有两种电流测量的基本技术，即分流安培计技术和反馈安培计技术。

There are two basic techniques for making current measurements: these are the shunt ammeter and the feedback ammeter techniques.

他只有一些安培计和一个安瓶。

He only had some ammeter and an ampoule.

然而，实际的安培计在输入端开路时的确有一些小的电流。

Practical ammeters, however, do have some small current that flows when the input is open.

表2-3给出了典型的反馈安培计在各种测量范围内最小的源电阻推荐值。

Table 2-3 summarizes minimum recommended source resistance values for various measurement ranges for a typical feedback ammeter.