Constant power operation of a two-dimensional flow sensor

To compensate for changes in ambient temperature, thermal flow sensors are usually heated to a constant temperature above ambient temperature. This operating mode, however, requires an extra ambient-temperature sensor. Using a simple model, it is shown that for a two-dimensional thermal flow sensor, similar compensation may be obtained by using a constant beating power, thus eliminating the need for an ambient-temperature sensor. The flow sensor's interface circuitry consists of two thermal sigma-delta modulators that heat the sensor with constant power and dynamically cancel the flow-induced temperature gradient. The modulator's bit-stream outputs are then a digital representation of the heat distribution in the sensor. Wind tunnel tests confirm the validity of the sensor model used and show that both flow speed and direction may be accurately determined from the bit-streams, with errors less than /spl plusmn/5% and /spl plusmn/3/spl deg/, respectively, for flow speeds between 1 and 25 m/s.

[1]  Kofi A. A. Makinwa,et al.  A wind-sensor with integrated interface electronics , 2001, ISCAS 2001. The 2001 IEEE International Symposium on Circuits and Systems (Cat. No.01CH37196).

[2]  Bastiaan Willem Vanoudheusden.  Integrated silicon flow sensors , 1989 .

[3]  Johan H. Huijsing,et al.  Design of thermal sigma-delta modulators for smart thermal sensors , 1995, Proceedings of ISCAS'95 - International Symposium on Circuits and Systems.

[4]  Johan H. Huijsing,et al.  An electronic wind meter based on a silicon flow sensor , 1990 .

[5]  Kofi A. A. Makinwa,et al.  Industrial design of a solid-state wind sensor , 2001, SIcon/01. Sensors for Industry Conference. Proceedings of the First ISA/IEEE. Sensors for Industry Conference (Cat. No.01EX459).

[6]  Henry Baltes,et al.  Two-dimensional integrated gas flow sensors by CMOS IC technology , 1995 .

[7]  B. W. van Oudheusden.  Integrated silicon flow sensors , 1989 .

[8]  K. Toda,et al.  Simple temperature compensation of thermal air-flow sensor , 1996 .

[9]  Louis Vessot King,et al.  On the Convection of Heat from Small Cylinders in a Stream of Fluid: Determination of the Convection Constants of Small Platinum Wires with Applications to Hot-Wire Anemometry , 1914 .

[10]  M. Elwenspoek,et al.  A new class of thermal flow sensors using /spl Delta/T=0 as a control signal , 2000, Proceedings IEEE Thirteenth Annual International Conference on Micro Electro Mechanical Systems (Cat. No.00CH36308).

[11]  Kofi A. A. Makinwa,et al.  A smart wind sensor using thermal sigma-delta modulation techniques , 2002 .

[12]  Eugeniusz Prociow,et al.  Analysis of an ambient temperature influence on the thermal thin-film microsensor , 1994 .