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1.
The uncertainty in a transducer/tensiometer system was assessed with temperature and pressure calibrations. A reference transducer/tensiometer pair was used to factor out temperature related deviations from two monitoring pairs. The reference pair removed most of the deviations, resulting in a high estimate of precision. In contrast to earlier reports of high accuracy, these estimates of accuracy were considerably reduced by a time correlated residual pattern. The calibrations suggested that the electronic components may be responsible for these residual errors and illustrated the need for experimentation which isolates the error among groups of components. The complexity of transducer/tensiometer networks, and the differing response of each component to thermal loading, demonstrated the necessity of using a reference system, which when properly designed can yield reliable pressure readings for soil water. 相似文献
2.
Laboratory and field experiments demonstrated that solid state pressure transducers are accurate and reliable devices for frequent measurements of soil suction. However, each transducer had to be individually calibrated before use and a hanging column procedure designed for this purpose is described. Analysis showed that each transducer had a linear response and that environmental conditions such as temperature had minimal influence. Twenty four tensiometers with pressure transducers were intalled in a forest soil to test their operation and their output was monitored by a data logger. An example of soil suction results measured during four storms is given to demonstrate their stability and their rapid response. The transducers were found to perform accurately and were only affected by temperatures below 0°C. 相似文献
3.
Fiber-optic (FO) technology is being used increasingly for measurement methods in a variety of environmental applications. However, FO pressure transducers are rarely used in hydrogeological applications. We review the current state of Fabry-Pérot interferometry-based FO pressure transducers, including their advantages and limitations, as another option for high-resolution pressure- or head-change measurements in conventional or advanced aquifer testing. Resolution and precision specifications of FO transducers meet or exceed commonly used non-FO pressure transducers. Due to their design, FO transducers can be used in small-diameter (inner diameter ≥1/4 inch) and continuous multichannel tubing (CMT), sampling points, multilevel packer systems, and Direct Push-based in situ installations and testing. The small diameter of FO transducers provides logistical advantages—especially for tests with monitoring at many zones in a number of wells and/or CMTs (e.g., no reels, placement just below water level in access tubes vs. within isolated zones, reduced weight and volume, small footprint at single point of data acquisition). Principal limitations are small measurement drift that may become evident for tests longer than a few hours, and higher-than-average cost. We present field examples of FO transducer performance in short-term tests with high consistency of acquired data and higher resolution (i.e., capturing significant hydrologic information) compared with commonly used non-FO transducers. Given the above, including advantageous logistical features, FO transducers can open new experimental possibilities in areas of high-resolution three-dimensional (3D) heterogeneity (flow and transport, remediation, critical zones); 3D fracture networks and fundamental hydromechanical behavior; complex 3D flow and leak detection (mines, dams, repositories, geothermal systems). 相似文献
4.
刘晓红 《地震学报(英文版)》1996,9(2):345-349
Ｔｈｅｍａｎｕｆａｃｔｕｒｅｏｆａｔｈｒｅｅ－ｄｉｍｅｎｓｉｏｎａｌｔｒａｎｓｄｕｃｅｒｕｓｅｄｉｎｌａｂｏｒａｔｏｒｙＸＩＡＯ－ＨＯＮＧＬＩＵ（刘晓红）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，... 相似文献
5.
There are currently no industry‐wide standards for the calibration and specification of water‐level monitoring pressure transducers. Consequently, specifications from different manufacturers are currently not directly comparable, and different branded sensors may not perform similarly under the same environmental conditions. This has been highlighted by the varied performance of 14 leading brands of pressure transducers under test conditions. In laboratory tests, transducers generally met product accuracy specifications, although temperature compensation was substandard in five absolute sensors. In a 99‐day field test, accuracy was typically within around ±10 mm for lower range pressure sensors, which exceeded some product specifications. Furthermore, there was evidence for linear and curved forms of instrument drift. As a result of the diverse performance of the transducers, it is recommended that an industry‐wide standard for calibration and specification is introduced. This would eliminate any uncertainty surrounding the current procedures and lead to more informed procurement by the user who would have a greater understanding of comparative instrument performance. Any new standard should also address sensor drift which is currently rarely cited in product specifications. 相似文献
6.
Evaporation involves the change in state of a liquid to a vapour. The evaporation rate from salt‐water resources depends mostly on saturated vapour pressure above its surface. On the other hand, the saturated vapour pressure is affected by the ion activity coefficient, which stems from the chemical salt concentration of water. Thus, an increase in concentration of water results in a reduction of saturated vapour pressure. In order to acquire the actual rate of evaporation from salt‐water resources, a uniform set of evaporation pans with different but specified salt concentrations were used, in a meteorological station under the same conditions. The difference in evaporation rate of each pan can only stem from the difference in chemical salt concentration and, indeed, the molar fraction of water in each saline solution. Therefore, by applying the water molar fraction in the pressure term of fresh‐water evaporation measurement formulas, these equations were developed further for determination of evaporation rate from salt‐water resources. The proposed formulas using very simple terms seem to be suitable for determination of evaporation rate from any water (typically saline, semi‐saline and fresh water) with a satisfactory precision. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
7.
2014年山西定襄七岩泉新增BHC-336智能定标器,对新、旧2套测氡仪的水氡测值,就稳定性、数据一致性、内在质量等进行对比分析,结果显示,因存在系统误差,2台测氡仪水氡测值稳定性均值存在差异,测量精度和性能具有一致性;与新测氡仪相比,旧测氡仪水氡测值相对偏差和均值标准误差更小,精度更高,数据相关程度较高,数据稳定性更好。定襄水氡对华北5级以上地震具有较好的映震能力,新测氡仪对2016年4月7日原平4.6级地震映震效能比旧测氡仪灵敏。 相似文献
8.
为了连续记录地壳长期倾斜运动和进行固体潮的观测研究,我们设计制造了 WSQ-1型电涡流自记水管倾斜仪.该仪器缸体采用浮子--横臂结构,并在设计中考虑了温度补偿.为本仪器专门研制的 WQB-B-1000型电涡流位移变换器是一种非接触式传感器,它具有灵敏度高、动态范围宽、稳定性好、对浮子导向要求低等优点.这种传感器的采用,简化了仪器结构,并保证了整机的良好性能.仪器输出两缸体的水位差与水位和信号,前者即测得的倾斜信号,而后者不仅作为整机稳定性指示,而且在利用位于水管中央的标定器进行标定时作为标定信号.测试和试记录证明,仪器格值优于5.10-9rad/mm(水管长度30m),测量水位差范围1mm(不需调整),平均漂移优于310-9rad/日,记录固体潮因子精度达0.003(M2波,88天). 相似文献
9.
为了能够精确地测量海底表层沉积物的声学参数,自主研制了一种新型海底沉积物声学原位测量系统,与国内外传统的声学原位测量系统相比,该系统能够实时显示声波波形,调整测量参数,其工作方式除了站位式测量之外,还实现了拖行式连续测量,极大地提高了工作效率.根据前期海试情况,对海底仪器结构进行了重新设计,使之可以同时测量海底沉积物及海底海水的声学参数,同时建立了双向数字信道,解决了测量过程中系统信号的干扰问题.该系统的结构分为两部分:甲板控制单元和水下测量单元,整套系统通过主机控制程序进行控制,采用GPS定位系统测定仪器的大地坐标.为了检验系统的稳定性及准确性,分别进行了实验室水槽实验和海上试验.利用水声测量设备对测量系统进行实验室水槽标定分析,实验结果表明系统测量值相对误差仅为0.04%,测量结果具有较高的精度.海上试验在青岛胶州湾和东海海域进行,获得了试验区域海底沉积物声速和声衰减系数的测量数据,将测量数据与他人的研究结果进行对比分析,结果表明测量数据与前人研究结果一致,较为准确.该原位测量系统在站位式测量和拖行式测量中都能够快速准确地测量出沉积物声速和声衰减系数,可以作为海底底质声学测量的调查设备. 相似文献
10.
《Continental Shelf Research》1998,18(6):695-714
In the present work, the potential of correlation methods applied to acoustic signals backscattered from suspended sediments, is examined with regard to the measurement of near-bed vertical profiles of the horizontal current velocity. The technique uses the cross-correlation of the backscattered signal between pairs of downward looking horizontally separated transducers, to measure the time taken for suspension structures to advect from one transducer to another. This approach requires a degree of spatial coherence in the suspension field, and advantage is taken of this coherence to measure the flow. To investigate the technique, backscattered data collected using an array of transducers has been examined. The array was deployed along stream in an estuarine environment, which was subject to strong rectilinear currents, and high levels of suspended sediment concentration. Using pairs of transducers with separations between 0.25–5.42 m, the structure of the suspension field has been assessed, the implication of these observations for measuring flow discussed, and nearbed measurements of current profiles obtained. The results show that in the estuarine environment investigated, if the transducer pair separation was of the order of a metre or less, and currents were sufficient to retain sediments in suspension, vertical profiles of the horizontal current could be measured. To assess the results conventional electromagnetic and impeller current meter measurements were collected at four heights above the bed. Comparison of the conventional reference measurements with the cross-correlation velocities show that the correlation method has the potential to provide reliable measurements of near-bed current profiles. 相似文献
11.
Several pressure sensors were deployed in a small lake to determine its storage change. It could be shown that a deep enough deployment and an averaging over a time interval of 1 hour and 5 measuring points allowed for a measurement of 1 or 2 kg/m2 (i.e. 2 mm of water column) of changes in the storage on the scale of the lake size. This accuracy for the lake storage could not be achieved by other methods, especially if conditions were difficult, e.g. snowfall, or in cases when precipitation was small. Finally, the pressure measurement - originally intended to roughly determine the water level - turned out to be a direct measurement of water mass in the lake, which was the proper magnitude for exchanges between atmosphere and lake. Hence the measurement of lake storage could become an interesting approach even for meteorological measurements, such as precipitation and evaporation on a water surface. 相似文献
12.
A community-based, real-time, groundwater level monitoring network consisting of 11 sites was built in Nova Scotia, Canada, using privately owned domestic wells and low-cost, custom-made water level meters. The real-time meters use an ultrasonic sensor to measure water levels and an Internet-of-Things device to transmit the data to the Internet by WiFi or cellular connection. The water level data are plotted in real-time on a time-series graph and are available immediately for online viewing and downloading. Based on observations at three sites, the real-time water level meter data compare well to pressure transducer measurements, with mean absolute errors of less than 0.02 m. The meters are simple to build, and components are readily available from online suppliers at low cost. 相似文献
13.
Wave transformation across a macrotidal shore platform under low to moderate energy conditions 
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下载免费PDF全文 Wayne J. Stephenson Larissa A. Naylor Helen Smith Bin Chen Ralph P. Brayne 《地球表面变化过程与地形》2018,43(1):298-311
We investigate how waves are transformed across a shore platform as this is a central question in rock coast geomorphology. We present results from deployment of three pressure transducers over four days, across a sloping, wide (~200 m) cliff‐backed shore platform in a macrotidal setting, in South Wales, United Kingdom. Cross‐shore variations in wave heights were evident under the predominantly low to moderate (significant wave height < 1.4 m) energy conditions measured. At the outer transducer 50 m from the seaward edge of the platform (163 m from the cliff) high tide water depths were 8+ m meaning that waves crossed the shore platform without breaking. At the mid‐platform position water depth was 5 m. Water depth at the inner transducer (6 m from the cliff platform junction) at high tide was 1.4 m. This shallow water depth forced wave breaking, thereby limiting wave heights on the inner platform. Maximum wave height at the middle and inner transducers were 2.41 and 2.39 m, respectively, and significant wave height 1.35 m and 1.34 m, respectively. Inner platform high tide wave heights were generally larger where energy was up to 335% greater than near the seaward edge where waves were smaller. Infragravity energy was less than 13% of the total energy spectra with energy in the swell, wind and capillary frequencies accounting for 87% of the total energy. Wave transformation is thus spatially variable and is strongly modulated by platform elevation and the tidal range. While shore platforms in microtidal environments have been shown to be highly dissipative, in this macro‐tidal setting up to 90% of the offshore wave energy reached the landward cliff at high tide, so that the shore platform cliff is much more reflective. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
14.
In experimental modal testing, the measurement locations and the number of measurements have a major influence on the quality of the results. In general, there are several alternative schemes for sensor placement, and the accuracy of the data increases as the number of sensors utilized increases. However, the number of transducers that can be attached to a real structure is limited by economic constraints. Therefore, algorithms that address the issue of limited instrumentation and its effects on resolution and accuracy are important from the standpoint of experimental modal analysis. The authors are particularly interested in structural dynamics based damage evaluation of large structures, and the development and implementation of suitable sensor location algorithms are critical for such a problem. A kinetic energy optimization technique (EOT) has been derived, and numerical issues are addressed and applied to real experimental data obtained from a model of an asymmetric long span bridge. Using experimental data from the bridge model, the algorithm proposed in this paper is compared to Kammer's EIM algorithm, which optimizes the transducer placement for identification and control purposes. 相似文献
15.
To quantify and model the natural groundwater-recharge process, two sites in south-central Kansas, U.S.A., were instrumented with various modern sensors and data microloggers. The atmospheric-boundary layer and the unsaturated and saturated soil zones were monitored as a unified regime. Data from the various sensors were collected using microloggers in combination with magnetic-cassette tape, graphical and digital recorders, analog paper-tape recorders, and direct observations to evaluate and automate data collection and processing.
Atmospheric sensors included an anemometer, a tipping-bucket raingage, an air-temperature thermistor, a relative-humidity probe, a net radiometer, and a barometric-pressure transducer. Sensors in the unsaturated zone consisted of soil-temperature thermocouples, tensiometers coupled with pressure transducers and dial gages, gypsum blocks, and a neutron moisture probe operated by an observer. The saturated-zone sensors consisted of a water-level pressure transducer, a conventional float gage connected to a variable potentiometer, soil thermocouples, and a number of multiple-depth piezometers.
Evaluation of the operation of these sensors and recorders indicated that certain types of equipment such as pressure transducers are very sensitive to environmental conditions. Extraordinary steps had to be taken to protect some of the equipment, whereas other equipment seemed to be reliable under all conditions. Based on such experiences, a number of suggestions aimed at improving such investigations are outlined. 相似文献
16.
O. M. Rozental 《Water Resources》2012,39(6):685-699
Analysis is given to the source of errors, invalidating the results of laboratory studies of water and the standards, norms, and regulations for ensuring the accuracy (validity and accuracy) of methods and results of measurements. The accreditation of laboratories, and their use of the means of measurements and reference standards, admitted for use in accordance with the established order, as well as the participation in interlaboratory comparison tests are shown to be necessary but not sufficient conditions for providing customers with reliable measurement data. To obtain measurement results with an error satisfying the established standards, one should demonstrate conscious and competent attitude toward the measurement problem in accordance with the basic ISO/MEK 17025 standard. It is shown that, under the conditions of increasing value of fresh water in the world, the metrological support of water-environmental control becomes an urgent and specific scientific problem. Therefore, it is proposed to develop water qualimetry??the direction of scientific and applied studies, making it possible to evaluate the characteristics of measurement errors in the characteristics under control to ensure their lying within the established limits with a specified probability. 相似文献
17.
D. G. Taimazov 《Seismic Instruments》2009,45(1):75-77
A solution to the problem of the high-precision measurement of minor displacements with a capacitance transducer by special selection of its plate configurations is proposed. For relevant parameters of geophysical devices, the calculation accuracy of a displacement transducer is ±0.1 nm within the ±100-mm range. 相似文献
18.
As seismic data quality improves, time‐lapse seismic data is increasingly being called upon to interpret and predict changes during reservoir development and production. Since pressure change is a major component of reservoir change during production, a thorough understanding of the influence of pore pressure on seismic velocity is critical. Laboratory measurements show that differential pressure (overburden minus fluid pressure) does not adequately determine the actual reservoir conditions. Changes in fluid pressure are found to have an additional effect on the physical properties of rocks. The effective‐stress coefficient n is used to quantify the effect of pore pressure compared to confining pressure on rock properties. However, the current practice in time‐lapse feasibility studies, reservoir‐pressure inversion and pore‐pressure prediction is to assume that n= 1. Laboratory measurements, reported in both this and previous research show that n can be significantly less than unity for low‐porosity rocks and that it varies with porosity, rock texture and wave type. We report the results of ultrasonic experiments to estimate n for low‐porosity sandstones with and without microcracks. Our results show that, for P‐waves, n is as low as 0.4 at a differential pressure of 20 MPa (about 3000 psi) for a low‐porosity sandstone. Thus, in pore‐pressure inversion, an assumption of n= 1 would lead to a 150% underestimation of the pore pressure. Comparison of the effective‐stress coefficient for fractured and unfractured samples suggests that the presence of microfractures increases the sensitivity of P‐wave velocity to pore pressure, and therefore the effective‐stress coefficient. Our results show that the effective‐stress coefficient decreases with the differential pressure, with a higher differential pressure resulting in a lower effective‐stress coefficient. While the effective‐stress coefficient for P‐wave velocity can be significantly less than unity, it is close to one for S‐waves. 相似文献
19.
Pelin Tohumcu Özener Kutay Özaydın Mehmet M. Berilgen 《Bulletin of Earthquake Engineering》2009,7(1):199-219
This paper presents the results of shaking table model tests which were carried out to investigate the pore water pressure
generation and related liquefaction mechanism in layered sand deposits. The experiments were performed on uniform sand columns,
silt interlayered sand columns and two layered sand columns deposited at various relative densities and subjected to different
input excitations. During the experiments excess pore water pressures were measured by pore pressure transducers installed
at three different depths and, surface settlements and thickness of water film developed under less permeable inclusions were
measured by a digital camera. The experimental results are discussed and compared to demonstrate the effects of relative density,
input acceleration and presence of a silt seam on the generation of excess pore water pressure in sand deposits subjected
to dynamic loading. The results showed that the presence of a less permeable silt interlayer within the sand deposit and existence
of a loose sand layer underlying dense sand deposits can have significant effect on the pore water pressure generation mechanism. 相似文献
20.
The ultrasonic technique for measuring travel times of compressional and shear waves using dual-mode transducers was adapted to a piston cylinder apparatus, allowing simultaneous measurements of travel times of compressional and shear waves of island arc samples under the high pressure and temperature conditions of island arcs. This method enables us to determine elastic properties and their pressure and temperature derivatives simultaneously. Furthermore, Vp/Vs can be directly determined from travel times of compressional and shear waves independently of length change due to compression or thermal expansion of rock samples under deep crustal conditions, providing more accurate Vp/Vs values than those determined from individual measurements of travel times of both elastic wave types using single-mode transducers. Experimental techniques and results are demonstrated using data on silicified pelitic schist from the Ryoke Belt to 0.6 GPa. The simultaneous measurement gives Vp = 5.60 km/s, ∂ Vp /∂ P = 0.090 (km/s)/GPa, Vs = 3.37 km/s, ∂ Vs /∂ P = 0.05 (km/s)/GPa, σ = 0.216, and Vp / Vs = 1.66 at ambient conditions. The temperature derivatives were constrained from fitting using linear functions of temperature, yielding ∂ Vp /∂ T = −0.518 × 10−3 (km/s)/K and ∂ Vs /∂ T = −0.182 × 10−3 (km/s)/K. Performing simultaneous measurements of travel times of compressional and shear waves using dual-mode transducers, it is possible to accurately determine Vp / Vs and Poisson's ratio of crustal minerals and rocks at deep crustal conditions to study the composition of the crustal interior, e.g. rock types and fluids below the hypocentral region of earthquakes or around bright spots. 相似文献