INTRODUCTION

　　It is widely acknowledged that RMS （Root of the Mean of the Square） measurement of waveforms furnishes the most accurate amplitude information.1 Rectify-andaverage schemes， usually calibrated to a sine wave， are only accurate for one waveshape. Departures from this waveshape result in pronounced errors. Although accurate， RMS conversion often entails limited bandwidth， restricted range， complexity and diffi cult to characterize dynamic and static errors. Recent developments address these issues while simultaneously improving accuracy. Figure 1 shows the LTC?1966/LTC1967/LTC1968 device family. Low frequency accuracy， including linearity and gain error， is inside 0.5% with 1% error at bandwidths extending to 500kHz. These converters employ a sigma-delta based computational scheme to achieve their performance.

　　Figure 2’s pinout descriptions and basic circuits reveal an easily applied device. An output fi lter capacitor is all that is required to form a functional RMS-to-DC converter. Split and single supply powered variants are shown. Such ease of implementation invites a broad range of application; examples begin with Figure 3.

　　Isolated Power Line Monitor

　　BEFORE PROCEEDING ANY FURTHER， THE READER IS WARNED THAT CAUTION MUST BE USED IN THE CONSTRUCTION， TESTING AND USE OF THIS CIRCUIT. HIGH VOLTAGE， LETHAL POTENTIALS ARE PRESENT IN THIS CIRCUIT. EXTREME CAUTION MUST BE USED IN WORKING WITH， AND MAKING CONNECTIONS TO， THIS CIRCUIT. REPEAT： THIS CIRCUIT CONTAINS DANGEROUS， HIGH VOLTAGE POTENTIALS. USE CAUTION.