High performance digital multimeter with 'internal calibration'

An approach that allows a digital multimeter to be calibrated using a minimum number of external reference standards is described. The approach centers around an extremely linear and flexible A/D converter. The linearity of the converter gives the instrument the ability to accurately measure the ratio of two DC voltages, while the speed of the converter allows for an accurate internal DC to AC transfer. In addition to reduced calibration cost and complexity, the approach allows for correction of time and temperature changes of all but a few very stable reference components. The end result is a digital multimeter able to perform DC and low-frequency AC measurements with high accuracy, precision, and speed and without the usual high cost of maintaining such an instrument.>