Method and apparatus for detecting and controlling mass flow

• US 5,944,048 A
• Filed: 07/08/1997
• Issued: 08/31/1999
• Est. Priority Date: 10/04/1996
• Status: Expired due to Term

• Current Assignee: Brooks Instrument LLC (Illinois Tool Works Inc.)
• Original Assignee: Emerson Electric Company
• Inventors: Campbell, Gary P., White, William W., Dille, Joseph C., Bump, Scott S.
• Primary Examiner(s): Ferensic, Denise L.
• Assistant Examiner(s): Kim, Joanne Y.
• Application Number:
  US08/889,641
• Time in Patent Office: 784 Days
• Field of Search: 137/487.5, 137/486, 73/861, 73/204.15, 73/204.16, 73/3
• US Class Current: 137/487.5
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6847 where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
• CPC Class Codes: G01F 1/6965 comprising means to store calibration data for flow signal calculation or correction
• CPC Class Codes: G01F 1/86 Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
• CPC Class Codes: G01F 15/024 involving digital counting
• CPC Class Codes: G01F 25/13 using a reference counter
• CPC Class Codes: G01F 25/15 specially adapted for gas meters G01F25/11 - G01F25/14, G01F25/17 take precedence
• CPC Class Codes: G01F 25/17 using calibrated reservoirs
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

A process mass flow instrument for measuring the mass flow rate of a process fluid including a fluid inlet, a fluid outlet, a flow passage connecting the fluid inlet and the fluid outlet, a fluid flow sensor which provides a raw output signal corresponding to an unknown mass flow rate and a processor which contains an empirically derived conversion routine for converting the raw output signal to an adjusted signal indicating the mass flow rate of the process fluid. A method for determining an unknown mass flow using an empirically derived conversion function, the function being derived by correlating the output signals of a mass flow instrument sensing the flow of a calibration fluid with the output signals of the mass flow instrument sensing the flow of the process fluid.

Claims

1. 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.

2. The method of claim 1 wherein acts a through k are performed for a plurality of calibration mass flow instruments, and the deriving a second conversion function act k comprises the acts of

averaging the ideal calibration mass flow instrument output signals calculated in act j for the plurality of calibration mass flow instruments;

and

correlating the calibration mass flow instrument adjusted signals converted in act i and the average ideal calibration mass flow instrument output signals.

3. The method of claim 2 wherein the averaging the ideal calibration mass flow instrument output signals act is repeated for three different calibration mass flow instruments.

4. The method of claim 1 wherein the known mass flow rates of act g is determined by performing the acts of

(i) providing a rigid evacuated chamber having a known volume;

(ii) coupling the calibration mass flow instrument to the chamber;

(iii) flowing the process gas through the calibration mass flow instrument into the chamber; and

(iv) measuring the rate of pressure and temperature rise in the chamber.

5. The method of claim 1 wherein calculating the desired calibration mass flow instrument output signal act e comprises the acts of

(i) determining a 100% flow rate for the calibration fluid flowing through the calibration mass flow instrument;

(ii) determining a raw output signal value that represents the 100% flow rate for the calibration mass flow instrument; and

(iii) dividing the known mass flow rate of the calibration fluid by the 100% flow rate for the calibration fluid and multiplying the result by the output signal value that represents the 100% flow rate.

6. The method of claim 1 wherein calculating the ideal calibration mass flow instrument output signal act j comprises the acts of

(i) determining a 100% flow rate for the process fluid flowing through the calibration mass flow instrument;

(ii) determining an adjusted output signal value that represents the 100% flow rate for the calibration mass flow instrument; and

(iii) dividing the known mass flow rate of the process fluid by the 100% flow rate of the process fluid and multiplying the result by the adjusted signal value that represents the 100% flow rate.

7. The method of claim 1 wherein calculating the desired process mass flow instrument output signal act n comprises the acts of

(i) determining a 100% flow rate for the calibration fluid flowing through the process mass flow instrument;

(ii) determining a raw output signal value that represents the 100% flow rate for the process mass flow instrument; and

(iii) dividing the known mass flow rate of the calibration fluid by the 100% flow rate of the calibration fluid and multiplying the result by the output signal value that represents the 100% flow rate.

8. The method of claim 1 wherein the deriving a first conversion function act f comprises the act of performing a polynomial regression, in which the calibration mass flow instrument raw output signals are the x inputs and the calibration mass flow instrument desired signals are the y inputs.

9. The method of claim 8 wherein the act of performing a polynomial regression comprises applying the LU Decomposition regression algorithm.

10. The method of claim 1 wherein the deriving a second conversion function act k comprises the act of performing a polynomial regression, in which the calibration mass flow instrument adjusted signals are the x inputs and the calibration mass flow instrument ideal signals are the y inputs.

11. The method of claim 10 wherein the act of performing a polynomial regression comprises applying the LU Decomposition regression algorithm.

12. The method of claim 1 wherein the deriving a third conversion function act o comprises the act of performing a polynomial regression, in which the process mass flow instrument raw output signals are the x inputs and the process mass flow instrument desired signals are the y inputs.

13. The method of claim 12 wherein the act of performing a polynomial regression comprises applying the LU Decomposition regression algorithm.

14. The method of claim 1 wherein the calibration mass flow instrument and the process mass flow instrument each include a processor having a memory, further comprising:

(i) loading a dummy calibration table into the calibration mass flow instrument'"'"'s memory prior to the flowing the calibration fluid act c;

(ii) creating a calibration fluid calibration table for the calibration mass flow instrument containing a plurality of adjusted signals indicating mass flow of the calibration fluid by applying a plurality of raw output signal values to the first conversion function derived in act f;

(iii) replacing the dummy calibration table with the calibration fluid calibration table prior to the flowing the process fluid act g;

(iv) the converting each of the calibration mass flow instrument raw output signals act i comprises indexing the calibration fluid calibration table using the calibration mass flow instrument raw output signal to determine the corresponding adjusted signal;

(v) creating a calibration fluid calibration table for the process mass flow instrument containing a plurality of adjusted signal values indicating mass flow of the calibration fluid by applying a plurality of raw output signal values to the third conversion function derived in act o;

(vi) creating a process fluid calibration table for the process mass flow instrument containing a plurality of ideal signals indicating mass flow of the process fluid by applying the adjusted signal values from the calibration fluid calibration table for the process mass flow instrument to the second conversion function derived in act k;

(vii) loading the process fluid calibration table into the process mass flow instrument'"'"'s memory; and

(viii) the converting each of the process mass flow instrument raw output signals act r and the converting each of the process mass flow instrument adjusted signals act s comprise indexing the process fluid calibration table using the process mass flow instrument raw output signal to determine the corresponding ideal signal.

15. A method of deriving a calibration conversion function for converting an output signal of a mass flow measuring instrument indicating the flow of a calibration gas to a signal indicating the flow of a process gas comprising the acts of:

a) providing a process fluid;

b) providing a calibration fluid which is not the same as the process fluid;

c) providing a mass flow instrument that provides a raw output signal corresponding to fluid flow through the mass flow instrument;

d) flowing the calibration fluid at a plurality of known mass flow rates through the mass flow measuring instrument;

e) determining the raw output signal for the calibration fluid flowing at each of the plurality of mass flow rates;

f) calculating a desired output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid;

g) deriving a first conversion function by correlating the raw output signals determined in act e with the calibration mass flow instrument desired signals calculated in act f;

h) flowing the process fluid at a plurality of known mass flow rates through the mass flow measuring instrument;

i) determining the raw output signal for each of the plurality of known mass flow rates of the process fluid;

j) converting each of the raw output signals determined in act i to a corresponding adjusted signal by applying each of the raw output signals to the first conversion function derived in act f;

k) calculating an ideal output signal that corresponds to each of the plurality of mass flow rates of the process fluid;

l) deriving a second conversion function by correlating the adjusted signals converted in act j and the calibration mass flow instrument desired signals calculated in act k.

16. The method of claim 15 wherein acts a through k are performed for a plurality of mass flow instruments, and the deriving a second conversion function act l comprises the acts of

averaging the ideal signals calculated in act k for the plurality of calibration mass flow instruments;

and

correlating the adjusted signals converted in act j and the average ideal signals.

17. The method of claim 16 wherein the averaging the ideal signals act is repeated for three different calibration mass flow instruments.

18. The method of claim 15 wherein the known mass flow rates of act h is determined by performing the acts of

(i) providing a rigid evacuated chamber having a known volume;

(ii) coupling the mass flow instrument to the chamber;

(iii) flowing the process gas through the mass flow instrument into the chamber; and

(iv) measuring the rate of pressure and temperature rise in the chamber.

19. The method of claim 15 wherein calculating the desired output signal act f comprises the acts of

(i) determining a 100% flow rate for the calibration fluid flowing through the mass flow instrument;

(ii) determining a raw output signal value that represents the 100% flow rate for the mass flow instrument; and

(iii) dividing the known mass flow rate of the calibration fluid by the 100% flow rate for the calibration fluid and multiplying the result by the output signal value that represents the 100% flow rate.

20. The method of claim 15 wherein calculating the ideal output signal act k comprises the acts of

(i) determining a 100% flow rate for the process fluid flowing through the mass flow instrument;

(ii) determining an adjusted output signal value that represents the 100% flow rate for the mass flow instrument; and

(ii) dividing the known mass flow rate of the process fluid by the 100% flow rate of the process fluid and multiplying the result by the output signal value that represents the 100% flow rate.

21. The method of claim 15 wherein the deriving a first conversion function act g comprises the act of performing a polynomial regression, in which the raw output signals are the x inputs and the desired signals are the y inputs.

22. The method of claim 21 wherein the act of performing a polynomial regression comprises applying the LU Decomposition regression algorithm.

23. The method of claim 15 wherein the deriving a second conversion function act l comprises the act of performing a polynomial regression, in which the adjusted signals are the x inputs and the ideal signals are the y inputs.

24. The method of claim 23 wherein the act of performing a polynomial regression comprises applying the LU Decomposition regression algorithm.

25. The method of claim 15 wherein the mass flow instrument includes a processor having a memory, further comprising:

(i) loading a dummy calibration table into the mass flow instrument'"'"'s memory prior to the flowing the calibration fluid act d;

(ii) creating a calibration fluid calibration table for the calibration mass flow instrument containing a plurality of adjusted signals indicating mass flow of the calibration fluid by applying a plurality of raw output signal values to the first conversion function derived in act g;

(iii) replacing the dummy calibration table with the calibration fluid calibration table prior to the flowing the process fluid act h; and

(iv) the converting each of the raw output signals act j comprises indexing the calibration fluid calibration table using the raw output signal to determine the corresponding adjusted signal.

26. A method of deriving a calibration conversion function for a process mass flow instrument comprising the acts of:

providing a process fluid;

providing a calibration fluid which is not the same as the process fluid;

calibrating the mass flow instrument with the calibration fluid;

re-calibrating the mass flow instrument with the process fluid; and

correlating the results of the calibrating act with the results of the re-calibrating act.

27. The method of claim 26 wherein the calibration mass flow instrument provides a raw output signal corresponding to fluid flow through the mass flow instrument, and the calibrating the mass flow instrument with the calibration fluid act comprises:

flowing the calibration fluid at a plurality of known mass flow rates through the mass flow measuring instrument;

determining the raw output signal for the calibration fluid flowing at each of the plurality of mass flow rates;

calculating a desired output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid; and

deriving a first conversion function by correlating the raw output signals with the desired signals.

28. The method of claim 27 wherein the re-calibrating the mass flow instrument with the process fluid act comprises:

flowing the process fluid at a plurality of known mass flow rates through the mass flow instrument; and

converting the raw output signals for each of the plurality of known mass flow rates of the process fluid to adjusted signals by applying the raw output signals to the first conversion function; and

calculating an ideal signal that corresponds to each of the plurality of mass flow rates of the calibration fluid.

29. The method of claim 28 wherein the correlating the results of the calibrating act with the results of the re-calibrating act comprises correlating the adjusted signals and the ideal signals.

30. 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, the method comprising the acts of:

providing a calibration fluid which is not the same as the process fluid;

providing a calibration mass flow instrument that provides a raw output signal corresponding to fluid flow through the calibration mass flow instrument;

calibrating the calibration mass flow instrument with the calibration fluid;

re-calibrating the calibration mass flow instrument with the process fluid;

deriving a process fluid conversion function by correlating the results of the calibrating act with the results of the re-calibrating act;

calibrating the process mass flow instrument with the calibration fluid;

flowing the process fluid through the process mass flow instrument at an unknown rate;

determining the output signal provided by the process mass flow instrument; and

applying the output signal to the process fluid conversion function.

31. The method of claim 30 wherein the calibrating the calibration mass flow instrument with the calibration fluid act comprises:

flowing the calibration fluid at a plurality of known mass flow rates through the calibration mass flow instrument;

determining the raw output signal for the calibration fluid flowing at each of the plurality of mass flow rates;

calculating a desired output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid; and

deriving a first conversion function by correlating the raw output signals with the desired signals.

32. The method of claim 31 wherein the re-calibrating the calibration mass flow instrument with the process fluid act comprises:

flowing the process fluid at a plurality of known mass flow rates through the calibration mass flow instrument;

converting the raw output signals for each of the plurality of known mass flow rates of the process fluid to adjusted signals by applying the raw output signals to the first conversion function; and

calculating an ideal output signal that corresponds to each of the plurality of mass flow rates of the process fluid.

33. The method of claim 32 wherein the deriving a process fluid conversion function act comprises correlating the adjusted signals and the ideal signals.

34. The method of claim 33 wherein the calibrating the process mass flow instrument with the calibration fluid act comprises:

flowing the calibration fluid at a plurality of known mass flow rates through the process mass flow instrument;

determining the raw output signal for the calibration fluid flowing at each of the plurality of mass flow rates;

calculating a desired output signal that corresponds to each of the plurality of mass flow rates of the calibration fluid; and

deriving a second conversion function by correlating the raw output signals with the desired signals.

35. The method of claim 34 wherein the applying the output signal act comprises:

converting the raw output signal for the unknown mass flow rate to a corresponding process mass flow instrument adjusted signal by applying the process mass flow instrument raw output signal to the second conversion function; and

converting the process mass flow instrument adjusted signal for the unknown mass flow rate 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.