理解、选择和有效地使用当前探测

　　理解、选择和有效地使用当前探测

　　编者按：这篇关于电流测量和电流探针的文章是关于探针及其正确使用的三部分系列中的第三篇。第1部分，覆盖的高阻抗无源探头。第二篇文章讨论了单端、差分和高压差分有源探针。第3部分将介绍电流测量和电流探头。

　　用示波器测量电流有三种常用技术。第一种是使用电阻（有时称为电流分流器）与所测量的电流串联。第二种是使用电流互感器。第三种是使用电流探头。由于这三种方法要求测量的电流通过测量传感器，所以它们都有一定的侵入性。

　　电流探头，因为它让用户测量导体的电流没有如果，是最少的侵入性技术。然而，用户需要了解当前探测的一些基本原理，以便从最新的探测设计中获得最大的利用率。

　　本文将介绍当前的各种测量方法，然后介绍当前的探针以及如何有效地使用它们。

　　The current shunt

　　The current shunt is generally designed into the circuit or related test fixture. The current is determined by measuring the voltage drop across the known resistance of the shunt. There is an engineering trade-off between the series resistance of the shunt and the desired sensitivity of the current measurement.

　　The idea is to get a reasonable voltage drop while at the same time not affecting the circuit’s performance. Also， the power rating of the shunt has to be sufficient for the current being measured. An example of a current shunt resistor is the Riedon RSA-10-100. This chassis-mounted resistor has a resistance of 0.01 W with a tolerance of ± 0.25% and a power rating of 1 watt. The resistor power rating sets the maximum current at 10 amps， producing an output voltage of 100 millivolts. An oscilloscope is used to measure the voltage across the shunt. Most oscilloscopes have provisions to scale that voltage into an equivalent current （Figure 1）.