Optical nitrate sensor compensation algorithm for multiparameter water quality measurement

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. An optical nitrate sensor for sampling a confined volume of water within a prescribed region of a sampling chamber, comprising: a UV LED combination configured to generate a first UV LED signal centered at 229 nm and a second UV LED signal centered in a range of 250-275 nm that traverse the confined volume of water within the prescribed region of the sampling chamber in order to sense nitrates in the water with first UV LED signal and dissolved organic matter (DOM) in the water with second UV LED signal; a reference photodiode configured to respond to part of the first UV LED signal and the second UV LED signal, and provide photodiode reference signaling containing information about the part of the first UV LED signal and the second UV LED signal received; a measuring photodiode configured to sense the first UV LED signal and the second UV LED signal that pass through the confined volume of water within the prescribed region of the sampling chamber, and provide photodiode measured signaling containing information about a nitrate absorption of the water related to the first UV LED signal and a DOM absorption background related to the second UV LED signal; a transimpedance amplifier configured to respond to the photodiode reference signaling and the photodiode measured signaling, and provide transimpedance amplifier signaling containing information about a photocurrent to voltage reference signaling conversion of the photodiode reference signaling without interaction with the water, and also a photocurrent to voltage measured signaling conversion of the photodiode measured signaling after interaction with the water; and a signal processor or signal processing module configured to: receive the transimpedance amplifier signaling, and determine corresponding signaling containing information about a DOM background corrected concentration of nitrates dissolved in the water by compensating the concentration of the nitrate absorption sensed in the water at 229 nm for the DOM background absorption sensed in the water in the range of 250-275 nm, based upon the transimpedance amplifier signaling received.

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

3. An optical nitrate sensor according to claim 1, where the UV LED is configured to respond to signaling and generate the first UV LED signal and the second UV LED signal.

4. An optical nitrate sensor, according to claim 1, wherein the signal processor or signal processing module is configured to determine the DOM background corrected concentration by subtracting the DOM background absorption from the nitrate absorption to compensate for leaves and soil extracts in the water that can optically interfere with a nitrate measurement.

5. An optical nitrate sensor, according to claim 1, wherein the signal processor or signal processing module is configured to: receive further signaling containing information about optical scattering from particulate in the water that appears as attenuation at all wavelengths of light; and determine turbidity corrected signaling containing information about a turbidity corrected concentration of nitrate dissolved in the water, based upon the further signaling received.

6. An optical nitrate sensor, according to claim 1, wherein the signal processor or signal processing module is configured to receive the photodiode reference signaling and the photodiode measured signaling, and implement a compensation algorithm for doing one or more of the following: determining an absorbance via a logarithm of a ratio of 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 .sub.i or .sub.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) .sub.j; or correcting an organic matter background via a subtraction of a turbidity compensated absorbance with a scale factor, , for the 275 nm absorbance; or determining or calculating an organic matter and turbidity corrected nitrate concentration via a polynomial of coefficients .sub.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, ( C.).

7. An optical nitrate sensor, according to claim 1, wherein the signal processor or signal processing module is configured to receive the photodiode reference signaling and the photodiode measured signaling, 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.

8. An optical nitrate sensor, according to claim 1, wherein the UV LED 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.

9. An optical nitrate sensor, according to claim 1, wherein the optical nitrate sensor comprises: a sensor body configured to confine a volume of the water within the prescribed region.

10. An optical nitrate sensor, 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.

11. A method for sampling a confined volume of water within a prescribed region of a sampling chamber with an optical nitrate sensor, comprising: generating with a UV LED combination a first UV LED signal centered at 229 nm and a second UV LED signal centered in a range of 250-275 nm that traverse the confined volume of water within the prescribed region of the sampling chamber in order to sense nitrates in the water with first UV LED signal and dissolved organic matter (DOM) in the water with second UV LED signal; responding with a reference photodiode to part of the first UV LED signal and the second UV LED signal, and providing photodiode reference signaling containing information about the part of the first UV LED signal and the second UV LED signal received; sensing with a measuring photodiode the first UV LED signal and the second UV LED signal that pass through the confined volume of water within the prescribed region of the sampling chamber, and providing photodiode measured signaling containing information about a nitrate absorption of the water related to the first UV LED signal and a DOM absorption background related to the second UV LED signal; responding with a transimpedance amplifier to the photodiode reference signaling and the photodiode measured signaling, and providing transimpedance amplifier signaling containing information about a photocurrent to voltage reference signaling conversion of the photodiode reference signaling without interaction with the water, and also a photocurrent to voltage measured signaling conversion of the photodiode measured signaling after interaction with the water; and receiving with a signal processor or signal processing module the transimpedance amplifier signaling, and determining corresponding signaling containing information about a DOM background corrected concentration of nitrates dissolved in the water by compensating the concentration of the nitrate absorption sensed in the water at 229 nm for the DOM background absorption sensed in the water in the range of 250-275 nm, based upon the transimpedance amplifier signaling received.

12. A method according to claim 11, wherein the method comprises providing with the signal processor or signal processing module the corresponding signaling containing information about the DOM background corrected concentration of nitrate dissolved in the water.

13. A method according to claim 11, wherein the method comprises responding with the UV LED to control signaling and generating the first UV LED signal and the second UV LED signal.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The drawing, which are not necessarily drawn to scale, includes FIGS. 1-5, as follows:

(2) FIG. 1A shows a block diagram of apparatus, e.g., having a signal processor or signal processing module for implementing signal processing functionality, according to some embodiments of the present invention.

(3) FIG. 1B shows a block diagram of a flowchart having steps for implementing a method, according to some embodiments of the present invention.

(4) FIG. 2 is a flowchart having steps for implementing at least part of a compensation algorithm, according to some embodiments of the present invention.

(5) FIG. 3 is a diagram having nodes showing at least part of a compensation algorithm, according to some embodiments of the present invention.

(6) FIG. 4 is a graph showing the effect of a turbidity correction at a fixed 2 ppm nitrate, e.g., including where the turbidity of 500 FNU can yield false nitrate concentration up to 30 ppm (diamonds), and including where implementing a correction algorithm according to the present invention can effectively yield accurate results (squares).

(7) FIG. 5 shows apparatus according to the present invention, which includes a UV LED and photodiode combination for implementing the optical signaling processing functionality together with a signal processor for implementing the signaling processing functionality, all according to some embodiments of the present invention.

(8) To reduce clutter in the drawing, each Figure in the drawing does not necessarily include every reference label for every element shown therein.

DETAILED DESCRIPTION OF BEST MODE OF THE INVENTION

FIG. 1A: Implementation of Signal Processing Functionality

(9) By way of further example, FIG. 1A shows apparatus 10 (e.g., an optical nitrate sensor) for implementing the associated signal processing functionality, according to some embodiments of the present invention. The apparatus 10 may include a signal processor or processing module 12 configured at least 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.

(10) In operation, the signal processor or processing module 12 may be configured to provide the corresponding signaling containing information about the corrected concentration of nitrate dissolved in the water, e.g., for further processing, consistent with that set forth herein. The scope of the invention is not intended to be limited to any particular type, kind or manner of further processing, and may include further processing techniques either now known or later developed in the future.

(11) By way of example, the functionality of the signal processor or processing module 12 may be implemented using hardware, software, firmware, or a combination thereof. In a typical software implementation, the signal processor or processing module 12 would include one or more microprocessor-based architectures having, e. g., at least one signal processor or microprocessor like element 12. One skilled in the art would be able to program with suitable program code such a microcontroller-based, or microprocessor-based, implementation to perform the signal processing functionality disclosed herein without undue experimentation. For example, the signal processor or processing module 12 may be configured, e.g., by one skilled in the art without undue experimentation, to receive the 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, consistent with that disclosed herein.

(12) Moreover, the signal processor or processing module 12 may be configured, e.g., by one skilled in the art without undue experimentation, to determine the 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, e.g., consistent with that disclosed herein. By way of example, the present application discloses techniques for determining the corresponding signaling containing information about the corrected concentration of nitrate dissolved in the water by compensating the concentration of nitrate for the DOM sensed in the water; however, the scope of the invention is not intended to be limited to any particular type or kind of signal processing implementation and/or technique for making the determination about the corrected concentration of nitrate dissolved in the water, based upon the signaling received.

(13) The scope of the invention is not intended to be limited to any particular implementation using technology either now known or later developed in the future. The scope of the invention is intended to include implementing the functionality of the signal processor(s) 12 as stand-alone processor, signal processor, or signal processor module, as well as separate processor or processor modules, as well as some combination thereof.

(14) By way of example, the apparatus 10 may also include, e.g., other signal processor circuits or components generally indicated 14, including random access memory or memory module (RAM) and/or read only memory (ROM), input/output devices and control, and data and address buses connecting the same, and/or at least one input processor and at least one output processor, e.g., which would be appreciate by one skilled in the art.

(15) By way of further example, the signal processor 12 may include, or take the form of, some combination of a signal processor and at least one memory including a computer program code, where the signal processor and at least one memory are configured to cause the apparatus to implement the functionality of the present invention, e.g., to respond to signaling received and to determine the corresponding signaling, based upon the signaling received.

FIG. 1B: The Basic Method

(16) According to some embodiments, the present invention may also include a method generally indicated as 20 comprising steps 20a, 20b and 20c, as follows: a step 20a for receiving in a signal processor or processing module like element 12 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 a step 20b for determining in the signal processor or processing module like element 12 corresponding signaling containing information about the a corrected concentration of nitrate dissolved in the water by compensating the concentration of nitrate for the DOM sensed in the water.
The method may also include one or more of the features set forth above, including a step 20c for providing the corresponding signaling containing information about the corrected concentration of nitrate dissolved in the water.

FIG. 2: The Flowchart

(17) FIG. 2 is a flowchart generally indicated as 50 having steps 50a to 50o for implementing at least part of a compensation algorithm, according to some embodiments of the present invention.

(18) The steps are briefly summarized as follows:

(19) Steps 50a and 50b may be implemented for determining a reference photodiode measurement and a measurement photodiode measurement;

(20) Steps 50c and 50d may be implemented for determining A.sub.229 and A.sub.275, e.g., based upon determining a log function ((M.sub.229/R.sub.229)/(blank ratio)) or a corresponding log function ((M.sub.275/R.sub.275)/(blank ratio));

(21) Steps 50e and 50f may be implemented for determining A.sub.tcorre229 and A.sub.tcorr275, e.g., based upon subtracting from A.sub.229 and A.sub.275 a summation function related to the absorbance as a polynomial correction of coefficients .sub.i or .sub.m, at 229 nm and 275 nm, respectively;

(22) Steps 50g and 50h may be implemented for determining a turbidity measurement and a temperature measurement;

(23) Steps 50i, 50j and 50k may be implemented for determining a turbidity corrected results only, e.g., based upon A.sub.tcorre229 and A.sub.tcorr275 corrections, where the turbidity compensated nitrate concentration, as milligrams/liter, can be calculated from the absorbance with the conversion factor(s) .sub.j, and where the organic matter background can be corrected via the subtraction of the turbidity compensated absorbance with the appropriate scale factor, , for the 275 nm absorbance.

(24) Steps 50l and 50m may be implemented for determining turbidity and NOM corrected results only, e.g., based upon the organic matter and turbidity corrected nitrate concentration being calculated via a polynomial of coefficients .sub.k; and

(25) Steps 50n and 50o may be implemented for determining turbidity, NOM and temperature corrected results only, e.g., based upon temperature corrections of the organic background and turbidity compensated data being calculated via a polynomial of coefficients, ( C.).

FIG. 3

(26) FIG. 3 is a diagram generally indicated as 60 having nodes 60a to 60d for implementing at least part of a compensation algorithm to obtain a corrected nitrate measurement in node 60e, according to some embodiments of the present invention.

(27) Node 60a implements a 229 nm absorbance measurement, e.g., including by using a UV LED, photodiodes, optical filters and analog circuits and firmware, consistent with that disclosed herein;

(28) Node 60b implements a 250 to 275 nm absorbance measurement, e.g., including by using firmware, consistent with that disclosed herein;

(29) Node 60c implements taking a temperature measurement, e.g., using internal and external sensors and firmware algorithms, consistent with that disclosed herein; and

(30) Node 60d implements taking a turbidity measurement, e.g., using external or integrated measurements and firmware algorithms, consistent with that disclosed herein.

FIG. 5: The Basic Photodiode Combination and Signal Processing Functionality

(31) By way of example, FIG. 5 shows apparatus generally indicated as 10 for providing optical nitrate sensor compensation for water quality monitoring of a body of water generally indicated as H.sub.2O in a sample chamber SC using a UV/LED and photodiode combination 20 and the signal processor 12.

(32) By way of example, the UV/LED and photodiode combination 20 may include a combination source 20a having a UV LED that provides LED optical signaling L.sub.M at 229 nm or 275 nm to a sampling window, as shown that may be made of quartz. The sampling window responds to the LED optical signaling L.sub.M at 229 nm or 275 nm and provides one part of the LED optical signaling L.sub.M to a reference photodiode PD.sub.R and another part of the LED optical signaling L.sub.M at 229 nm or 275 nm through the body of water. The photodiode combination 20 also includes a monitor photodiode combination 20b having a measuring photodiode PD.sub.M that measures received LED optical signaling L.sub.M at 229 nm and 275 nm that passed through the water, and provides measured photodiode signaling S.sub.m, 229 and S.sub.m, 275 containing information about optical absorbsion by the water related to the LED signaling L.sub.M at 229 nm and 275 nm absorbed.

(33) By way of further example, the UV/LED and photodiode combination 20 may also include a programmable gain amplifier PGA configured to receive the reference signaling S.sub.R, 229 or S.sub.R, 275 from the reference photodiodes PD.sub.R, and also receive the measured signaling S.sub.m, 229 and S.sub.m, 275 from the measurement photodiode PD.sub.M, and provide programmable gain amplifier signaling PGA (S.sub.R/M, 229; S.sub.R/M, 275) to the signal processor 12 for further processing, e.g., consistent with that set forth herein. Programmable gain amplifier are known in the art, and the scope of the invention is not intended to be limited to any particular type or kind thereof, e.g., either now known or later developed in the future.

(34) The signal processor 12 is configured to receive the programmable gain amplifier signaling PGA (S.sub.R/M, 229; S.sub.R/M, 275), and determines output signaling S.sub.out containing information about the optical nitrate sensor compensation, e.g., including a turbidity correction to compensate for dissolved organic matter (DOM) contained within the water. The signal processor 12 is configured to perform signal processing functionality based upon optical nitrate sensor compensation algorithms disclosed herein to make the determination related to the optical nitrate sensor compensation to the concentration of nitrate dissolved in the water. The signal processor 12 is also configured to provide the output signaling S.sub.out for suitable further processing, e.g., including generating suitable display signaling for showing/displaying the information about the corrected concentration of nitrate dissolved in the water, and/or the optical nitrate sensor compensation to the concentration of nitrate, on a display/monitor, etc.

(35) The signal processor may also be configured to provide control signaling Sc to control the operation of the UV LED, PD.sub.R and PD.sub.M, e.g., to provide UV LED light at either 229 nm or 275 nm, receive/sense reference signaling at either 229 nm or 275 nm, and/or receive/sense measured signaling at either 229 nm or 275 nm, consistent with that set forth herein.

The Optical Components

(36) By way of example, and as one skilled in the art would appreciate, optical components like LEDs, photodiodes, measurement photodiodes, reference photodiodes, optical filters, optical fiber or fibers, light pipes, LED arrays, optical sampling windows, optical pickoff windows, focusing lens, sapphire or UV grade fused silica rods, optical spectrum analyzers are all known in the art, and the scope of the invention is not intended to be limited to any particular type or kind thereof that may be used herein. The scope of the invention is intended to include using such optical components that may be now known in the art or later developed in the future.

Computer-Readable Storage Medium

(37) According to some embodiments of the present invention, the apparatus may also take the form of a computer-readable storage medium having computer-executable components for performing the steps of the aforementioned method. The computer-readable storage medium may also include one or more of the features set forth above.

Optical Nitrate Sensor Compensation Algorithms for Multiparameter Water Quality Monitoring

(38) This application relates to the subject matter disclosed a companion patent application having Ser. No. 15/451,853, filed 7 Mar. 2017, entitled Optical Nitrate Sensor for Multiparameter Water Quality Monitoring, which claims benefit to provisional patent application Ser. No. 62/304,678 (911-023.3-1//N-YSI-0033), filed 7 Mar. 2016. The optical nitrate sensor disclosed in the companion application may be used in conjunction with the optical nitrate sensor compensation algorithm disclosed in the instant application, and vice versa. Moreover, and by way of example, the companion patent application provides at least one technique for determining a concentration of nitrate dissolved in the water based upon a first UV optical absorbance of light centered at 229 nm, which may be compensated based upon that disclosed herein. The scope of the invention is intended to include, and embodiments are envisioned using, e.g., other techniques for determining a concentration of nitrate dissolved in the water that are both now known, and later developed in the future.

The Scope of the Invention

(39) While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, may modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed herein as the best mode contemplated for carrying out this invention.