《家电维修基础2》2.5 电阻器的检测

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2.5  电阻器的检测

电阻器好坏的判定方法有很多种,最简单易行的方法是用万用表电阻挡检测。

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2.5.1  电阻器的检测方法

对普通电阻器的检测主要使用万用表的欧姆档,通过测量组织来判断是否出现断路、短路及阻值变化等故障。

一般检测电路中的电阻器,可采用两种方法:一种是在路检测,一种是开路检测;下面分别介绍。

1. 在路检测

这种检测方法无需将元器件卸下,而是使用万用表直接对电路板上的电阻进行检测。这种检测方法较为简便,但有时候会因电路中其它元器件的干扰,从而造成测量值的偏差,因此在使用在路检测时一定要考虑电路中其它元器件对电阻器的干扰。

在路检测的具体操作步骤如下:

① 将电路板的电源断开

② 对电阻器进行观察,看待测电阻器是否损坏、爆裂,有无烧焦、引脚断裂、引脚铜箔线断路或虚焊等情况。

③ 根据电阻器的标称阻值,调整万用表的量程到合适的电阻挡,并将万用表的两只表笔分别放到待测电阻器的两个引脚,测量一个阻值\(R_1\)。

④ 将万用表的两只表比对调,然后再测量一个阻值\(R_2\)。

⑤ 比较两次测量的阻值,取较大的作为参考值(如\(R_1\)),如果\(R_1\)等于或十分接近被测量电阻的标称阻值,则可以判定该电阻正常;如果\(R_1\)大于被测电阻的标称组织,则可以判定该电阻损坏;如果\(R_1\)远小于标称阻值(即有一定阻值),此时并不能确定电阻是否损坏,还有可能是由于电路中并联有其它小阻值电阻造成的,这时就需要采用脱开电路板检测的方法近一步证实。

2. 开路检测

开路的检测方法有两种,一种是使用电烙铁将电阻一端引脚焊下,脱开电路板,然后再测量;令一种是切断电阻器一端引脚的铜箔线,然后再测量。开路检测方法,主要对单独的电阻器进行独立检测,与在路检测相比,开路检测有效的避免了电路中的干扰,从而确保测量的准确性。

开路检测的具体步骤如下:

① 将电阻器从电路板中焊下。

② 为电阻器进行观察,看待测电阻器是否损坏、破裂,有无烧焦、引脚断裂、引脚铜箔线断路或虚焊等情况。

③ 根据电阻器的标称阻值,调整万用表的量程到合适的电阻挡,并将万用表的两只表笔分别放到待测电阻器的两个引脚,测量一个阻值\(R\)。

④ 将测量电阻值与电阻器的标称阻值进行比较,如果\(R\)等于或十分接近被测电阻的标称阻值,则可以断定该电阻正常;如果\(R\)大于被测电阻的标称阻值,则可以断定该电阻损坏;如果\(R\)远小于标称阻值(即有一定阻值)或为0,则可断定此电阻内部短路损坏。

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2.5.2  用指针万用表检测电阻

用指针万用表检测电阻的方法如下:

<1> 选择测量档位及量程。将万用表功能旋钮旋到“Ω”档(即电阻档)任一量程(×1、×10、×100、×1k、×10k)。通常情况下,100Ω以下的电阻选择×1或×10量程,1~10kΩ电阻选择×1k或×10k量程,100kΩ以上电阻选择×10k量程。

<2> 调零。用一只手将两只表屏金属棒短接(用手将表比金属棒捏在一起),另一只手调节“调零旋钮”,使万用表指针指示在刻度盘的右端“0”位。

<3> 测量。将万用表两支表笔分别稳定接触电阻器的两个电极,并从欧姆刻度盘上读取指针指示的数据,将数据乘以量程值所得结果为该电阻阻值。

注意:

若指针向右偏转太多,就换一个稍低量程重测;若指针向右偏转太少,就换一个稍高的量程重测;尽量使指针指示在靠度盘的中间部位,每换一次量程,都需要重新调零。

<4> 判断好坏。将所测得的结果与电阻的标注值进行比较。所测结果与标注阻值约相等,说明该电阻正常,是好的。否则,若相差太大,远远超过其精度允许范围,说明该电阻已损坏。若在各量程测量时指针均不偏转,说明电阻已开路损坏。

注意:

测量高值电阻时,尽量不要用手直接接触电阻的两电极,以防人体电阻引起测量误差。

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2.5.3  用数字万用表检测电阻

用数字万用表检测电阻的方法如下:

<1> 选择测量档位及量程。一般200Ω以下电阻选择“200”量程,200Ω~2000Ω电阻选择“2k”量程,2~200kΩ电阻选择“200k”量程,大于200kΩ电阻选择“2M”量程,大于2MΩ电阻选择“20M”量程,大于20MΩ电阻选择“200M”量程。

<2> 测量。将万用表的表笔分别稳定接触电阻的两个电极,在显示屏上会显示一个数字,该数字即为电阻的阻值。

<3> 判断好坏。所测结果与该电阻标称阻值相近,说明该电阻是好的;若相差太大,则说明有问题。

注意:

在测量时做显示“1.”(表示溢出),这是量程选的低了,可选一个高量程档位重新测量。若无论哪个量程测量时显示屏都显示“1.”,表明该电阻已开路损坏。若显示“00.0”,可能是量程选的太大了,可选一个更低点的量程重测。对于高值电阻,可能会出现数字有跳变的现象,读取一个最小的值即可;若数字大范围跳变,说明该电阻不可靠,不能再用。


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