锅炉液位控制系统设计

设计了一种数字式锅炉液位控制系统，并给出了硬件原理图和软件流程图。该控制系统是用MCS-51系列单片机及其相关硬件来实现，利用传感器（干簧管阵列）测量液位数据、CPU循环检测传感器输出状态，并用光柱和LED指示液位高度。当锅炉液位低于用户设定的值时，系统自动打开泵上水，当水位到达设定值时，系统自动关闭水泵。经几个月试运行，表明该控制系统设计合理、可行。     

使用CCD的实时液位测量系统研究

本文描述了一种实用的液位测量系统。该系统采用线阵ＣＣＤ作为传感器，由微机系统完成数据采集、处理、参数分析及显示，并控制随动测量头进行定位跟踪测量。实现了大范围、高精度的自动化监测。     

High-speed liquid film sensor for two-phase flows with high spatial resolution based on electrical conductance

A sensor is presented, that allows high-speed measurements of two-phase film flows. The sensor consists of electrodes flush to the wall, that measure the electrical conductance in a liquid film. This sensor has a time resolution of 10 kHz and 64×16 measuring points, with a spatial resolution of 3.12 mm² and a maximum film thickness range of 0.8 mm. The shape of the sensor electrodes is optimized by calculating the potential field of the liquid film. The calculated sensor characteristic is compared with experimental data received by imposing static liquid films of known thickness on top of the sensor. Further dynamic measurements of co-current air–water flow in a horizontal channel have been conducted. The statistical analysis concerning film thickness distribution and flow patterns is generally in agreement with literature. The high time and spatial resolution allows a wave analysis over a wide range of wavelengths and wave velocities. By using a continuous wavelet transform, a significant amount of additional information has been retrieved, particularly in regard to ripple waves. Preliminary experiments show the ability of the sensor to detect droplet deposition onto the liquid film. An autoregressive filter has been applied to separate droplet impacts from periodic wavy structures.     

Model Based Tuning of Controller for Non‐Linear Hemispherical Tank Processes

Abstract

A non linear liquid level process represented by a 5 liter hemispherical tank was subjected to dynamic analysis using a step response technique. The data fitted a first order plus dead time model with an error of less than 3 percent. The level was measured using an on‐line Honeywell capacitance sensor. From the model parameters, PI and fuzzy tuned PI controllers were designed using MATLAB. The closed loop performance was studied for both the servo and regulator problems. Based on the overshoot, rise time, settling time, and ISE, it is found that the Fuzzy tuned PI controller is better suited for this process.     

基于超声波传感器的无线液位测量系统

针对诸多行业储液罐液位测量的特点和技术要求,设计了一种基于超声波传感器的无线液位测量系统.系统由液位检测模块、无线数传模块和上位机工作站组成.传感器将接收到的信号经数据处理后由无线数传模块送上位机工作站,工作站是由VC设计的一个数据处理平台,具有多路液位显示、超限报警、数据存储和打印等功能.     

高精度原油储罐液位计研究

通过对数字式电容液位计及等值基准电容补偿法的研究，提出将数字式电容液位计与压差法相结合，由数字式电容液位计测量原油液位和油水界面的高度，等值基准电容法补偿由于环境温度、极板腐蚀和油液粘结带来的测量误差，采用压差法测量混油密度，依据混油密度和液位高度求得油重及容积；通过高精度A/D板采集模拟和数字信号，连续对储罐内原油的液位、密度、温度等各种参数进行运算，并由智能监测仪实施全自动显示，其测量精度可达到毫米级。     

基于单片机实现的容错式锅炉液位传感器

依据现有锅炉液位检测的现状，设计了一种数字式锅炉液位传感器。该传感器利用单片机的并口测量液位数据，串口与上位机进行通讯，并能对传感器的故障进行诊断。经现场试运行表明：该传感器系统设计合理、可行，具有一定的容错能力，为系统维护及故障查找提供了方便，具有较高的性价比。     

Influence of Snow Temperature Interpolation Algorithm and Dielectric Mixing-Model Coefficient on Density and Liquid Water Content Determination in a Cold Seasonal Snow Pack

The SNOWPOWER measurement method combining high- and low-frequency measurements has been tested under Canadian cold temperate climate for determination of liquid water content and density of a snow pack. Since, cold and shallow seasonal snow pack are very often found in northern environment, it was shown that both snow temperature and exponent coefficient of common dielectric mixing models have to be considered to improve measurement accuracy. Indeed, Looyenga’s mixing-model coefficient at the fourth order together with the weighted average snow temperature measured along the sensor cable and calculated by linear or and cubic spline interpolation provided the most accurate results and good correspondence with manual snow density and snow liquid water content measurements. The best accuracy for snow density shows a relative error of 0.70% and an absolute error of 2.5 kg/m⁻³ compared to the reliable reference measurements. The mean relative error on the liquid water content was 0.62% and the absolute error 0.15%. The SNOWPOWER sensor system seems to have promising chances to become an operational tool for large-scale monitoring of the snow cover properties.     

新型光纤液位传感器的设计和应用

文中介绍了一种功能型光纤液位传感器,与传统的液位开关相比,该传感器具有检测现场无电,防静电、无机械活动部件和长期运行稳定可靠,液面指示精度高,体积小等优点,并给出其几种应用形式及现场使用情况。     

泡沫液位传感器的研制

泡沫是一种特殊的两相流形态，其力学、热学、光学等多种性能均与单相气体或液体有很大区别，由于泡沫的形成机理多样、性质变化复杂，至今尚无完善的研究理论体系，泡沫的液位测量在国内外也是一个空白。开发了一种基于传热原理的测量泡沫液位的传感器，介绍了传感器的构造和原理，以及测量误差和动态响应的计算分析。     

静压式油罐计量技术

主要介绍一种用于大、中型油罐计量的新型传感器。这种传感器以高精度扩散硅压力传感器测量油罐底部压力,以浮子钢带式液位计测量液位。测量值经现场数据处理后送至二次仪表或计算机,最后可给出静压、液位、温度、密度、容积和质量等参数,从而实现油罐储量的自动计量。     

新型的智能化液位温度测量系统

介绍了磁致伸缩液位传感器的工作原理及C8051F015单片机的主要特性，以及核心器件EPM7256AE和DS18820的功能及使用方法，研制了基于C8051F015、EPM7256AE和DS18820的数字式智能化液位温度测量系统。该系统能同时实现液位、界位、多点温度测量，并用RS-485串行通信进行远距离传输，不仅测量精度高，而且稳定性好。     

Micro wire-mesh sensor for two-phase flow measurement in a rectangular narrow channel

A micro wire-mesh sensor (μWMS) based on an electrical conductivity measurement between electrodes installed on the walls has been developed for gas–liquid two-phase flow measurements in a narrow rectangular channel. This measuring method applies a principle of conventional wire-mesh tomography, which can measure the instantaneous void fraction distributions in the cross-section of the relatively large flow channel. In two-phase flow measurement using μWMS the void fraction distributions in the narrow channel were obtained by the measured conductivities between electrodes arranged on each wall. Therefore, the gas phase structures and the bubble behaviors can be investigated in the flow channel with narrow gap. In the present paper, a μWMS for the air–water flow between parallel flat plates with a gap of 3 mm was developed and simultaneous measurements with a high speed video camera were conducted to compare the measured results in bubbly flow.     

测量带压容器液位或液位差的差压传感器

介绍一种差压传感器的结构原理和性能特点，该传感器适于带压容器液位或液位差的测量，其电气接口与压力接口相互隔离，便于防爆设计。     

Comparison of water measurement results in polyol ester‐based lubricating fluids determined by the coulometric karl fischer method and a thin‐film polymer capacitive water sensor

Field samples of MIL‐PRF‐23699 and DOD‐L‐85734, both polyol ester‐based fluids, were evaluated for water concentration by the coulometric Karl Fischer (KF) method according to ASTM D 6304 and with a prototype thin‐film polymer capacitance‐based sensor at Naval Air Systems Command (NAVAIR). The NAVAIR KF results showed a consistent negative bias, 190 ppm on average, compared to the results obtained with the water sensor. Since the calibration of the water sensor was performed by the sensor manufacturer using a different KF instrument and reagent/co‐solvent system, the ∼190 ppm negative bias probably reflects the difference in KF results between sensor manufacturer and NAVAIR. A limited round robin test, involving several laboratories using different instruments, reagents, solvents, and techniques, showed that water concentrations determined by the KF method can vary significantly from laboratory to laboratory. A larger round robin test was conducted to assess more accurately the variability in water measurement results. The results of the two round robin tests show that the particular KF instrument, reagents/solvents, and procedures being utilised by the various participating laboratories lead to a KF measurement variability of 20–30% for polyol ester‐based lubricating fluids. The results show that it is possible to obtain ∼190 ppm difference, observed between the water sensor and KF measurements at NAVAIR, between two laboratories. The results of the round robin tests showed a maximum repeatability of 9%. The significant difference between the repeatability and reproducibility indicates that there is potential for improved reproducibility of KF measurements through standardisation of, for example, instrument type, reagent/solvent system, test method, and laboratory procedure. Further work is required to determine the optimum KF test parameters for polyol.     

Environmental sensors based on micromachined cantilevers with integrated read-out

An AFM probe with integrated piezoresistive read-out has been developed and applied as a cantilever-based environmental sensor. The probe has a built-in reference cantilever, which makes it possible to subtract background drift directly in the measurement. Moreover, the integrated read-out facilitates measurements in liquid. The probe has been successfully implemented in gaseous as well as in liquid experiments. For example, the probe has been used as an accurate and minute thermal sensor and as a humidity sensor. In liquid, the probe has been used to detect the presence of alcohol in water.     

IM85—1型光纤液位传感器系统

本文介绍一种基于光弹效应的光强调制型的集计算机、微电子学和波导光学为一体的高精度光纤液位传感器，该传感器的突出优点是能完成全光一次信号检测，现场无须带电，从原理上消除了燃烧和爆炸的隐患，特别适用于一类防爆区。该传感器系统在设计上系Ｃ＾４系统，便于与现代化的计算机管理联网。     

Capacitance sensor for void fraction measurement in water/steam flows

A capacitance sensor operating at RF range for void fraction measurements was developed. Two electrodes of the capacitor are mounted on the outer side of pipe walls. The variations in the percentage of phases in two-phase flow cause changes of the equivalent permittivity of the dielectric between the electrodes. The capacitor is connected in a resonant circuit of an oscillator tuned to high frequency of 80 MHz. The changes of frequency generated by the oscillator are the measure of the void fraction in the two-phase flow. An eight-channel system with capacitance sensors of this type was used for determination of the phase conversion along a steam injector.     

Application of Fabry-Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495 nm/kPa and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.     

New sensor developments

The new sensors are the result of new materials, techniques, and calculation and decision capabilities. They are more accurate, reliable, rugged, noncontacting and digital. A microprocessor is integrated with nearly every sensor system, giving both local and milewide access to all information. Many of the new sensors are basic in function — smell, taste, tactile, machine vision, and sound. For example, new odor meters indicate temperature rise as the odorous gas oxidizes or due to an electrode conductivity changes; guidelines are established for quality standards or acceptable odor levels. Or the outputs from several sensors of variables associated with the flavor of liquid are combined in a trial and error relationship until a satisfactory correlation is achieved by artificial intelligence. Thin-film sensors for tactile measurements are based upon electrical conductivity changes with pressure; microprocessor scanning of electrodes results in a quick display of sensitive field-effect transistor pH meter for a drop of sample; chemical environmental sensors; and a micro-gas chromatograph. Fast Fourier Transforms (FFT) applied to a Doppler flowmeter enhance the speed and sensitivity by a factor of ten. Self-calibrating sensors with corrections for either variables include a new radiometer with laser-corrected emissivity and a self-calibrating fiber optic temperature sensor insensitive to emissivity. Infrared photoacoustic sensing is the newest generation of advanced technology sensors for gas analysis, and it results in a most stable zero and span. Other noteworthy new products include hybrid photodetectors, solid-state toxic gas detectors, ultrasonic and microwave radar level and distance gages, microminiature color camera, color scanner, surface quality meter, and multi-wave length spectral analyzers.