Analysis of the design and application of a constant temperature automatic calorimeter based on S3C2410

　　Performance characteristics of the calorimeter: 5.2-inch touch-screen LCD screen with advanced American technology, integrated installation method to ensure the firmness of the touch screen. Infrared technology, CRT display materials are used to make the touch screen more durable. Multi-layer composite film covering ensures that color distortion, reflectivity and clarity are in the best state, sensitive sensing, high positioning accuracy, effective area up to 90% wear resistance, life span up to 10 years, Chinese character display, no external computer required. It can be operated directly or controlled by computer. Chinese menu-style operation interface, simple structure, intuitive and easy to learn, easy to operate, stable and reliable performance, adopts internal and external tube photoelectric isolation with strong anti-interference ability. Unique foaming insulation technology is adopted, and it is not affected by external temperature during the experiment.

　　Automatic water filling, no need to adjust water temperature, just put the aerobic bomb into the barrel, the instrument can automatically complete all tests. Reasonable structure, excellent workmanship, reliable performance, low failure rate.

　　The results are accurate, and it adopts a unique cooling correction system, water circulation system and software automatic error compensation system. It also has the functions of large outer tube water storage capacity and good thermal stability.

　　In recent years, with the continuous maturity of embedded technology, its cost has continued to decline, and its advantages of variable scale, flexible expansion, high real-time performance and stability, and small system kernel have gradually emerged.

　　1 Basic principles

　　The constant temperature calorimeter measures calorific value by the oxygen bomb method. The heat released by the combustion of the substance placed in the oxygen bomb is transferred to the water and the instrument system through the bomb tube, and then the calorific value of the substance is calculated according to the change in water temperature. The basic block diagram of its measurement is shown in Figure 1. According to the basic principle of the oxygen bomb method, the calorific value calculation formula is as follows:

　　Where: E is heat capacity, unit: J/K; q1 is ignition heat, unit: J; q2 is the total heat generated by additives such as wrapping paper, unit: J; m is the mass of the sample, unit: g; Tc is the temperature at the end of the main period, unit: ℃; Tb is the temperature at the beginning of the main period, unit: ℃, C is the cooling correction value, unit: ℃.

　　It can be seen from the above formula that as long as the outlet water temperature and related parameters are measured, the calorific value of the coal sample can be calculated.

　　2 System Design

　　2.1 Hardware Design

　　The S3C2410 processor is a 32-bit microcontroller produced by Samsung based on the ARM920T processor core of ARM and manufactured using a 0.18um process. The processor has: independent 16KB instruction cache and 16KB data cache, MMU, LCD controller supporting TFT, NAND flash controller, 3-way UART, 4-way DMA, 4-way Timer with PWM, I/O port, RTC, 8-way 10-bit ADC, Touch Screen interface, IIC-BUS interface, IIS-BUS interface, 2 USB hosts, 1 USB device, SD host and MMC interface, 2-way SPI. The S3C2410 processor can run at up to 203MHz.

　　The connection block diagram of S3C2410 and various parts of the calorimeter is shown in Figure 2. After the hardware connection, the software driver is required for each part and the port of S3C2410.

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　　2.1.1 ARM board selection

　　This design chooses the S3C2410 processor, which is widely used in the market and is typical in structure and resources, mainly based on the following reasons:

　　(1) High cost-effectiveness and the most widely used. As a classic ARM9 series processor, S3C2410 has the most complete information and the most development kits for various drivers, which is conducive to developers' development.

　　(2) By adopting the design concept of separating the core board and the base board, users can easily use the Core-Board for secondary development.

　　2.1.2 Sensor Selection

　　Most of the current calorimeters use platinum resistance as the temperature measuring element; although it has the advantages of high accuracy, the maximum nonlinear error of platinum resistance can reach 2% in the range of 0 to 800°C without correction, and they are analog sensors, and the output signal needs to be converted to analog/digital, which not only complicates the circuit and increases the cost, but also increases the error.

　　The quartz crystal temperature sensor HTS-206 is one of them. It is produced by EPSON Corporation of Japan. Its oscillation frequency is around 40 kHz and its operating temperature range is -55 to +125°C. Its measurement accuracy can reach 0.05°C after correction using the multi-point difference method. The conditioning circuit of the quartz crystal resonator HTS-206 consists of three main parts: an oscillation circuit, a frequency divider, and a counter. Its conditioning circuit is shown in Figure 3.

　　The previous method of measuring frequency is to connect an FPGA chip to the chip, but the operating frequency of HTS-206 is about 40 kHz, which is consistent with the working performance of S3C2410. In order to save costs, the output of HTS-206 is rectified and amplified, and then passed through the EINT0 port of S3C2410, using the FIQ interrupt mode.

　　Use software to set the gate time of the interrupt as Tw, and record the number of change cycles (or pulses) N of the measured signal. Then the frequency of the measured signal is:

    2.1.3 Control part

　　The control part is composed of oxygen filling control, water filling and discharging control, water level control, ignition control, lifting motor control, etc.

　　The oxygen charging circuit mainly controls the charging and discharging of the oxygen bomb. When the experiment starts, a signal is sent to open the valve. When the oxygen bomb is inflated to a certain pressure, a signal is sent to S3C2410. S3C2410 receives the signal and controls the valve to close.

　　The water filling and discharging and water level control system mainly completes the tasks of water filling, drainage and positioning of the inner and outer cylinders. The water levels of the inner and outer cylinders are measured by two detectors respectively, and the water levels are compared by using the program, so as to achieve the purpose of determining the water quantity of the inner and outer cylinders.

　　The ignition system controls the ignition device in the oxygen bomb. The specific control requirements are: the ignition wire ignition is carried out after the self-check. If everything is normal, ignition is carried out. If the ignition is successful, a signal is sent to S3C2410 to start the temperature measurement system. If the ignition fails, the test is exited.

　　2.1.4 S3C2410 Network Communication

　　As shown in Figure 4, S3C2410 uses CS8900A-Q3 controller to expand network interface module. Its transmission rate is 10 Mb/s. CS8900 works in 16-bit mode, and the default working mode of network card chip reset is I/O connection. Since the interrupt levels of CS8900A and S3C2410 are opposite, a NOT gate is required between the interrupt signal lines. The sending and receiving ends of the signal are connected to CS8900A through the RJ45 interface, and then transmitted to S3C2410, thus forming a hardware channel for Ethernet signal transmission.

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　　2.2 Software Design

　　2.2.1 Establishing the development environment

　　Before developing software for S3C2419, you need to establish a suitable development environment through the following steps.

　　(1) Port UBOOT to the S3C2410 development board.

　　(2) Use H-JATG software to read the CPU information of the board, and use the AXD Debugger software in the ADS development environment to establish a simulation development environment.

　　(3) Simulate and establish a minimum system, initialize each port, and set parameters such as clock and power. After the simulation is successful, use ADS to download the initialization file to the mainboard.

　　2.2.2 System programming

　　As shown in Figure 5, according to the requirements of GB (T) 213-2003, the oxygen filling time is set to 18 s. When the oxygen filling pressure is greater than 3.2 MPa, it is displayed that the oxygen filling pressure is too high and the experiment is terminated. The ignition and control parts are omitted, and the main procedures are as follows:

　　At the beginning of the experiment, the data was sampled once per second. After 8 minutes of the experiment, the data was sampled once every 1 minute. The experiment ended. Then we entered the data processing part. This part includes data printing, storage and data transmission on the Internet. Due to space limitations, this part of the program is not listed.

　　3 Conclusion

　　Calorimeter is an important measuring instrument for energy production and energy consumption enterprises. Its measurement accuracy and efficiency directly affect economic benefits. In order to improve the measurement accuracy of calorimeter, the temperature measurement accuracy, accuracy, stability and many other aspects of the entire calorimetric system need to be improved and enhanced.

　　The design strictly complies with GB (T) 213-2003 standard, and is different from the 8-bit data transmission mode of the single-chip microcomputer used in the previous calorimeter. Instead, it uses the 32-bit data transmission mode of the S3C2410 chip. At the same time, it has high stability and can work normally in complex environments. Therefore, the calorimeter is an important instrument that is necessary for energy production and energy consumption enterprises. Its measurement accuracy and efficiency directly affect the economic benefits. The calorimeter can be used in the power, coal, coke, petroleum, chemical, cement, military, food, feed, wood, charcoal, scientific research and other industries to measure the calorific value of solid, liquid and other combustible materials. Due to its wide range of applications, the development of a calorimeter with higher measurement accuracy and efficiency has a good development prospect and economic benefits.