What is a Galvanometer

In this article, we will discuss the galvanometer, an electrical measuring instrument used to detect the amount and direction of electric current in an electric circuit. So, let’s start with the definition of galvanometer.

Introduction to Galvanometer

A galvanometer is a measuring instrument used in electrical and electronic circuits to measure the strength of electric current and detect the direction of the current. The working of the galvanometer is based on the principle of electromagnetic induction.

A galvanometer is a type of moving coil instrument which consists of a moving coil of conductor wire placed in a magnetic field produced by permanent magnets. When an electric current flows through the coil, it generates a magnetic field around the coil. The two magnetic fields, one generated by permanent magnets and another generated by an electric current through the coil, interact with each other. Due to this magnetic interaction, the coil experiences a torque which rotates it on its axis. A pointer is attached to the coil that deflects on a scale to show the reading of the current.

Galvanometer is mainly used in electronic bridges and potentiometers to indicate the zero current reading or null deflection.

Construction of Galvanometer

The following figure depicts the construction of a typical galvanometer.

It consists of a coil of very fine insulated wire wound on an aluminium frame. The coil is suspended between the poles of a permanent magnet with the help of a filament made up of phosphor bronze. This filament also acts as one lead of the coil. This suspension system allows the coil to rotate freely. A pointer made up of non-magnetic material is attached to the coil. This pointer deflects on a calibrated scale to indicate the direction of the current and provide the strength of the current.

In a galvanometer, a control mechanism is also employed to control the sensitivity and range of measurement. This control mechanism typically consists of adjustable springs or weights that introduce additional torque to counterbalance the effect of the magnetic field on the coil.

To obtain stable readings in measurement, a damping mechanism is provided in the galvanometer. The damping mechanism consists of a copper ring in which eddy currents are induced that opposes the movement of the coil and prevents its oscillations.

Parts of a Galvanometer

The following are some of the major parts of a galvanometer:

• Moving Coil – It is the part of a galvanometer that carries the electric current which has to be measured.
• Permanent Magnet – This part generates the working magnetic field in the galvanometer required to produce the coil’s movement.
• Pointer – It is part of a galvanometer that deflects on a scale to indicate the measured electric current.
• Scale – This part is calibrated to show the magnitude and direction of the measured electric current.

Working of Galvanometer

The working of a galvanometer is based on the principle of electromagnetic interaction, where a magnetic force causes a current-carrying coil/conductor to move. The movement of the coil is directly proportional to the strength of the electric current flowing through it.

In a galvanometer, a permanent magnet generates a magnetic field in which a moving coil is placed. When an electric current passes through the coil, the moving coil rotates. A pointer is attached to this moving coil that can deflect on a calibrated scale to measure the intensity of the electric current.

When the electric current is stopped to flow through the coil, the coil and hence the pointer come to their initial position under the influence of the control spring.

Advantages of Galvanometer

The major benefits of galvanometer are listed below:

• Galvanometer has high sensitivity.
• The working of the galvanometer is less affected by the stray magnetic fields.
• Galvanometer can measure both the magnitude as well as the direction of the electric current in the circuit.
• Galvanometers are highly accurate and reliable.
• Galvanometers have uniform scales.

Disadvantages of Galvanometer

The following are some major disadvantages of galvanometers:

• Galvanometer can only be used to measure direct current (dc) in a circuit.
• Galvanometers can give incorrect readings due to the ageing of the device and magnets, damaged control spring, mechanical stress, etc.
• Galvanometer can be damaged due to overload.
• The restoring torque of the galvanometer can be changed due to temperature variations.

Applications of Galvanometer

Galvanometers are widely used in the following applications:

• Galvanometers are used to detect the direction of current in a circuit.
• Galvanometers can also be used to measure the strength of current flowing through a circuit.
• Galvanometer can be used as an ammeter by connecting a resistance in parallel to its coil.
• Galvanometer can be used as a voltmeter by connecting a resistance in a series of its coil.

Hence, this is all about the definition, construction, working, advantages, and applications of the galvanometer.