Ampermeters are devices for measurement of current in electrical circuits. By the principle of work the ampermeters are - magnetoelectric, electromagnetic, thermoelectric, electrodynamic and others.
The device by means of which measure force of the current proceeding on a chain is called the ampermeter. As values which are given by the device (current) depend on resistance of elements in the ampermeter, it has to be very low.
The internal device of the ampermeter depends on the purposes of use, a type of current and the principle of work.
There are ampermeters which react not to the size of resistance of the conductor, and to heat radiated by it or magnetic waves.
Magnetoelectric ampermeters
The devices reacting to the magnetic phenomena (magnetoelectric) apply to measure currents of very small values in chains with a direct current. In them there is nothing superfluous, except the coil connected to it shooters and scales with divisions.
Electromagnetic ampermeters
Unlike magnetoelectric they can be applied also to networks with alternating current, most often in chains of industrial function with a frequency of fifty hertz. The electromagnetic ampermeter can use for measurements in chains with a big current.
Thermoelectric ampermeters
Use for measurement of alternating current with high frequency. In the device the heating element (the conductor with a high resistance) with the thermocouple is established. Because of the passing current the conductor heats up, and the thermocouple fixes size. Because of the arising heat the frame with an arrow on a certain corner deviates.
Electrodynamic ampermeters
It is possible to use not only for measurements forces of a direct current, but also variable. Because of features of the device, it can be applied in such networks where frequency reaches two hundred hertz.
The electrodynamic ampermeter is used generally as the control measuring instrument for check of devices.
They strongly react to third-party magnetic fields and to overloads. Because of it as measuring instruments are used seldom.
Ferrodynamic
Very reliable devices which have high durability and are affected by the magnetic fields arising not in the device a little. Such ampermeters establish in the automatic controlling systems as recorders. Happens so that the scale of the device is not enough and it is necessary to increase values which should be measured. That to reach it shunting is used (the conductor with a high resistance joins parallel to the device). For example, to establish value of force in hundred amperes, and the device is designed for only ten, attach the shunt at which the value of resistance is nine times lower, than at the device.