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欧姆表是测量电阻的常用仪器,它测量电阻的误差主要有两方面的原因。一是与表的精度等级有关,二是由于表内电池陈旧而产生。本文仅对后一个问题进行讨论。欧姆表测量电阻的基本原理是全电路欧姆定律,实质上是用伏安法测电阻,所以欧姆表的表盘是倒刻度的。测量电阻之前都需要进行欧姆调零操作,即将两表笔相接,调节R使表头指针满偏。如图1(1)所示,电池陈旧以后,电动势下降,内电阻增大。为了考虑问题
Ohmmeter is a common instrument for measuring resistance. It measures the resistance error for two main reasons. One is related to the accuracy level of the watch, and the other is due to the old battery in the watch. This article only discusses the latter issue. The basic principle of an ohmmeter’s resistance measurement is the full-circuit Ohm’s law, which essentially measures the resistance with volt-ampere measurement, so the ohmmeter’s dial is scaled down. Before measuring the resistance, it is necessary to perform the ohmic zero adjustment operation, that is, to connect the two table pens, and adjust R to make the head pointer full. As shown in Fig. 1(1), after the battery is old, the electromotive force drops and the internal resistance increases. To consider the problem