Research Of Measure Method And Measure System On Capacitive Humidity Sensor

Humidity sensor has been extensively used in various fields. This subject is set forth to deal with the batch test problem which influences the production and quality of humidity sensors. The aim of the subject is to solve the high-precision measure problem of humidity sensors, reduce measure error, improve production efficiency, reduce the cost of production, and strengthen the competitive power of homemade humidity sensors. The paper introduces the research of capacitive humidity sensor measure system from the respects of measure method and system design. The main object of the measure system is the macromolecule capacitive humidity sensor that is extensively used at present. In the paper, the theory analysis, simulation verification and application design are carried out about the crucial techniques of the measure system, such as measure method, measure error tracking correction technique, over-sampling technique and digital filter techniques. Therefore, the crucial problems in the theory and design of the capacitive humidity sensor measure system are solved. The following tasks are accomplished in this paper: 1. Digital disperse complex number voltage measure method and establishment of its mathematics model. The theory analysis of the complex number voltage measure method based on DSP is carried out, and the mathematics model is built. Mathematics analysis about the measurement by digital disperse means is carried out and the disperse parameter is given. 2. The error tracking correction technique of digital disperse complex number voltage measure. The main measure errors of the complex number voltage measure method are analyzed. The mathematics method of error correction is put forward, and the tracking correction mathematics model of measure error is built. 3. Harmonic analysis measure method. Fourier transform is applied to the measure system. The signal is extracted from measure data by Fourier transform, and the interference noise is isolated from measure data effectively. 4. Digital filter technique theory analysis and application design. Traditional digital filter technique is applied to the measure system, and IIR low-pass digital filter design is completed. Wavelet analysis theory is applied to the measure system, and the wavelet filter is designed. 5. The theory analysis of the frequency spectrum and distortion of sine wave signal. The theory analysis of the frequency spectrum and distortion of sine wave signal which is loaded on the sensors as drive signal is carried out. It provides evidence for the determination of D/A bits, the points of every sine wave, and the operation amplifier of the sine wave signal generation circuit. 6. Improve the measure precision and anti-interference capability by using over-sampling technique. Many kinds of noise are brought about during the data acquisition, and the ADC of TMS20LF2407 is 10 bits, it cannot meet the requirement of high-precision measurement, so the ADC distinguish ability and anti-interference capability are effectively improved by making full use of fast A/D conversion rate of DSP and over-sampling technique in the software design. 7. The hardware design of measure system. Hardware of the measure system based on DSP uses DSP device as the core. The D/A device is used to generate sine wave signal which is used in the measure system. The A/D of DSP device is used to carry out data acquisition at a high speed. The selection of multi-channel sensor is accomplished through multi-channel analog electronic switch. The communication interface of measure system uses the interface devices of USB 1.1 protocol, and the firmware design is accomplished by using the software offered by the manufacturer. 8. The design of virtual panel and data processing software. The virtual panel can provide human-computer interface between user and system, and carry out data processing and real-time monitoring of the submachine. The data processing software can carry out the display, distribution, storage, printing and database management of the sensors'performance parameters. The measure system integrates the functions of the environment humidity simulation, data acquisition, data communication and data analysis. It can solve the urgent problem of quick and precise batch measurement of humidity sensor's performance parameters. This subject provides reference means and system framework for constructing similar measure systems.