恒温式微热板电阻真空传感器的研究

微热板(MHP)作为一种微结构广泛运用在各种微传感器中。本文通过对微热板的传热分析,从理论上分析了恒温模式下工作温度和结构尺寸对微热板电阻真空传感器工作特性的影响;设计了一种边长为93μm、四臂支撑的方形微热板结构的电阻真空传感器,支撑桥长65μm、宽21μm,微热板与衬底之间的气隙高度为0.5μm;采用表面微机械加工技术成功实现了该传感器的加工。测试结果显示,该微热板真空传感器气压测量范围约2Pa～105Pa,且响应特性与理论计算结果相符。     

A thin-film resistive sensor for measuring atomic hydrogen flux density

An eight-channel thin-film resistive atomic hydrogen (AH) sensor is described. It is intended to measure the AH flux density in an atomic-molecular mixture at a reduced gas pressure (10^?2–10^?4 Pa), particularly under the action of infrared and visible radiation noise, in a computer-aided mode. The sensor can be used for measuring a distribution of the AH flux density of the large cross-section beam. The range of AH flux density measurements is 5 × 10¹³ ? 10¹⁶ atoms/(cm² s), the measurement time is 1–10 min, and the measurement error is 10%. The sensitive element of the sensor is made using planar technology, which offers a chance to attain a high resolution in spatial distribution mesurements.     

微热板式气压传感器结构设计与热分析

给出了采用牺牲层技术制作的微热板式气压传感器的加工工艺和工作原理.分析了微热板各层薄膜厚度、微热板下气隙高度、支撑桥尺寸、微热板面积大小对传感器加工、工作性能的影响,并结合实际工艺条件设计了一种采用不同支撑桥尺寸的传感器结构.理论分析了恒温加热方式下微热板各种传热途径随气压的变化关系;用有限元方法模拟了恒流加热方式下气压对传感器温度分布和温度大小的影响.分析结果显示,气压较高时微热板传热以气体导热为主,而气压较低时以支撑桥导热为主;微热板区域温度分布较均匀,温度大小受气压影响较大;设计的传感器测量范围为10～10⁵Pa,功耗在毫瓦级,且具有尺寸小、热响应快、易与电路集成等优点.     

基于定容燃烧法的快速煤质分析

在自制的定容氧弹燃烧装置上，测量了多种煤样在氧弹内燃烧期间气体压力随燃烧时间变化的关系。通过理论分析和试验研究，得出了发热量和挥发分与压力曲线的定量关系。同时，通过测量尾气中碳氧化物的含量求出煤中的碳含量。对本法的测量结果与标准方法的测量结果进行了比较。实验结果表明，通过定容燃烧法测量发热量、挥发分和碳含量是可行的。     

A new approach to gas flow calibration

Primary gas flow standards create calculable flow rates using two different techniques. Displacement systems rely upon the accurate determination of the first order change in position of an object being displaced by gas flowing at a constant pressure. Pressure, volume, temperature and time (PVTt) systems provide a nearly constant mass flow of gas to an accumulation tank of known volume over a fixed time interval. Measurements of pressure, temperature and time are used to calculate flow rate.     

A novel target-type low pressure drop bidirectional optoelectronic air flow sensor for infant artificial ventilation: measurement principle and static calibration

An optoelectronic target-type volumetric air flow-rate transducer for bidirectional measurements is presented. The sensor is composed of a T-shaped target and two nominally identical LED-photodiode couples which are operated in differential mode. The sensitive surfaces of the photodiodes are differentially shadowed by the deflection of the target, which in turn depends on the gas flow-rate. The principle of operation is described in mathematical terms and the design parameters have been optimized in order to obtain the highest sensitivity along with minimal pressure drop and reduced dimensions. The sensor is placed in a 20 mm diameter hose and was tested with air flow-rate in the typical temperature range of mechanical ventilation between 20 and 40 °C. The theoretical model was validated through experiments carried out in the volumetric flow range from -7.0 to +7.0 l min(-1). The nonlinear behavior allows sensitivities equal to 0.6 V l(-1) min for flow rates ranging from -2.0 to +2.0 l min(-1), equal to 2.0 V l(-1) min for flow rates ranging from -3.0 to -2.0 l min(-1) and from +2.0 to +3.0 l min(-1), up to 5.7 V l(-1) min at higher flow rates ranging from -7.0 to -3.0 l min(-1) and from +3.0 to +7.0 l min(-1). The linear range extends from 3.0 to 7.0 l min(-1) with constant sensitivity equal to 5.7 V l(-1) min. The sensor is able to detect a flow-rate equal to 1.0 l min(-1) with a sensitivity of about 400 mV l(-1) min. The differential nature of the output minimizes the influence of the LEDs' power supply variations and allows to obtain a repeatability in the order of 3% of full scale output. The small pressure drop produced by the sensor placed in-line the fluid stream, of about 2.4 Pa at 7 l min(-1), corresponds to a negligible fluid dynamic resistance lower than 0.34 Pa l(-1) min.     

基于铁基纳米晶合金薄带的压磁式压力传感器的研究

对一种利用Fe基纳米晶软磁合金薄带作为敏感材料的新型压磁式压力传感器进行了可行性研究。介绍了该传感器的结构、工作原理、输出特性以及主要参数的选择。然后通过试验,分析了传感器的静态特性以及温度变化对输出的影响。试验结果表明,该传感器的最大线性误差为2.22%(满量程),最大不重复误差为0.97%(满量程),未经放大的最大灵敏度为0.2073μV/Pa,零点每摄氏度温漂小于1.22%(满量程)。该传感器具有结构简单、工作可靠、成本低廉,以及测压范围宽等优点。     

Micro-flow metering and viscosity measurement of low viscosity Newtonian fluids using a fibreoptical spatial filter technique

The paper describes an experimental method that is capable of measuring liquid flows of the order of millilitres per hour. Volume flow of laminar flows of Newtonian liquids in pipes or channels can be determined by measurement of the centreline velocity and application of the equation of Hagen-Poiseuille. Micro-flow meters with double fibre-array sensor were developed for the measurements of liquid volume flow in capillaries and micro-channels. The main units of the micro-flow meters are a laser-diode system, a double fibre-array sensor and different transparent capillaries or micro-channels. The accuracy of the measured water volume flow was tested with a balance and a syringe pump with given volume flow. Furthermore, the influence of the size of tracer particles on the volume flow results was also determined. This method of flow metering of Newtonian liquids needs no calibration and the results are not influenced by changes in temperature, pressure or nature of Newtonian liquid. An additional measuring result is the determination of the viscosity function by the application of a stripe model of the two-dimensional micro-channel flow. Possible applications of the fibreoptical micro-flow meter lie in micro- volume flow measurements of different Newtonian liquids and in viscosity measurements of Newtonian and non-Newtonian liquids.     

差动电容式倾角传感器的研究

利用差动电容原理设计了倾角传感器,产生倾角时,借助气体和液体电介质,使传感器敏感元件的二个电极间覆盖的有效面积发生变化,导致相应电容发生变化。同时,利用温度传感器结合MCU智能控制热膜为倾角传感器敏感元件部分保持恒温。这种设计不但扩大了传感器的工作温度范围至（-45－＋120）℃,还提高了倾角传感器的非线性、重复性、迟滞和精度。     

基于MEMS技术的金属应变式压力传感器优化设计

文中从金属应变式压力传感器的基本理论出发,以硅弹性膜铂应变电阻压力传感器为原型,推导了圆形和方形弹性膜片上电阻的变化率(dR/R)公式。通过比较,选用方形弹性膜为压力承压膜,以优化承压膜的宽厚比为出发点,用有限元方法对不同厚度方形膜片(宽度为2 mm)进行应力分析。由硅材料的屈服应力与最大位移的限制,确定了最优的膜厚范围;根据有限元仿真的结果对压力传感器进行优化设计,对所做压力传感器芯片进行测试,在6.00×104~1.06×105Pa的范围内,其精度优于50 Pa.     

A new visualisation and measurement technology for water continuous multiphase flows

This paper reports the performance of a research prototype of a new multiphase flow instrument to non-invasively measure the phase flow rates, with the capability to rapidly image the flow distributions of two- and three-phase (gas and/or oil in water) flows. The research prototype is based on the novel concepts of combining vector Electrical Impedance Tomography (EIT) sensor (for measuring dispersed-phase velocity and fraction) with an electromagnetic flow metre (EMF, for measuring continuous-phase velocity with the EIT input) and a gradiomanometer flow-mixture density metre (FDM), in addition to on-line water conductivity, temperature and absolute pressure measurements. EIT–EMF–FDM data fusion embedded in the research prototype, including online calibration/compensation of conductivity change due to the change of fluids' temperature or ionic concentration, enables the determination of mean concentration, mean velocity and hence the mean flow rate of each individual phase based on the measurement of dispersed-phase distributions and velocity profiles. Results from first flow-loop experiments conducted at Schlumberger Gould Research (SGR) will be described. The performance of the research prototype in flow-rate measurements are evaluated by comparison with the flow-loop references. The results indicate that optimum performance of the research prototype for three-phase flows is confined within the measuring envelope 45–100% Water-in-Liquid Ratio (WLR) and 0–45% Gas Volume Fraction (GVF). Within the scope of this joint research project funded by the UK Engineering & Physical Sciences Research Council (EPSRC), only vertical flows with a conductive continuous liquid phase will be addressed.     

Measurements and analysis of time constant of the KRISS dynamic flow control system

Time constant is an important property of the continuous flow systems that can be used to estimate the dynamic equilibrium time for the reaction vacuum chamber of such systems. This work is concerned with measurements and analysis of time constant of a dynamic flow control system assembled at the KRISS vacuum laboratory. Being a new system, it was important to know some basic characteristics of the system, including the time constant as well, in the pressure range of 0.1–133 Pa during continuous gas flow. Three types of gases were used for this purpose and the results were compared. It was observed that time constant was dependent on pressure across the conductance-reducer (CR) that was installed in the by-pass pumping line of the system. At low upstream pressures, the time constant was large and vice versa.     

Self-powered wireless thermoelectric sensors

Sensors capable of measuring various performance parameters of an operational power generation unit could help improve system performance and overall efficiencies. For example, measurement of temperatures, temperature differences, or exhaust gas concentrations could provide both a quick quantitative and qualitative assessment of system health and allow for operation of power units with smaller safety margins and therefore higher efficiencies. For this study a technique is presented that can transmit data about an operational system wirelessly in real-time to an external location. For these experiments thermoelectric element leads were connected to a solenoid coil. When the thermoelectric was exposed to a temperature difference a current was generated in the thermoelectric and solenoid coil resulting in a magnetic field. A receiver was then used to measure the changes in magnetic field of the system. Two primary configurations were developed to test this wireless sensor configuration: dynamic and static. For dynamic measurements a pendulum and pneumatic air cylinder were used to simulate a moving component that may pass the external Hall sensor such as a fan or turbine blade. For dynamic measurements it was determined that for accurate results it is very important to maintain the distance constant between the Hall sensor and solenoid coil. For stationary measurements the temperature difference across the thermoelectric was related to output measurements from the Hall sensor. Overall, results show that data can be wirelessly transmitted to an external location using this method.     

The Joule–Thomson effect in natural gas flow-rate measurements

A numerical procedure for the calculation of the Joule–Thomson (JT) coefficient of a natural gas is derived. The AGA-8 extended virial-type characterization equation is used to calculate the rate of change of the compression factor with respect to the temperature at constant pressure. The DIPPR/AIChE generic ideal heat capacity equations are used to derive the molar heat capacity of a natural gas mixture. The accuracy of the natural gas flow-rate measurements, based on differential devices, is analysed with respect to the temperature drop, characterized by the JT effect. The results obtained are illustrated graphically. The procedure derived enables compensation for the JT effect in natural gas flow-rate measurements.     

A CO2 tracer-gas method for local air leakage detection and characterization

A method for local measurement of air leakage rate is presented that can be used to accurately and quickly assess leakage rates across a surface, such as around a valve or hatch in a pressurized gas tank or a window in a building. The method uses a small local enclosure with constant volume placed about a region on the structure under investigation (e.g., a window), which is depressurized and injected with a small concentration of carbon dioxide as a tracer gas. The time variation of the pressure and carbon dioxide concentration inside the enclosure are monitored and used to quantify the leakage flow rate as a function of pressure difference. This method uses a small enclosure with internal mixing so that a quasi-steady-state condition is quickly achieved. Because of the small size of the enclosure, advanced data processing techniques are necessary to reduce uncertainty in determination of the rate of change of the carbon dioxide concentration that arises from sensor variability. Results of a laboratory demonstration of the proposed leakage detection and characterization device are reported for the problem of leakage through a circular hole in a plate with prescribed pressure differences. Experimental results from the laboratory tests are found to be in excellent agreement with results of a numerical simulation of leakage flow through a hole, as well as predictions from a number of empirical equations for this problem found in the literature.     

Self-heating probe instrument and method for measuring high temperature melting volume change rate of material

The castings defects are affected by the melting volume change rate of material. The change rate has an important effect on running safety of the high temperature thermal storage chamber, too. But the characteristics of existing measuring installations are complex structure, troublesome operation and low precision. In order to measure the melting volume change rate of material accurately and conveniently, a self-designed measuring instrument, self-heating probe instrument, and measuring method are described. Temperature in heating cavity is controlled by PID temperature controller; melting volume change rate υ and molten density are calculated based on the melt volume which is measured by the instrument. Positive and negative υ represent expansion and shrinkage of the sample volume after melting, respectively. Taking eutectic LiF+CaF2 for example, its melting volume change rate and melting density at 1 123 K are -20.6% and 2 651 kg/m-3 measured by this instrument, which is only 0.71% smaller than literature value. Density and melting volume change rate of industry pure aluminum at 973 K and analysis pure NaCl at 1 123 K are detected by the instrument too. The measure results are agreed with report values. Measuring error sources are analyzed and several improving measures are proposed. In theory, the measuring errors of the change rate and molten density which are measured by the self-designed instrument is nearly 1/20-1/50 of that measured by the refitted mandril thermal expansion instrument. The self-designed instrument and method have the advantages of simple structure, being easy to operate, extensive applicability for material, relatively high accuracy, and most importantly, temperature and sample vapor pressure have little effect on the measurement accuracy. The presented instrument and method solve the problems of complicated structure and procedures, and large measuring errors for the samples with high vapor pressure by existing installations.     

Novel liquid flow sensor based on differential pressure method

In this article, a novel liquid flow sensor which is composed of a special structure conduit main body and a differential pressure sensor was designed, fabricated, and calibrated. The conduit main body includes an inlet channel section with a branch conduit connecting one end of the pressure sensor, a throat channel section, and an outlet channel section with a branch conduit connecting another end of the pressure sensor. The basic principle is to employ a differential pressure sensor to measure the pressure difference between the inlet channel and outlet channel of the conduit main body when fluid passes through it. The pressure difference between the two ends of the differential pressure sensor (i.e., the two branch conduits located in the inlet and outlet channel sections) is of either forward or backward flow and directly interrelates with the volume flow rate (mass flow rate or flow velocity) via the conduit main body, so the volume flow rate or mass flow rate or flow velocity can be calculated and the flow direction can be determined from the detected pressure difference. This liquid flow sensor is characterized by using only one differential pressure sensor of a simple structure, the error of which is less than 1%.     

神经网络在SnO_2气敏元件浓度测量中的应用

气体传感器属于传感器技术领域,在传感器行业中占有重要的地位.然而气体传感器阵列的交叉敏感性严重影响气体传感器对混合气体的测量.基于Matlab平台的神经网络工具箱,分别构建BP神经网络和RBF(径向基)神经网络,对由涂敷不同敏感材料的声表面波振荡器组成的阵列在4种混合气体灵敏度响应数据进行定量识别研究,结果表明RBF神经网络在气体定量识别方面更具优势.     

A study of mass flow rate measurement based on the vortex shedding principle

Mass flow rate measurement is very important in the majority of industry processes because the mass of fluid is not affected by ambient temperature and pressure as the volume will be. Conventional mass flow rate is normally derived from the volumetric flow rate multiplied by fluid density. The density can be obtained by a densitometer or calculated according to the temperature and pressure measured by a thermometer and pressure gauge respectively. However the measurement accuracy is not always satisfactory. Flowmeters directly measuring mass flow rate have been studied and developed recently, such as Coriolis and thermal flowmeters. Unfortunately they still have some limits in practical applications. A new method in which mass flow rate can be directly measured based on the vortex shedding principle is presented in this paper. As a vortex flowmeter, von Kàrmàn vortex shedding is generated by a bluff body (vortex shedder), leading to a pressure drop and pressure fluctuation. A single differential pressure sensor is employed to detect the pressure difference between upstream and downstream sides of the vortex shedder. Both vortex shedding frequency and pressure drop are contained from the output signal of the differential pressure sensor, so that the mass flow rate can be obtained from the pressure signal. Numerical simulation has been done to analyze the characteristics of the fluid field and design the measurement device. The Computational Fluid Dynamics (CFD) codes Fluent were used in the numerical simulation. Experiments were carried out with water and gas, and the results show that this method is feasible and effective to measure the mass flow rate. This method has also robustness to disturbances such as pipe vibration and fluid turbulence.     

Volume and rate measurement of slowly generated gas bubbles

The use of an inverted burette arrangement that allowed volume and time-course tracking of bubble movement via camera imaging is shown here to improve on the classical inverted jar (or beaker) method for measuring gases generated in small volumes and at slow rates (below 1 mL/s). In tests involving discrete gas volume measurements delivered at 0.57 mL/s, comparison with pre-set air volume delivered by a syringe pump showed high correspondence, linearity, and repeatability. Tests with continuous gas flows at 0.2, 0.32 and 0.57 mL/s revealed average bubble count versus volume trends that displayed high linearity to indicate that the bubble volumes (at any flowrate) were constant. The average bubble count versus time also showed linear trends and repeatability indicating that the time intervals between the appearance of any two bubbles (at a particular flowrate) were uniform. The analytical and simulated results helped to explain why bubble size determination by high speed camera recording for measuring gas volume and flowrate is fraught with inherent problems. An analysis using light ray tracing showed that flowrate determination using such an approach would necessitate complicated image correction when two cameras are used for simultaneous recording due to distortion effects resulting from refraction. A virtual gate approach involving the binarization of images recorded with a standard camera is shown to be more feasible in establishing the flowrate using bubble counting or finding the time interval between bubbles.