Airflow sensor and control circuit
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United States of America Patent
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-
Nov 28, 1989
Grant Date -
N/A
app pub date -
Feb 27, 1987
filing date -
Feb 27, 1987
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The airflow sensor uses a flow sensing bridge having a thermal element which senses airflow as a function of electrical energy applied to the bridge. Energy is applied to the bridge to maintain the thermal element at a constant temperature and constant resistance. A differential amplifier monitors the balanced and unbalanced state of the bridge and controls the application of energy to the bridge to maintain a balanced state. A microcomputer with analog to digital converter senses the level of energy applied to the bridge and converts this energy level to a digital signal indicative of airflow. The raw digital signal is corrected using calibration lookup tables and thermal compensation correction tables in the microcomputer memory circuits. The microcomputer outputs a variable frequency signal indicative of the measured mass airflow. In the alternative to the differential amplifier, the bridge may be balanced using the microcomputer in a sample and hold voltage to current converter configuration.
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