The principle of the DC current measurement circuit of the multimeter
The main component of an analog multimeter is a magnetoelectric ammeter, usually called a meter head. But a meter can only measure currents less than its sensitivity.
In order to expand the range of the measured current, it is necessary to add a shunt resistance to it, so that the current flowing through the meter is a part of the measured current to expand the range.
In order to obtain a certain accuracy when measuring currents of different sizes, the ammeters are designed with multiple ranges.
The most widely used is the closed-circuit tapped shunt circuit, and its circuit is shown in the figure.
In the figure, R1 to R5 are collectively referred to as the total shunt resistance RS. In order to facilitate adjustment and batch production, the total shunt resistance RS mostly adopts a large integer resistance value of kiloohms, and a variable wire wound resistance R0 is connected in series with the meter head. , when the parameters of the meter are changed, it can still be compensated and adjusted easily.
