Rasha S M Ali, M Helmy A Raouf
（Dept. of Electrical Quantities Metrology, National Institute for Standards (NIS), Giza 12211-136, Egypt）
Abstract： A new system for measuring low-ohmic standard resistors through a dual current sources bridge is introduced. It is used for low resistance measurements from 1 mΩ to 1 Ω at 1∶1 ratio, which is suitable for the laboratories without cryogenic current comparators (CCC) or direct current comparators (DCC) bridges. Behavior of this bridge is evaluated by comparing its measured values with the unknown resistor values obtained by another method. The accuracy of the introduced bridge is in the level of 10-5 for the 1 mΩ resistor, and in the level of 10-4 for the 10 mΩ, 100 mΩ and 1 Ω resistors. Moreover, a dual voltage sources system for the measurement of DC standard resistors from 1 kΩ to 100 MΩ is also presented. In this system, a modification is made on the modified Wheatstone bridge to evaluate its performance by adding another digital multimeter to measure the ratio between the unknown and the standard resistors simultaneously. This bridge is verified by comparing the measured values of 10 kΩ resistor obtained by the two methods with its actual value. The bridge accuracy is in the level of 10-6 except for the 1 kΩ resistor, and the bridge asymmetry is also evaluated. It is found the asymmetry is in the level of 10-6 for the resistors from 10 kΩ to 100 MΩ and in the level of 10-5 for 1 kΩ resistors. The introduced bridges operations are controlled by LabVIEW programs designed specially for this purpose, and the expanded uncertainty is also evaluated for all measurement results.
Key words： direct current comparators; voltage null detector; modified Wheatstone bridge; ratio technique; resistance measurements; uncertainty
CLD number： TM934.12 Document code： A
Article ID： 1674-8042（2019）02-0109-07 doi： 10.3969/j.issn.1674-8042.2019.02.002
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用于测量直流电阻标准的自动双源系统
Rasha S M Ali, M Helmy A Raouf
（国家标准化研究所 电气计量研究所， 吉萨 12211-136， 埃及）
摘要： 介绍了一种通过双电流源电桥测量低欧姆标准电阻的新系统， 用于1 mΩ ~1 Ω之间比率为1∶1的低阻值电阻测量。 该电桥适用于没有低温电流比较器(CCC)或直流比较器(DCC)电桥的实验室。 通过将电桥的实测值与另一种方法得到的未知电阻值进行比较， 对电桥的性能进行了评价。 该电桥对1 mΩ电阻的准确率达到10-5级， 对10 mΩ, 100 mΩ 和 1 Ω 电阻的准确率达到10-4级。 此外， 利用双电压源系统测量了1 kΩ~100 MΩ的直流标准电阻。 通过增加另一个数字万用表改进惠斯通电桥以同时测量未知电阻与标准电阻的比值对该系统性能进行了评价。 将10 kΩ电阻用两种方法获得的测量值与实际值进行对比对该电桥进行了验证。 除了1 kΩ电阻， 电桥对其他电阻的准确率达到了10-6级。 此外， 对电桥的不对称性也进行了评价。 实验发现， 不对称率对10 kΩ~100 MΩ的电阻为10-6级， 对1 kΩ的电阻为10-5级。 该电桥的操作由专门为此设计的LabVIEW程序进行计算机控制， 并对所有测量结果的不确定度进行了评估。
关键词： 直流比较器； 电压零位计； 改进的惠斯通电桥； 比率技术； 电阻测量； 不确定度
引用格式：Rasha S M Ali, M Helmy A Raouf. Automated dual source systems for measurement of DC resistance standards. Journal of Measurement Science and Instrumentation, 2019, 10（2）： 109-115. ［doi： 10.3969／j.issn.1674-8042.2019.02.002］
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