自动门
自动门:测量中的有关注意事项
发布时间:2015/6/1
自动门讯:
测量中的有关注意事项
任何测量过程,都有它们各自的客观需要,并且有一定的精确度要求。应该看到,提高和保证测量的精确度,往往并不单纯取决于选择高精确度测量仪表,而是和测量方案、方法、场合、接线方式有关,是一个综合性问题。
1.被测量 电路在测量时引入内阻损耗
如果一个具有高内阻的被测电路,若采用低内阻的电压表测量其两端的电压,电表的示值和其实际的电压值相比要偏低。即使不计入电压表本身的误差,测量结果的绝对误差及相对误差也会增加很多。
2.被测谐振电路在测量是引入失谐
如果一个具有谐振回路的被测电路,当测量谐振回路两端的电压时凹凸琀听输入电阻和输入电容并在其谐振回路两端,从而引起的读数误差,有时也是十分严重的。其中输入电阻的引入将降低谐振回路的等效品质因素Q值,导致示值偏低。输入电容的引入将使谐振曲线偏移,从而造成失谐性的误差。
3.因测量引起被测电路反馈参数变化而造成的测量
例如用毫安表串入晶体管发射极回路中测量射极电流。由于毫安表内阻的引入而改变了该晶体管射电流负反馈的参数,导致显著的测量误差。
同理,在测量中,由于测量食品的输入阻抗,引线的分布参数等因素改变了被测电路的反馈参数时,也将造成测量误差,恶行时会引起被测电路的自激或振荡电路的停振。
由于测量电路的接法不妥,或者由于接入测量仪表后,吸取了被测电路的能量,改变了被测电路的参数,从而使被测电路偏离了正常的工作状态,造成了明显的测量误差。
因此,在一切测量过程中,应尽量保持被测的正常工作状态,使测得的数值具有足够的真实性。原则 上应尽量减少向被测电路吸取能量,尽量减少因测量而引起被测电路的参数变化。
应该注意:不能用普通的电压表去测量标准电池,以免标准电池过荷损坏;不能用万用表测量检流计或微安表头的内阻,以免表头指针冲击损坏或线圈损坏;不能用万用表去测量酒石酸钾钠压电晶体的内阻,以免压电的逆效应将晶体振裂等。
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