Method and apparatus for detecting and controlling mass flow

A method of determining an unknown mass flow rate of a process fluid flowing through a process mass flow instrument, the process mass flow instrument providing a raw output signal corresponding to mass flow of the process fluid through the process mass flow instrument, the method comprising the acts of:

• a) providing a calibration mass flow instrument that provides a raw output signal corresponding to fluid flow through the calibration mass flow instrument;
• b) providing a calibration fluid which is not the same as the process fluid;
• c) flowing the calibration fluid at a plurality of known mass flow rates through the calibration mass flow measuring instrument;
• d) determining the calibration mass flow instrument raw output signal for the calibration fluid flowing at each of the plurality of mass flow rates;
• e) calculating a desired calibration mass flow instrument output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid;
• f) deriving a first conversion function by correlating the calibration mass flow instrument raw output signals determined in act d with the calibration mass flow instrument desired signals calculated in act e;
• g) flowing the process fluid at a plurality of known mass flow rates through the calibration mass flow measuring instrument;
• h) determining the calibration mass flow instrument raw output signal for each of the plurality of known mass flow rates of the process fluid;
• i) converting each of the calibration mass flow instrument raw output signals determined in act h to a corresponding calibration mass flow instrument adjusted signal by applying each of the calibration mass flow instrument raw output signals to the first conversion function derived in act f;
• j) calculating an ideal calibration mass flow instrument output signal that corresponds to each of the plurality of mass flow rates of the process fluid;
• k) deriving a second conversion function by correlating the calibration mass flow instrument adjusted signals converted in act i and the calibration mass flow instrument ideal signals calculated in act j;
• l) flowing the calibration fluid at a plurality of known mass flow rates through the process mass flow measuring instrument;
• m) determining the process mass flow instrument raw output signal for each of the plurality of mass flow rates of the calibration fluid;
• n) calculating a desired process mass flow instrument output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid;
• o) deriving a third conversion function by correlating the process mass flow instrument raw output signals determined in act m and the process mass flow instrument desired signals calculated in act n;
• p) flowing the process fluid at an unknown mass flow rate through the process mass flow measuring instrument;
• q) determining the process mass flow instrument raw output signal for the unknown mass flow rate of the process fluid;
• r) converting the process mass flow instrument raw output signal for the unknown mass flow rate determined in act q to a corresponding process mass flow instrument adjusted signal by applying the process mass flow instrument raw output signal to the third conversion function derived in act o;
• and
• s) converting the process mass flow instrument adjusted signal for the unknown mass flow rate converted in act r to a final output signal indicating the actual mass flow rate of the unknown flow of the process fluid by applying the process mass flow instrument adjusted signal to the second conversion function derived in act k.