Recurring to rnathematic figure and examples and aiming at such questions as unbalanced current and induced voltage and high frequency interference , this paper has not only researched anti - jamming ability and measuring process of both three - electrode method and four - electrode method which are combined with reverse phase method , but also summarized actual measuring experiences 通过数学推导和实例，围绕消除地网不平衡电流、电压极电流极引线问互感电压、高频干扰等问题，分析了三极法、四极法结合倒相法测量接地电阻的抗干扰能力和测量过程，并总结了实际测试经验。
The paper recommends that the placement of voltage - electrode is 0 . 509s when the distance from the border of grounding grids to current - electrode is s that is the long border length of grids . ( 3 ) the paper use two - layer theory to describe non - uniform soil . with the different two - layer soil model , some conclusions and formula that have great reference value are presented numerically 综合各种因素考虑，推荐在距离地网边缘距离为地网长边长度s的位置布置电流极，并在0 . 509s布置电压测量极，在满足工程精度要求的同时也极大的提高了测量效率。
Network education teaching on internet divides into synchronous and asynchronous teaching two classes . the synchronous teaching transfers the multimedia classroom ’ s scene and teacher ’ s media in teaching with ddn / adsl / atm and sky satellite to distance classroom at real - time by internet audio and video technology so that the teacher questions their students and their students ask the question as well or the students consult their teacher , which realizes the similar teaching at a classroom . the courseware on demand ( cod ) is a important study method in asynchronous teaching , that the courseware was stored in the computer server , the student demand the courseware according to their plan to self - study , accompanying that the teachers answer the students ’ question on internet , bbs at the same time , which complete the asynchronous teaching 利用internet实现网络教学可以分为同步式和异步式两种:同步式教学主要应用internet的网络音视频技术,通过地网( ddn / adsl / atm )或天网(卫星)将多媒体教室中教师授课内容和授课情景实时转播到远端多媒体听课教室,学生可在远端即时回答老师的提问或向老师提问,实现了与真实课堂类似的实时交互式教学;异步教学的重要学习方式是课件点播( coursewareondemand ) ,即将多媒体课件放在服务器上,学生依据个人学习进度通过网络点播所需课件进行自主学习,同时与教师在网上辅导答疑、网上讨论等环节相结合,完成网络教学的异步教学过程。
