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在把电流表改装成伏特表或安培表的实验中,一般的步骤是:①读出电流表的满度电流I_9。②测出电流表的内阻R_9。③根据分压原理或分流原理计算出所需要的串联(伏特表)电阻或并联(安培表)电阻。④连接好计算出的电阻后,改装表跟标准表进行校对。若误差较大,还要再作调整才能达到要求。假如一个表头只有刻度而没有数值,还必须测出满度电流。如此多的手续也不能说不烦,其实,在实用上为了简便起电,步骤①、②、③全都可以省去,也不必关心满度电流是否已知。现以改装成量程为3伏的伏特表为例谈一下这种方法。
In the experiment of modifying an ammeter into a voltmeter or ammeter, the general steps are: 1 Read the full-scale current I_9 of the ammeter. 2 The internal resistance R_9 of the ammeter is measured. 3 Calculate the required series (voltmeter) resistance or parallel (ampere meter) resistance based on the partial pressure principle or the shunt principle. 4 After connecting the calculated resistance, the modification table is calibrated against the standard table. If the error is large, it must be adjusted again to meet the requirements. If a meter has only scale and no value, full-scale current must be measured. So many procedures can not be said to be not annoying, in fact, in order to facilitate the simple power, steps 1, 2, 3 can all be omitted, do not have to care about whether the full-scale current is known. Let us talk about this method with a voltmeter that is converted into a 3-volt range.