FIGURE 5.20 Sampling technique (Courtesy of Fluke Corp Reproduced with permission.) AND converter for display This method responds to the power dissipated in the resis- tors: therefore, it responds to the true rms value of the input signal including all of its harmonics. In the log/antilog analog method, Fig 5.19, the output of the range amplifier is a representation of the input voltage, ACV, This voltage is applied to the input of the absolute value amplifier. Positive and negative input cycles are converted to a pulsat ing dc at point 1. (Diamonds in the figure represent test points proportion al to the square of the input current is supplied to point 2 by the squaring amplifier. A current proportional to the voltage is supplied to point 3. The output voltage of the integrator, Vo has a value proportional to the average level of the pulsating dc current supplied to point by Q3. Since the input current at point 1 is a direct function of the voltage being measured, and the output voltage is a direct function of the aver age square of the current at point the digitized output vo resents the true rms 1, value of the input voltage. 5.20 samples the input waveform during short in fast Digital sampling, shown in Fig. tervals of time relative to the period of the input waveform. A/D the result quickly digitizes each sample. Its value is squared by the microprocessor, and micro- in memory. When a sufficient number of samples have been taken, the the processor takes the square root of the average value of the squares. Mathematically rms value of the samples in the sampling technique is expressed as where N total number of samples v ith voltage sample i sample number such as that 1 i s N