Fluid flow sensor with thermistor detector

摘要

An airflow sensor formed on a silicon chip comprises a silicon base covered with an insulating polyimide layer, a lineal resistance heater on the chip energized with current pulses to propagate thermal waves, and a thermistor on the chip downstream of the heater to detect the arrival of each thermal wave. Circuitry determines flow rate as a function of the measured propagation time of the thermal wave. The thermistor may be replaced by a bridge of four resistive elements of which only one or two are sensitive to the thermal wave. The thermistor material is platinum, polycrystalline silicon or amorphous silicon which exhibit high temperature coefficients of resistance.