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1、基于单片机的气敏传感器测试系统谭永红 雷 跃摘 要 本文介绍一种新型的气敏传感器测试系统的设计方法。该系统基于具有语音处理功能的凌阳SPCE061A单片机，能同时进行多路传感器测试、过程控制，及用虚拟仪器完成数据处理，并能用语音直接播报测试结果，克服了目前气敏传感器人工操作测试带来的效率低、误差大、操作人员长时间工作等问题。关键词 气敏传感器 单片机 语音播报 一、引言 气敏传感器是能够感知环境中某种气体及其浓度的一种敏感器件，它将气体成分、浓度等有关的信息转换成电信号，从而可以进行检测、监控、报警；还可以通过接口电路与计算机组成自动检测、控制和报警系统。目前，人们对气敏传感器的测试方法主要停
2、留在用人工手动的方式来操作，开发出一种实用高效的智能化传感器测试装置是极为必要的。而语音信号是信息的又一主要载体，如果在这些测量场合能用语音直接报出结果，将给操作人员带来极大方便，下面就介绍一种具有新功能的新型的气敏传感器测试系统。 二、气敏传感器测量原理 作为气体敏感材料的半导体氧化物的气电转换机理是：在不同气体中，半导体氧化物材料发生的氧化还原反应不同，从而引起材料电导（电导与电阻互为倒数）的不同变化，使传感器分辨出被测气体。因此，只要能测量出已知气体中气体传感器电导的变化，就可测量出该气敏传感器的性能指标。气敏传感器的测试电路如图1所示，负载电阻RL串联在传感器中，串联回路施加工作电压V
3、C，VF为热丝两端加热电压。在洁净空气中，传感器的电阻RO较大，在负载电阻RL上的输出电压 图1 气敏传感器的测试电路较小；当在待测气体中时，传感器的电阻 RO变得较小，则负载电阻RL上的输出电压较大，其电压值与VRL器件的电阻值RO之间的关系如下：RO=式中：为VC测量电压，一般为5V；VRL为负载电压；为RL负载电阻（已知）；RO为元件的电阻值。 随着已知气体浓度不同，负载电压产生不同变化，传感器的元件阻值也会产生相应的变化，而根据不同气体环境下元件电阻的阻值，就可判断出该传感器的指标是否符合标准值。三、系统硬件设计 气敏传感器测试系统如图2所示，由元件测试箱和PC微机两部分组成。元件测试
4、箱主要包括了元件箱和单片机系统两部分。元件箱的主要作用是模拟气敏元件的各种现场使用环境，所有被测传感器就放置在元件板上，可由单片机系统中的电子开关巡回选择。当充入某种浓度气体时，被测传感器的阻值发生相应的变化，引起传感器负载输出电压也发生变化，该电压信号被采样保持后，送入单片机系统进行处理。 在单片机系统中选用凌阳SPCE061A单片机，其内部具有七通道10位电压A/D模数转换器和两个10位D/A数模转换通道，这样节省电路板面积，简化了硬件电路。使用者只需在软件编程时加入启动A/D转换的指令即可完成操作。为了保持数据采集的准确性，需要进行N次数据采集然后取平均值，即每次采集进来的负载电压VRL
5、经 图2 测试系统过A/D转换后要送给单片机的算术逻辑单元，同N1次的A/D转化结果进行取算术平均值运算。把最终结果放到存储区，等待上位机进行数据分析和判断。对于语音功能的实现，则要利用单片机内部的D/A数模转换器，把事先已设置好的语音信号如“开始测量”、“测量结束”等经过该数模转换通道送到扬声器。 SPCE061A内部自带两个10位D/A转换通道，比较容易实现语音功能。 四、系统软件设计 系统的软件包括两部分。一是下位机的软件，它主要完成对传感器输入信号的采集、存储以及定时，通过RS-232串行接口向PC机发送数据，同时实现语音数据编码处理、存储、解码处理以及D/A转换等功能。下位机主程序框
6、图如图3所示，而中断子程序和语音子程序在此不再赘述。另一部分是数据分析软件，它采用Visual C+6.0开发系统，具有一个良好的人机操作界面，可以随时测量和采集传感器的任意参数，并可查看系统任一通道的响应曲线以及历史运行记录。 图4是本系统的上位机虚拟仪器中的测量结果和数据分析窗口，其中显示出的8个通道的传感器在正常空气中的元件电阻阻值为RO，当注入两种已知浓度不同的气体时，元件电阻阻值分别为R1和R2，以此可计算出它在这两种情况下的灵敏度。图5是随机抽取的第一通道传感器的响应曲线，它能较全面地反映出某一通道的传感器在设定图3 程序框图 时间内的输出特性。从图中可看出，第一通道的被测气敏 元
7、件在注入已知浓度气体的情况下，在2S左右阻值达到稳定,即传感器输出开始稳定。输出特性参数见图5窗口显示数据，可判断、比较元件是否符合标准要求。 图4 微机虚拟仪器分析窗口 图5 响应曲线五、语音功能的实现 气敏传感器测试系统的语音功能的实现，主要体现在当测量传感器数据的同时, 扬声器中会发出语音提示，如“开始测量”、“开始测量电阻RO”、“开始测量电阻R1”、“开始测量电阻R2”、“开始响应曲线绘制”、“复位”等。 当测量结束后，系统会播报：“RO测量完毕”、“R1测量完毕”、“R2测量完毕”等。 语音处理大致可以分为A/D转换、编码处理、存储、解码处理以及D/A转换等步骤。SPCE061A单
8、片机具有内置自动增益控制功能的麦克风输入方式，同时具备双通道10 位DAC方式的音频输出功能，因此可以解决上述语音处理问题。SPCE061A的开发软件具有一个SACMLI库，可以将A/D、编码、解码、存储、D/A做成相应的模块, 对于每个模块都有其应用程序接口API，在了解每个模块所要实现的功能及其参数的内容后，调用该API函数即可实现语音处理功能。对于常用的SACMA2000和SACM480两种放音算法则要涉及到语音资源的添加问题，即将所需要的WAV文件按照需要的压缩比进行压缩,变成资源表形式在程序中调用。这样,当把录制好的语音文件经过压缩存入存储器后，在程序执行过程中调用该语音模块的API
9、函数即可实现语音输出功能了。六、结语 本设计是选用凌阳SPCE061A单片机作为气敏传感器测试系统的控制核心，测试系统具有语音播报功能，测试的精度达到了0.5，适合于气敏传感器生产及研制单位用来批量地检测传感器的性能指标，具有较高的实用价值。 参 考 文 献1 陈杰，黄鸿. 传感器与检测技术M，北京：高等教育出版社，20032 何希才，薛永毅. 传感器及其应用实例M，北京：机械工业出版社，20043 彭传正，林春景. 凌阳单片机原理与实践M，北京：北京航空航天大学出版社，20064 罗亚非. 凌阳十六位单片机应用基础M，北京：北京航天航空航天大学出版社，2001 （原刊于中国科技信息2007年
10、第6期）Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through
11、 the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky,
12、 and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot t
13、apping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of s
14、pace - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straigh
15、t line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that
16、 same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry clea
17、ning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission contro
18、l as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited
19、cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial air
20、liners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll b
21、ack the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like divi
22、ng into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the mo
23、re dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main
24、chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgart
25、ner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
