Effect of Time-Domain Reflectometry probe location on soil moisture measurement during wetting and drying processes

In this paper studies on the impact of the location of Time-Domain Reflectometry probes in soil samples on the moisture measurement are presented. In particular, we were interested if the commonly accepted assumption that moisture measurements performed by TDR probes correctly average the value of the soil water content in a soil sample. Soil samples having different physical properties, both undisturbed and disturbed, were used. Our results show that the soil moisture measurement depends on the placement of the TDR probe in the sample, and a TDR probe placed vertically measures the arithmetic mean of soil moisture for the whole sample, for both the wetting and the drying cycles. This result is general and does not depend on the analyzed sample.     

Parallel Plates Compared with Conventional Rods as TDR Waveguides for Sensing Soil Moisture

Dielectric methods of estimating the water content of soils, especially TDR, have become accepted as routine measurement techniques. Basic to the TDR technique is the waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which water content is estimated. In this study we compare the use of flat stainless steel plates with cylindrical stainless steel rods. We suggest that the use of plates gives a more even distribution of electromagnetic energy within the soil volume sampled and reduces the so called ``skin effect' where the electromagnetic energy is concentrated close to the surface of the electrodes. Plates will not be suitable for all measurement purposes but wherever they can be applied they should result in more representative measurements from the medium under investigation. Calculations of electrical field intensity are presented to compare the relative energy density between the electrodes. Field and laboratory studies were alsoconducted considering some of the practicalities of using the alternative waveguides.     

Measuring and Modeling of Direct Ground Wave Depth Penetration Under Transient Soil Moisture Conditions

This study represents the first attempt to investigate the GPR direct ground wave sampling depth by comparing GPR estimated soil moisture contents with data from horizontally and vertically installed time domain reflectometry (TDR) probes at different depths. The GPR direct ground wave method (200 MHz centre frequency) was used to estimate the temporal soil moisture dependence during uniform irrigation and drainage. Uniform irrigation and drainage experiments were conducted in an experimental pit (2.5 × 1.0 × 0.8 m) filled with repacked sandy loam soil. The GPR moisture contents measurements were more consistent with the moisture contents from vertically installed TDR than horizontally installed TDR. An analytical solution for one-dimensional drainage of water was used to estimate the change in GPR ground wave sampling depth during drainage. The analytical solution was first fit to vertical TDR data to obtain an estimate of the soil hydraulic parameters and the GPR sampling depth was then estimated by fitting the drainage solution to the measured GPR data. The GPR direct ground wave sampling depth using the analytical solution during drainage varied from −20 cm at high moisture content to −50 cm at the lowest moisture content.     

激光加工机器人自标定研究

介绍一种机器人自标定方法,通过固定于机器人末端执行器上的探针与工作空间中的约束平面接触,建立运动学约束方程,利用机器人内部传感器读数来辨识机器人运动学参数,约束平面的位置无需准确知道。该方法无需任何外部测量设备,适于定期现场再标定。对某激光加工机器人的仿真结果表明,该方法可以达到其它标定法如几何参数标定法所能达到的标定精度。     

Multiple parameters׳ estimation in horizontal well logging using a conductance-probe array

In this paper, a new method is proposed to simultaneously estimate three parameters in horizontal well logging with oil–water two-phase stratified flow by using a conductance-probe array. It is known that an ideal sensor׳s response is determined by the water level and the azimuth angle of the sensor in a horizontal well, and is proportional to the conductivity of the water phase. In terms of the sensor model, the three parameters are estimated simultaneously by using the conductance probe array by the aid of experimental calibration. Firstly, the sensor is calibrated by static experiments with water of known conductivity. For all possible combinations of water level and azimuth angle, the sensor responses are collected and stored in a sample set as the sample data. In actual use, the sensor is first transported to the desired position in the horizontal well underground and the sensor response is collected as the measured data. Then, through the steps of threshold filtering, data normalization and matching calculation, the sample data that best matches the measured data is searched from the sample set. Finally, the parameters are estimated by the aid of the matched sample. The experimental results show that the estimation errors of water level and azimuth angle are within ±2% and ±3°, respectively and the relative error of water conductivity is no more than ±2%. Moreover, comparing with the estimation method previously proposed by the authors, the new method is of higher reliability, higher accuracy and wider range for water level estimation.     

Observations of Contact Measurements Using a Resonance-Based Touch Sensor

A study of the contact mechanisms between a resonator probe sensor and a broad range of engineering surfaces is presented. The resonator-based touch sensor used in these studies consists of a prismatic beam clamped at one end with a spherical probe attached at the other. Pairs of piezoelectric (PZT) elements cemented at either side of the beam along its axis are employed; one to actuate and the other to pick up the strain signals. Over a band of frequencies near to a resonance, the sensor behaves like second-order system. When oscillated near to its resonant frequency, interactions between the probe tip and specimen are detected by monitoring phase or frequency shifts using phase-locking techniques. As the probe approaches and contacts a surface, a range of phenomena are observed. Approximate theoretical models have been developed to predict the effects characteristic of added mass, stiffness, and damping (i.e., kinetic, potential and dissipative energy transfer) for contacts between clean solids and when contaminant films are present. These models predict that phase and frequency shifts can either increase or decrease depending upon the dominant phenomena in the contact region. For example, when a solid surface is contacted by a clean probe, the resonant frequency can either increase or decrease depending upon the ratio of elastic modulus to density, and this is demonstrated with contact measurements made on metals and rubbers. A systematic method for the identification of the dominant effect (if there is one) based on observations of frequency or phase shifts using either constant phase or constant frequency monitoring is presented.     

High temperature fast response pressure probe for use in liquid metal droplet dispensers

A miniature fast response high temperature pressure probe, with demonstrated use in liquid metals up to 255 °C (528 K), has been developed. Innovative packaging technologies have been applied to integrate a conventional piezoresistive silicon pressure sensor into the probe, without the need of an auxiliary water-cooling system. In situ static calibrations are used to verify the linearity of the pressure signal and the stability of the pressure sensitivity (0.5% standard deviation over 70 min at 255 °C). Dynamic calibration, completed in an air shock tube facility, yields the probe's natural frequency. This frequency, when corrected for probe operation in liquid tin, is found to be 100 kHz. The reliability and accuracy of the probe is assessed by mounting it in a tin droplet dispenser for use in an extreme ultraviolet light source. Droplet dispensers typically include an excitation mechanism, which can be based on the generation of acoustic pressure waves to impose a desired droplet frequency. The probe accuracy is verified by the comparison of pressure measurements with laser Doppler vibrometry measurements of the pressure generating structure. A reference pressure measurement, conducted at representative conditions, shows a complex frequency response, with peaks distributed over three orders of magnitude and maximum amplitude of 440 mbar. Time variance of the excitation mechanism due to thermal transients is studied by monitoring the pressure response during operation. Finally, the linearity of the excitation system, with respect to the excitation amplitude, is verified by response measurements. In conclusion, the developed probe is capable of characterizing the excitation mechanism of a liquid metal droplet dispenser. Additionally, real-time monitoring of the performance of the excitation system during long-term operation is possible.     

Development of a contact-type probe for measurements of ultra-fine-pitch gears and application to pseudo roughness evaluation

Gears used in actuators for robot articulations are showing a trend toward having smaller modules. Thus, profile measurements of small module gears are strongly desired. Our aim was to develop a probe artifact that enables ultra-fine-pitch cylindrical gears to be measured, by minimizing the size of the probe head. The configurations of the contact-type probe and holder were designed under consideration of interference with an adjacent tooth during profile measurements of an objective tooth. After manufacturing the artifact, a 0.1-module spur gear was measured as a trial, and reasonable results were obtained. In addition, a calibration plate for roughness was measured using the developed probe artifact. The evaluated roughness showed a strong correlation with the “true roughness”. Therefore, the developed probe can be expected to enable “pseudo” roughness to be evaluated.     

Experimental study on response of hot wire and cylindrical hot film anemometers operating under varying fluid temperatures

The working principle of constant temperature anemometer (CTA), used for fluid velocity and/or turbulence measurements, is based on convective heat transfer from a sensor (a hot wire or a hot film) to the fluid being measured. Response of a CTA, working in temperatures other than its calibration temperature, involves errors which must be corrected for reliable measurement data. We have experimentally studied the effect of variations in fluid temperature on the response of hot wire and cylindrical hot film anemometers, and have discussed the application of different correction factors. Effects of overheat ratio (sensor temperature) and fluid velocity on the CTA output voltage correction factor have been discussed. The results show that the error in the CTA response depends on the sensor temperature, and it shows a decrease with increasing sensor temperature (increasing overheat ratio). The results also show that the error correction factor depends on the overheat ratio and fluid velocity. The required error correction factor also depends on whether the fluid temperature decreases or increases with respect to the calibration temperature of the CTA. In spite of differences in sensor characteristics, our work on cylindrical hot film sensors shows that the correction factors for hot wire and hot film sensors are similar and close in magnitude.     

基于双二极管调制的边缘电场土壤水分传感器特性

研究了一种用于土壤水分测量的边缘电场平面传感器,设计了平面电容土壤水分传感器的双T二极管调制检测电路和数据处理系统,通过参数优化得到一种能够实现在线测试的土壤水分平面传感器及检测装置.试验表明,随着土壤含水量的变化,传感器的响应有较大的变化,且在低于25%的含水量范围内,土壤含水量与被测电压之间近似线性关系,这种平面型土壤水分传感器在农业种植方面展示了广阔的应用前景.     

一种水下灵巧手指端力传感器的研究

采用水压力补偿技术，设计了基于圆筒式测力结构的水下灵巧手指端力传感器，分析了其工作原理。采用有限元法计算了圆筒式测力结构的应变分布，验证该结构的合理性，由此推导出测量原理方程。采用有限元法对模型进行模态分析，确定了传感器的工作带宽。在陆上对传感器进行标定实验，根据实验数据计算出标定矩阵。性能测试结果显示，在陆上和浅水环境中测量结果一致，验证了该传感器在陆上标定是可行的。该传感器可用于水下，且测试精度满足目前水下灵巧手研究的要求。     

基于光纤传感技术的三维地应力传感器

为了实现对地下岩层空间应力状态及其变化规律的有效监测,基于光纤光栅传感技术与平面应力状态测量原理,提出了一种平面应变花与光纤光栅传感技术相结合的监测方法。通过利用碳纤维层积复合材料对光纤光栅封装做成应变传感单元,九个应变传感单元分别组成两组直角应变花与一组等角应变花,三组应变花分别放置于三个圆柱形探头S1,S2,S3上,三个探头以一定的机械结构连接构成地层空间应力的监测的三维地应力传感装置。对光纤应变传感单元进行温度与应力的标定实验,在室内对整体传感装置进行了应力加载模拟实验。实验结果表明:光纤应变传感单元的应力分辨率为0.017 2 MPa;应力监测为0~60 MPa;探头S1最大主应力的监测平均误差为16.31%,探头S2最大主应力的监测平均误差为24.36%,S3探头的绝对误差为0.006 8 MPa;实际加载应力与传感器测量的应力空间角度误差平均值为1.24°。传感器的监测结果与实际加载应力的变化规律相一致,可满足对地下岩层空间应力状态连续监测的要求。     

Calibrated cylindrical Mach probe in a plasma wind tunnel

A simple cylindrical Mach probe is described along with an independent calibration procedure in a magnetized plasma wind tunnel. A particle orbit calculation corroborates our model. The probe operates in the weakly magnetized regime in which probe dimension and ion orbit are of the same scale. Analytical and simulation models are favorably compared with experimental calibration.     

Microwave Dielectric Study on Water Structure and Physical Properties of Aqueous Systems Using Time Domain Reflectometry with Flat-End Cells

Microwave dielectric measurements were performed in the frequency range from 1 mHz up to 30 GHz using a time domain reflectometry (TDR) method for emulsions and gels. Flat-end sample cells have been used in the TDR measurement to contact a small spot of the surface of those viscoelastic and solid samples without any destruction. Relaxation processes due to various water structures were observed for these aqueous systems. Relaxation parameters thus obtained offer information about these water structures and amounts. The relaxation strength obtained from the high frequency process due to free water can be an adequate measure of water content in spite of some ambiguities for different water structures in some materials. Comparisons of actual water contents in emulsion with those estimated from the relaxation strength indicate that water structure is affected by the interaction between water and micelle. Unfreezable water observed in DNA gel under the freezing point consists of bound water and a fraction of free water. Bound water molecules are still unfreezable to keep the double helical structure of DNA, when the fraction of free water is frozen at lower temperatures. These water structures determine physical properties of moist materials. TDR measuring technique with the flat-end cell is effective to investigate water structures in viscoelastic moist materials and to evaluate physical properties and structures of complex molecular systems.     

Water density formulations and their effect on gravimetric water meter calibration and measurement uncertainties

In the gravimetric calibration method of water meters, the volume of water that has passed through the equipment under test (EUT) is generally collected into a tank and the quantity (mass) determined by weighing. The mass of water collected is then converted into a volume. This conversion of mass into volume requires knowledge of the water density, which can be estimated, measured directly or determined by other means. The error of measurement of the EUT is determined by comparing the volume recorded by the EUT and the volume collected in the tank. The density of water is, therefore, one of the major causes of measurement uncertainty in laboratory calibration of water meters using the gravimetric method. Water meter calibration facilities commonly use density formulations proposed by the International Standards Organisation (ISO) and the Organisation for International Legal Metrology (OIML). In Australia, additional guidance in water density determination is provided by the National Measurement Institute (NMI). In this study, testing was undertaken using ten positive displacement water meters arranged in series in the test rig to evaluate some of the common water density formulations used in Australia. The effect of these different formulations on the water meter error measurement was determined, as well as the effect on the measurement uncertainties. The results shows that the use of these different density formulations evaluated do not significantly affect the water meter error of measurement or the uncertainty of measurement. There was no apparent correlation between the water meter error and the meter position in the test rig. It was also determined that if the water density was adjusted only for temperature effects, a maximum of 0.05 and 0.15% drift in meter error and measurement uncertainty respectively, can be expected.     

Optical-interference calibration of inductive displacement sensors

The technique and results of measurements of the sensitivity of an inductive sensor of small displacements are described. The sensitivity was measured by optical-interference monitoring of the displacement of a metallic reflector fixed to a piezoceramic element. It is shown that this technique ensures the calibration of an eddy-current sensor to an accuracy of no worse than 1 μm.     

A study on the neutron monitoring system of LHD based on Monte Carlo simulations

Neutron monitoring is quite important because fusion neutrons are a direct evidence of fusion reactions. In calibration experiments of a neutron monitoring system, Monte Carlo calculations play an important role to correct various effects. To perform Monte Carlo calculations for a helical type fusion device, we make a program that can automatically generate an input file of a helical coil geometry for the MCNP code. The neutron spatial distributions and spectra for the helical devices are calculated in the geometries automatically generated by this program. We also discuss in calibration experiments.     

Calibration for the sensitivity of multi-beam angle sensor using cylindrical plano-convex lens

A highly sensitive and compact multi-beam angle sensor (MBAS), which utilizes the principle of operation of an autocollimator, was developed to detect the differential of the local slope components (angle difference) of a point on the mirror surface and using Fourier series, we can obtain the profile data from the angle difference. In order to investigate the application of the MBAS for high precision aspheric surface measurements, two types of calibration methods using plane mirror and cylindrical plano-convex lens has been proposed to measure the sensitivity of the MBAS. The calibration data analysis results using plane mirror agree well with the measurement results of the cylindrical plano-convex lens data. Comparison of the two methods confirms that the second method (using cylindrical plano-convex lens) is more adapted for measurement with ultra high level of uncertainty. Further, the second method is simple, corresponding to a direct calculate in the sensitive parameters aiming to minimize the cost.     

An active MEMS probe for fine position and force measurements

This paper deals with the development and calibration of a single degree-of-freedom probe that is capable of regulating an input position and measuring force or applying a constant input force and measuring deflection. Such a probe is useful in making sensitive measurements on thin films, nano- and microstructures, and fluids. The probe is actuated by an electrostatic comb drive with an integrated capacitive sensor. COTS electronics and a capacitance-to-voltage IC are used to develop a closed-loop controller for the system, capable of regulating position over a range of about 40 μm to within a 5 nm resolution and controlling forces up to 300 μN with a resolution of 25 nN. The design and fabrication of the probe are discussed. The calibration of the device is performed using multiple methods to cross check each other. The use of the probe is demonstrated in the measurement of surface tension and probing the response of a soft polymer to small forces.     

Evaluation of Water Content and Ionic Concentrations of Soils via Frequency Domain Analysis of TDR Waveform

This study addresses the development of a method for evaluating the water content and ionic concentrations of subsurface polluted soils by analyzing the TDR waveforms in the frequency domain. Soil specimens were prepared with different water contents and NaCl concentrations. A known electrical pulse with multiple harmonics was generated and induced through soil specimens. Reflected signals were then analyzed in the frequency domain and represented in terms of the magnitude and phase shift. Multivariate statistical analysis was performed for various magnitudes and phase shifts, which are dependent on water content and concentrations. Regression equations were obtained; hence, for a known reflected amplitude and phase shift, water content and ionic concentrations could be determined.