Digital Instrumentation for the Time Integral of the Square of a Slowly Fluctuating Voltage

A portable digital instrument is described that provides a decimal readout of 1) the time integral of the square of a fluctuating voltage and of the measuring time on two decimal displays, and 2) the amplitude distribution of the voltage. The instrument has no low-frequency limitations. For periodic inputs, measurement may take place over one cycle. For either periodic or random inputs, measurement may be made to commence on a start signal and run for a programmed time. Readout is available immediately at the end of the measuring time, so that the instrument can be used in on-line real-time process control. The voltage under measurement is sampled systematically, and the sampled data are processed using a unique special-purpose digital computer. The paper describes the principles on which measurements are based, and the design and error characteristics of an instrument in which, for most waveforms (e. g., sine, ramp, white noise), the maximum error is in the region of 1 percent and the upper frequency limit is about 1 kHz.