Method for calibrating a differential pressure fluid flow measuring system

• US 5,710,370 A
• Filed: 05/17/1996
• Issued: 01/20/1998
• Est. Priority Date: 05/17/1996
• Status: Expired due to Fees

• Current Assignee: Dieterich Standard, Inc. (Emerson Electric Company)
• Original Assignee: Dieterich Technology Holding Corp.
• Inventors: Shanahan, Eugene Miles, Gray, Robert James, Garnett, John Everett, Dragnea, Gabriel
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US08/650,140
• Time in Patent Office: 613 Days
• Field of Search: 73/3, 73/1.35, 364/571.05
• US Class Current: 73/1.35
• CPC Class Codes: G01F 1/50 Correcting or compensating means

Abstract

In a flow measurement system comprising a primary flow sensor and a secondary electronic conversion apparatus for converting high and low fluid pressure signals from the primary flow sensor to an electronic signal output representative of fluid flow, a process for calibrating the system as an integral unit, comprising the steps of applying a plurality of known reference fluid flow rates to the primary flow sensor over the system'"'"'s operative range of flow conditions, sensing the electrical output of the secondary electronic conversion apparatus for each of the said plurality of reference fluid flow rates, establishing a correction factor for each of said recorded values of electrical output which will tend to linearize the relationship between fluid flow rate and the electrical output of the measuring system, and storing the correction factors in non-volatile memory in a microprocessor which is part of the secondary electronic conversion apparatus.

Claims

1. A system calibration process for a differential pressure flow measuring system for fluid flowing in a confined conduit, where such system comprises a primary flow sensor and a secondary electro-mechanical conversion apparatus, including electronic memory, for converting high and low fluid pressure signals derived from the primary flow sensor to an electric signal output representative of fluid flow, comprising the steps of;

calibrating the secondary apparatus against known pressures over the operating range of the apparatus to obtain initial output characterization data and storing the characterization data in the electronic memory,

sensing the fluid impact pressure and the fluid static low pressure for a plurality of known reference fluid flows to establish a plurality of high and low pressure signals over a range of flows,

with the use of the initial output characterization data, transducing the said high and low pressure signals into measured electrical differential pressure signals representative of the difference between the sensed high and low pressure for each of the plurality of reference flow rates,

determining a correction factor for the output of the secondary apparatus for each of the plurality of reference flow rates as a function of the deviation of each value of measured differential pressure from the nominal differential pressure corresponding to each of the said plurality of reference flow rates,

modifying the data from the initially characterized secondary apparatus by overwriting, in the electronic memory, the initial characterization data with the calculated correction values.

2. The method of claim 1 wherein the step of determining correction factors for the output of the secondary apparatus for each of the plurality of reference flow rates includes the step of determining the nominal differential pressure output of the system by defining the nominal flow coefficient of the primary.

3. The method of claim 2 and further including the step of determining the average actual flow coefficient value for the plurality of reference flows.

4. The method of claim 3 wherein the step of determining correction factors for the output of the secondary apparatus for each of the plurality of reference flow rates includes the step of correcting the measured differential pressure output values for the deviation of the actual flow coefficient from the nominal flow coefficient.

5. The method of claim 4 wherein the step of determining a correction factor for the output of the secondary apparatus for each of the plurality of reference flow rates includes the step of subjecting the values of the measured differential pressure and the determined nominal differential pressure values to a statistical regression analysis to establish the correction factors.

6. For a differential pressure flow measuring system comprising a primary flow sensor and a secondary electro-mechanical conversion apparatus for converting high and low fluid pressure signals from the primary flow sensor to an electronic signal output representative of fluid flow, a system calibration process, comprising the steps of;

applying a plurality of known reference fluid flow rates to the primary flow sensor over the system'"'"'s operative range of flow conditions,

sensing the electrical output of the secondary electronic conversion apparatus for each of the said plurality of reference fluid flow rates;

establishing a correction factor for each of the plurality of reference flow rates which will tend to characterize a desired relationship between the fluid flow rate and the electrical output of the measuring system, and

storing the correction factors in non-volatile memory.

7. The method of claim 6 and further including the step of initially linearizing the secondary electro-mechanical apparatus against known pressures over the operating range of the apparatus to obtain data for linearizing the output of the said electro-mechanical apparatus.

8. A system calibration process for differential pressure flow measurement in a system having fluid flowing in a confined conduit, and having a primary flow sensor and a secondary electro-mechanical conversion apparatus, including electronic memory, for converting high and low fluid pressure signals derived from the primary flow sensor to an electric signal representative of fluid flow, comprising the steps of;

sensing the fluid impact pressure and the fluid static low pressure for a plurality of known reference fluid flows to establish a plurality of high and low pressure signals over a range of fluid flows,

transducing the said high and low pressure signals into measured electrical differential pressure signals representative of the difference between the sensed high and low pressure for each of the plurality of reference flow rates,

establishing a desired relationship between the reference flow rates and the electrical output of the secondary apparatus for each of the plurality of the reference flow rates,

overwriting into the electronic memory the said established desired relationship of the secondary apparatus.

9. The method of claim 8 and further including the step of initially characterizing the secondary electro-mechanical apparatus against known pressures over the operating range of the apparatus to obtain data for characterizing the output of the said electro-mechanical apparatus.

10. The method of claim 8 where the step of establishing a desired relationship includes that of linearization.

11. For a differential pressure flow measuring system comprising a primary flow sensor and a secondary electro-mechanical conversion apparatus for convening high and low fluid pressure signals from the primary flow sensor to an electronic signal output representative of fluid flow, a system calibration process, comprising the steps of;

applying a plurality of known reference fluid flow rates to the primary flow sensor over the system'"'"'s operative range of flow conditions,

sensing the electrical output of the secondary electronic conversion apparatus for each of the said plurality of reference fluid flow rates;

establishing a correction factor for each of the plurality of reference flow rates which will tend to linearize the relationship between fluid flow rate and the electrical output of the measuring system as a function of the deviation of each value of measured differential pressure from the nominal differential pressure corresponding to each of the plurality of reference flow rates,

storing the correction factors in non-volatile memory, and

initially linearizing the secondary electro-mechanical apparatus against known pressure over the operating range of the apparatus to obtain data for linearizing the output of the said electro-mechanical apparatus.

12. For a differential pressure flow measuring system comprising a primary flow sensor and a secondary electro-mechanical conversion apparatus for converting high and low fluid pressure signals from the primary flow sensor to an electronic signal output representative of fluid flow, a system calibration process, comprising the steps of;

applying a plurality of known reference fluid flow rates to the primary flow sensor over the system'"'"'s operative range of flow conditions,

sensing the electrical output of the secondary electronic conversion apparatus for each of the said plurality of reference fluid flow rates;

establishing a correction factor for each of the plurality of reference flow rates which will tend to linearize the relationship between fluid flow rate and the electrical output of the measuring system as a function of the deviation of each value of measured differential pressure from the nominal differential pressure corresponding to each of the plurality of reference flow rates,

storing the correction factors in non-volatile memory,

initially linearizing the secondary electro-mechanical apparatus against known pressure over the operating range of the apparatus to obtain data for linearizing the output of the said electro-mechanical apparatus, and

modifying the initial linearization data for the secondary electro-mechanical apparatus with the determined correction factors.

13. A system calibration process for differential pressure flow measurement in a system having fluid flowing in a confined conduit, and having a primary flow sensor and a secondary electro-mechanical conversion apparatus, including electronic memory, for converting high and low fluid pressure signals derived from the primary flow sensor to an electric signal representative of fluid flow, comprising the steps of;

sensing the fluid impact pressure and the fluid static low pressure for a plurality of known reference fluid flows to establish a plurality of high and low pressure signals over a range of fluid flows,

transducing the said high and low pressure signals into measured electrical differential pressure signals representative of the difference between the sensed high and low pressure for each of the plurality of reference flow rates,

establishing a desired relationship between the reference flow rates and the electrical output of the secondary apparatus for each of the plurality of the reference flow rates at a function of the deviation of each value of measured differential pressure from the nominal differential pressure corresponding to each of the plurality of reference flow rates,

overwriting into the electronic memory the said established desired relationship of the secondary apparatus, and

initially characterizing the secondary electro-mechanical apparatus against known pressures over the operating range of the apparatus to obtain data for characterizing the output of the said electro-mechanical apparatus.

14. The method of claim 13 and further including the step of modifying the data obtained by initially characterizing the secondary electro-mechanical apparatus with the determined correction factors.

15. The method of claim 14 and further including the step of storing the correction factors in non-volatile memory.