PMMC Instruments as Fluxmeters

PMMC (Permanent Magnet Moving Coil) instruments are widely used in electrical and electronic measurements. These instruments operate on the principle of the interaction between a magnetic field produced by a permanent magnet and a current-carrying coil. They are commonly used as ammeters and voltmeters.

PMMC instruments can also be used as fluxmeters, which are instruments used to measure magnetic flux. Magnetic flux is a measure of the total magnetic field passing through a given area. Fluxmeters are useful for various applications, such as magnetic field mapping, magnet testing, and magnetic material characterization.

Using a Low Resistance Shunt

One way to use a PMMC instrument as a fluxmeter is by using a low resistance shunt. A shunt is a low-resistance path connected in parallel with the PMMC instrument. By connecting a low resistance shunt in parallel with the coil, the current passing through the coil can be diverted through the shunt, reducing the deflection of the coil.

When used as an ammeter, the PMMC instrument is designed to have a coil with a low resistance to minimize power loss. However, when used as a fluxmeter, the low resistance of the coil can result in a large current passing through the coil, causing excessive deflection. By using a low resistance shunt in parallel, the majority of the current is diverted through the shunt, allowing for more accurate measurement of the magnetic flux.

Removing the Control Spring

The correct answer to the given question is option 'B', which states that PMMC instruments can be used as fluxmeters by removing the control spring. The control spring in a PMMC instrument is responsible for providing the restoring torque that opposes the deflection of the coil. By removing the control spring, the deflection of the coil is not opposed, allowing the coil to freely move in response to the magnetic field.

When the control spring is removed, the PMMC instrument essentially becomes a moving coil galvanometer, which is a highly sensitive instrument for measuring small currents. The coil in a moving coil galvanometer is very light and has a large moment of inertia, allowing it to respond to even very weak magnetic fields. By removing the control spring in the PMMC instrument, the coil becomes more sensitive to the magnetic field and can accurately measure the magnetic flux.

Conclusion

In conclusion, PMMC instruments can be used as fluxmeters by removing the control spring. This allows the coil to freely move in response to the magnetic field, increasing the instrument's sensitivity to measure magnetic flux accurately. Other methods, such as using a low resistance shunt or a high resistance in series, can also be employed to improve the accuracy of flux measurements with PMMC instruments. However, in the context of the given options, removing the control spring is the correct answer.