The galvanometer is the device used for detecting the presence of small current and voltage or for measuring their magnitude. The galvanometer is mainly used in the bridges and potentiometer where they indicate the null deflection or zero current.
There are various types of galvanometer. They are-
- Tangent Galvanometer: it works by using a compass needle to compare the magnetic field generated by an unknown current to the magnetic field of the Earth. It was used earlier. It was first given by Claude Pouillet in 1837. It contains an insulated copper wire coil on a non-magnetic circular frame.
- Astatic Galvanometer: it does not use the Earth’s magnetic field for measuring the current. It was developed by Leopoldo Nobili in 1825. It contains two magnetized needles that run parallel to each other, suspended by a silk thread, with their magnetic poles reversed. The lower needle gets deflected by the passing current’s magnetic field. The second needle cancels out the diapole movement of the first one to cancel out the effects of Earth’s magnetic field.
- Mirror Galvanometer: it is used to achieve higher sensitivity for detecting extremely small currents. It contains horizontal magnets which are suspended from a fine fiber inside of the vertical coil, with an attached mirror to its magnets. A beam of light reflects from the mirror acts as a long mass-less pointer by falling on a graduated scale across the room.
- Ballistic Galvanometer: it is sensitive in mature and used to measure the quantity of charge that is discharged through it. The moving part of the galvanometer has a large moment of inertia, giving it a long oscillation period. It may be of the moving coil type or of the moving magnet type.
