Hot Selling Rail DC Wireless Multifunction Meter for Electrical Current Energy Measurement

Generally, it is possible to directly measure currents in the order of microamps or milliamps. To measure larger currents, the ammeter should have a parallel resistor (also known as a shunt). The measurement mechanism mainly uses a magnetoelectric electric meter. The resistance value of the shunt is such that when the full range current passes through, the ammeter deflects fully, i.e. the ammeter indication reaches the maximum. For a few amperes of current, a dedicated shunt can be installed in the ammeter. For currents above a few amperes, an external shunt is used. The resistance value of a large current shunt is very small. 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, with two current terminals and two voltage terminals.

An ammeter is made according to the action of a magnetic field force on an energized conductor in a magnetic field. There is a permanent magnet inside the ammeter that generates a magnetic field between the poles. In the magnetic field, there is a coil with a hairspring at each end of the coil. The springs are connected to a terminal post of the ammeter, and between the spring and the coil, there is a rotating shaft connected. There is a pointer on the rotating shaft relative to the front end of the ammeter. When a current passes through, the current passes through the magnetic field along the spring and rotating shaft, and the current cuts the magnetic induction line. Therefore, under the action of the magnetic field force, the coil deflects, driving the rotating shaft and pointer to deflect. Because the magnitude of the magnetic field force increases as the current increases, it is possible to observe the magnitude of the current through the deflection of the pointer. This is called a magnetoelectric ammeter, which is the kind we usually use in the laboratory.