Advantages and Disadvantages of a Moving Coil Galvanometer

We must measure the current/voltage in microampere/volt or nano ampere/volt in several electrical and electronic circuits. Even though most galvanometers are meant to study and detect the tiny flow of electrical charges or potential differences across the terminals, they cannot identify microcurrent and voltages. This is where the moving coil galvanometers come into play. 

There are two types—a suspended galvanometer and a pivotal galvanometer.

Working Principle of a Moving Coil Galvanometer

According to the theory of magnetic induction, if a closed coil is connected to a galvanometer and a magnet is brought closer to it, the galvanometer’s pointer deflects from its default position. 

The deflection will happen due to the induction of an electric current within the coil. The direction to which the pointer will move depends on the magnetic pole. 

If the poles are reversed, it will cause opposite deflection. Once the magnet rests, the pointer will return to its original default value as the current will stop flowing. This entire arrangement is a moving coil galvanometer. It allows us to detect and measure the microampere currents within a circuit. The same behaviour can be observed when the magnet is static and the coil moves.

Advantages of Using a Moving Coil Galvanometer 

The main advantage of a moving coil galvanometer is that this instrument can detect the current and potential differences for various types of electrical and electronics circuits. There are many other advantages listed below:

• It is sensitive

As the instrument detects the presence of current or voltage through magnetic induction, a slight change in the field density, number of coils or the flux incident area will change the readings. Therefore, it is susceptible and needs to be handled carefully. 

It is represented as S = dθ/dl

The sensitivity of a moving coil galvanometer is controlled by: 

• Number of coil turns
• Magnetic field strength
• Coil area
• Couple per unit twist 

Usually, a sensitive moving coil galvanometer will produce a more significant deflection of the arrow from its default value even when a small amount of current flows through the circuit. It helps understand how the circuits will behave and the output voltages in response to induced currents.

• Accurate Readings

Due to its high sensitivity, the readings obtained are more accurate and reliable. It doesn’t matter whether the circuit components are electronic or electrical; values for the current and voltage obtained will be as close to the original values as possible.

Thus, this instrument is used to study the outputs of sensitive circuits like that of a barometer, a weight measuring device, etc. 

• Uniform Scaling 

If an instrument is scaled incorrectly, it will lead to an increase in discrepancies. As a result, erroneous values will cause a problem in circuit designing, improvement of existing circuit performance, etc.

Besides, you will also get the moving coil galvanometers in different scale ranges as per requirements, such as 100mA to 1000 mA or 250 mA to 1000 mA.

• Can be used as an Ammeter or Voltmeter

When connected to low resistance in a parallel circuit, the entire arrangement behaves like a dynamic ammeter. On the contrary, it will act like a voltmeter when connected in series to high resistance.

Challenges of Using the Moving Coil Galvanometer

• It can’t be used to measure alternating forms of currents. 
• If the magnetic field changes due to the ageing of the magnets, the values read will be wrong.
• Owing to the high sensitivity, errors are bound to creep into the readings. 
• The temperature will affect the performance of a galvanometer as it causes the coil to expand or contract. 

Conclusion

It is important to understand the advantages and disadvantages of a moving coil galvanometer when using the instrument and designing or modifying circuits. It is available in two forms and has a vast area of application.According to the resistance value and connection type, you can use it as an ammeter or voltmeter. It will become easier to measure both the currents and voltages across terminations. However, the current measured will only be of DC type as you won’t be able to detect the alternating currents.