Patent ID: 8504311

Claim:
A mass flow controller comprising: a bridge circuit including a first, second, third, and fourth nodes, a first resistive component being connected between the first and second nodes, a second resistive component being connected between the second and third nodes, a first sensing element being connected between the first and fourth nodes, a second sensing element being connected between the fourth and third nodes; a first processing portion to provide a first output that is indicative of a differential voltage between the second and fourth nodes; a second processing portion to provide a second output indicative of a top voltage between the first node and the third node; a look-up table that maps flow values of a calibration gas with calibration data, the calibration data being based upon values of the differential voltage and the top voltage that correspond to the flow values of the calibration gas; and a control portion configured to: identify a flow value fcal in the calibration data that has a calibration ratio Rcal that corresponds to an operational ratio R, wherein the operational ratio R is based upon the ratio of the top voltage to the differential voltage and the calibration ratio Rcal is based upon a ratio of a calibration-top-voltage to a calibration-differential-voltage; obtain a saturation factor SF, the saturation factor SF defined by a ratio of amplitudes of a calibration vector Vcal and an operational vector V such that SF=abs(Vcal)/abs(V), the direction of the calibration vector defined by the calibration ratio Rcal and the direction of the operational vector V defined by the operational ratio R; and calculate an unknown flow f=fcal/SF.