Swamp Resistance and Condenser in Moving Iron Instruments



Introduction:


Moving iron instruments are commonly used for measuring both AC and DC quantities. However, these instruments are not ideal and have certain limitations and errors associated with them. In order to improve the accuracy of these measurements, additional components like swamp resistance and condenser are used.

Explanation:

1. Moving Iron Instruments:


Moving iron instruments are based on the principle that a movable iron piece is attracted towards a stationary coil when a current passes through it. The deflection of the iron piece is proportional to the current flowing through the coil. These instruments are used for measuring both AC and DC quantities.

2. Error in Measuring AC Quantities:


AC quantities have a varying magnitude and direction, which can lead to errors in the measurement of moving iron instruments. The iron piece in these instruments tends to follow the instantaneous value of the current, resulting in inaccuracies. The main error in measuring AC quantities is due to the non-linear relationship between the current and the deflection of the iron piece.

3. Swamp Resistance:


Swamp resistance is a resistance connected in series with the coil of the moving iron instrument. It is used to minimize the error caused by the non-linear relationship between the current and the deflection of the iron piece. The swamp resistance limits the current flowing through the coil and makes the relationship between the current and deflection more linear. This helps in reducing the errors while measuring AC quantities in moving iron instruments.

4. Error in Measuring DC Quantities:


DC quantities have a constant magnitude and direction, but there can still be errors in the measurement of moving iron instruments. The errors in measuring DC quantities are mainly due to the self-inductance of the coil and the capacitance between the coil and the iron piece.

5. Condenser:


A condenser, also known as a capacitor, is connected in parallel with the coil of the moving iron instrument. It is used to reduce the errors caused by the self-inductance of the coil and the capacitance between the coil and the iron piece. The condenser helps in improving the accuracy of the measurements by compensating for these errors.

Conclusion:


In summary, swamp resistance and condenser are additional components used in moving iron instruments to reduce errors while measuring AC quantities. The swamp resistance helps in linearizing the relationship between current and deflection, while the condenser compensates for errors caused by self-inductance and capacitance. These components improve the accuracy of the measurements and make the moving iron instruments more reliable for AC quantity measurements.