Galvanometer - How it Works

In electronics, a galvanometer is an instrument used to detect and measure the electric current. The fact that, not many of us use this device in our day-to-day life makes it more than obvious that not many people would be aware of how it works. The working principle of a galvanometer is quite interesting, and if you feel it would be boring like all the other science projects you did in your school, you are surely in for a surprise.

In 1820, Danish physicist Hans Christian Oersted noted that a magnetic needle gets deflected as it comes in contact with an electric current. This observation by Oersted went on to become the basic principle of the working of a galvanometer. In the same year, German physicist Johann Schweigger worked on this principle, and came up with the first galvanometer. The credit for the invention of the first moving-coil galvanometer, which is widely used even today, goes to French physicist Jacques Arsene D'Arsonval. A few years later, Edward Weston made quite a few changes to this design, and improvised it.

How it Works

The galvanometer works on the basis of electromechanical transduction, which responds to the current that it is subjected to on basis of the strength of the current and its rate of flow. Other than these two factors, it also responds to any sort of stimuli, which tends to strengthen the current, or blockage, which tends to weaken the current. Among the various types of galvanometers, the two most commonly used ones are:

• Moving-coil galvanometer with the coil either mounted on pivots or suspended by thin metal strips.
• Moving-magnet galvanometer with the needle mounted on the pivot in itself is a permanent magnet surrounded by the coil.

When the instrument is subjected to a source of direct current, the current tends to flow through the coil. This flow of charge from the coil produces a magnetic field in the surrounding. This magnetic field tends to act against the permanent magnet, which makes the coil twist and push against the spring. This fluctuation in turn moves the pointer, which indicates the scale showing the electric current. The direction of the current through the coil directly determines the direction of rotation, while the strength of the current determines the amount of rotation. In order to ensure that the magnetic field is uniform, the pole pieces need to be carefully designed. Failing to do so would result in disproportionate angular deflection of the pointer to the current.

Galvanometers have been in use since the 19th century. Even though modern technology has introduced several such devices which overshadow this device in certain aspects, it still remains one of the most preferred choice when it comes to detection or measuring electric current flowing from and to a source.