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The relevant time constant is the product of the effective capacitance in microfarads and the
! S( _; @% e7 u& _4 leffective discharge resistance in megohms. If it is difficult to determine the effective; Q1 X5 h" D( q- z* j4 V
capacitance and resistance values, a measurement of voltage decay at the point of external4 ~& V3 a/ ~: r' Y& X
disconnection can be used. When conducting the voltage decay measurement, the result is0 o5 g1 w. L! ~/ _* Q8 r5 U
referred to an instrument having an input impedance consisting of a resistance of+ n5 Z" t0 r8 U
100 MΩ ± 5 MΩ in parallel with an input capacitance of 20 pF ± 5 pF.# R& F6 J% V4 F3 a: R7 o0 r! F
从标准的内容来说,确实是要求100 MΩ ± 5 MΩ 阻抗,但是我个人觉得阻抗越大,分流就越小,测到的数据就越接近真实情况。但标准不知道是怎么考虑的,为什么不在100M前面加上at least 之类的字眼。 |
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