Abstract

A gas flow sensor system, using hot wire flow and temperature sensors, compensates and corrects for various factors, such as water vapor content and gas composition in the measured gas, gas temperature, physical differences in the sensors, ambient atmospheric pressure, and nonlinearities in the system. Physical differences in the sensors are corrected by adjusting the magnitude of the constant current flowing to the temperature sensor. Water vapor content and gas temperature corrections are made by modifying a flow temperature signal based on the resistance of the temperature sensor to form a flow reference signal indicative of a desired resistance difference between the resistances of the temperature and flow sensors, which resistance difference varies with the flow temperature signal. The flow reference signal is compared to a flow resistance signal (indicative of the resistance of the flow sensor) and the resulting flow correction signal is used to control the current flow to the flow sensor. A flow output signal based on the current flow to the flow sensor provides an indication of flow rate. This flow output signal can then be corrected for the composition of the gas being measured. This composition corrected output can then be further corrected for nonlinearities in the system by use of a look-up table. This further corrected output signal can then be still further corrected for such factors as ambient pressure and standard temperature.