An Integrating Analog-to-Digital Converter for Differential Transducers

An improved dual-slope analog-to-digital converter for measurements made with a pair of resistive or capacitive differential transducers is described. The converter can be contrasted with the conventional method in which the transducers are placed in a bridge, the bridge output is amplified, and the conversion is made. In the new converter the transducers are part of the integrator. As a result, conversion of the signal to a time interval takes place at an earlier stage, eliminating the bridge and the amplifier. The method has the same advantages as the dual-slope method and several additional ones. The fractional change in the transducers is obtained as the ratio of the difference and sum of two time periods. As a result, the converter does not need an accurate voltage reference. In addition, errors due to offset in the integrating amplifier are eliminated.