Gja. Vandijk et Jh. Huijsing, BRIDGE-OUTPUT-TO-FREQUENCY CONVERTER FOR SMART THERMAL AIR-FLOW SENSORS, IEEE transactions on instrumentation and measurement, 44(4), 1995, pp. 881-886
A fully integrated bridge-output-to-frequency converter has been reali
zed as signal-conditioning circuitry for a one-chip smart thermal mass
-flow sensor. The frequency converter reads out four separate resistor
bridges of the air-flow sensor in order to realize high sensitivity a
nd directional flow measurement over the full angle range of 360 degre
es. The converter selects the sensor bridges individually by means of
a microprocessor-controlled analog multiplexer. The flow velocity and
direction are also calculated by the microprocessor. The relative meas
urement cancels all first-order errors. The center frequency is 10 kHz
and the sensitivity 1 Hz/(mu V/V). A bridge-offset of 10 mV/V is allo
wed, and the linearity error is 0.1%.