PRECISION CALIBRATION PROCEDURE FOR MAGNETIC LOSS TESTERS USING A DIGITAL 2-CHANNEL FUNCTION GENERATOR

For the precision calibration of power meters used for magnetic loss m easurements, a two-channel precision generator developed at the PTB is used. The staircase functions of the generator matched to the wattmet ers by a current and voltage amplifier are smoothed by low-pass Bessel filters. The complex transfer functions of the filters have been meas ured for different ranges of voltage, current and frequency. The wavef orms to be generated are corrected by means of fast Fourier transforma tion (FFT) and by multiplying the Fourier coefficients by the inverse complex transfer function. The accuracy of this calibration procedure was estimated to be 0.1%.