理解、選擇和有效地使用當前探測

　　編者按：這篇關于電流測量和電流探針的文章是關于探針及其正確使用的三部分系列中的第三篇。第1部分，覆蓋的高阻抗無源探頭。第二篇文章討論了單端、差分和高壓差分有源探針。第3部分將介紹電流測量和電流探頭。

　　用示波器測量電流有三種常用技術。第一種是使用電阻（有時稱為電流分流器）與所測量的電流串聯。第二種是使用電流互感器。第三種是使用電流探頭。由于這三種方法要求測量的電流通過測量傳感器，所以它們都有一定的侵入性。

　　電流探頭，因為它讓用戶測量導體的電流沒有如果，是最少的侵入性技術。然而，用戶需要了解當前探測的一些基本原理，以便從最新的探測設計中獲得最大的利用率。

　　本文將介紹當前的各種測量方法，然后介紹當前的探針以及如何有效地使用它們。

　　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）.