Working Principle The rms (root mean square) value is the only amplitude characteristic of a waveform which does not depend on shape of the waveform. Therefore, 'the rms value is the most useful means to quantify signal amplitude in a.c. measurements. The rms value measures the ability of an a.c. signal to deliver power •to a resistive load, thus measuring the equivalent heating value of the signal. This means rms value of all a.c. waveform is equal to the d.c. value which produces the same amount of heat as the a.c. waveform' when connected to the same resistive load.
For a d.c. voltage V, this heat is directly proportional to the amount of power dissipated in the resistance R and therefore, power
The rms value of a waveform can be measured by measuring the heat gen¬erated by the waveform in a resistive load and comparing it with the heat generated by a known d.c. voltage in an equivalent load .. Heat measurement is . done by thermal rms detectors 'which are made using small resistors with a thermocouple or thermistor attached to it. Thermal rms detectors are capable' of measuring rms values for signal frequencies in excess of a few hundred, megahertz (MHz).
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