Question:
A PMMC instrument can be used as ammeter and as voltmeter with the help of
A PMMC instrument can be used as ammeter and as voltmeter with the help of
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PMMC Conversion. Ammeter: Low R shunt in parallel. Voltmeter: High R multiplier in series.
Updated On: May 6, 2025
- A low resistance shunt, a low series resistance
- A low resistance shunt, a high series resistance
- A high series resistance, a low resistance shunt
- A low series resistance, a high shunt resistance
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The Correct Option is B
Solution and Explanation
A Permanent Magnet Moving Coil (PMMC) instrument is fundamentally a sensitive current-measuring device (galvanometer) with a low internal resistance
- To use as an Ammeter: To measure larger currents, most of the current must bypass the PMMC movement
This is achieved by connecting a very low resistance, called a shunt, in parallel with the movement
(Low resistance shunt)
- To use as a Voltmeter: To measure voltage, the instrument must draw minimal current and must withstand the applied voltage
This is achieved by connecting a very high resistance, called a multiplier, in series with the movement to limit the current for a given voltage
(High series resistance)
Therefore, a PMMC instrument needs a low resistance shunt to function as an ammeter and a high series resistance to function as a voltmeter
Option (2) correctly lists these requirements in the order ammeter, voltmeter
Option (3) lists them in reverse order
- To use as an Ammeter: To measure larger currents, most of the current must bypass the PMMC movement
This is achieved by connecting a very low resistance, called a shunt, in parallel with the movement
(Low resistance shunt)
- To use as a Voltmeter: To measure voltage, the instrument must draw minimal current and must withstand the applied voltage
This is achieved by connecting a very high resistance, called a multiplier, in series with the movement to limit the current for a given voltage
(High series resistance)
Therefore, a PMMC instrument needs a low resistance shunt to function as an ammeter and a high series resistance to function as a voltmeter
Option (2) correctly lists these requirements in the order ammeter, voltmeter
Option (3) lists them in reverse order
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