Why can a null measurement be more accurate than one using standard voltmeters and ammeters? What factors limit the accuracy of null measurements?
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There are few drawbacks of the measuring devices like voltmeter, ammeter etc. so null measurement can be an alternative way for measuring such quantities.
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In a voltmeter , which is connected in parallel to the circuit’s segment , whose voltage is to be measured , withdraws some extra current from the circuit , as it is impossible to introduce a resistor with infinite resistance in series with the coil resistor.
Whereas, in an ammeter, which is connected in series with the circuit, having a shunt resistor parallel to the coil resistor, reduces the flow of current in the circuit.
Both these standard measurement devices i.e. voltmeter and ammeter lacks the accuracy as they both uses current from the circuit.
Whereas in a null measurement, there is no current flowing through the measurement device and hence there is no alteration of the circuit is measured, and that’s why these measurement methods are more accurate.