[Principle of ammeter] What is the working principle of ammeter?

[The principle of the ammeter] What is the working principle of the ammeter

The working principle of the ammeter

The principle of the ammeter The working principle is well understood. The ammeter is made according to the action of the magnetic field force on the conducting conductor in the magnetic field. There is a permanent magnet inside the ammeter, which generates a magnetic field between the poles. There is a coil in the magnetic field. There is a hairspring spring at each end of the coil. Each spring is connected to a terminal of the ammeter. On the front of the ammeter, there is a pointer. Pointer deflection. Since the magnitude of the magnetic field force increases with the increase of the current, the magnitude of the current can be observed through the deflection of the pointer. This is called a magnetoelectric ammeter, which is the kind we usually use in the laboratory.

What is the principle of the ammeter

Generally, it can directly measure the current of the order of microampere or milliampere. In order to measure the larger current, the ammeter should be connected in parallel. Resistors (aka shunts). The measurement mechanism of the magnetoelectric meter is mainly used. When the resistance value of the shunt is to make the full-scale current pass, the ammeter is fully deflected, that is, the indication of the ammeter reaches the maximum. For currents of a few amps, special shunts can be set in the ammeter.

For currents above several amps, the working principle of the ammeter uses an external shunt. The resistance value of the high-current shunt is very small. In order to avoid errors caused by the addition of lead resistance and contact resistance to the shunt, the shunt should be made into a four-terminal form, that is, there are two current terminals and two voltage terminals. For example, when an external shunt and millivoltmeter are used to measure a large current of 200A, if the standardized range of the millivoltmeter used is 45mV (or 75mV), then the resistance value of the shunt is 0.045/200=0.000225Ω (or 0.075/200=0.000375Ω). If a ring (or step) shunt is used, a multi-range ammeter can be made.