To judge the quality of the ammeter, we must first know the working principle of the ammeter: the ammeter is made according to the force of the energized 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. The springs are connected to a terminal of the ammeter. The spring and the coil are connected by a shaft, and the shaft is opposite. At the front end of the ammeter, there is a pointer. When there is current passing, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic induction line. Therefore, the magnetic field force causes the coil to deflect, driving the rotating shaft and pointer to deflect. Since the magnitude of the magnetic field force increases with the increase of the current, the magnitude of the current can be observed by the degree of deflection of the pointer.
We understand the principle of an ammeter, so we probably have the following methods to judge the quality of an ammeter:
1. Use a multimeter to measure whether the two terminals of the ammeter are open. If they are open, it can be judged as bad.
2. If the current meter line shows a large error, you can use the multimeter current file to connect the meter pen and the ammeter in series to measure the current deviation. This method is suitable for measurement where the current is not too large.
3. The moving coil of the ammeter is broken, and the needle will not move if the moving coil is broken.
4. If the coil is not open, check whether the needle is blocked by foreign objects.
In addition to the above methods, some misjudgment factors should be excluded:
1. The range of the ammeter is inappropriate, the range is too large and the current is relatively small.
2. Improper selection of ammeter, use DC ammeter to measure AC current.