ZC29B型接地电阻表工作原理和调修.doc

ZC29B型接地电阻表的工作原理和调修 相旸 （云南省计量测试技术研究院，云南 昆明 650228） 摘要：接地电阻测量仪 关键词：接地电阻测量仪；相敏整流电路；ZC29B-2；工作原理；调修 Analyzing the structure and studying the repairing of model ZC29B earth resistance tester Xiang Yang (Yunnan institute of metrology and testing technology, Yunnan Province, Kunming 650228) Abstract: The earth resistance tester is in the Menu of China Compulsive Verification, and the researcher who engaged in this work has large of work to do to accomplish this task each year. As this tester is used in open-air, the decreasing of metrology capacity or damage may occur. For the purpose of finding the effective methods of solving this troubles, the author gives the circuit diagram of model ZC29B-2 earth resistance tester, depicts the simple model of it, and explains the mechanism that the tester how to work for short, then analyzes phase-sensitive AC-DC-CONVERTER circuit in the diagram. Last, provides several ways of solving this problems that usually happens in the calibration of earth resistance tester, which ensuring the calibration of earth resistance tester in an effective and High-quality way. Keyword: Earth Resistance Tester; Phase-sensitive AC-DC-CONVERTER Circuit; ZC29B-2; Mechanism; Repairing 1 引言 接地电阻测量仪 2 ZC29B型接地电阻表的工作原理和调修 ZC29B型接地电阻表的工作原理 接地电阻测试仪又称接地电阻表，ZC29B型接地电阻测试仪是目前使用量较大的一种，它由手摇发电机、电流互感器、滑线电阻及检流计等组成，全部机构装在塑料壳内，外有皮壳便于携带。附件有辅助探棒、导线等，装于附件袋内。为便于说明其工作原理，画出ZC29B-2型接地电阻表的电器线路图如下。 图 1 ZC29B-2型接地电阻表的电器线路图 ZC29B型接地电阻表可测量理论接地电阻值，其测量方式可由如下的简化接地电阻测量模型解释，假设图1中“大地”的电阻率是常数，将以“E”、“P”和“C”三个端钮相连接的接地棒为中心，地面下半径为定长的半球的体电阻计算出来，当这三个半球的半径达到一定距离后，这3个体电阻的阻值就基本不变了，称这样的电阻为流散电阻，设与“E”、“P”和“C”三个端钮对应的流散电阻的值分别为RE、RP和RC。除去这三个流散电阻后，大地余下的部分对这个接地电阻表来说，就可以看作电阻值忽略不计的导线。可知，“E”端钮所测的电阻等于连接于 “E” 端钮的接地线的电阻、接地体的电阻（这里为接地棒的电阻）和流散电阻三部分之和，一般情况下，流散电阻的值比前两者都要大得多。这时“E”端钮所测得的流散电阻即是理论接地电阻值。 ZC29B型接地电阻表工作时，先由手摇发电机生成交流电势差，由电势差引起的交流电流I1通过由手摇发电机、RE、RC、R5和电流互感器一次侧构成的电流回路。同时电流互感器的二次侧感应出与一次侧成固定比例的电流I2。I1通过RE时产生的电势的相量值由P端采样送到晶体管相敏整流电路，I2通过滑线电阻时产生的电势的相量值由滑线电阻的中心抽头采样送到晶体管相敏整流电路，当这两者的幅值或相位有差别，并且大于该相敏整流电路的分辨力时，检流计就做