Reynolds number correction function for mass flow rate sensor

A method of measuring a rate of a gas flow, comprising:

• dividing the flow between a bypass tube and a sensor tube, wherein a bypass ratio equals a total flow rate through the sensor divided by a flow rate through just the sensor tube;
• heating an upstream portion and a downstream portion of the sensor tube using heater elements;
• measuring a difference in resistance between the heater elements, wherein the resistance is calibrated based on known flow rates of a reference gas;
• measuring the flow rate through the sensor tube and the bypass tube based upon the calibrated resistance from the heater elements;
• and
• multiply the measured flow rate by a multi-gas correction function and a Reynolds number correction function to compensate for differences between the bypass ratios of the reference gas and the gas being measured.

A method for controlling mass flow, comprising:

• providing a main conduit having an upstream portion and a downstream portion;
• connecting the upstream portion of the main conduit to the downstream portion of the main conduit through a sensor tube and a bypass tube so that flow through the main conduit is divided through the sensor tube and the bypass tube, wherein a bypass ratio equals a total flow rate through the sensor divided by a flow rate through just the sensor tube;
• heating an upstream portion and a downstream portion of the sensor tube using heater elements;
• measuring a difference in resistance between the heater elements, wherein the resistance is calibrated based on known flow rates of a reference gas;
• measuring the flow rate through the main conduit based upon the calibrated resistance from the heater elements;
• multiply the measured flow rate by a multi-gas correction function and a Reynolds number correction function to compensate for differences between the bypass ratios of the reference gas and the gas being measured;
• controlling mass flow through the main conduit;
• receiving a desired flow rate;
• comparing the desired flow rate to the Reynolds number-corrected flow rate through the main conduit;
• and
• changing mass flow through the main conduit until the Reynolds number-corrected flow rate through the main conduit equals the desired flow rate through the main conduit.