Combination of two MC1594 multipiiers and two opamps gives RMS detector for squaring instantaneous input values, averaging over time interval, then taking square root to give RMS value of input wave-form. First multiplier, used to square input waveform, delivers output current to first opamp for conversion to voltage and for aver-aging by means of capacitor in feedback path. Second opamp is used with second multiplier as feedback element for taking square root. Technique eliminates thermal response time drawback of most other RMS measuring circuits. Input voltage range for circuit is 2 to 10 V P-P; for other ranges, input scaling can be used. Since direct coupling is used, output voltage in. dudes DC components of input. Maximum input frequency is about 600 kHz, and accuracy is about 1%,-K. Huehne and D. Aldridge, True RMS Measurements Using IC Multipliers, EDN Magazine, March 20, 1973, p 85-86.
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