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Which of the following material will be preferred as a shunt for extending the range of measurement of a voltmeter
Copper
Steel
Aluminum
Manganin
Manganin
Manganin is the preferred material for shunts used in extending the range of measuring instruments (such as ammeters, and conceptually shunts or multipliers in instruments) because of its extremely low temperature coefficient of resistance and high resistance stability over time. It ensures that the shunt resistance remains virtually constant even as temperature varies during operation, thereby minimizing temperature-induced measurement errors.
Manganin is the preferred material for shunts used in extending the range of measuring instruments (such as ammeters, and conceptually shunts or multipliers in instruments) because of its extremely low temperature coefficient of resistance and high resistance stability over time. It ensures that the shunt resistance remains virtually constant even as temperature varies during operation, thereby minimizing temperature-induced measurement errors.
RsтАЛ=mтИТ1RmтАЛтАЛ тАФ Shunt resistance required to extend ammeter/instrument range
m=ImтАЛIтАЛ тАФ Multiplying power of the shunt
╬ФR=R0тАЛтЛЕ╬▒тЛЕ╬ФT тАФ Resistance variation with temperature
When current passes through a shunt resistor, heat is generated (I2R), causing the temperature of the resistor to rise. For accurate extension of an instrument's range, the resistance ratio between the meter and the shunt must remain constant. Manganin (an alloy of 84% Copper, 12% Manganese, and 4% Nickel) has an nearly zero temperature coefficient of resistance (approx10┬░тИТ5/┬░C) and low thermal EMF against copper, keeping measurement errors minimal.
Manganin alloy composition: 84% Cu, 12% Mn, and 4% Ni.
Extremely low temperature coefficient of resistance (alphaтЙИ0.00001/┬░C).
Low thermoelectric EMF with copper terminals, preventing stray voltage generation.
Negligible variation in resistance with temperature changes.
High long-term stability and immunity to atmospheric corrosion.
Minimizes thermal parasitic EMF when connected to copper leads.
Higher cost compared to standard copper or steel wire.
Lower electrical conductivity compared to pure copper.
Precision DC ammeter shunts
Standard resistance boxes and bridge circuits
Laboratory-grade measuring instruments
Note: While the question mentions 'shunt for extending the range of measurement of a voltmeter' (normally shunts extend ammeters and series multipliers extend voltmeters), Manganin is universally used for both shunts and multipliers due to its zero temperature coefficient properties.
Option A (Copper) has a high temperature coefficient of resistance (╬▒тЙИ0.00393/┬░C), making it unsuitable for precision resistors.
Option B (Steel) and Option C (Aluminum) suffer from higher temperature coefficients and magnetic effects or oxidation issues.
D is correct тАФ Manganin is preferred due to its extremely low temperature coefficient of resistance and low thermal EMF against copper.
Always remember that Manganin is used for DC instrument shunts and resistance boxes due to zero temperature coefficient and low thermal EMF, whereas Constantan (Eureka) is often used for AC applications.