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