What is Ammeter? How does it works

What is an ammeter?

An ammeter is a measuring instrument that is used to measure the electrical current that passes through a circuit. These instruments are composed of a galvanometer and a series of parallel resistors called shunt.


The galvanometer also serves to measure electrical current but in very small quantities


How does an ammeter work?

An ammeter is composed of a galvanometer that is constructed with an indicator needle, a spring, a coil, and 2 permanent magnets and its operation is based on magnetism. The needle is connected by a spiral-shaped spring to the axis of a rectangular coil, which is suspended due to the magnetic field of the magnets.

Because the coil is controlled by the magnetic poles of the magnets when a current passes over it generates its own magnetic field which causes it to rotate depending on the direction and strength of this electrical intensity.


An ammeter usually has several measurement scales. This is where the shunt resistors series come into play since each represents a different scale. The resistors are placed in parallel to the coil so that most of the electric current passes through them and only a small part through the coil, but that that small part remains proportional to the total intensity.

Shunt resistor

How do I use an ammeter?

There are different types of ammeters but there are only 2 ways to measure the current.


Hook ammeter

With this type of ammeter making a current measurement is quite simple since it is only necessary to put the cable that you want to measure inside the clamps and it will show you the measured current on its display.


Conventional ammeter 

If you are a beginner with this instrument, making a measurement can be a bit more complicated because it is necessary to open the electrical circuit and connect it so that the ammeter with the circuit is in series.


What types exist?

We can find a wide variety of ammeters, most are classified by their construction. Whether mechanical, thermal, digital, analog, etc.


This type was one of the first to be built, its operation is based on an indicator needle which stops at the number or fraction of the measured value.

Within this category, we can find the type and electromechanical type.


Its operation is based on the expansion of a conductor, since the expansion is proportional to the heat and, according to the law of joule, the heat is proportional to the square of the current, this instrument is capable of measuring alternating or direct current, since the heat is the same for one way or the other. The current passes through a resistor, which heats up as the current passes and passes through a thermoelectric pair which is connected to a galvanometer.

Thermal ammeter


Its operation is based on that of the coil with the magnets, only that there is a great variety of this class.

  • Mobile coil
  • Mobile magnet
  • Ferromagnetic or mobile iron
  • Electrodynamic



These instruments originated with the advancement of technology since they eliminate reading errors because the measurements are displayed on a screen with numbers and all moving parts were exchanged for electronic circuits.

Digital ammeter

Amperometric clamp

This is practically the most used in the industry since to make a measurement it is not necessary to open the circuit, just put the cable inside the clamps and this will indicate the measured value. Its operation is based on the magnetic field generated by the cables when a current passes over them.

Hook ammeter