Kunshan ammeter manufacturer introduces the principle of ammeter:

The ammeter is made according to the action of magnetic force on the electrified conductor in the magnetic field. There is a permanent magnet inside the ammeter,

The magnetic field is generated between the poles. There is a coil in the magnetic field. There is a spring at both ends of the coil. Each spring is connected to a terminal of the ammeter. A rotating shaft is connected between the spring and the coil, and there is a pointer at the front end of the rotating shaft relative to the ammeter. The pointer deflects. As the magnetic force increases with the current, the current can be observed by the deflection of the pointer. This is called magnetoelectric ammeter, which is the kind we usually use in the laboratory.

Generally, it can directly measure the current in the order of microampere or milliampere. In order to measure larger current, the ammeter should have parallel resistor (also known as shunt). It mainly adopts the measuring mechanism of magnetoelectric meter. The resistance value of the shunt should make the ammeter full deflection when the full range current passes through, that is, the ammeter indication reaches large. For several ampere current, special shunt can be set in ammeter. For a few amperes or more, an external shunt is used. The resistance value of high current shunt is very small. In order to avoid the error caused by the lead resistance and contact resistance attached to the shunt, the shunt should be made into four terminal form, that is, there are two current terminals and two voltage terminals. For example, when the external shunt and millivoltmeter are used to measure the large current of 200A, if the standardized range of the millivoltmeter is 45mv (or 75mV), the resistance value of the shunt is 0.045/200 = 0.000225 Ω（ Or 0.075/200 = 0.000375 Ω）。 If ring (or step) shunt is used, multi range ammeter can be made.