接触电阻的准确测量

导线或金属导体接触有电阻,电势存在,通常称之为接触电阻,接触电势。本文就两导线接触后准确测量接触电阻随外加拉力及电压的变化的规律进行实验。实验结果表明：接触电阻随外加拉力的增加有所减小接触电阻随外加电压的增加有所增大。同时对其它外界因素如振动,接触面积,表面清洁度,以及交流情况等给予了讨论。     

接触电阻的分析与测量

通过分析接触电阻产生的原因及其影响因素来认识准确测量接触电阻的意义。从理论出发介绍接触电阻的测量方法,介绍了四线端子法的测量原理及优势。     

变压器直流电阻测量方法改进方案的探讨

电力变压器绕组具有大电感和小电阻的固有特点,测量直流电阻时充电时间常数很大,长期以来技术人员研究各种方法试图缩短测量时间。本文研究了电力变压器直流电阻快速测量的各种方法,分析了方法的优缺点,简介了变压器直流电阻测量改进方案。     

基于接触电阻法测量润滑油膜厚度的方法研究

提出了一种基于接触电阻法测量润滑油膜厚度的方法,研制了一台可实时测量接触电阻以评价润滑膜厚的旋转摩擦试验机,分析了边界润滑与混合润滑区域中油膜厚度与接触电阻的相关性。该装置实现了在高精度加载与速度控制下,获得确定工况下的润滑状态,通过精密电路设计实时测量接触区内部接触电阻,并与相同工况下光干涉法测得的润滑膜厚进行对应,获得了接触电阻-润滑膜厚对应关系,拟合曲线相关系数为0.98,剩余标准差为4.56 nm。为在实际工况中表征润滑状态提供了技术支撑和数据支持。     

新型纳米级电接触电阻测量的新技术

研究纳米级材料的电气特性通常要综合使用探测和显微技术对感兴趣的点进行确定性测量。但是,必须考虑的一个额外因素是施加的探针压力对测试结果的影响,因为很多材料具有压力相关性,压力会引起材料的电气特征发生巨大的变化。现在,一种新的测量技术能够将纳米材料的电气和机械特性表示为施加探针压力的函数,     

瞬时开关动作特性校验台回路电阻的测量和误差分析

一、瞬时开关动作特性校验台内部结构的回路电阻分析瞬时开关动作特性校验台(以下简称校验台)的回路电阻主要是由开关动、静触头的固有电阻和接触电阻产生的,其中固有电阻是指无接触部件的导电回路的电阻,接触电阻是指连接部件的附加电阻,而且它对整个回路电阻影响最大。接触电阻又分为表面     

新型热流计测量技术的探索研究

目前的热流计在测量热量时需要测量供热管道的流量以及进出口温度,然后再对其进行积分计算.其技术非常复杂,而且精度低,仪器成本高,难以普及.为了解决这一系列问题,本文主要依据能量守恒定律提出了一种新型的能量测量装置,并对该装置的测量原理进行了理论分析.通过数值模拟,在理论上对其进行了验证.数值模拟的结果证实该型热流计测量结果与系统流体的流量无关,这也是本测量方法不同于其它常规热流计的优点之一,摆脱了流量对能量测量的影响,同时也简化了计算过程,大大降低了成本.     

ISO 10012:2003国际标准讲座第八讲测量管理体系分析和改进(续7)

测量管理体系分析和改进是组成测量管理体系的四大过程之一，通过对测量管理体系各过程的现状分析和评价，识别和发现测量管理体系的不合格或异常，并针对产生不合格或异常的原因，制定纠正措施或预防措施，以实现测量管理体系的持续改进。     

基于改进优序法的服务接触研究

根据系统科学原理,构建了一个定量评价服务接触的模型,并采用基于顺序统计量的优序评价法对服务接触进行排序和分类,为区分服务接触水平、优化服务资源配置打下基础.研究结果表明:1)该模型得到的服务接触水平评价结果和传统概念模型相一致;2)优序法可以有效地应用于服务接触水平划分过程,为服务生产和传递过程的设计以及服务营销策略的制定提供了量化的、科学的依据.     

Modeling of Transient Thermal Contact Resistance out of Conjugate Gradient Method

Temperature profile at contacting pairs of any material combination is crucial in many engineering applications. A new experimental approach is suggested to estimate the contact heat transfer coefficient as well as the thermal contact resistance. This method is based on temperature infrared measurements of contact bodies and then solve the inverse problem with conjugate gradient method. Different affecting parameters are studied namely; surface roughness, presence of interlayer, applied pressure and bodies temperature difference. The time dependant heat transfer coefficients resulting from the proposed method need to be validated by a computer model. Close results are shown with slight deviation by the increase of the applied pressure and the temperature difference.     

利用改进的挂重法测定丝的张力

提出了改进挂重法的一种途径:采用可转动的折射镜与被放置在高度可调节架上的望远显微镜,用镜的叉丝给丝的像定位,借助于游标精确地测量折射镜的转角,按照文中介绍的公式计算丝的张力。这种改进方法的相对精度为±1％。     

电接触测试系统中接触压力研究

接触压力是电接触测试系统的重要参数。电接触测试系统对接触压力的控制指标主要是加载精准度和保持稳定度。本文讨论了三种不同的接触压力加栽保持方案,并针对精密定位电接触系统和微动电接触系统的特点提供接触压力加载保持方案选择的建议。     

端度类量具接触法测量的要点

狭义上的端度类量具,多指量块。而在光学机械量仪中,端度类测量仪器是指测量两端面外尺寸的量块、量具或零件的仪器,如测长机、测长仪、光学计等。所以广义上的端度类量具可以指凡是以量具两端面外尺寸为使用尺寸的量具,包括量块、量棒、内径千分尺、套管尺塞尺等。在测量各类端度类量具时,往往选择用端度类光学仪器来直接读出被测量具的偏差。测量时,要根据被测量具两端不同的测量面,选择合适的测头测帽,并寻找正确的转折点,以减少接触法测量中的测量误差。该文总结了各类端度类量具测量中遇到的测头选择问题和相应转折点的寻找方法。     

电阻变化法测量绕组温升的探讨

绕组温升是安全标准中的一项重要指标。因导体电阻随温度变化呈现某一规律,所以,测试出断电瞬时的电阻值就可推算出绕组温升。由于绕组断开电源后,温度逐渐下降,所以测得的电阻值并不是绕组断电瞬时的电阻值,我们可以通过短时间间隔读取的电阻测量值,利用作图法和回归分析法来确定断电瞬时的电阻值,从而推算出绕组温升。     

Improved Contact X-Ray Microradiographic Method to Measure Mineral Density of Hard Dental Tissues

Contact X-ray microradiography is the current gold standard for measuring mineral densities of partially demineralized tooth specimens. The X-ray sensitive film specified in the last J Res NIST publication on the subject is no longer commercially available. OBJECTIVES: Develop a new microradiographic method by identifying a commercially available film with greater than 3000 lines per millimeter resolution, which is sensitive to X rays, and develop correct film processing for X-ray microradiographic application. METHODS: A holographic film was identified as a potential replacement film. Proper exposure was determined utilizing a thick nickel plate to create test-strips. Film development was bracketed around manufacturer suggestions. Film linearity was determined with aluminum step-wedges. Microradiographs of 100 μm thick tooth sections, before and after acidic challenges, were a final test for film. Magnified images were captured with a digital microscope camera with 0.305 micrometers per pixel resolution. RESULTS: The appropriate film exposure was 30 minutes at 80 kV(p) and 3 mA with a development time of 2 minutes. Step-wedge experiments show the system to be linear in terms of pixel intensities with respect to x-ray attenuation for normalized pixel intensity values that are 10% to 90% of full scale (r(2) = 0.997) which encompasses the full exposure region of tooth tissue. Enamel sections were analyzed and show distinctive differences between erosion and demineralization. The image capture device resolution of 0.305 micrometers per pixel limits the system resolution. CONCLUSION: Use of the identified holographic film when combined with the described processing modifications has resulted in an improved X-ray microradiographic method for the measurement of mineral density of dental hard tissues. The method described can be further improved by using a higher resolution digitization system. The method is appropriate for quantitatively measuring changes in mineral density and erosion.     

Improved Impedance Measuring Accuracy with Computer-Operated Transmission Measuring Sets

Computer-operated transmission measuring sets and network analyzers have been used to measure the impedance of components used in modern communications systems. The component is interfaced to the test set using a suitable coupling network for the impedance level and frequency range. Optimized or adaptive coupling networks may be employed to extend the range and accuracy of impedance measurements by an order of magnitude compared to a single fixed-topology coupling network.