基于单片机的数字电压表设计与仿真

由于纯硬件数字电压表结构复杂,测量精度低,价格高,而在日常使用中,使用频率高,导致万用表经常损坏,故障率高,给使用和维修带来很多不便.为了设计一种高精度数字电压表,采用AT89C52单片机和ADC0809模/数转换相结合的方法,做了大量Proteus仿真实验,获得了普通纯硬件数字电压表无法达到的测量效果.实验结果证明,使用软硬件相结合设计的数字电压表,具有结构简单,测量精度高,故障率低等功能.     

基于FPGA的新型数字电压表设计

准确可靠的电压测量在大学物理教学中具有重要意义。在研究目前主流电压表设计方案的基础上,提出一种基于FPGA技术的新型数字电压表的设计方法,极大地增强了系统集成度和电路可靠性。以Altera公司高性价比的CycloneⅡ系列EP2C5T144芯片为控制核心,以较高性能的模／数转换器为信号采集芯片,完成电压数据的采集、转换、处理、显示,并实现了档位的自动转换和较宽的测量范围。详细讨论仪表关键电路的设计思路以及关键算法的实现步骤。测试结果表明,该仪表测量误差不大于0．02V,具有较高的测量精度,满足教学实验中的电压测量要求。     

采用时间标签抗干扰算法的高精度直流电压测量

提出了采用一种改进的移动防脉冲抗干扰平均数字滤波算方法,设计了一种高精度、高性价比的直流电压表。在传统滤波法基础上,算法设计采用时间标签实现了移动防脉冲干扰平均数字滤波的采样值实时更新,从而提高了采样的时效和精度;硬件设计采用高精度的A/D转换芯片HI-7159A。实验证明该电压表的精度最高可达到5 ppm。     

一种量程自动切换数字电压表的设计

利用单片机AT89C51、A/D转换模块和LED数码显示器,实现了一种具有量程自动切换功能的直流数字电压表,该电压表具有测量精确度高,性能稳定,扩展功能强及显示清晰度高等特点。     

Measured Output Voltages of Piezoelectric Devices Depend on the Resistance of Voltmeter

Piezoelectric mechanical energy harvester (MEH) has been developed as an important emerging variant of piezoelectric devices. Experiments in the literature show that the voltage–time curves of piezoelectric devices encompass both positive and negative characteristics even though the strain in the piezoelectric material is always positive during the applied cycling load. This does not agree with the results predicted by the piezoelectric theory of open circuit. Here, both the experiments and theory are performed to understand this important problem. A zirconate titanate (PZT) MEH is fabricated and the output voltages are recorded with three voltmeters. It is found that the measured voltages depend on the resistance of voltmeter. The peak value of voltage increases with the increase of the resistance of voltmeter, which is contrary to the established knowledge that the measurement results are independent of the instruments used. A theoretical model considering the voltmeter with finite resistance is established. The charge is allowed to go through the voltmeter and switch the directions during increasing and releasing of strain. The results by this model agree well with those from the experiments. The findings suggest that the resistance of voltmeter should be reported for voltage measurement of the piezoelectric devices.     

Variation of velocity/field curve of GaAs in the temperature range 40?180°C

A high-power microwave technique has been used to measure the velocity/field characteristic of GaAs. A small increase in the threshold field has been observed when the temperature was increased from 40°C to 180°C.     

A novel method of temperature compensation for multiplexed liquid crystal displays

A new, simple technique for compensating the drive voltages to allow for temperature changes of multiplexed liquid crystal displays is described. No components apart from the display and drive electronics are required and compensation over the temperature range 0°C to 50°C has been achieved.     

Q band interferometer for high temperature measurements

A Q band interferometer for determining the complex permittivity of solids and liquids between 20°C and 1300°C has been developed. The Roberts and Von Hippel standing-wave method was used. The technique involves the utilization of a computer-assisted digital voltmeter for data acquisition and treatment. Results for a 67SiO₂?33Na₂O within the temperature range 20–400°C and in the liqid state (950°C) are presented.     

Precision enhancement in 8 mm interferometry

A Q band interferometer for determining the complex permittivity of materials having dielectric loss factor within 10^?3 to 1, has been developed. The technique involves the use of a computer-assisted digital voltmeter for data acquisition and treatment. The method of computing the dielectric parameters from the deduced VSWR and minima displacement is outlined and precision increase with this type of measurement is discussed. Results for polar solutes in non polar and in polar solvants are presented. Measurements on solids within the temperature range 20–400°C are also discussed in conclusion.     

Growth temperature dependence of low-noise MESFET in molecular-beam epitaxy

The substrate growth temperature dependence of electrical properties for a low-noise MESFET fabricated on MBE-grown material has been demonstrated. The optimum noise figure and its associated gain were attributed to the higher epilayer quality and mobility at a growth temperature of 650°C between temperatures of 550°C and 700°C.     

Growth of Al0.3Ga0.7As by molecular beam epitaxy in the forbidden temperature range using As2

Using a thermal cracker and polycrystalline arsenic source material, dimeric arsenic was obtained and utilised to grow Al0.3Ga0.7As layers in the temperature range of 600?700°C with excellent surface morphologies. It has been previously found that, with tetrameric arsenic, excellent surface morphologies were possible only below 630°C and above 690°. Based on these observations, it is postulated that above 630°C tetrameric arsenic has a surface lifetime that is too short to provide enough coverage even when the beam flux is increased dramatically. At and above 700°C, tetrameric arsenic is cracked more effectively by the surface energy gained from the substrate leading to a good surface coverage and to good surface morphologies.     

Chemical change from diffused hydrogen gas to hydroxyl ion in silica glass optical fibres

The chemical change from hydrogen gas that diffuses into silica glass for optical fibres to hydroxyl function has been investigated. Hydrogen molecules that diffuse into GeO2-doped silica glass at 500°C easily change into OH ions by thermal energy, while this chemical change does not occur in pure silica glass at 500°C. Also, germanium-doped silica fibre, in which hydrogen gas is dissolved at room temperature, shows OH ion absorption loss increase with chemical change by heat treatment at above 100°C, while pure silica core fibre shows no OH ion absorption loss increase by the same treatment.     

Excess noise in the radiation from c.w. d.h. GaAlAs-diode lasers

The dependence of excess noise in the radiation from c.w. d.h. GaAlAs-diode lasers as a function of d.c.-pump current has been investigated at microwave frequencies (1 and 4 GHz) in the temperature range from ?30°C to +20°C. Measurements are compared to the results of excess-noise computations obtained from a simple, analytical, laser model.     

Temperature dependence of the Kerr effect in a silica optical fibre

The temperature dependence of the electro-optic Kerr effect has been measured in a silica-cored monomode optical fibre. The Kerr constant was measured as 5.3×10?16 mV?2 at 23°C with a temperature coefficient of +0.56% per deg C over the range 23 to 88°C. This measurement has implications for optical-fibre temperature and electric field sensors.     

1.3 ?m InGaAsP index-guided multirib waveguide laser array

Phase-locked InGaAsP index-guided multirib waveguide laser arrays emitting at 1.3 ?m have been fabricated. These devices have threshold currents in the range 400?500 mA at 30°C and have been operated to pulsed output powers as high as 400 mW. More than 100 mW of output power has been obtained up to an ambient temperature of 60°C. The lasers emit in multilongitudinal modes with a far-field divergence of 20° × 40°.     

基于虚拟仪器的多路电压测量的设计与实现

针对在电路测量中需要同时测量几处电压而没有足够的电压表、多点测量操作不便的问题,本文在利用虚拟仪器技术的基础上设计出了一种新型多路数字电压表。该多路虚拟数字电压表除数据采集由DAQ实现外,其他功能均由软件LabVIEW实现。其设计具有灵活性和可扩展性,有利于系统的集成。经过测试,该多路数字电压表性能稳定,能够很好的达到多路测量的目的。     

New a.d. convertor with special application to medium precision platinum resistance thermometry

Platinum resistance thermometers mounted on ceramic formers have a potential uncertainty, after calibration, of 0.01°C over a range exceeding ?30 to +250°C. To achieve this requires resistance measurements of higher precision than is conveniently available from commercial digital instruments. A new time-interval type of a.d. convertor has been developed for this purpose and incorporated in a simple digital resistance meter with a full scale reading of 300.000 ? and an uncertainty of 1 m?.     

Aging characteristics of InGaAsP/InP DFB lasers

Aging tests of InGaAsP/InP DFB lasers with a constant light output of 5 mW/facet and ambient temperatures 25°C and 40°C have been carried out. Up to the present, with an aging time of more than 2000 h for six lasers, appreciable degradations have been observed in their driving currents and spectra. This indicates that the corrugation grating near the active region has little influence on short-term reliability of DFB lasers.     

Low threshold current transverse junction lasers on semi-insulating substrates by m.b.e.

Preparation by m.b.e. of GaAs-AlxGa1?xAs transverse junction lasers on semi-insulating substrates is described. Pulsed current thresholds of 32 mA have been achieved at room temperature (25°C) in initial devices. Single-mode c.w. operation has been achieved with heat-sink temperatures up to 35°C.     

High-Temperature Measurements of Q-Factor in Rotated X-Cut Quartz Resonators

The Q-factors of piezoelectric resonators fabricated from natural and synthetic quartz with a 34° rotated X-cut orientation have been measured at temperatures up to 325°C. The synthetic material, which was purified by electrolysis, retains a high enough Q to be suitable for high-temperature pressure-transducer applications, whereas the natural quartz is excessively lossy above ~200°C application. The present results are compared to results obtained previously at AT-cut resonators.