Measuring apparatuses and methods of using them

• US 20070174013A1
• Filed: 01/20/2006
• Published: 07/26/2007
• Est. Priority Date: 01/20/2006
• Status: Active Grant

• Current Assignee: Teledyne Isco, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Teledyne Isco, Inc. (Thermo Fisher Scientific Incorporated)
• Inventors: Liescheski, Phillip
• Granted Patent: US 7,532,992 B2
• Time in Patent Office: Days
• US Class Current: 702/85
• 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 water or other value and a transducer for measuring a physical parameter that causes interference error. A calibration polynomial is used to correct the output signal for interference or nonlinearity. 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 of the dependent variable, the primary independent variable and the at least one interference related independent variable 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 resulting in a calibration polynomial.

Claims

1. A measuring instrument for measuring a value and providing a calibrated signal, comprising:

at least one primary sensor for sensing the value wherein the at least one primary sensor generates a primary measurement signal;

at least one secondary sensor for generating at least one interference related signal for sensing at least one interference related value that reduces the precision of the primary measurement signal generated by the at least one primary sensor; and

a microcontroller containing a criteria optimized correction polynomial having the at least one primary measurement signal and said at least one interference related signal as independent variables and said calibrated signal as a dependent variable;

said microcontroller being connected to receive said at least one primary measurement signal and said at least one interference related signal, whereby said microcontroller corrects said at least one primary measurement signal for said at least one interference related signal to provide said calibrated signal.

2. A measuring instrument in accordance with claim 1 wherein the measuring instrument is an apparatus for determining a volumetric rate of flow of a liquid within a flow bed comprising:

a measuring apparatus for measuring an average rate of flow of the liquid in the flow bed;

said at least one primary sensor being a pressure sensor, wherein the at least one primary sensor may be positioned at a bottom of a flow path for the liquid whereby the at least one primary measurement signal is related to the depth of the liquid;

said at least one secondary sensor being a temperature measuring sensor;

said criteria-optimized correction polynomial having depth and temperature as independent variables;

said microcontroller further including means for multiplying measured values by average velocity to provide a volumetric velocity.

3. A measuring instrument in accordance with claim 2 wherein the measuring apparatus comprises:

means for transmitting an ultrasonic signal into the liquid in the flow bed;

means for receiving reflected ultrasonic signals; and

means for utilizing digital signals to calculate an approximate average velocity by performing a Fourier transform on the digital signals and averaging certain of the coefficients of the Fourier transform.

4. A measuring instrument in accordance with claim 2 wherein the measuring apparatus comprises:

means for transmitting an ultrasonic signal into a fluid stream at an angle so that it traverses at least a representative portion of the cross sectional area of the fluid stream;

means for receiving reflected ultrasonic signals from said at least a representative portion of the cross sectional area of the fluid stream;

means for converting the received reflected ultrasonic signals to electrical signals representing reflection from said at least a representative portion of the cross sectional area of the fluid stream; and

means for utilizing substantially all of the electrical signals representing reflection from said at least a representative portion of the cross sectional area of the fluid stream to calculate an approximate average velocity of the fluid stream;

wherein said means for utilizing substantially all of the electrical signals representing reflection from at least a representative portion of the cross sectional area of the fluid stream to calculate an approximate average velocity of the fluid stream includes means for performing a Fourier transform on said electrical signals and averaging certain of the coefficients of the Fourier transform.

5. A measuring instrument in accordance with claim 1 wherein a primary value is temperature, the at least one primary sensor is an organic vapor chemical sensor and the at least one secondary sensor measures humidity.

6. 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; and

adding the most significant cross terms.

7. A method in accordance with claim 6 in which the step of forming a preparatory calibration polynomial comprises the steps of:

selecting a number of terms of a polynomial; and

adding low degree cross terms.

8. A method in accordance with claim 7 in which the step of selecting a number of terms of a polynomial includes the steps of:

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; and

adding some trial cross terms.

9. A method in accordance with claim 6 wherein the step of obtaining a plurality of data sets of the dependent variable, the primary independent variable and the at least one interference related independent variable includes the steps of:

obtaining a series of output values from one of a first of a primary transducer and a secondary transducer while said one of the first of a primary transducer and the secondary transducer is at a first stimuli point and the other of the primary transducer and the secondary transducer is subject to a series of other stimulating points; and

obtaining a series of output values, each at a different stimuli value of a series of stimuli values from the other of the primary and secondary transducers.

10. The method of claim 6 in which 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; and

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

11. The method of claim 6 further including the steps of:

adding 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.

12. A method of making an instrument, comprising the steps of:

selecting a design criteria;

preparing a criteria-optimized calibration curve;

selecting a primary transducer and at least one secondary transducer;

programming a microcontroller to correct a value measured by the primary transducer using the criteria-optimized calibration curve; and

using the corrected value.

13. A method according to claim 12 wherein the step of programming a microcontroller to correct the value measured by the primary transducer using the criteria-optimized calibration curve includes the steps of:

forming a preparatory calibration polynomial that includes as terms 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 the least significant terms of the preparatory calibration polynomial; and

adding the most significant cross terms.