Measuring and testing – Volume or rate of flow – Thermal type
Patent
1991-12-30
1993-08-24
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
Thermal type
G01F 168
Patent
active
052378683
ABSTRACT:
A thermal flow sensor comprising a bridge circuit positioned in a fluid and including a platinum wire as a thermal resistor, an air temperature sensor and a pair of resistors, and a temperature control circuit for controlling a current flowing through the platinum wire to keep the bridge circuit in a thermally balanced condition. A voltage V.sub.h depending on a flow rate and output from the bridge circuit is input to a non-inverting input terminal of an operational amplifier. A sum of the currents output from the first and second constant current circuits connected to the non-inverting and inverting input terminals of the operational amplifier is set to zero by a constant current control circuit when the output voltage V.sub.h is equal to or less than a predetermined value and gradually increases from zero with an increase in the output voltage V.sub.h when V.sub.h is higher than the predetermined value.
REFERENCES:
patent: 4400974 (1983-08-01), Nishimura et al.
patent: 4907446 (1990-03-01), Inada et al.
Goldstein Herbert
Mitsubishi Denki & Kabushiki Kaisha
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