An Ultra-Stable AC Power Supply for an Absolute Volt Determination

A 159.2 Hz power supply with 85 VA power output and very stable amplitude was designed and constructed for use in an absolute volt experiment. The rms value of the ac voltage is regulated at the level of a dc reference voltage (based on unsaturated standard cells), using a feedback control circuit. The measured amplitude drift is less than 0.5 ppm/h and is typically less than 1 ppm in 4 h. The measured amplitude temperature coefficient is 0.6 ppm/°C and the distortion is less than 0.02%.