Measuring apparatuses and methods of using them

• US 7,532,992 B2
• Filed: 01/20/2006
• Issued: 05/12/2009
• Est. Priority Date: 01/20/2006
• Status: Expired due to Fees

• Current Assignee: Teledyne Isco, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Teledyne Isco, Inc. (Thermo Fisher Scientific Incorporated)
• Inventors: Liescheski, Phillip B.
• Primary Examiner(s): Lau; Tung S
• Assistant Examiner(s): SUN, XIUQIN
• Application Number:
  US11/337,011
• Publication Number:
  US 20070174013A1
• Time in Patent Office: 1,208 Days
• Field of Search: 702/100, 702/99, 703/8
• US Class Current: 702/100
• CPC Class Codes: G01D 18/008 with calibration coefficients stored in memory
• CPC Class Codes: G01D 3/022 having an ideal characteristic, map or correction data stored in a digital memory
• CPC Class Codes: G01D 3/0365 the undesired influence being measured using a separate sensor, which produces an influence related signal
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G01F 1/50 Correcting or compensating means
• CPC Class Codes: G01F 23/18 Indicating, recording or alarm devices actuated electrically

Abstract

A measuring instrument includes a transducer for measuring the depth of liquid and a transducer for measuring a physical parameter that causes interference error. A calibration polynomial is used to correct the output signal. The calibration polynomial includes the signal generated by the transducers as independent variables and the output signal as the dependent variable. The calibration polynomial is formed by a correction polynomial having at least one primary measurement signal and at least a first interference related signal as independent variables and a calibrated signal as a dependent variable. To form the calibration polynomial, a preliminary calibration polynomial including the primary independent variable and at least one interference related independent variable is developed. A plurality of data sets is generated from a test fixture. This data is used to eliminate the least significant terms of the preparatory calibration polynomial and to add the most significant cross terms.

Claims

1. A method of calibrating an instrument, comprising the steps of:

forming a preparatory calibration polynomial including a primary independent variable and at least one interference related independent variable;

obtaining a plurality of data sets of a dependent variable, the primary independent variable and the at least one interference related independent variable;

using the data sets to eliminate least significant terms of the preparatory calibration polynomial;

adding the most significant cross terms;

selecting a number of terms of a polynomial;

adding low degree cross terms

choosing a maximum degree of the highest degree of an independent variable;

preparing a plurality of terms of the preparatory calibration polynomial wherein each term of said plurality of terms includes a different one of said independent variables and a different degree of the independent variable;

adding some trial cross terms.

2. A method of calibrating an instrument, comprising the steps of:

forming a preparatory calibration polynomial including a primary independent variable and at least one interference related independent variable;

obtaining a plurality of data sets of a dependent variable, the primary independent variable and the at least one interference related independent variable;

using the data sets to eliminate least significant terms of the preparatory calibration polynomial;

adding the most significant cross terms wherein the step of using the data sets to eliminate least significant terms of the preparatory calibration polynomial includes the steps of;

eliminating one term at a time of the preparatory calibration polynomial, determining the coefficients of remaining terms;

determining the maximum deviation until the maximum deviation has been determined for several of the terms;

permanently eliminating the terms having the least effect on the maximum deviation.

3. A method of calibrating an instrument in accordance with claim 2 wherein a corrected calibration polynomial is obtained;

and the corrected calibration polynomial is used to obtain a calibrated signal from a measured signal.

4. A method in accordance with claim 3 wherein the corrected calibration polynomial is stored in a microcontroller.

5. A method in accordance with claim 4 wherein the instrument measures the rate of flow of a liquid.

6. A method in accordance with claim 4 wherein the instrument measures impurities in water.

7. A method in accordance with claim 4 wherein the instrument measures the depth of a liquid.

8. A method of calibrating an instrument, comprising the steps of:

forming a preparatory calibration polynomial including a primary independent variable and at least one interference related independent variable;

obtaining a plurality of data sets of a dependent variable, the primary independent variable and the at least one interference related independent variable;

using the data sets to eliminate least significant terms of the preparatory calibration polynomial;

adding the most significant cross terms one at a time;

calculating coefficients for the polynomial each time a cross term is added;

determining the maximum deviation; and

permanently adding cross terms having the most beneficial effect on the maximum deviation.