Wide range semiconductor flow sensors

Micromachined flow sensors based on thin film germanium thermistors offer high flow sensitivities and short response times. Using the controlled overtemperature scheme, the measurable air flow velocity ranges from +/-0.01 to +/- 200 m/s and the response time to large step changes of the air velocity is less than 20 ms. In the constant power mode, a signal rise time of 1.6 ms has been demonstrated by the application of shock waves. An air flow measuring range from 0.6 ml/h to at least 150 l/h has been achieved, e.g. with a rectangular flow channel of 0.54 mm(2) cross-sectional area. Using a lookup table transformation, a linearized output signal can be obtained within 25 mu s. (C) 2000 Elsevier Science S.A. All rights reserved.