According to DigoPaul, an ammeter is a device that allows the measurement of the amps that the electric current has. To accurately understand the meaning of the concept, we must therefore know what amps are and what electric current is.
The electrical current is produced by the movement of electric charges in a material. It is a quantity that reflects the electricity that, in a unit of time, flows through the conductive material. The ampere, in this framework, is the unit that allows quantifying the intensity of the current.
Taking up the notion of an ammeter, this instrument measures the intensity of the current flowing in an electrical circuit. By connecting the ammeter to the electrical circuit, it is possible to discover the amount of amperes (i.e. the intensity) of the circulating current.
The measurement consists of making the electric current flow through the apparatus. The internal resistance of the ammeter is very small so that there is no voltage drop at the time of measurement. If you want to measure the current without opening the circuit, you need to use a particular class of ammeter known as the amperometric clamp (defined below), which measures the intensity indirectly by the magnetic field that generates the current in question.
There are several types of ammeters, which broadly can be divided into three groups: analog, digital and amperometric clamps.
The description provided in the preceding paragraphs is nothing other than the foundation of the older ammeters, which were analog. As in many other areas, although this technology has been designed a long time ago, it is still used today.
Analog ammeters present the measurement result with the help of a needle that is positioned at the corresponding point between the minimum and maximum available on the display panel. In this group of devices we find two subgroups: electromechanical and thermal ammeters.
Broadly speaking, we can say that electromechanical ammeters rely on the mechanical interaction that takes place between electrified conductors, between a magnetic field and a current, or between two currents. Its design is relatively simple: they have two organs, one mobile and one fixed, and a needle to indicate the resulting value.
This type of ammeter is undoubtedly quite bulky and this leads to greater wear on its parts, as well as a greater probability of measurement error. On the other hand, it quickly outperforms other models and is useful for readings in fixed positions. This group includes magnetoelectric, electromagnetic, electrodynamic and ferromagnetic ammeters.
With respect to thermal ammeters, they take advantage of the expansion of conductors when subjected to high temperatures, which is proportional to heat and, according to Joule’s law, this is also the square of the current regardless of its direction or nature, which is why these devices are useful for reading both direct and alternating current.
Thanks to advances in technology, this type of ammeter was born, more versatile and practical to use than analogue ones. Among its fundamental advantages are less wear (in the absence of moving parts) and a significant reduction in the probability of error. Instead of a panel with a needle, they have a screen where you can view the reading results.
This kind of ammeter is also known as a clamp or hook, and is very useful since it allows an instantaneous measurement of current without the need to interrupt or open the circuit. Since it has no electrical windings, there is no risk of it catching fire.