True RMS Reading Voltmeter

True RMS Reading Voltmeter

The scale of general voltmeters (average reading voltmeters) is calibrated in terms of the RMS value of sinusoidal waveform only. So to read the RMS value of any waveform we use True RMS Reading Voltmeter.

In this The input signal is amplified by an AC amplifier and then the electrical energy is converted in heat energy and the temperature change is measured by the main thermal couple and hence the heat energy is again converted into electrical energy and it is then measured by the PMMC meter. Here a Balancing thermocouple is used to remove the non-linear behavior of the main thermocouple.

Here the electrical energy is converted into heat energy E and we know heat energy is proportional to the square of RMS current and voltage hence the value of RMS voltage is measured by.

Electrical energy -> Heat Energy -> Electrical Energy

Here The DC amplifier is used to amplify the potential difference created by the thermocouple.

Note: thermocouple is a device used to measure the temperature in this in this there is a potential difference is devoloped in the two rods of thermocouple according to the temperature (the two rods are of different material)

Note: The scale of the PMMC meter can be calibrated in terms of the RMS input voltage of any waveform.

Advantage: RMS voltage of any waveform can be measured.

Disadvantage: Uneconomical, chances of error are more due to many parts are present. and Energy loss.