MEASUREMENT OF AC VOLTAGES WITH DIGITAL VOLTMETERS

摘要

A principle of using high-resolution digital voltmeters (DVs) Hewlett-Packard 3458A1) for the measurement of AC voltages in DCV range is described. The method of approximate synchronous sampling is used, having only one sample per cycle of a working frequency close to 16 Hz, when the mean value of one-third cycle is measured. The beginning of integration is shifted for the same interval for every subsequent period of the measured voltage. From the samples, the RMS value of the "derived" sine is determined using subsequent numeric synchronisation. The phase angle of the first sample of the "derived" sine is calculated as regression line coefficient. To ensure accurate phase difference measurement between two voltages, a synchronised triggering is used. A method for the determination of the difference between the sampling frequency of two DVs and the main frequency is presented. For the voltage ratio and phase difference measurements, the uncertainties of 0,1 ppm and 0,1 μrad respectively were achieved.