An automatic bridge for inductive voltage dividers

We describe an automatic ac voltage ratio standard based on an injection-type bridge and two test inductive voltage dividers (IVD) for applications at low audio frequencies. The ratio standard is generated by self-calibrating two test IVD's by an automated "boot-strap" procedure. The bridge is the heart of our reference standard for ac voltage ratios as well as a calibration system for IVD's. The ratio accuracy of our bridge calibration is better than 0.05 ppm at 500 Hz. In addition, we describe two IVD designs used in this work. >