WO2014139100A1

WO2014139100A1 - A method of calibrating led peak wavelength of a water analyzer by adjusting led forward current

Info

Publication number: WO2014139100A1
Application number: PCT/CN2013/072530
Authority: WO
Inventors: Jie Shen; Yikang Gu
Original assignee: General Electric Company
Priority date: 2013-03-13
Filing date: 2013-03-13
Publication date: 2014-09-18

Abstract

Methods of calibrating water analyzer LEDs are disclosed. One method is a direct method in which a target forward current value is calculated for the LED at each measurement location of the water analyzer using the target peak wavelength and the wavelength-current relation curve for the LED at each measurement location. Another method is an indirect method in which a target forward current value for the LED at each measurement location of a water analyzer is ascertained by comparing the absorbance measurement value for each measurement location of the water analyzer to corresponding standard absorbance measurement values, and adjusting the forward current value for the LED at each measurement location that does not compare favorably with the corresponding standard absorbance measurement value until the absorbance measurement value for each measurement location compare favorably with the corresponding standard absorbance measurement values. Water analyzers are disclosed for use with the methods.

Description

A METHOD OF CALIBRATING LED PEAK WAVELENGTH OF A WATER ANALYZER BY ADJUSTING LED FORWARD CURRENT

FIELD OF THE INVENTION

[0001] This invention pertains to the calibration of LED peak wavelength, more specifically to the calibration of the LED peak wavelength by adjusting LED forward current.

BACKGROUND OF THE INVENTION

[0002] Light emitting diodes (LEDs) are generally manufactured in batches using standard semiconductor fabrication techniques. A single semiconductor wafer will typically yield multiple LEDs. Although the fabrication process can be controlled to obtain LEDs that emit light at a specific color, there are generally significant variations in the output wavelength of the LEDs when a forward current of a common value is applied to the LEDs. Usually, the peak wavelength variation between LEDs produced on a single semiconductor wafer is between about +/-5nm.

[0003] However, in colorimetry applications, such as a water analyzer, the absorbance measurement value is dependent upon the LED peak wavelength. Therefore, in colorimetry applications, the acceptable criterion of peak wavelength variation between LEDs is +/-lnm. Accordingly, a need exists for a method of calibrating LED peak wavelength.

BRIEF SUMMARY OF THE INVENTION

[0004] In one aspect of the invention, a method of calibrating water analyzer light emitting diodes (LEDs) comprising: providing a plurality of LED and obtaining a wavelength-current relation curve for each LED using a commercial spectrometer; providing a water analyzer having a processor with memory, and a plurality of measurement locations; installing one of the LEDs in each of the measurement locations of the water analyzer, wherein the forward current value is individually adjustable for the LED at each of the measurement locations; storing the wavelength-current relation curves for the LEDs in the water analyzer memory; determining a target peak wavelength for the plurality of LEDs; calculating a target forward current value for the LED of each measurement location using the target peak wavelength and the wavelength-current relation curve for the LEDs; and storing the target forward current values for the LEDs in the memory.

[0005] In another aspect of the invention, the method further comprises retrieving the target forward currents for each of the LEDs from the memory and providing the target forward currents to each of the LEDs when measuring an absorbance of a sample in the water analyzer.

[0006] In another aspect of the invention, each wavelength-current relation curve is comprised of a plurality of discrete points. In another aspect of the invention, each wavelength-current relation curve has one discrete point for every milliamp between 1 and 25 milliamps. In another aspect of the invention, the target peak wavelength is the mean peak wavelength of the plurality of LEDs when the plurality of LEDs are provided with a uniform forward current. In another aspect of the invention, the uniform forward current is 15mA.

[0007] In another aspect of the invention, the target forward current for each of the LEDs corresponds to a wavelength on the wavelength-current relation curve for the LED that is within about lnm of the target peak wavelength. In another aspect of the invention, the target forward current for each of the LEDs corresponds to a wavelength on the wavelength-current relation curve for the LED that is within about 0.5nm of the target peak wavelength. In another aspect of the invention, the target forward current for each of the LEDs corresponds to a wavelength on the wavelength-current relation curve for the LED that is about equal to the target peak wavelength.

[0008] In another aspect of the invention, the target forward current for each of the LEDs is calculated using a linear fitting algorithm when the target peak wavelength is located between two of the discrete points on the wavelength-current relation curve for the LED.

[0009] In a further aspect of the invention, a method of calibrating water analyzer light emitting diodes (LEDs) comprises: providing a first and a second water analyzer, wherein each of the water analyzers are comprised of a processor having memory, a display that interfaces with the processor, and a testing area; wherein the testing area is comprised of a plurality of measurement locations; wherein each measurement location is comprised of an LED and a photosensor that interface with the processor; wherein the LED of each of the measurement locations is provided with an individually adjustable forward current by the processor; providing a standard card and inserting the standard card into the testing area of the first water analyzer; measuring and displaying an absorbance of the standard card at each of the measurement locations of the first water analyzer, and designating the absorbances as standard absorbance measurement values for the measurement locations; inserting the standard card into the testing area of the second water analyzer; measuring and displaying an absorbance value of the standard card at each measurement location of the second water analyzer; comparing the displayed absorbance measurement values at each measurement location of the second water analyzer with the standard measurement values for each corresponding measurement location of the first water analyzer; individually adjusting the forward current value of the LED at each measurement location of the second water analyzer having an absorbance measurement value that does not compare favorably with the corresponding standard absorbance measurement value, wherein the forward current values are individually adjusted until the absorbance measurement value at each measurement location of the second water analyzer compares favorably with the corresponding standard absorbance measurement values; and storing the forward current value of the LED at each measurement location of the second water analyzer in memory as target forward current values.

[0010] In another aspect of the invention, the method further comprises providing the LED at each of the measurement locations of the second water analyzer with forward current values equivalent to the stored target forward current values when measuring an absorbance of a sample in a testing card inserted into the testing area of the second water analyzer.

[0011] In another aspect of the invention, the second water analyzer is further comprised of a keypad, wherein the forward current values of the second water analyzer are adjusted using the keypad. [0012] In another aspect of the invention, the standard absorbance values are obtained while providing a uniform current to the LED at each of the measurement locations of the first reader. In another aspect of the invention, the uniform current is 15mA.

[0013] In another aspect of the invention, an absorbance measurement value for one of the measurement locations of the second water analyzer compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for the measurement location of the second water analyzer is within about lnm of the corresponding standard absorbance measurement value.

[0014] In another aspect of the invention, an absorbance measurement value for one of the measurement locations of the second water analyzer compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for the measurement location of the second water analyzer is within about 0.5nm of the corresponding standard absorbance measurement value.

[0015] In another aspect of the invention, an absorbance measurement value for one of the measurement locations of the second water analyzer compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for the measurement location of the second water analyzer is about equal to the corresponding standard absorbance measurement value.

[0016] In a further aspect of the invention, a water analyzer is comprised of a processor having memory, a light emitting diode (LED) circuit, and a photosensor circuit; wherein the processor control the LED and photosensor circuits; wherein the LED circuit is comprised of a plurality of LEDs, each LED having a forward current independently controllable by the processor.

[0017] In another aspect of the invention, the LED circuit is further comprised of a digital to analog converter and a voltage to current amplifier; wherein the photosensor circuit is further comprised of an analog to digital converter and a current to voltage amplifier; wherein the processor is configured to calculate a target forward current value for the LED of each measurement location using a target peak wavelength and a wavelength-current relation curve for the LEDs. Advantages of the present invention will become more apparent to those skilled in the art from the following description of the embodiments of the invention which have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modification in various respects.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0018] These and other features of the present invention, and their advantages, are illustrated specifically in embodiments of the invention now to be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

[0019] FIG. 1 is a depiction of a water analyzer in accordance with an embodiment of the invention;

[0020] FIG. 2 is a depiction of a water analyzer testing card in accordance with an embodiment of the invention;

[0021] FIG. 3 is a depiction of a water analyzer standard card in accordance with an embodiment of the invention;

[0022] FIG. 4 is a depiction of the relationship between an LED, photosensor, and testing card or standard card within a water analyzer in accordance with an embodiment of the invention;

[0023] FIG. 5a is a schematic of the LED forward current circuit in accordance with an embodiment of the invention;

[0024] FIG. 5b is a schematic of the photosensor circuit in accordance with an embodiment of the invention;

[0025] FIG. 6a is a schematic of the LED forward current circuit in accordance with another embodiment of the invention;

[0026] FIG. 6b is a schematic of the photosensor circuit in accordance with an embodiment of the invention;

[0027] FIG. 7a is a schematic of the LED forward current circuit in accordance with another embodiment of the invention;

[0028] FIG. 7b is a schematic of the photosensor circuit in accordance with an embodiment of the invention;

[0029] FIG. 8a is a schematic of the LED forward current circuit in accordance with another embodiment of the invention; [0030] FIG. 8b is a schematic of the photosensor circuit in accordance with an embodiment of the invention;

[0031] FIG. 9 is a wavelength-current relationship curve for an LED;

[0032] FIG. 10a is a flow chart of a method of calibrating a water analyzer in accordance with an embodiment of the invention;

[0033] FIG. l Ob-c is a flow chart showing the operations taking place within the processor during the method depicted in FIG. 9a in accordance with an embodiment of the invention; and

[0034] FIG. 1 1 is a flow chart of another method of calibrating a water analyzer in accordance with an embodiment of the invention.

[0035] It should be noted that the drawing(s) and description are to be regarded as illustrative in nature and not as restrictive. The same reference numbers are generally used to refer to corresponding or similar features in the different embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", is not limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Range limitations may be combined and/ or interchanged, and such ranges are identified and include all the sub-ranges stated herein unless context or language indicates otherwise. Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions and the like, used in the specification and the claims, are to be understood as modified in all instances by the term "about".

[0037] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present. [0038] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0039] The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

[0040] FIG. 1 shows one embodiment of a water analyzer 10 having a base 15 and cover 20. Base 15 has a keypad 30, display 25, and LED board 40. LED board 40 has a plurality of LEDs 1 15 and is mounted to the topside of base 15 that is covered by cover 20. Photosensor board 35 is mounted on the underside of cover 20 and has a plurality of photosensors 215. When cover 20 is closed, cover 20 and base 15 form testing area 60 for placement of a testing card 55 or standard card 70. Testing area 60 is free of light produced by sources external to testing area 60 and only contains light produced by LEDs 1 15. The current output of photosensor 215 is representative of the peak wavelength of light received by photosensor 215. Accordingly, the current output of photosensor 215 can be used to deduce the wavelength of light generated by LED 1 15.

[0041] The pattern of LEDs 1 15 on LED board 40 and the pattern of photosensors 215 on photosensor board 35 are mirror images of each other. Accordingly, each LED 1 15 on LED board 40 has a corresponding photosensor 215 on photosensor board 35. Each LED 1 15 and corresponding photosensor 215 form a measurement location 65.

[0042] Turning to FIG. 2, testing card 55 contains a plurality of sample areas 56 arranged to match the layout of measurement locations 65, such that a sample area 56 is located between an LED 1 15 and corresponding photosensor 215 at each measurement location 65. Testing card 55 is made of a material that does not absorb or reflect the emitted light of LED 1 15.

[0043] Turning to FIG. 3, standard card 70 is made of a material that absorbs a known wavelength range and reflects a known wavelength range of the spectrum of light LED 1 15 is capable of emitting when provided with a given forward current. In one embodiment, standard card 70 is uniform in composition and color, such as blue or green. Further, the material of standard card 70 may include, but is not limited to, plastic or glass. It is contemplated that the color of standard card 70 will be dictated by the light color emitted by LED 1 15. Accordingly, a blue standard card 70 will be used for a water analyzer 10 having a blue LED 1 15 at each measurement location 65, and a green standard card 70 will be used for a water analyzer 10 having a green LED 1 15 at each measurement location 65.

[0044] FIG. 4 illustrates the placement of a testing card 55 or standard card 70 within testing area 60 between photosensor 215 and LED 1 15 of a measurement location 65. As can be seen, in operation, a sample area 56 of testing card 55 is situated at each measurement location 65 between LED 1 15 and photosensor 215. In accordance with Beer's law, the wavelengths absorbed by a given solution in sample area 56 can be used to deduce the presence of a particular substance in the solution at sample area 56.

[0045] Alternatively, FIG. 4 illustrates the placement of a standard card 70 within testing area 60 between photosensor 215 and LED 1 15 of a measurement location 65. Accordingly, since standard card 70 absorbs a known wavelength range and reflects a known wavelength range of the spectrum of light that LED 1 15 is capable of emitting, a user can calibrate the wavelength of light emitted from LED 1 15 by adjusting the forward current provided to LED 1 15 until the amount of current produced by photosensor 215 indicates that LED 1 15 is emitting the desired wavelength of light.

[0046] Turning to FIGS. 5A-8B, water analyzer circuit 300 is comprised of LED circuit 100 and photosensor circuit 200. FIGS. 5 A, 6A, 7A, and 8 A are block diagrams of embodiments of LED circuit 100, and FIGS. 5B, 6B, 7B, and 8B are block diagrams of embodiments of photosensor circuit 200. As one can see, LED circuit 100 and photosensor circuit 200 share a common processor 45, display 25, and keypad 30. Processor 45 has memory 50.

[0047] It is contemplated that in some embodiments, processor 45 and memory 50 are combined into the same package. Further, it is contemplated that processor 45 may be one or more microcontrollers, programmable logic controllers, digital signal processors, field-programmable gate arrays, programmable logic devices, application specific integrated circuits, and/or other known logic circuitry. Additionally, it is contemplated that in some embodiments, at least one of analog to digital converter 205, digital to analog converter 105, multiplexer 220, and demultiplexer 120 are also contained in the same package as processor 45 and memory 50. Further, display 25 and keypad 30 are connected to and communicate with processor 45. Additionally, processor 45 uses the SPI bus to control the forward current delivered to LEDs 1 15 and ascertain the peak wavelength of light detected by photosensor 215.

[0048] FIG. 5 A, shows an embodiment of LED circuit 100 of water analyzer 10. In this embodiment, LED circuit 100 is comprised of processor 45 having memory 50, display 25, keypad 30, digital to analog converter (DAC) 105, voltage to current amplifier 1 10, and LED 1 15 mounted on LED board 40. LED circuit 100 has a plurality of DACs 105a-105n, a plurality of voltage to current amplifiers H Oa-l lOn, and a plurality of LEDs 1 15a-l 15n. LED circuit 100 has a plurality of LED channels 101 with each channel 101 a-n being comprised of a DAC 105, voltage to current amplifier 1 10, and LED 1 15. The forward current provided to each LED 1 15 is individually controllable by processor 45 and the value of the forward current provided to each LED 1 15 is stored in and recalled from memory 50.

[0049] It is understood that "n" as used in the paragraph above in conjunction with a part number represents the letter, or combination of letters, of the alphabet corresponding to the quantity of the particular part present in LED circuit 100. More specifically, for DAC 105, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of DACs 105 in LED circuit 100. For voltage to current amplifiers 1 10, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of voltage to current amplifiers 1 10 in LED circuit 100. For LED 1 15, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of LEDs 1 15 in LED circuit 100. For LED channels 101 , it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of LED channels 101 in LED circuit 100.

[0050] For purposes of brevity, the operation of only one LED channel 101a will be described. However, it is understood that the other LED channels 101b-n will operate in a similar fashion. In operation, processor 45 controls the forward current provided to LED 1 15a of LED channel 101a via the SPI bus by providing a digitized representation of the LED forward current value to DAC 105a. DAC 105a then converts the digitized representation of the LED forward current value into an analog voltage representation of the LED forward current value and provides the analog voltage representation of the LED forward current value to voltage to current amplifier 1 10a. Voltage to current amplifier 1 10a then provides forward current to LED 1 15a. The forward current provided to LED 1 15a by voltage to current amplifier 1 10a has a value that corresponds to the analog voltage value received by voltage to current amplifier 1 10a from DAC 105a. LED 1 15a then emits light having a peak wavelength that is dictated by the forward current received from voltage to current amplifier 1 10a in accordance with the wavelength -current curve for LED 1 15a.

[0051] In some embodiments of LED circuit 100, keypad 30 and display 25 are used to input the wavelength-current curve for each LED 1 15, which is then stored in memory 50. In some embodiments, the wavelength-current curve can be in the form of a plurality of discrete points, and a linear fitting algorithm is used to obtain values located between two discrete points. In other embodiments, the wavelength-current curve can be in the form of an equation. Further, in some embodiments, the user can use keypad 30 and display 25 to store individual forward current values in memory 50 for each LED 1 15.

[0052] Turning to other embodiments of LED circuit 100 shown in FIGS. 6a, 7a, and 8a it can be seen that some embodiments of LED circuit 100 employ at least one demultiplexer (DEMUX) 120, with each DEMUX 120 having at least one LED channel 101. In FIG. 6a, each LED channel 101 is comprised of DAC 105, voltage to current amplifier 1 10, and LED 1 15. Further, in FIG. 7a, each LED channel 101 is comprised of a voltage to current amplifier 1 10 and an LED 1 15. Further, in FIG. 8a, each LED channel 101 is comprised of an LED 1 15. As can be seen, in some embodiments of LED circuit 100, such as the one shown in FIG. 6a, a DAC 105 is present in every LED channel 101 between DEMUX 120 and voltage to current amplifier 1 10.

[0053] Further, in other embodiments of LED circuit 100, such as the one shown in FIG. 7a, only one DAC 105 is present in LED circuit 100 for converting all LED channels 101 and is located between DEMUX 120 and processor 45. It is understood that when only one DAC 105 is present in LED circuit 100, DAC 105 receives, converts, and provides an individualized forward current value to each LED channel 101. [0054] Additionally, in other embodiments of LED circuit 100, such as the one shown in FIG. 8a, only one DAC 105 and voltage to current amplifier 1 10 are present in LED circuit 100 for converting all LED channels 101. In these embodiments, DAC 105 is located between processor 45 and voltage to current amplifier 1 10. Further, voltage to current amplifier 1 10 is located between DAC 105 and DEMUX 120. Additionally, DEMUX 120 is located between voltage to current amplifier 1 10 and LED 1 15. It is understood that when only one DAC 105 and voltage to current amplifier 1 10 are present in LED circuit 100, DAC 105 and voltage to current amplifier 1 10 receives, converts, and provides an individualized forward current value to each LED channel 101.

[0055] FIG. 5B shows an embodiment of photosensor circuit 200 of water analyzer 10. In this embodiment, photosensor circuit 200 is comprised of processor 45 having memory 50, display 25, keypad 30, analog to digital converter (ADC) 205, current to voltage amplifier 210, and a plurality of photosensors 215 mounted on photosensor board 35. Photosensor circuit 200 has a plurality of ADCs 205a-205n, a plurality of current to voltage amplifiers 210a-210n, and a plurality of photosensors 215a-215n. More specifically, photosensor circuit 200 has a plurality of photosensor channels 201 with each channel 201 a-201n being comprised of an ADC 205, current to voltage amplifier 210, and photosensor 215. A representation of the value of current generated by each photosensor 215 is provided to processor 45, which uses the value of current generated by photosensor 215 and current -wavelength curve of photosensor 215 to ascertain the peak wavelength of light received by photosensor 215 from LED 1 15. The peak wavelength of light received by photosensor 215 from LED 1 15 is then stored in memory of processor 45 and provided to user via display 25.

[0056] It is understood that "n" as used in the paragraph above in conjunction with a part number represents the letter, or combination of letters, of the alphabet corresponding to the quantity of the particular part present in photosensor circuit 200. More specifically, for ADC 205, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of ADCs 205 in photosensor circuit 200. For current to voltage amplifier 210, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of current to voltage amplifiers 210 in photosensor circuit 200. For photosensors 215, it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of photosensors 215 in photosensor circuit 200. For photosensor channel 201 , it is understood that "n" represents the letter, or combination of letters, of the alphabet corresponding to the quantity of photosensor channels 201 in photosensor circuit 200

[0057] For purposes of brevity, the operation of only one photosensor channel 201 a will be described. However, it is understood that the other photosensor channels 201b-n will operate in a similar fashion. In operation, photosensor 215a receives light from LED 1 15a and produces a current value corresponding to the peak wavelength of light received from LED 1 15a. Current generated by photosensor 215a is delivered to current to voltage amplifier 210a, which provides an analog voltage representation of the photosensor current to analog to digital converter (ADC) 205a. ADC 205a then converts the analog voltage representation of the photosensor current into a digital representation of the current value produced by photosensor 201a and provides the digital representation to processor 45 via the SPI bus. Processor 45 then uses a current-wavelength curve for photosensor 215a to convert the digital representation of the current value produced by photosensor 215a into the value of the peak wavelength of light generated by LED 1 15a and received by photosensor 215a. The value for the peak wavelength of light received by photosensor 215a from LED 1 15a is then stored in memory of processor 45 and provided to user via display 25.

[0058] In some embodiments of photosensor circuit 200, keypad 30 and display 25 are used to input current -wavelength curve for each photosensor 215, which is then stored in memory 50. In some embodiments, the current-wavelength curve can be in the form of a plurality of discrete points, and a linear fitting algorithm is used to obtain values located between two discrete points. In other embodiments, the current -wavelength curve can be in the form of an equation.

[0059] Turning to other embodiments of photosensor circuit 200 shown in FIGS. 6b, 7b, and 8b, it can be seen that some embodiments of photosensor circuit 200 employ at least one multiplexer (MUX) 220, with each MUX 220 having at least one photosensor channel 201. In FIG. 6b, each photosensor channel 201 is comprised of ADC 205, current to voltage amplifier 210, and photosensor 215. Further, in FIG. 7b, each photosensor channel 201 is comprised of a current to voltage amplifier 210 and a photosensor 215. Additionally, in FIG. 8b, each photosensor channel 201 is comprised of a photosensor 215. As can be seen, in some embodiments of photosensor circuit 200, such as the one shown in FIG. 6b, an ADC 205 is present in every photosensor channel 201 between MUX 220 and current to voltage amplifier 210.

[0060] Further, in other embodiments of photosensor circuit 200, such as the one shown in FIG. 7b, only one ADC 205 is present in photosensor circuit 200 for converting all photosensor channels 201 and is located on the SPI bus between MUX 220 and processor 45. It is understood that when only one ADC 205 is present in photosensor circuit 200, ADC 205 receives, converts, and provides the output of each photosensor channel 201 to processor 45.

[0061] Additionally, in other embodiments of photosensor circuit 200, such as the one shown in FIG. 8b, only one ADC 205 and current to voltage amplifier 210 are present in photosensor circuit 200 for converting all photosensor channels 201. In these embodiments, ADC 205 is located between processor 45 and current to voltage amplifier 210. Further, current to voltage amplifier 210 is located between ADC 205 and MUX 220. It is understood that when only one ADC 205 and current to voltage amplifier 210 is present in photosensor circuit 200, ADC 205 and current to voltage amplifier 210 receives, converts, and provides the output of each photosensor channel 201 to processor 45.

[0062] FIG. 10a shows one embodiment of a method of calibrating each LED 1 15 at measurement locations 65 of water analyzer 10. In step 301 , a plurality of LEDs 1 15 are provided and a wavelength-current relation curve is obtained for each LED 1 15 using a commercial spectrometer. In one embodiment, the wavelength-current relation curve is a plurality of discrete points ranging from 1 -25mA, having a frequency of one point every milliamp. An exemplary wavelength-current relation curve for an LED is shown in FIG. 9.

[0063] In step 305, a water analyzer 10 is provided having a processor 45, memory 50 for processor 45, and a plurality of measurement locations 65. Each measurement location has an LED 1 15 and a photosensor 215. Processor 45 is capable of independently controlling the forward current delivered to each LED 1 15 of measurement locations 65. [0064] In step 310, an LED 1 15 is installed at each measurement location 65 of water analyzer 10.

[0065] In step 320, the wavelength-current relation curve for each LED 1 15 at each measurement location 65 of water analyzer 10 is stored in memory 50 of processor 45 of water analyzer 10.

[0066] The target peak wavelength for the LEDs installed in reader 10 is determined in step 320. In one embodiment, the target peak wavelength is the mean peak wavelength of the LEDs 1 15 installed in water analyzer 10 when the plurality of LEDs 1 15 are provided with a uniform current. In one embodiment, the uniform current is 15mA, however it is contemplated that a person having ordinary skill in the art can choose to use another uniform current value.

[0067] In one embodiment, processor 45 determines the target peak wavelength using the wavelength-current relation curves for LEDs 1 15 stored in memory 50 in step 315. Processor 45 determines the target peak wavelength by calculating the mean peak wavelength of the installed LEDs for a uniform forward current value on each LED wavelength-current relation curve. In one embodiment, the uniform forward current value is 15mA, however it is contemplated that a person having ordinary skill in the art can choose to use another uniform forward current value.

[0068] Processor 45 controls the forward current provided to each LED 1 15. Further, the forward current value is independently adjustable for LED 1 15 at each measurement location 65.

[0069] In step 325, the target forward current for LED 1 15 at each measurement location 65 is calculated by processor 45 using the target peak wavelength and the wavelength-current relation curve for each LED. Processor 45 uses a linear fitting algorithm when the target peak wavelength is located between two discrete points on a wavelength-current relation curve. Since linear fitting is an approximation, in some embodiments, the target forward current calculated by processor 45 results in LED 1 1 5 outputting a wavelength that is within about l nm of the target peak wavelength. In other embodiments, the target forward current calculated by processor 45 results in LED 1 15 outputting a wavelength that is within about 0.5nm of the target peak wavelength. Further, in additional embodiments, the target forward current calculated by processor 45 results in LED 1 15 outputting a wavelength that is about equal to the target peak wavelength.

[0070] The operations taking place within processor 45 during steps 315 -325 are shown in FIGS. 10b- 10c.

[0071] In step 330, processor 45 provides a current value equivalent to the target forward current to LED 1 15 at each measurement location 65 when measuring an absorbance of a sample in testing card 55 placed in testing area 60 of water analyzer 10.

[0072] Turning to FIGS. 9b-9c, in step 315a counter variable "c" is set to 1 , constant "n" is set equal to the number of measurement locations 65 in water analyzer 10, and constant "fc" is set equal to the uniform forward current of choice. In this embodiment, fc is set equal to 15 milliamps.

[0073] In step 315b, the user is prompted via display 25 to enter the wavelength- current relation curve for LED 1 15 at measurement location "c". In step 315c, the user entered wavelength-current relation curve for LED 1 15 at measurement location "c" is stored in memory 50. In step 315d, if c is less than n, the program will proceed to step 315e, else the program will proceed to step 315f. In step 315e, c is incremented by 1 and the program proceeds back to step 315b. As can be seen, steps 315b-e are repeated until the wavelength-current relation curves for LED 1 15 at each measurement location 65 are entered into memory 50. Once all of the wavelength-current relation curves are entered into memory 50, c is reset to 1 in step 315f and the program proceeds to step 320a.

[0074] In step 320a, the peak wavelength for LED 1 15 at measurement location "c" is calculated for a forward current equivalent to "fc" and stored in memory 50. In step 320b, if c is less than n, the program will proceed to step 320c, else the program will proceed to step 320d. In step 320c, c is incremented by 1 and the program proceeds back to step 320a. As can be seen, steps 320a-c are repeated until the peak wavelength for LED 1 15 at each measurement location 65 is calculated and stored in memory 50.

[0075] In step 320d, processor 45 calculates the mean value of the peak wavelengths calculated in the iterations of steps 320a-c and stores the mean value in memory 50 as the target peak wavelength. In step 325a, c is reset to 1 and the program proceeds to step 325b in which the target forward current is calculated for LED 1 15 at measurement location "c" and stored in memory 50. Processor 45 calculates the target forward current using the target peak wavelength and wavelength-current relation curve of LED 1 15 at measurement location c. Processor 45 performs this calculation by ascertaining the current value on the wavelength-current relation curve for LED 1 15 at measurement location c that corresponds to the target peak wavelength and saves the calculated forward current value as the target forward current value for LED 1 15 at measurement location c. If the target peak wavelength is located between two of said discrete points on the wavelength-current relation curve, a linear fitting algorithm is used to ascertain the target forward current value for LED 1 15 at measurement location c.

[0076] In step 325c, if c is less than n, the program will proceed to step 325d, else the program will proceed to step 325e. In step 325d, c is incremented by 1 and the program proceeds back to step 325b. As can be seen, steps 325b -d are repeated until the individual target forward current vales for LED 1 15 at each measurement location 65 are calculated and stored in memory 50.

[0077] In step 325e, the user is informed via display that calibration of LED 1 15 at each measurement location 65 has been completed.

[0078] FIG. 1 1 shows another embodiment of a method of calibrating each LED 1 15 at measurement locations 65 of water analyzer 10. In step 401 , a first water analyzer 10 and a second water analyzer 10 are provided. Each water analyzer 10 has a testing area 60 with a plurality of measurement locations 65. Measurement locations 65 are arranged in the same pattern as the sample areas 56 on testing card 56. Additionally, measurement locations 65 have an LED 1 15 and a photosensor 215. Further, each water analyzer 10 has a processor 45 with memory 50.

[0079] In step 405, a standard card 70 is provided and inserted into the testing area of first water analyzer 10. In step 410, the absorbance at each measurement location 65 of the first water analyzer 10 is measured and displayed to the user via display 25. These absorbance measurements in step 410 are recorded and designated as the standard absorbance measurement values for each respective measurement location 65. In some embodiments, a uniform forward current value is provided to LED 1 15 at each measurement location 65 of first water analyzer 10. In one embodiment, the uniform forward current value is 15mA, however it is contemplated that a person having ordinary skill in the art can select a different uniform forward current value. [0080] In step 415, standard card 70 is inserted into testing area 60 of the second water analyzer 10. In step 420, the absorbance at each measurement location 65 of the first water analyzer 10 is measured and displayed to the user via display 25.

[0081] In step 425, the displayed absorbance measurement values for each measurement location 65 of the second water analyzer 10 are compared with the corresponding standard absorbance measurement values to see if the corresponding absorbance measurement values compare favorably. In one embodiment, an absorbance measurement value for a measurement location 65 of second water analyzer 10 compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for a measurement location 65 of second water analyzer 10 is within about lnm of the corresponding standard absorbance measurement value. In another embodiment, an absorbance measurement value for a measurement location 65 of second water analyzer 10 compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for a measurement location 65 of second water analyzer 10 is within about 0.5nm of the corresponding standard absorbance measurement value. In a further embodiment, an absorbance measurement value for a measurement location 65 of second water analyzer 10 compares favorably with the corresponding standard absorbance measurement value when the absorbance measurement value for a measurement location 65 of second water analyzer 10 is about equal to the corresponding standard absorbance measurement value.

[0082] In step 430, the forward current value of LED 1 15 at each measurement location 65 having a absorbance measurement value that does not compare favorably with the corresponding standard absorbance value is adjusted until the absorbance measurement value of each measurement location 65 of the second water analyzer 10 compares favorably with the corresponding standard absorbance value. Since the forward current value provided to each measurement location 65 of second water analyzer 10 is individually adjustable, it is contemplated that processor 45 is capable of delivering and memory 50 is capable of storing a different forward current value to LED 1 15 at each measurement location 65. In step 435, the forward current values for LED 1 15 at each measurement location are stored in memory 50 as target forward current values. [0083] As can be seen in steps 425-435, target forward current values are ascertained for LED 1 15 at each measurement location 65 and stored in memory 50. A target forward current value for LED 1 15 at a measurement location 65 is a forward current value for the measurement location 65 that results in an absorbance measurement value of standard card 70 that compares favorably with the corresponding standard absorbance value for the measurement location 65 of first water analyzer 10.

[0084] In step 440, processor 45 provides LEDs 1 15 at measurement locations 65 of the second water analyzer 10 with current values equivalent to the stored target forward current values stored in memory 50 of second water analyzer 10 when measuring an absorbance of a sample in testing card 55 located in testing area 60 of second water analyzer 10.

[0085] While this invention has been described in conjunction with the specific embodiments described above, it is evident that many alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the preferred embodiments of this invention, as set forth above are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of this invention. Therefore, the scope of the present invention is defined by the appended claims, and all devices, processes, and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.

[0086] WHAT IS CLAIMED IS:

Claims

A method of calibrating water analyzer light emitting diodes (LEDs) comprising: providing a plurality of LED and obtaining a wavelength-current relation curve for each LED using a commercial spectrometer; providing a water analyzer having a processor with memory, and a plurality of measurement locations; installing one of said LEDs in each of said measurement locations of said water analyzer, wherein the forward current value is individually adjustable for said LED at each of said measurement locations; storing said wavelength-current relation curves for said LEDs in said water analyzer memory; determining a target peak wavelength for said plurality of LEDs; calculating a target forward current value for said LED of each measurement location using said target peak wavelength and said wavelength-current relation curve for said LEDs; and storing said target forward current values for said LEDs in said memory.

The method of claim 1 , wherein said wavelength-current relation curve is comprised of a plurality of discrete points.

The method of claim 2, wherein said wavelength -current relation curve has one discrete point for every milliamp between 1 and 25 milliamps.

4. The method of claim 1 , wherein said target peak wavelength is the mean peak wavelength of said plurality of LEDs when said plurality of LEDs are provided with a uniform forward current.

5. The method of claim 4, wherein said uniform forward current is 15mA.

6. The method of claim 1 , wherein said target forward current for each of said LEDs corresponds to a wavelength on said wavelength-current relation curve for said LED that is within about lnm of said target peak wavelength.

7. The method of claim 1 , wherein said target forward current for each of said LEDs corresponds to a wavelength on said wavelength-current relation curve for said LED that is within about 0.5nm of said target peak wavelength.

8. The method of claim 1 , wherein said target forward current for each of said LEDs corresponds to a wavelength on said wavelength-current relation curve for said LED that is about equal to said target peak wavelength.

9. The method of claim 1 , wherein said target forward current for each of said LEDs is calculated using a linear fitting algorithm when said target peak wavelength is located between two of said discrete points on said wavelength-current relation curve for said LED.

10. The method of claim 1 further comprising retrieving said target forward currents for each of said LEDs from said memory and providing said target forward currents to each of said LEDs when measuring an absorbance of a sample in said water analyzer.

1 1. A method of calibrating water analyzer light emitting diodes (LEDs) comprising: providing a first and a second water analyzer, wherein each of said water analyzers are comprised of a processor having memory, a display that interfaces with said processor, and a testing area; wherein said testing area is comprised of a plurality of measurement locations; wherein each measurement location is comprised of an LED and a photosensor that interface with said processor; wherein said LED of each of said measurement locations is provided with an individually adjustable forward current by said processor; providing a standard card and inserting said standard card into said testing area of said first water analyzer; measuring and displaying an absorbance of the standard card at each of said measurement locations of said first water analyzer, and designating said absorbances as standard absorbance measurement values for said measurement locations; inserting said standard card into said testing area of said second water analyzer; measuring and displaying an absorbance value of said standard card at each measurement location of said second water analyzer; comparing the displayed absorbance measurement values at each measurement location of said second water analyzer with said standard measurement values for each corresponding measurement location of said first water analyzer; individually adjusting said forward current value of said LED at each measurement location of said second water analyzer having an absorbance measurement value that does not compare favorably with said corresponding standard absorbance measurement value, wherein said forward current values are individually adjusted until said absorbance measurement value at each measurement location of said second water analyzer compares favorably with said corresponding standard absorbance measurement values; and storing said forward current value of said LED at each measurement location of said second water analyzer in memory as target forward current values.

12. The method of claim 1 1, wherein said standard absorbance values are obtained while providing a uniform current to said LED at each of said measurement locations of said first reader.

13. The method of claim 12, wherein said uniform current is 15mA.

14. The method of claim 1 1 , wherein an absorbance measurement value for one of said measurement locations of said second water analyzer compares favorably with said corresponding standard absorbance measurement value when said absorbance measurement value for said measurement location of said second water analyzer is within about lnm of said corresponding standard absorbance measurement value.

15. The method of claim 1 1 , wherein an absorbance measurement value for one of said measurement locations of said second water analyzer compares favorably with said corresponding standard absorbance measurement value when said absorbance measurement value for said measurement location of said second water analyzer is within about 0.5nm of said corresponding standard absorbance measurement value.

16. The method of claim 1 1 , wherein an absorbance measurement value for one of said measurement locations of said second water analyzer compares favorably with said corresponding standard absorbance measurement value when said absorbance measurement value for said measurement location of said second water analyzer is about equal to said corresponding standard absorbance measurement value.

17. The method of claim 1 1 , wherein said second water analyzer is further comprised of a keypad, wherein said forward current values of said second water analyzer are adjusted using said keypad.

18. The method of claim 1 1, wherein said method further comprises providing said LED at each of said measurement locations of said second water analyzer with forward current values equivalent to said stored target forward current values when measuring an absorbance of a sample in a testing card inserted into said testing area of said second water analyzer.

19. A water analyzer comprised of a processor having memory, a light emitting diode (LED) circuit, and a photosensor circuit; wherein said processor control said LED and photosensor circuits; wherein said LED circuit is comprised of a plurality of LEDs, each LED having a forward current independently controllable by said processor.

20. Said water analyzer of claim 19, wherein said LED circuit is further comprised of a digital to analog converter and a voltage to current amplifier; wherein said photosensor circuit is further comprised of an analog to digital converter and a current to voltage amplifier; wherein said processor is configured to calculate a target forward current value for said LED of each measurement location using a target peak wavelength and a wavelength-current relation curve for said LEDs.