Non-linear temperature compensation for a micromachined bi-directional thermal flow sensor

Thermal flow sensors have been developed for a variety of applications over the years. Their application in automotive environments with high accuracy, has been challenging due to the large (-40 to 125C) temperature range. To achieve an accuracy of 2% over this temperature range, special sensor construction, flow tube geometry and/or elaborate electronic compensation is required. We present here a mixed analog/digital compensation technique with non-linear TCO (Temperature Coefficient of offset) correction capability for a constant temperature Bi-directional airflow sensor. The resulting system achieves sensitivity of 3mv/% mass flow at idle flow rates (2-5 gm/sec) with an accuracy of 2% over a flow range of 2gm/sec - 100 gm/sec and intake temperature range.