共查询到20条相似文献，搜索用时 578 毫秒
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介绍了自旋阀巨磁电阻器件的结构和工作原理,设计了一种基于巨磁电阻的液位测量和控制的新型传感器装置,并对液位传感器装置进行了定标.该装置具有灵敏度高、体积小、稳定性好和成本低的优点,用该液位传感器装置测量液位高度的不确定度一般小于3%. 相似文献
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丁希顺 《安阳师范学院学报》2005,(2):71-73
精确地对压力容器内部液体液位,易燃易爆液体液位的测量,是现代测量科学的重要课题.本文设计一种利用单片微型计算机与光纤传感器组成的液位测量系统,它利用液面对光纤入射光和反射光原理实现对液位的测量,使用频分复用技术分别取出多个传感器的输出信号,并同时可以增大测量的安全性.文中详细论述了液位信息检测、电路处理的原理,给出了整体电路设计框图和软件流程.实验结果表明,系统液位测量范围为10cm～300cm,具有较高的测量精度. 相似文献
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用PIC16C63单片机的捕捉功能来计算超声波在液体中的传播时间，进而计算出超声波在液体中的传播距离来实现对液位的精确测量。该系统测量精度高，性能稳定可靠。本介绍了利用PIC16C63捕捉功能测量脉冲间隔的方法和超声波液位传感器的组成。 相似文献
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《实验室研究与探索》2017,(7):64-67
提出了一种利用光声效应产生的声音信号激励圆柱形封闭腔体产生共振,实现非接触式实时液位自动测量的装置。利用调制激光照射在封闭、透明腔体内的黑色涂层上,当激光信号频率与腔体机构固有频率达到一致时,腔体内的光声信号振幅将达到最大。腔体内的振动情况由顶部驻极体电容式麦克风进行检测。待测容器与密封腔体底部连通,液位变化,则共振频率随之变化。结合单片机设计相应的软件进行液位自动测量,同时利用手机APP实现液位的无线监测。测量过程在1 min之内完成,测量精度可达1 mm。应用光声效应产生腔体共振,通过测量共振频率来测量液位,是光声效应的独创性应用。 相似文献
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曹文祥 《武汉工程职业技术学院学报》2019,(2)
新型液位传感器可用于构成检测液体深度的系统,广泛应用于液位测量、测量环保、消防水箱检测等领域。相较传统的液位检测系统,它具有价格低、测量精度高、灵敏度高、智能化、便于携带等优点,越来越适应市场的需要,受到用户的青睐。设计了一种静压液位传感器,量程0-5m,输出信号为4-20mA电流变送器电路对信号进行传输,可抗干扰和实现远距离,同时以AT89S51为微处理器作为系统控制电路,对信号进行控制、处理。为便于数据通信,设计基于VB开发环境的串口通信程序,方便用户对观察数据的实时监控和保存。 相似文献
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为了探究电容式液位计在液氮绝热气瓶液位测量中的精度及相对误差变化规律,利用单电容和三电容液位计进行液位测量实验,并与称重实验进行对比验证。结果显示:单电容和三电容液位计的相对误差分别为4.9%和1.9%,单电容液位计相比目前应用的圆筒电容液位计平均测量精度已提升了5%左右,三电容液位计测量精度较单电容提高3%。从信号变送器的设计方面分析精度提高的原因为三电容液位计对液氮介电常数进行了精确修正,探究得到电容液位计相对误差的变化规律及原因。实验中使用的电容液位计还可用于液氢、液氧以及液化天然气等低温容器的液位测量中,能够促进低温液体在各领域中的应用推广。 相似文献
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Inverse heat conduction method （IHCM） is one of the most effective approaches to obtaining the boiling heat transfer coefficient from measured results. This paper focuses on its application in cryogenic boiling heat transfer. Experiments were conducted on the heat transfer of a stainless steel block in a liquid nitrogen bath, with the assumption of a 1D conduction condition to realize fast acquisition of the temperature of the test points inside the block. With the inverse-heat conduction theory and the explicit finite difference model, a solving program was developed to calculate the heat flux and the boiling heat transfer coefficient of a stainless steel block in liquid nitrogen bath based on the temperature acquisition data. Considering the oscillating data and some unsmooth transition points in the inverse-heat-conduction calculation result of the heat-transfer coefficient, a two-step data-fitting procedure was proposed to obtain the expression for the boiling heat transfer coefficients. The coefficient was then verified for accuracy by a comparison between the simulation results using this expression and the verifying experimental results of a stainless steel block. The maximum error with a revised segment fitting is around 6%, which verifies the feasibility of using IHCM to measure the boiling heat transfer coefficient in liquid nitrogen bath. 相似文献
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目前高校实验室排放的废液已经引起社会各界的重视,很多高校也制定了相关的管理办法。根据当前高校实验室废液排放的特点,对其进行了分类,并论述了其对环境的危害。针对高校实验室废液管理存在的问题,提出了进一步加强管理的建议。 相似文献
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浓缩与澄清─—两难问题浅析 总被引：2，自引：1，他引：1
固液分离过程中澄清与浓缩的两难问题由来已久．本文讨论了在使用高分子絮凝剂保证澄清效果的前提下如何提高浓缩产物的固体含量,同时设法改善浓缩物的性质使之便于进一步压缩处理的有关问题．文中论述了相关的研究结果、研究方法及潜在的研究方向．分析了聚集体尤其是絮凝体内液体介质的赋存状态,提出了改进絮凝物脱水的某些新机制． 相似文献
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“小精灵”口服液10,20,40ml/kg可使小鼠进行日本式迷宫试验的走错次数显著减少,在跳台法实验中,小鼠的出错次数分别减少18％,44.5％,69％.对学习记忆机制分析结果表明,“小精灵”口服液可显著增加小鼠脑中的神经递质乙酰胆碱含量. 相似文献
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应用高效液相色谱仪进行检测时必须考虑样品处理过程中的细节问题.本文以注射用青霉素钾为试验样品,依据2010年版《中华人民共和国兽药典》一部标准,用两台高效液相色谱仪进行比对试验,发现两台仪器的检测结果相对偏差较大（为1.8％）,通过分析排查最终发现是样品处理中的细节问题影响了结果,改进后两台高效液相色谱仪检测到的含量相对偏差在可控范围内（0.13％）,结果有明显改善. 相似文献
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发泡聚乙烯醇是一种环保型的泡沫塑料,广泛应用于在清洁材料、过滤材料、医用材料等领域,但尚未见在包装领域应用的报道.本文详细讨论了发泡聚乙烯醇的3种发泡方法(机械发泡法、化学发泡法、成孔剂发泡法)、制备技术以及性能(耐热性、耐化学药品性、力学性能、吸液性能等)方面的研究进展,并对其在液态产品缓冲吸液包装上的应用可行性进行了分析,提出进一步研究的主要思路. 相似文献
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In low-stakes assessments, some students may not reach the end of the test and leave some items unanswered due to various reasons (e.g., lack of test-taking motivation, poor time management, and test speededness). Not-reached items are often treated as incorrect or not-administered in the scoring process. However, when the proportion of not-reached items is high, these traditional approaches may yield biased scores and thereby threatening the validity of test results. In this study, we propose a polytomous scoring approach for handling not-reached items and compare its performance with those of the traditional scoring approaches. Real data from a low-stakes math assessment administered to second and third graders were used. The assessment consisted of 40 short-answer items focusing on addition and subtraction. The students were instructed to answer as many items as possible within 5 minutes. Using the traditional scoring approaches, students’ responses for not-reached items were treated as either not-administered or incorrect in the scoring process. With the proposed scoring approach, students’ nonmissing responses were scored polytomously based on how accurately and rapidly they responded to the items to reduce the impact of not-reached items on ability estimation. The traditional and polytomous scoring approaches were compared based on several evaluation criteria, such as model fit indices, test information function, and bias. The results indicated that the polytomous scoring approaches outperformed the traditional approaches. The complete case simulation corroborated our empirical findings that the scoring approach in which nonmissing items were scored polytomously and not-reached items were considered not-administered performed the best. Implications of the polytomous scoring approach for low-stakes assessments were discussed. 相似文献
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《教育实用测度》2013,26(4):359-375
Many procedures have been developed for selecting the "best" items for a computerized adaptive test. There is a trend toward the use of adaptive testing in applied settings such as licensure tests, program entrance tests, and educational tests. It is useful to consider procedures for item selection and the special needs of applied testing settings to facilitate test design. The current study reviews several classical approaches and alternative approaches to item selection and discusses their relative merit. This study also describes procedures for constrained computerized adaptive testing (C-CAT) that may be added to classical item selection approaches to allow them to be used for applied testing, while maintaining the high measurement precision and short test length that made adaptive testing attractive to practitioners initially. 相似文献
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Åge Diseth 《Scandinavian Journal of Educational Research》2013,57(2):219-230
Three different tests of intelligence and the Approaches and Study Skills Inventory for Students were administered to 89 Norwegian undergraduate psychology students. The purpose was to investigate the relationship between intelligence, approaches to learning and academic achievement. Factor analysis supported a one-factor solution of the three intelligence tests as an expression of general intelligence. No relationship between general intelligence and approaches to learning was observed. The WAIS vocabulary test of intelligence and the surface approach to learning were negatively correlated. The WAIS vocabulary test of intelligence and the surface approach to learning predicted academic achievement. A curvilinear relationship between surface approach and academic achievement was observed. Multiple regression analysis showed interaction effects between deep-strategic and surface-strategic approaches to learning as predictors of academic achievement. The findings support the construct validity of approaches to learning due to its independence of intelligence. 相似文献