The function of shunt

A shunt is generally a fixed value low resistance used to expand the current range. Usually connected in parallel with the moving coil of the ammeter or galvanometer. The shunt works based on whether it is a DC current. If it is a DC current, the shunt will generally adopt an expanded fixed value low resistance, and then measure the voltage generated at both ends of the resistor when the current passes through the resistor. It is usually connected in parallel. There are two forms of internal connection and external connection on the moving coil of ammeter or galvanometer. The shunt is essentially a resistor with a very small resistance value. When the DC current passes through the shunt, the shunt will produce a voltage drop, thereby providing a display for the DC ammeter. However, it should be noted that the shunt and ammeter are matched and cannot be confused. A shunt is a resistor that can pass a very large current. Commonly used ammeters of 15A, 20A and 35A require a shunt. The impedance of the shunt = the full-scale voltage on the meter head / the full-scale current on the meter head, such as a 20A ammeter. Shunt resistance = 75mv × 10-3/20A = 0.00375. After the impedance is constant, according to Ohm's law U=IR, the current is proportional to the voltage. The current is linear and the voltage is linear. So we can use a voltmeter with a full scale of 75mv to display the current current. Therefore, the ammeter we use is actually a voltmeter. Shunts are widely used to expand the measuring current range of instruments. There are fixed-value shunts and precision alloy resistors, which can be used in instruments, communication systems, electronic machines, automated control power supplies and other circuits for current limiting and current sharing sampling and testing. . The principle is shown in the figure below. The detected voltage is used by instruments, control circuits, etc.