Abstract: This paper introduces the concept of virtual instruments and the functions and characteristics of its software development platform, LabVIEW. A virtual instrument for automatic temperature control of each section of a ductile iron pipe annealing furnace is developed using LabVIEW, and the hardware and software design principles and applications of this virtual instrument are explained. Keywords: LabVIEW, temperature control system, virtual instrument. China's ductile iron pipe production began in the late 1980s. Due to its thin walls, ductile iron pipes can save about 53% of metal compared to continuously cast gray iron pipes. Their tensile strength and elongation are close to those of steel pipes, while their durability and corrosion resistance are significantly better than ordinary steel pipes. Therefore, they are widely used internationally in water, oil, and natural gas transportation projects, showing good development prospects. Currently, most domestic and international manufacturers use the cold-molding method to produce ductile iron pipes. The pipes produced by the cold-molding method are hard and brittle, requiring high-temperature (>920℃) annealing treatment to promote the decomposition of eutectic cementite and form a structure dominated by ferrite with a small amount of pearlite, thus achieving a higher elongation and enabling the mechanical properties of ductile iron pipes to meet international standards. Currently, there are various types of annealing equipment for ductile iron pipes. Yongtong Cast Iron Pipe Company uses a 60-meter-long horizontal continuous annealing furnace, which is divided into four stages for annealing. After high-temperature graphitization annealing, the pipes are cooled to the eutectoid temperature (around 750℃) and then held at that temperature to eliminate pearlite. Therefore, the entire annealing curve consists of four segments: heating, holding, rapid cooling, and slow cooling. Figure 1 shows some commonly used annealing curves in domestic and international ductile iron pipe production. [align=center] Figure 1 Annealing Curve of Centrifugal Ductile Iron Pipe[/align] The temperature control system mainly controls the combustion of blast furnace gas and air at each stage, measuring, displaying, and adjusting the control parameters. Our company's annealing furnace temperature control system mainly detects and adjusts the gas and air flow rate, temperature, and furnace pressure in each stage. Because the continuous annealing process for ductile iron pipes is complex, especially in temperature control, the annealing temperature and time requirements differ for different products and different sections, requiring timely manual or automatic adjustments with an error requirement within ±20℃. It is obvious that using traditional instrument control would result in a large number of instruments and systems, prone to failure, and requiring a heavy maintenance workload. Adhering to the principle of economy and practicality, the company boldly adopted the new automated process control technology, LabVIEW, as the platform for a data acquisition and temperature measurement and control system to meet the higher requirements of pipe casting production. 1. Virtual Instruments and LabVIEW The concept of virtual instruments was proposed by National Instruments (NI) in the mid-1980s. A virtual instrument uses a computer as a unified hardware platform, fully utilizing the computer's intelligent functions such as computation, storage, playback, retrieval, display, and file management. Simultaneously, it software-izes the specialized functions and panel controls of traditional instruments, combining them with the computer to form a completely new instrument system that is identical to traditional hardware instruments in appearance and function, while fully utilizing the intelligent resources of the computer. Compared with traditional instruments, virtual instruments have many advantages: they can handle more complex and faster processing of test quantities, offer richer and more diverse ways to express test results, facilitate the storage and exchange of test data, are cheaper, and have faster technological updates. Its biggest feature is that it transforms the way instrument manufacturers define instrument functions into a way users define instrument functions themselves, meeting a wide variety of application needs. Because the testing functions and panel controls of virtual instruments are all software-based, any user can modify the software to change its functionality and scale, fully embodying the design philosophy that software is the instrument. The technological foundation of virtual instruments is computer technology, and its core is computer software technology. The most representative graphical programming software is LabVIEW (Laboratory Virtual Instrument Engineering Workbench), developed by National Instruments (NI). It was the world's first 32-bit compiled program development system for instruments using graphical programming technology. Its goal was to simplify program development, improve programming efficiency, and allow scientists and engineers to fully utilize computer resources and powerful functions to quickly and easily complete their tasks; it is known as the language of scientists and engineers. LabVIEW uses WYSIWYG visualization technology to create the human-computer interface, providing many control objects for instrument panels, such as meters, knobs, switches, and coordinate planes. Users can use an editor to change the control objects to suit their specific work areas. LabVIEW provides a variety of powerful toolboxes and function libraries and integrates many instrument hardware libraries. LabVIEW is portable, supporting multiple operating systems; LabVIEW applications developed on any platform can be directly ported to other platforms. 2. Establishment and Application of Virtual Instruments for Annealing Furnace Temperature Control System 2.1 Instrument Detection Optimization Design Blast furnace gas flow rate detection typically uses orifice plates. After two years of application, the shortcomings of orifice plates in blast furnace gas flow rate detection have become increasingly apparent, failing to meet the process requirements of annealing furnace production. Due to the complexity of blast furnace gas composition, the orifice plate and pressure guide pipe become clogged, significantly reducing detection accuracy and drastically increasing maintenance. Therefore, a new generation of patented intelligent target flow meter was selected. It possesses all the advantages of orifice plates; the sensor does not contact the medium, and it measures the gas velocity through the principle of mechanical levers. It is unaffected by easily sticky or corrosive media, greatly improving the reliability and accuracy of flow detection. For temperature detection, the K-type thermocouple was replaced with an S-type thermocouple, enabling it to detect temperatures up to 1300℃, significantly extending the thermocouple's service life. The slow cooling section was originally supplied with air directly to the first and second slow cooling sections by a blower. The air volume was adjusted by regulating the opening of the valves on the blower duct. In actual production, this often resulted in motor burnout due to overheating, and the maintenance of the two GT50 actuators gradually increased. Therefore, after careful analysis of the causes and technical aspects, it was decided to use a frequency converter to directly drive the blower motor to regulate the air volume. This not only saves energy but also reduces the maintenance of the regulating valves. 2.2 Virtual Instrument Software Design The software design consists of two parts: a front panel and a flowchart. On the front panel, input is implemented using input controls (Control), and the program's results are displayed using output controls (Indicator). The flowchart is a graphical source code that completes the program's functions. It specifies the input and output of signal data, controlling the signal acquisition and analysis processes. The virtual instrument, developed using LabVIEW 8.0, can simultaneously monitor the temperature, pressure, and flow rate of each heating zone of the annealing curve in real time. The panel has four numerical display windows and four graphical display windows in the center, displaying the data. To ensure accurate data reading, two reading methods are designed: mouse reading and keyboard control via a cursor on the display screen. The system allows setting the number of sampling points and sampling frequency. The channel selection button represents the memory channel, corresponding to the reading channel; each channel can hold a set of raw signal data read from an external port or a data file. The save data command button corresponds to the display screen; pressing it saves the data displayed on the screen. There are two saving methods: saving to a file or printing. Saved data can be displayed in various ways, such as bar charts, 3D plots, and histograms. The data analysis library (button) allows for statistical, regression, and analysis (function calls, etc.) of the measured data. The help menu (button) helps users familiarize themselves with the instrument's functions and operations. Pressing the exit button closes the virtual instrument. As the mainstream development language for virtual instruments, LabVIEW's excellent graphical development environment not only includes various objects for developing virtual instrument panels and rich functions for signal analysis, but also provides an external PID control toolkit, allowing users to extend virtual instruments to the field of industrial automation control. Considering the characteristics of the application customer's system: the object is relatively simple, the nonlinearity is not high, most of them do not have time-varying and fuzzy uncertainty, and the equipment investment cost requirement is low, it is more suitable to use conventional PID control. Therefore, conventional PID control algorithm is selected. Considering that in the production process, if the computer fails and the gas and air valves are automatically closed, it may cause the entire furnace of cast pipes to be scrapped. Therefore, this solution adopts incremental PID control algorithm to automatically control the temperature of the annealing furnace. Moreover, this control algorithm will not cause a large change in the position of the actuator. It can automatically adjust the valve opening according to the temperature change, effectively ensuring the continuity of cast pipe production and the reliability of the system. Figure 2 is the block diagram of the incremental PID control system. The program for implementing the PID control function using the functional software provided by LabVIEW is shown in Figure 3. [align=center] Figure 2 Block diagram of incremental PID control system Figure 3 Flowchart of PID control function[/align] 2.4 Hardware structure of virtual instrument The hardware platform of virtual instrument mainly includes hardware for data acquisition, signal analysis and processing, and signal output display. Because the signal obtained directly from the sensor is very weak, a precision isolation instrumentation amplifier from Burr Brown Instruments, USA, specifically designed for data acquisition and possessing high precision and strong anti-interference capabilities, was selected as the main amplifier for the signal processing unit. The data acquisition system uses the Iotech WaveBook/512 Data Acquisition System, with the following main performance indicators: sampling frequency, 1MHz; number of channels, 8; A/D accuracy, ±0.025%; anti-aliasing filter; FIFO buffer, 64kΩ. 3. Optimized Heat Treatment Curves and Application Effects The heating rate and holding temperature of the annealing furnace are achieved by adjusting the flow rates of gas and air. Through system optimization, the maximum heating rate has increased from 40℃/h to 50℃/h, and the control accuracy of each furnace section temperature has improved from 80℃ to 20℃. Since normal operation, instrument detection accuracy has improved, operation has been stable, and no malfunctions have occurred. The system retains both manual and automatic control schemes. Manual operation can still be used in case of computer failure, and seamless switching between manual and automatic modes can be performed at any time. The measured heat treatment curves are shown in Figure 4. [align=center] Figure 4 Measured curve of heat treatment[/align] 4 Conclusion Virtual instruments are a product of the combination of electronic technology and computer technology. They are a high-efficiency solution with the best cost performance for industrial detection and control. By using LabVIEW to optimize the temperature control system of the annealing furnace, various problems that occurred in the production process were solved, the failure rate of the system was greatly reduced, and the accuracy of the instrument detection parameters was improved. This not only ensured the continuity of production, but also improved the product qualification rate. According to preliminary calculations, the product qualification rate increased from 97.9% to 98.8%, and the economic benefits in just one month reached more than 800,000 yuan. 5. References [1] Li Yang, Zheng Yingna, Zhu Zhengtao. Graphical programming language LabVIEW environment and its openness. Computer Engineering [2] Liang Haihong, Zhao Haishun et al. System optimization of 60x7.5m regenerative annealing furnace. Foundry