Dew point measurement for organic vapor mixture using a quartz crystal sensor

A dew point measurement device for organic vapor mixtures using a quartz crystal sensor was proposed, and its performance was examined with acetone–methanol mixtures. The device has a sensor module to accommodate the quartz crystal sensor and a cooling system. The variation in resonant frequency of the sensor indicates the condensation of sample vapor, which tells the beginning moment of condensation, i.e., dew point. The measurement results with the proposed device were compared with the predicted dew points from the UNIQUAC equation and other experimental outcome to examine the performance of the device. Though some measurement error was yielded, it is proved that the proposed device is useful for measuring the dew points of organic vapors at different pressures.     

采用无电极谐振音叉的石英真空传感器设计

提出了一种基于气体输运现象的双参数谐振石英真空传感器(QRVS).与传统QRVS不同,在(zyw)-18°15′切型的石英音叉片本体无任何电极设置,构成“无电极型谐振音叉”;采用频率和等效串联电阻值的双参数谐振敏感机制,且音叉厚度t与两叉臂间距g之比为t/g =10.为了增大叉臂与真空中残存气体的机械摩擦阻尼,在叉臂的前端制备了4枚通透沟槽.为了抑制寄生振动模式,提高品质因数Q值和叉臂根部的机械疲劳寿命,在两叉臂的边缘分别制作了半圆形台阶,在支撑隔离区加工了2～5枚矩形槽.典型样品实测数据表明:真空测量范围为10-3～ 105 Pa,分辨率为3×10-3 Pa,准确度为10％F.S,稳定性为1.5 ×10-3Pa,达到了设计要求.     

一种差动输出石英谐振式力传感器研制

介绍了一种具有差动输出石英力传感器,该传感器由轮辐式弹性结构和2只石英力敏谐振器组成。利用分别位于正负应力区2只力敏元件感知作用力的大小,进而进行差动输出,以实现零点温漂与时漂自补偿。分析了弹性梁的结构特性;介绍了双端音叉石英力敏谐振器的结构、力学特性及力传感器的制作过程。对传感器进行了静态测试,结果表明:传感器测量范围为0～300N,静态精度为0.05%。     

一种船用气象要素相对湿度传感器

针对陆地用气象要素相对湿度传感器难以适应海洋高湿、高盐雾、高腐蚀环境的问题,研制了一船用气象要素相对湿度传感器。采用高精度湿敏元件,设计出频率发生电路,将空气相对湿度的变化量转换为频率信号;通过设计的频率电压转换电路将频率信号转换为电压信号;设计的线性化调理电路将变化的电压信号进行线性化处理,使电压的变化能够线性化地对应于空气相对湿度的变化。通过特殊结构和可靠性设计,满足了气象要素相对湿度传感器的海洋环境适应性。测试结果表明:研制的船用气象要素相对湿度传感器测量精度高、线性化好,能够适应于海洋环境。     

Design and fabrication of a resonant pressure sensor by combination of DETF quartz resonator and silicon diaphragm

A new type of resonant pressure sensor is presented which is realized by combination of a double-ended tuning fork (DETF) quartz resonator and a silicon diaphragm. To examine the feasibility and investigate the performance of this innovation, theoretical analysis and finite elements method are employed to optimize the structure parameters. Micromachining technology are involved in the fabrication of the silicon diaphragm and the DETF quartz resonator, which are fabricated separately and bounded together afterwards. Performances of the sensor prototypes are experimentally investigated. Preliminary testing results demonstrate that the sensor features a high sensitivity of approximately 452.5 Hz/kPa in the operating range of 0–6 kPa at room temperature, with a non-linearity <0.035 % FS and a hysteresis of 0.055 % FS. In addition, the maximum zero-drift is about 0.5 Hz/h which reveals favorable frequency stability. Thus, the feasibility of this scheme is verified. Due to the excellent performances such as high accuracy, high sensitivity, low cost and simple fabrication, this novel resonant sensor provides a commendable solution for low pressure measurement.     

不同热湿环境对超声波测量影响

在超声波测量中,空气相对湿度与温度会对测量结果带来误差。理论上分析了超声波测量过程中空气中的相对湿度与温度对测量声速结果的影响;同时搭建实验平台对不同热湿环境下超声波测量信号大小、声速影响进行研究,获取了空气中湿度、温度对超声波测量的影响规律,为不同热湿环境下超声波测量精度的提高奠定理论实验基础以及参考依据。     

A new type humidity sensor using micro-air-bridge heaters

A new type absolute-humidity sensor with very quick response, very small power consumption and high sensitivity, which is based on the detection of the thermal conductivity change in humid air at heated temperature above 400°C, has been developed and demonstrated. Since this new type absolute-humidity sensor is able to be easily heated up above 400°C within 30–40 msec because of a micro-air-bridge heater structure, the surface of its sensing area is refreshed by burning out adsorbed dusts, oil, etc. Thermal conductivity _mix of mixed gas expressed by Sutherland-Wassiljewa equation is applied to the humid air to study this absolute humidity sensor. Only a single micro-air-bridge heater operation driven by double pulse-currents for this humidity sensor is also proposed.     

Magnetic-field measurements using an integrated resonant magnetic-field sensor

The present paper introduces a magnetic-field sensor based on a resonating single-crystal silicon structure. The excitation of the resonator is achieved by the Lorentz force generated by a sinusoidal current flowing through a rectangular coil deposited on the surface of the structure. The amplitude of the vibration, which is proportional to the magnetic field, is detected by sensing capacitors. Because of the high-quality factor of the resonator, a lower detection limit of 1 nT, or even smaller might be realised when the device is vacuum-packaged. This paper describes the working principle, the fabrication procedure as well as open- and closed-loop measurement results.     

恒定低温法在低湿区露点检测中的应用

在低湿区环境下的露点检测中,电容式露点传感器测量的频率与露点值呈现非线性,且受环境温度影响很大,此外,湿度越低,测量的分辨力也越低。采用了一种恒定低温方法来检测低湿区露点,即传感器的环境温度恒定保持在0℃以下,可大大提高低湿区的测量分辨力,再根据露点值与频率值间具有的确定的非线性关系,将采集的频率经牛顿插值计算后就可得到露点值。采用该方法大大提高了电容式露点仪在低湿区露点检测的分辨力,扩展了其测量范围。     

Optical humidity sensor using porphyrin immobilized Nafion composite films

A Nafion–TMPyP composite film was used in an optical humidity sensor. The composites were prepared with various molar ratios between the sulfonic groups and TMPyP molecules, R = [–SO₃H]/[TMPyP]. The UV–vis measurement of the composite films suggested that the TMPyP molecules were well dispersed at in the range of R = 60–100, but formed aggregates at R ≤ 20. Furthermore, the FTIR indicated that sulfonic group interacted with TMPyP. The reflectance change with relative humidity (%RH) occurred at 426.4 and 465.4 nm with the isosbestic point at 437.5 nm, and also in the Q-band region. The sensors of R = 30 and 40 sensitively responded to humidity in the lower humidity region (10–20%RH), but saturated or even decreased with further increase in humidity. At R = 60, the sensitivity slightly decreased but a measurable range was extended to around 70%RH. Remarkable deterioration in sensitivity occurred at R = 100. The TMPyP molecules were stably immobilized on a Nafion matrix, even in liquid water, without solving out.     

High relative humidity measurements using gelatin coated long-period grating sensors

A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling strength of the LPG spectrum varies with RH. Experimental investigations on the sensor yield a sensitivity of 0.833%RH/dB with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877, ±0.203 and ±0.04%RH, respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity of the sensor. Results show that higher order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.     

Study of long-term drift of a porous silicon humidity sensor and its compensation using ANN technique

Aging of porous silicon (PS) material is one of the important constraints for its large-scale commercial use as an accurate and reliable humidity sensor. It causes gradual drift of the sensor output with the passage of time. Present paper reports the systematic studies on the aging of the porous silicon humidity sensor with an objective to develop a signal-processing unit to compensate its long-term drift. Drift of the porous silicon sensor is first determined experimentally by periodic recalibration of the sensor with respect to a standard sensor. An ANN-based model is then developed, which can compensate drift due to its aging. Compensating ANN model is then hardware implemented using a simple electronics circuit. Experimental results using the circuit show that drift of approximately 13.5% has been compensated effectively.     

Design and characterization of a humidity sensor realized in LTCC-technology

A new type of integrated temperature and humidity sensor applying Low Temperature Cofired Ceramics technology (LTCC) has been developed and characterized. The proposed device is based on the detection of the difference of thermal conductivity between water vapor and dry air. In this approach, sensing elements are implemented using heated metal film resistors (Pt-elements), where one is exposed to the humid environment that causes the sensor element to cool down with increased humidity, while the other one is sealed from the environment. LTCC-tapes are used for the formation of caps as well are acting as substrate. Sensor design is based on finite element analyses (FEA) where the critical design parameters have been analyzed with regard to the performance characteristic of the device.     

A novel wind sensor concept based on thermal image measurement using a temperature sensor array

This paper presents a novel concept of designing wind sensors without moving parts. The measurement concept is based on the evaluation of the thermal image around a circular heater. Forced convection, caused by the wind, modulates this thermal image, which reveals information about both flow velocity and flow direction. The new concept uses an array of temperature sensors to capture the thermal image. Temperature data are transferred to a computer or a micro controller by a multiplexer. A program running on the computer extracts the values of speed and direction from the thermal image. The paper discusses different evaluation algorithms and compares their results. Three-point-estimators such as Gaussian estimator, peak centroid estimator, and parabolic estimator are used to improve the resolution of the direction measurement. The result of velocity measurement is also presented.     

ANN modeling of a smart MEMS-based capacitive humidity sensor

This paper presents a design of a smart humidity sensor. First we begin by the modeling of a Capacitive MEMS-based humidity sensor. Using neuronal networks and Matlab environment to accurately express the non-linearity, the hysteresis effect and the cross sensitivity of the output humidity sensor used. We have done the training to create an analytical model CHS “Capacitive Humidity Sensor”. Because our sensor is a capacitive type, the obtained model on PSPICE reflects the humidity variation by a capacity variation, which is a passive magnitude; it requires a conversion to an active magnitude, why we realize a conversion capacity/voltage using a switched capacitor circuit SCC. In a second step a linearization, by Matlab program, is applied to CHS response whose goal is to create a database for an element of correction “CORRECTOR”. After that we use the bias matrix and the weights matrix obtained by training to establish the CHS model and the CORRECTOR model on PSPICE simulator, where the output of the first is identical to the output of the CHS and the last correct its nonlinear response, and eliminate its hysteresis effect and cross sensitivity. The three blocks; CHS model, CORRECTOR model and the capacity/voltage converter, represent the smart sensor.     

Vibration modes of a resonant silicon tube density sensor

We present an investigation of the resonance parameters for a new sensor for on-line measurements of fluid density. The sensor consists of a tube system made of single crystalline silicon. The tube system is excited electrostatically into mechanical resonance and the vibration is detected optically. Using a simplified theoretical analysis, the resonance frequency can be shown to be proportional to 1√ρ, where ρ is the density of the silicon and the fluid weighted according to their areas in a cross section of the tube. Thus, a change in fluid density results in a change in the resonance frequency. This dependence is demonstrated by measurements for four different vibrations modes. The quality of the vibration is also investigated through measurements of the Q-values of the vibration modes. The tubes are made using anisotropic silicon KOH etching and silicon-to-silicon fusion bonding micromachining techniques. The dimensions of the tube system are 8.6×17.7 mm with an outer tube thickness of 1 mm and a wall thickness of 100 μm. Total tube length is 61 mm, and the sample volume is 0.035 ml. The sensor has a very good density sensitivity of the order of -200 ppm/(kgm^-3) and a high Q of the order of 3000 for air in the tube     

Prediction of indoor temperature and relative humidity using neural network models: model comparison

The use of neural networks grows great popularity in various building applications such as prediction of indoor temperature, heating load and ventilation rate. But few papers detail indoor relative humidity prediction which is an important indicator of indoor air quality, service life and energy efficiency of buildings. In this paper, the design of indoor temperature and relative humidity predictive neural networks in our test house was developed. The test house presented complicated physical features which are difficult to simulate with physical models. The work presented in this paper aimed to show the suitability of neural networks to perform predictions. Nonlinear AutoRegressive with eXternal input (NNARX) model and genetic algorithm were employed to construct networks and were detailed. The comparison between the two methods was also made. Applicability of some important mathematical validation criteria to practical reality was examined. Satisfactory results with correlation coefficients 0.998 and 0.997 for indoor temperature and relative humidity were obtained in the testing stage.     

MEMS based humidity sensor using Si cantilever beam for harsh environmental conditions

The RF applications like voltage controlled oscillators, tunable filters, resonators etc., requires tunable capacitors in their designs. This paper presents the design of wide range MEMS tunable capacitors for RF applications. This design consists of an air suspended bottom plate and a fixed top plate. The top fixed plate and the suspended bottom plate form the tunable capacitor. The capacitance range of this tunable capacitor is from 69.172 to 138.344 nF. This range is wider compared with the conventional MEMS tunable capacitors of tuning ranges in pico Farads. The fabrication process is similar to that of the existing standard integrated circuit fabrication processes, which makes this design suitable for integrated RF applications.     

Non-contact measurement of eyeblink by using Doppler sensor

In this report, we introduce an experimental method for eyeblink measurement by utilizing Doppler effect phenomena. In the cognitive science literature, eyeblink has been proposed as a complex phenomenon and acts as a representative of higher nervous processes. We developed an experimental setup in which the measurement of the eyeblink was conducted using a Doppler sensor accompanied by an accelerometer and an EOG (electrooculography) recording. From our experimental results, we found that the Doppler frequency related to blinking contains a dominant frequency at 2 Hz. Finally, we showed that when blinking is accompanied with head and body movements, eyeblink signal is separable by deploying the principal component analysis (PCA).