Electronic Design

Take The Right Steps To Achieve Accurate Measurements</A><BR><FONT CLASS=body11>Sponsored by: <A HREF="http://www.national.com" TARGET=_blank CLASS=body11>NATIONAL SEMICONDUCTOR</A></FONT><A>

Current measurements are used in a variety of equipment for control or safety functions. Measuring the voltage drop across a low-value resistor is the most common method of measuring the current flowing in a circuit. The current flow through the load also flows through the RSENSE resistor, also known as a shunt resistor, which creates a voltage drop, VM, across the resistor.

Figure 1 depicts two current-measurement approaches. Ammeters were developed in the early history of electronics, and they're still used today. Typically, the meter itself may read full-scale when the current through it is 100 µA or 1 µA. So to read larger currents, it is connected in parallel with a resistor that shunts most of the current around the meter. That way, the meter can be scaled to measure any magnitude of current.

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