OPTICAL NITRATE SENSOR COMPENSATION ALGORITHM FOR MULTIPARAMETER WATER QUALITY MEASUREMENT

• US 20170299511A1
• Filed: 03/09/2017
• Published: 10/19/2017
• Est. Priority Date: 03/09/2016
• Status: Active Grant

• Current Assignee: YSI Incorporated (Xylem, Inc.)
• Original Assignee: YSI Incorporated (Xylem, Inc.)
• Inventors: PALASSIS, Christopher John, POON, Melanie C.K.
• Granted Patent: US 10,955,341 B2
• Time in Patent Office: Days
• CPC Class Codes: G01J 1/42 using electric radiation detectors optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/53 within a flowing fluid, e.g. smoke
• CPC Class Codes: G01N 21/59 Transmissivity G01N21/25 takes precedence
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 2201/062 LED's
• CPC Class Codes: G01N 33/188 Determining the state of nitrification biological treatment of water by aerobic or anaerobic processes for denitrification of water C02F3/305

Abstract

An optical nitrate sensor features a signal processor or signal processing module configured to:

• • receive signaling containing information about a concentration of nitrate dissolved in the water based upon a first UV optical absorbance of light centered at 229 nm, and also containing information about a dissolved organic matter (DOM) sensed in the water based upon a second UV optical absorbance of associated light centered in a range of 250 nm to 275 nm; and
  • determine corresponding signaling containing information about a corrected concentration of nitrate dissolved in the water by compensating the concentration of nitrate for the DOM sensed in the water, based upon the signaling received.

Claims

1. Apparatus comprising:

a signal processor or signal processing module configured to;

receive signaling containing information about a concentration of nitrate dissolved in the water based upon a first UV optical absorbance of light centered at 229 nm, and also containing information about a dissolved organic matter (DOM) sensed in the water based upon a second UV optical absorbance of associated light centered in a range of 250 nm to 275 nm; and

determine corresponding signaling containing information about a corrected concentration of nitrate dissolved in the water by compensating the concentration of nitrate for the DOM sensed in the water, based upon the signaling received.

2. Apparatus according to claim 1, where the signal processor or signal processing module is configured to provide corresponding signaling containing information about the corrected concentration of nitrate dissolved in the water.

3. Apparatus according to claim 1, where the signaling includes first signaling containing information about a measurement (M) of the first UV optical absorbance of nitrate dissolved in water of a UV light that is generated by a UV LED centered at 229 nm and that traverses a confined volume of the water within a prescribed region of a sensor body.

4. Apparatus according to claim 1, where the signaling includes second signaling containing information about a measurement of the second UV optical absorbance of the DOM in the water of a UV light that is generated by a UV LED centered in a range of 250 nm to 275 nm and that traverses a confined volume of the water within a prescribed region of a sensor body.

5. Apparatus according to claim 1, where the signaling includes

first signaling containing information about a first measurement (M) of the first UV optical absorbance of nitrate dissolved in water of a first UV light that is generated by a first UV LED centered at 229 nm and that traverses a confined volume of the water within a prescribed region of a sensor body, and also about a first reference sample (R) of a first portion of the first UV light not traversing the confined volume of the water;

and

second signaling containing information about a second measurement of the second UV optical absorbance of the DOM in the water of a second UV light that is generated by a second UV LED centered in a range of 250 nm to 275 nm and that traverses the confined volume of the water within the prescribed region of the sensor body, and also about a second reference sample (R) of a second portion of the second UV light not traversing the confined volume of the water.

6. Apparatus according to claim 5, wherein the signal processor or signal processing module is configured to determine background corrected signaling containing information about a background corrected concentration of nitrate dissolved in the water, based upon the second signaling received.

7. Apparatus according to claim 6, wherein the signal processor or signal processing module is configured to determine the background corrected signaling by subtracting the second signaling from the first signaling to compensate for leaves and soil extracts in the water that can optically interfere with a nitrate measurement.

8. Apparatus according to claim 5, wherein the signal processor or signal processing module is configured to:

receive further second signaling containing information about optical scattering from particulate in the water that appears as attenuation at all wavelengths of light; and

turbidity corrected signaling containing information about a turbidity corrected concentration of nitrate dissolved in the water, based upon the further second signaling received.

9. Apparatus according to claim 1, wherein the signal processor or signal processing module is configured to receive reference (R) and measurement (M) photodiode signaling that are evaluated at 229 nm and ˜

275 nm, and implement a compensation algorithm for doing one or more of the following;

determining an absorbance via a logarithm of a ratio of the reference (R) and measurement (M) photodiode signaling and a ratio of a non-absorbing or blank standard, including where the non-absorbing or blank standard is determined in relation to deionized water;

or

subtracting a turbidity correction from the absorbance as a polynomial correction of coefficients α

_i or γ

_m, at 229 nm and ˜

275 nm, respectively, including where turbidity data signaling contains information about turbidity data provided from an internal or external optical measurement in nephelometric units;

or

determining or calculating a turbidity compensated nitrate concentration from the absorbance with a conversion factor(s) β

_j;

or

correcting an organic matter background via a subtraction of a turbidity compensated absorbance with a scale factor, δ

, for the 275 nm absorbance;

or

determining or calculating an organic matter and turbidity corrected nitrate concentration via a polynomial of coefficients ε

_k;

or/and

determining or calculating temperature corrections of organic background and turbidity compensated data signaling containing information about the organic background and turbidity compensated data via a polynomial of coefficients, μ

(°

C.).

10. Apparatus according to claim 1, wherein the signal processor or signal processing module is configured to receive reference (R) and measurement (M) photodiode signaling that are evaluated at 229 nm and ˜

275 nm, and implement a compensation algorithm for correcting a nitrate measurement by doing one or more of the following;

making a temperature correction using an internal or external temperature sensor;

making a turbidity correction using an external or integrated turbidity measurement.

11. Apparatus according to claim 1, wherein the apparatus includes, or forms part of an optical nitrate sensor.

12. Apparatus according to claim 11, wherein the optical nitrate sensor comprises:

a first UV LED for providing first UV light centered at 229 nm and that traverses a confined volume of the water within a prescribed region of a sensor body; and

a second UV LED for providing second UV light centered in a range of 250 nm to 275 nm.

13. Apparatus according to claim 11, wherein the optical nitrate sensor comprises:

a sensor body configured to confine a volume of the water within a prescribed region.

14. Apparatus according to claim 1, wherein the signal processor or signal processing module is configured to determine a measurement of the UV optical absorbance based upon the following equation:

Absorbance=−

log(optical transmittance)=−

log(M/a R),

where a is a proportionality constant that can be adjusted for electrical gain normalization.

15. Apparatus according to claim 3, wherein the signaling containing information about the measurement (M) is measured and received from a measurement photodiode, where a photocurrent is generated and is subsequently converted into a voltage via a transimpedance amplifier.

16. Apparatus according to claim 3, wherein the signaling containing information about a reference sample (R) that is measured and received from a reference photodiode, where a photocurrent is generated and is subsequently converted into a voltage via a transimpedance amplifier.

17. Apparatus according to claim 3, wherein the UV light traverses the confined volume of the water over a varying path length that depends on a concentration range of interest for the nitrate concentration determined.

18. A method comprising steps for

receiving in a signal processor or processing module signaling containing information about a concentration of nitrate dissolved in the water based upon a first UV optical absorbance of light centered at 229 nm, and also containing information about a dissolved organic matter (DOM) sensed in the water based upon a second UV optical absorbance of associated light centered in a range of 250 nm to 275 nm;

and

determining in the signal processor or processing module corresponding signaling containing information about a corrected concentration of nitrate dissolved in the water by compensating the concentration of nitrate for the DOM sensed in the water, based upon the signaling received.

19. A method according to claim 18, wherein the method comprises providing from the signal processor or signal processing module the corresponding signaling containing information about the corrected concentration of nitrate dissolved in the water.

20. A method according to claim 18, wherein the method comprises receiving in the signal, some combination of the following:

first signaling containing information about a first measurement (M) of the first UV optical absorbance of nitrate dissolved in water of a first UV light that is generated by a first UV LED centered at 229 nm and that traverses a confined volume of the water within a prescribed region of a sensor body, and also about a first reference sample (R) of a first portion of the first UV light not traversing the confined volume of the water; and

second signaling containing information about a second measurement of the second UV optical absorbance of the DOM in the water of a second UV light that is generated by a second UV LED centered in a range of 250 nm to 275 nm and that traverses the confined volume of the water within the prescribed region of the sensor body, and also about a second reference sample (R) of a second portion of the second UV light not traversing the confined volume of the water.