1.A moving coil voltmeter draws a large current,hence a large power from the test circuit during measurement.Generally current drawn by the voltmeter does not make much difference in electrical circuits but when measurement is involved in electronic circuits,current drawn by the voltmeter load the test circuit,and therefore,voltmeter shows an error in the reading.
In electronic voltmeter power required for deflection of a permanent magnet moving coil (PMMC) movement is not drawn from the test circuit but supplied from the amplifier whose output is proportional to the test circuit voltage i.e., input is proportional to the test circuit voltage i.e., input to the amplifier,so power drawn from the test circuit becomes almost negligible.So electronic voltmeters draw very small power from the test circuit and it can be said that it has a very high input impedance.This feature of electronic voltmeter is indispensable for voltage measurements in many high impedance circuits such as encountered in communication of the order of microvolts.
2.Voltage of the order of microvolts are measured in electronic circuits which is not possible with the sensitive PMMC voltmeters but these voltage can be measured with electronic voltmeter by using its amplifying properties.
3.Electronic voltmeters measure voltage both at audio-as well as radio-frequency power level,as the action of thermionic valves or transistors can be made independent of frequency up to 10 Hz- 100 M Hz or even higher.Hence such an instrument has an externally wide frequency range,if the circuit is property designed.The high frequency range may also be attributed to low input capacitance of most electronic devices.
4.Transistorized voltmeters can be designed for measuring very high voltages such as hundreds or thousands of volts.
In electronic voltmeter power required for deflection of a permanent magnet moving coil (PMMC) movement is not drawn from the test circuit but supplied from the amplifier whose output is proportional to the test circuit voltage i.e., input is proportional to the test circuit voltage i.e., input to the amplifier,so power drawn from the test circuit becomes almost negligible.So electronic voltmeters draw very small power from the test circuit and it can be said that it has a very high input impedance.This feature of electronic voltmeter is indispensable for voltage measurements in many high impedance circuits such as encountered in communication of the order of microvolts.
2.Voltage of the order of microvolts are measured in electronic circuits which is not possible with the sensitive PMMC voltmeters but these voltage can be measured with electronic voltmeter by using its amplifying properties.
3.Electronic voltmeters measure voltage both at audio-as well as radio-frequency power level,as the action of thermionic valves or transistors can be made independent of frequency up to 10 Hz- 100 M Hz or even higher.Hence such an instrument has an externally wide frequency range,if the circuit is property designed.The high frequency range may also be attributed to low input capacitance of most electronic devices.
4.Transistorized voltmeters can be designed for measuring very high voltages such as hundreds or thousands of volts.
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