrial control software makes it very convenient to develop HMIs that meet actual needs. For the HMI of the precision machining automatic monitoring system proposed in this paper, several configuration software options are available, including widely used ones such as Kingview, WinCC, and ForceControl. From a cost-effectiveness perspective, this paper selected Kingview configuration software, whose software structure diagram is shown in Figure 3. 2.2.2 Communication Connection and Programming between PLC and Host Computer During system operation, the programming port of the S7-200 PLC is connected to an RS232C serial communication port of the IPC via a PPI cable for program writing, debugging, and host computer monitoring. KingSCADA communicates with the PLC using the Modbus communication protocol. Modbus is a general-purpose language designed for industrial control. Through this protocol, controllers can communicate with each other, and controllers can communicate with other devices via networks (such as Ethernet). Modbus data transmission is master/slave type, with message format being request/response frames. No handshake is required; the slave device returns a response frame until the response time expires. For broadcast messages, the slave device does not return a response frame. In networks that allow multiple stations, such as RS485, at most one slave device can respond to the master device's request. The Modbus protocol can use both ASCII and RTU transmission modes; this system supports the RTU format. KingSCADA accesses the relevant register addresses of the PLC through the serial port to obtain the status of the devices controlled by the PLC or modify the values ​​of relevant registers. In actual programming, there is no need to write programs to read and write PLC registers. KingSCADA provides a data definition method. After defining I/O variables, the variable names can be directly used for system control, operation display, trend analysis, data recording, and alarm display. To ensure that the S7-200 PLC can communicate normally with the IPC, in addition to correctly setting the PLC during configuration (baud rate 9600b/s, 7 data bits, 1 stop bit, no parity, station number 2) and loading the PLC's communication driver, a program as shown in Figure 4 also needs to be written in the PLC. Its function is to make the PLC's communication parameters consistent with the host computer's settings. 2.2.3 Sensor Calibration Algorithm When fitting a function using the least squares curve fitting method, if the approximation order is too high, resulting in slow calculation speed, piecewise curve fitting should be used. The principle is: select multiple test points for precise testing of the sensor in segments, and draw the fitting curves of each segment of the sensor based on the test data. Then, use the fitting function to generate correction values ​​and generate a piecewise lookup table. Using Kingview's tools to directly look up values ​​in a table will obviously affect measurement accuracy. However, employing a piecewise linear interpolation method will effectively improve system accuracy. Therefore, combining piecewise function fitting algorithms and linear interpolation will effectively improve the system's measurement accuracy. The compensation process using linear interpolation involves first determining the interval in which the measured value falls, then retrieving the corresponding values ​​at the interval endpoints, and using the formula: [Formula omitted for brevity]. Here, M is the measured output value, and (M1, P1) and (M2, P2) are the values ​​at the interval endpoints. 3. Main Functions of the Measurement and Control System The wing precision machining level measurement and control system proposed in this paper, based on configuration software and PLC, can monitor the measurement position in real time according to different process parameters. Process personnel can easily set and modify various process parameters through a user-friendly HMI. The system mainly has the following functions: (1) Basic information display function: display the basic information of each point (horizontal coordinate, vertical coordinate, zero position, etc.); (2) Process parameter configuration and modification function: set and modify the optimal value of each point variable (such as local shape deviation, installation error, left and right height difference, etc.); (3) Real-time/historical curve display function: the system stores the measured parameters of each point into the corresponding Excel database in real time and displays the real-time/historical curve on two types of HMIs; (4) Alarm function: alarm function is set for the communication points of the system and the deviation of each point. Once these factors reach the limit, the HMI will issue an alarm message to notify the user; (5) Report function: the data report mainly reflects the data and status in the production process. By statistically analyzing the long-term production process, the production status of the equipment can be grasped and analyzed; (6) Manual/automatic switching function: the circuit design realizes manual, semi-automatic and fully automatic modes, and can realize seamless switching between automatic/semi-automatic and manual operation modes of the monitoring system; (7) Sensor automatic correction function: the software corrects the nonlinearity and temperature drift of the sensor by using a comprehensive algorithm of piecewise fitting and linear interpolation. (8) Other functions: In addition to the basic functions mentioned above, this system also provides login permission protection and printing functions. The former provides corresponding access permissions for users at different levels to protect the security and stability of the system. The latter provides users with the function of printing basic system information and real-time/historical curves. 4 Conclusion This system utilizes the powerful data processing and graphics performance capabilities of industrial control computer configuration software, the strong anti-interference capability of PLC, and its suitability for industrial sites. It integrates advanced automation technology, computer technology, communication technology, fault diagnosis technology, and software technology, and features high reliability, easy maintenance, and high measurement accuracy (0.1%). This system realizes centralized data management, automatic control, fault detection, and other functions. After its implementation, it has achieved good process control requirements, has a high cost-performance ratio, and has received unanimous praise from users. It is suitable for promotion and use in China's aviation industry.