【作者】 赵祺；

【导师】 王剑钢；

【作者基本信息】 吉林大学 ， 生物医学工程， 2007， 硕士

【摘要】 随着现代科技的进步,可燃气体的应用越来越广,在人民的生产生活中的地位也越来高。与传统燃料相比,可燃气体具有可再生、燃烧充分、污染小、热量高、价格低廉等优点,已经成为居民生活和工业领域的重要热源。但其致命的缺点是极易泄露,一旦泄露就可能会对人民的生命财产造成巨大的威胁。所以是否能够准确可靠的检测可燃气体的浓度成为可燃气体能够广泛使用的前提。本装置采用高稳定性SnO2半导体金属氧化物传感器和单片机为技术核心,并辅以温度传感器和湿度传感器对工作环境中的温度和湿度进行补偿,完成CO和CH4气体及环境温度、湿度的检测。并采用优化的专用软件对各种传感器的非线性、温度漂移等进行修正和补偿,与传统的气体检测装置相比具有稳定性更好、准确性更高等优点。同时还具有声光报警、液晶数据显示、数据传输等功能,是一种具有较好实用价值的可燃气体检测装置。装置通过在温度为20℃,相对温度为65%的CH4的环境中进行的测试,根据对于实际可燃气体浓度和通过系统测得的气体浓度的比较,系统基本达到了设计要求,能够准确对可燃气体作出快速准确的检测的相应的控制功能。更多还原

【Abstract】 With the progress of modern technology, combustible gases are used in industry and our daily lives more and more, which include Methane (CH4), CO etc. These gases can provide a lot of advantages and value for the people’s production and lives. However, they are more difficult to control compared with the solid coal and liquid petroleum, because they are gaseous substances. Leak may cause an explosion, fire or poisoning, which will be a serious threat to safety of people’s lives and property. Without detecting the content of combustible gases that are in industry and home quickly and accurately to eliminate combustible gases leakage, it can not guarantee to safely use combustible gases and healthily develop industrial production. Researching on the high-performance portable combustible gases detection instrumentation is an interested problem. Based on this purpose, in the paper I design a portable intelligent combustible gases detection system with the combustible gases sensor.In this design, the main function of portable combustible gases detector is to detect content of combustible gases (CH4 and CO) of the measured gas accurately, and to display combustible gases concentrations through the LCD. When the gas concentration reaches a certain threshold value, it will give off acousto-optic alarm. To enhance practical value, the system is also designed a human interface with the computer, communication port with computer, battery power detection device, gas pump module. In order to achieve the above functions, system should have gas detection sensor, temperature detection sensor, humidity detection sensor, signal conversion and adjust module, AD conversion chip, MCU, LCD, input keyboard, acousto-optic alarm module,RS-232 communication module, battery power detection module and gas pump control module.Technical parameters of the system are as follow. Detection range of CO is 0~150ppm; measurement accuracy of CO is not more than 20ppm; alarm threshold value is 30ppm. Detection range of CH4 is 0~5000ppm; measurement accuracy of CH4 is not more than 500ppm; alarm threshold value is 3500ppm. The working voltage of the system is +9V; the temperature is -20~+70°C, and relative humidity is 10~95%RH.Gas sensor is the starting point of the system as well as the core and emphasis of the system, so choosing a suitable sensor is critical for a successful system. The system adopts SnO2 semiconductor metal oxide gas sensors--TGS842 sensor which is made by FIGARO Company of Japan. TGS842 has high sensitivity to combustible gases, long-term stability, and good selectivity for a special gas. At different temperatures TGS842 manifests different sensitivity for different gases. Meanwhile TGS842 has a short response time and very simple external circuit. I design a controllable heating circuit according to character that TGS842 manifests different sensitivity for different gases at different temperatures. We can control the temperature of sensor through controlling the heating voltage. Heating voltage of sensor can switch between +2V and +5V. As the sensor is embedded installation, it is necessary to use an gas pump to pump gas into apparatus. This will speed up the flow velocity of measured gas, so that sensor can detect the change of external gas concentrations much faster. In addition, using the gas pump can accelerate the change of the sensor’s surface temperature, which is convenient for sensor to switch in different temperature. Resistance changes of gas sensor are transformed to voltage conversion value by sensor signal detection circuit. The voltage is amplified and adjusted by AD623 amplifier, which can be controlled by MCU to switch different gain between different gases. The adjusted signal can be turned into digital signal, which can be identified by MCU only after AD conversion. Temperature and humidity detection modules adopt an integrated digital temperature and humidity sensor, which include a capacitance polymer humidity sensor and a temperature sensitive component made of energy-gap materials. Those sensitive components, an 14 bit AD converter and a serial interface circuit are design on the same chip. It will be able to exactly know the technical parameters of temperature and humidity in the sensors working environment by using SHT71. Then system can provide reliable temperature and humidity compensation for the gas sensor signal. System adopts TLC2543 as AD conversion chip, which is 12 bit high precision AD chip. TLC2543 has 11 analog input channels and it communication with MCU via a serial way that can save resource of MCU Very much. Its conversion time is just 10μs so that it doesn’t need external sampling keeping circuit. The calculate core of system is STC89C58, which has 32KB FLASH memorizer that can support ISP function, is can download program via RS-232 serial port without special programmer that is easy for programming and testing. It also has 1280B RAM and 16KB E2PROM. In addition, it has soft watchdog and low power design. Human interface with the computer is used SMG12864ZK Chinese characters LCD display module and 2*2 keyboard which are mode key (MODE), plus key(+), subtract key(-) and enter key(ENTER). The system can switch in different mode with those control buttons, and alarm value can be realized the dynamic setting. The system place an RS-232 serial port to communicate with the external. As the only communication port of system serial port is very important. With the serial port, we can use the computer on-line to demarcate sensor, set up the alarm value online, and order MCU to show the gas concentration of environment as well as the alarm value which is already set up. We can also download the new sensor-driver program and system update program from the PC to MCU through the serial port. Acousto-optic alarm module adopt alarm buzzer and three color LED to display the state of system and gas concentrations.The software of system is compiled with C51 compiler system. And the main program has been divided into several sub-module. The major functions of software are such as setting initial state of the system, identification of gas composition and concentration, temperature and humidity measurement, compensation to the gas concentration according to the temperature and humidity, serial communications, scanning keyboard and model choice, displaying the gas concentration, acousto-optic alarm and so on. Interrupt service routine of timer 0 is the core of the system, because many of the major functions are embedded in the interrupt service routine. The time that timer 0 set up is 50ms, which means main function will have a routing cycle per 50ms. Interrupt service routine includes combustible gas detection subroutine, the detection subroutine of temperature and humidity, correcting subroutine for gas concentrations, dynamic setting subroutine for alarm value, change display, trigger watchdog and so forth. Serial communication module is also a key of the system, whose communication protocol has been drawn for facilitating the continued development and application of system upgrading. To enhance system reliability, we will set up timer 2 through software to achieve watchdog function, trigger watchdog on time and correct to avoid program error.The test of system is carried out at a CH4 environment in which temperature is 20°C, and relative humidity is 65%. Based on the contrast of actual gas concentration and the measured gas concentrations, the system basically accord with the design requirements. It can be achieve rapid and accurate response to combustible gas.更多还原