Constant power operation of a two-dimensional flow sensor using thermal sigma-delta modulation techniques

To compensate for ambient-temperature drift two-dimensional thermal flow sensors are typically heated to a constant temperature above ambient temperature. This operating mode requires all extra sensor to measure ambient temperature. It shown that similar compensation may be obtained by maintaining the sensor's heating power constant; thus eliminating the need for the ambient-temperature sensor. Constant power operation may be achieved by a simple electronic interface consisting of true thermal sigma-delta modulators. These control the distribution of heat in the sensor such that flow-induced temperature gradients are cancelled. The bit-stream output of the modulators then represents the (flow-dependent) heat distribution in the sensor. Flow speed and direction may then be determined from the decimated bit-streams.