Abstract:
The method and apparatus as shown in the present invention is to measure the absorption of light by material contained in a liquid. A transmitted signal is sent through a measurement window to a measurement chamber to a target point just inside the measurement window. The reflected signal indicates the amount of light absorbed by a material in the measurement chamber which allows for the amount of materials in a liquid to be determined. Adjustments are made through an optical block and a light control molecule to correct for variations in light intensity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is an improvement over U.S. Pat. No. 7,935,938, issued on May 3, 2011, entitled “Apparatus for Measuring Fluorescent Material in a Liquid,” which patent is hereby incorporated by reference, and a continuation-in-part of U.S. patent application Ser. No. 14/812,026, filed on Jul. 29, 2015. 
     
    
     BACKGROUND OF THE NVENTION 
       [0002]    Technical Field 
         [0003]    This invention relates to an apparatus for measuring fluorescent material in a liquid and, more particularly, to measuring material in a liquid through the absorption of light. 
         [0004]    Description of the Prior Art 
         [0005]    With the world&#39;s dependency on oil, more oil is being processed in oil refineries and shipped by pipelines than ever before. Many of the pipes (a) leading from/to oil production or (b) within refining operations require measuring the amount of oil that may be in a liquid (mainly water) flowing in the pipes. To aid in this process, in-line measuring apparatuses are commonly used to measure the amount of oil that is present in the pipe. 
         [0006]    When subject to certain lights, oil has a natural fluorescence. The common way of determining the amount of oil presence is to measure the amount of fluorescence that can be processed. The measuring of the amount of oil present is commonly done by a fluorometer. A typical in-line fluorometer has an excitation light source which transmits the light onto the sample to a measurement region through a measurement window. When the oil in sample absorbs the light, it fluoresces. The resultant fluorescence light is transmitted back through the measurement window and is received by the fluorescence detector. By measuring the amount of fluorescent light, the amount of oil present in the water can be determined However, in the prior systems, the measurement was accurate only up to a certain concentration of oil in water. The incorporated reference would only detect oil in water up to approximately 1,000 parts per million (hereinafter “ppm”) before measurements started losing accuracy. 
         [0007]    Applicant has discovered modifications that can be made to the incorporated reference to greatly improve the accuracy of measurements of oil-in-water in ppm at higher concentrations, which significantly increases accuracy of measurements from 1,000 ppm to 100,000 ppm (10%) of oil in water. 
         [0008]    Further, Applicant has discovered that a very similar apparatus may be used to measure other materials in a liquid through an absorption of light technique. The absorption of light technique requires a light source plus continual adjustments to mitigate any inaccuracies of changes in the light source output. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to extend the range of measurements of the incorporated reference to higher ppm of oil in water. 
         [0010]    It is another object of the present invention to modify the incorporated reference to use a single channel through which an excitation signal is transmitted and a fluorescent signal is received from a measurement chamber. 
         [0011]    It is yet another object of the present invention to utilize an optical fiber for (1) transmitting the excitation signal and (2) receiving the fluorescent signal from the oil in water to determine in ppm a concentration of oil therein. 
         [0012]    It is a further object of the present invention to modify the incorporated reference to use a laser as an excitation signal and spectrometer as a detector of the fluorescent signal. 
         [0013]    It is yet another object of the present invention to modify the incorporated reference so that the target point for the fluorescent is close to the inner face of the measurement window. 
         [0014]    It is yet another object of the present invention to modify the incorporated reference wherein the transmitted signal and the fluorescent signal are arranged such that the line of sight of the excitation signal and a fluorescent signal lie in a common plane which is not perpendicular with the inner surface of the measurement window. 
         [0015]    It is still another object of the present invention wherein the line of sight of the excitation signal is at an obtuse angle with the line sight to the fluorescent signal. 
         [0016]    It is another object of the present invention to have a measurement chamber with a measurement window with a single channel through which an excitation signal is transmitted and a fluorescent signal is detected using bifurcated fiber optics and an ultrasonic transducer for keeping the measurement window clean. 
         [0017]    It is another object of the present invention to modify the incorporated reference so that lines of sight of (1) an excitation signal and (2) another light guide intersect in a measurement chamber to define a target region from which fluorescent light may be detected, said target region being located within the measurement chamber substantially at the inner face. 
         [0018]    In the continuation-in-part application, it is another object of the present invention to provide a method and apparatus for measurement of material in a liquid through absorption of light. 
         [0019]    In the continuation-in-part application, it is further object of the invention to provide a light source of a constant intensity. 
         [0020]    In the continuation-in-part application, it is also an object of the present invention to mitigate any inaccuracies as a result of a change in intensity of the light output. 
         [0021]    In the continuation-in-part application, it is yet another object of the present invention to provide a stable sample measurement, irrespective of variations in light source output. 
         [0022]    The apparatus and method for measuring material in a liquid through use of an absorption technique is shown in the continuation-in-part application. The apparatus comprises a measurement chamber containing a liquid to be analyzed, a light source to transmit the light at a defined target region of the measurement chamber, the absorbed light from the target region being measured by a detector to determine the concentration of material within the measurement chamber, the angle between the transmitted light and the absorbed light being very small. The apparatus includes an optical block comprising beam splitters and an optical attenuator. A software module mitigates any inaccuracies as a result of a change in intensity of the light output from the emission source. The optical attenuator is adjusted to increase or decrease the light intensity to a level similar to that received from the target region. The software module controls light stability, which software module uses a mathematical model to compensate for deviations in sample measurements due to variations in optical system components and the environment. This results in a stable sample measurement, irrespective of light source output. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic view of an apparatus embodying the present invention. 
           [0024]      FIG. 2  is a pictorial view of a measurement chamber from the apparatus as shown in  FIG. 1 . 
           [0025]      FIG. 3  is a schematic view of a preferred spatial relationship between a transmitted excitation light and a received fluorescent signal from the apparatus shown in FIG. 
           [0026]      1 . 
           [0027]      FIG. 4( a )  is measurements of fluorescent materials at different ppm in the incorporated reference of U.S. Pat. No. 7,935,938. 
           [0028]      FIG. 4( b )  is measurements of the fluorescent material at different ppm in a system incorporating the current improvements over the incorporated reference. 
           [0029]      FIG. 5  is a modified schematic from  FIG. 1  further illustrating changes from the incorporated reference. 
           [0030]      FIG. 6  is a schematic view of an apparatus for measurement of material in a liquid through absorption of light. 
           [0031]      FIG. 7  is a pictorial view of a measurement chamber to be used with the apparatus shown in  FIG. 6 . 
           [0032]      FIG. 8  is an enlarged pictorial view of the optical block shown in  FIG. 6 . 
           [0033]      FIG. 9  is a graft of light intensity versus wavelength showing the spectral output of a dual path system. 
           [0034]      FIG. 10  is a flow chart illustrating the operational logic of the light control module in  FIG. 6 . 
           [0035]      FIGS. 11A-11D  are illustrative diagrams comparing light intensity to wavelength with various samples. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]    Having previously incorporated by reference U.S. Pat. No. 7,935,938, over which the present invention is an improvement, all reference numerals given herein below will start with the number  110  or higher so that none of the reference numerals will conflict with the reference numerals of the incorporated reference. 
         [0037]    Referring to  FIG. 1  of the present invention, a measurement chamber  110  is shown with water flowing there through. A measurement window  112  is provided on one side of the measurement chamber  110 . In contact with the measurement window  112  is a coupling mass  114 , with piezoelectric transducers  116  being located in the coupling mass  114  but away from the measurement window  112 . 
         [0038]    Connecting through the coupling mass  114  to the measurement window  112  is a single channel  118 . Through the single channel  118 , an excitation signal  122  is transmitted and fluorescent light  120  is collected or received using the light guides  123  and  125 , respectively. The excitation signal  122  can be lasers, light emitting diodes or lamps  126 . What is required is that the excitation signal  122  cause oil particles contained in the water flow to fluoresce so that the fluorescent light  120  can be detected by fluorescent detector  124 . The excitation signal  122  is provided by an excitation source  126 . The piezoelectric transducers  116  are energized by ultrasonic power supply  128 . 
         [0039]    The apparatus as shown in  FIG. 1  has a master circuit board  130 . While the composition and configuration of the circuitry may vary, an illustrated example of the circuitry includes an ultrasonic power supply control  132  for the ultrasonic power supply  128 . A signal processing/conditioning unit  134  prepares a signal for the excitation source  126  (i.e., lasers/LEDs/lamps) and conditions the fluorescent light signal received from the fluorescent detector  124 . 
         [0040]    An interface unit  136  provides interfacing between the signal processing/conditioning unit  134 , ultrasonic power supply control  132  and the computer  138 . The computer  138  will have an internal display module, plus the computer  138  can either (1) connect to an RS232 connector or (2) to the Ethernet. The computer  138  will be appropriately programmed to operate the apparatus shown in  FIG. 1 . The computer  138  may be at the site with the rest of the apparatus shown in  FIG. 1 , or remotely located. 
         [0041]    A power supply conditioning unit  140  is provided to operate the circuitry shown in  FIG. 1 . 
         [0042]    Fluid flow through the measurement chamber  110  may be controlled by valve control interface  142 , which controls operation of valve  144  or valve  146 . Valve  144  may be located at one end of the measurement chamber  110 , and valve  146  may be located at the opposite end thereof so that a liquid sample may be captured within measurement chamber  110  if desired. 
         [0043]    Referring now to  FIG. 2 , a water sample  148  is shown, which water sample  148  could be inside of measurement chamber  110 . A measurement window  112  is provided through which access is obtained to the water sample  148 . The excitation signal  122  is transmitted through the measurement window  112  to a target point  150 , which target point  150  is just inside the measurement window  112 . Any oil contained in the water sample  148  at target point  150  will create a fluorescent light  120  that is received back through the measurement window  112 . As can be seen in  FIG. 2 , the angle between the excitation signal  122  and the fluorescent light  120  is very small. The excitation signal  122  and the fluorescent light  120  are very close together and are within a narrow envelope  152 . 
         [0044]    Referring to  FIG. 3 , a further pictorial illustration of how the excitation signal  122  and the fluorescent light  120  are transmitted and received is illustrated. The single channel  118  (a) provides the excitation signal  122  and (b) receives the fluorescent light  120 . Inside of the single channel  118  are fiber optic ends  154  and  156 . The fiber optic ends  154  may be a single fiber optic that is split on the end thereof, are two separate strands of fiber optics contained in single channel  118 . In either event, the fiber optic ends  154  and  156  are in close proximity to each other. The angle at which the excitation signal  122  strikes the transmission window  112  is at a substantial angle to the perpendicular plane  158  of the transmission window  112 . Likewise, the angle at which the fluorescent light  120  is received from the target point  150  is also at a substantial angle with respect to the perpendicular plane  158 . 
         [0045]    Using the invention as shown in the incorporated reference, it is difficult to make measurements of oil-in-water for both conventional light and medium crude oils if the ppm&#39;s exceed the 1,000 ppm range. This is demonstrated in  FIG. 4A  attached hereto where measurements are made of a crude oil for parts per million (ppm) varying from 0 to 5,000. As can be seen in  FIG. 4A  if the ppms exceed 1,000, the relationship becomes non-linear and concentration quenching occurs between concentrations 1,000 ppm and 5,000 ppm.  FIG. 4A  gives the light intensity plotted versus the wavelength for a crude oil at varying ppms. The light intensity plotted versus ppm is shown in the upper right plot. 
         [0046]    Modifying the prior invention incorporated by reference to utilize the features shown herein for crude oil is again run, but at higher ppm&#39;s range of 0 to 100,000 (see  FIG. 4B ). As can be seen in the upper right chart of  FIG. 4B , the light intensity continues as a linear function of the ppms up to approximately 100,000 ppm. This illustrates how the incorporated invention once modified as illustrated herein increases the sensitivity of the incorporated reference at higher ppm′ of light-to-medium weight crude oil. 
         [0047]    Different oils were examined and the results obtained were similar to the discussed results. 
         [0048]    Referring to  FIG. 5 , the apparatus as shown in  FIG. 1  is given in further detail with the single channel  118  being illustrated in an enlarged view. In this embodiment as shown in  FIG. 5 , the excitation source  112  of lasers has a laser drive  160 . 
         [0049]    A single cable  162  connects to the ultrasonic transducer  164 , which then has a single channel  118  pointing at the target point  150  through the measurement window  112 . 
         [0050]    Inside of the single channel  118  are the fiber optic ends  154  and  156 . The fiber optic ends  154  and  156  may be a single fiber optic split on each end thereof, or two separate fiber optic strands. In either event, fiber optic ends  154  and  156  are located adjacent to each other. Therefore, the angle between the excitation signal  122  and the fluorescent light  120  is very small; however, that angle is enlarged in  FIG. 5  for purposes of illustration. 
         [0051]      FIGS. 6-10  are added in the continuation-in-part patent application. To avoid confusion with U.S. Pat. No. 7,935,938 and U.S. patent application Ser. No. 14/812,026, filed on Jul. 19, 2015, the numerals applied to  FIGS. 6 through 10  will start with the number  200  or higher. 
         [0052]    Referring to  FIG. 6 , a measurement chamber  200  is shown. Water flows through the measurement chamber  200  in the direction indicated by the arrows. The measurement chamber  200  has a measurement window  202  in one side thereof. Coupled to the measurement window  202  is a coupling mass  204  with piezoelectric transducers  206  located on one end of the coupling mass  204 . A single channel  208  extends through coupling mass  204  to the measurement window  202 . The single channel  208  has (a) a transmitting fiber optic end for delivering a transmitted signal  210  to a target point  212  and (b) a receiving fiber optic end adjacent thereto for receiving absorbed light  214  from target point  212 . 
         [0053]    A light source  216  transmits light through an optical block  218  to give a transmitted signal  210  through the single channel  208  to the target point  212 . Part of the transmitted signal  210  (i.e., light) is absorbed by material at the target point  212 . The absorbed light is reflected to give the amount of absorbed light  214 . 
         [0054]    The transmitted signal  210  is created by any suitable type of excitation light signal that can be generated by lasers, light emitting diodes or lamps as may be contained in the light source  216 . 
         [0055]    The transmitted signal  210  from the light source  216  is transmitted through the measurement window  202  onto the material in the liquid to be measured at target point  212 . A part of a transmitted signal  210  is absorbed into some organic molecules present in the material at specific wavelengths and the absorbed light is detected. The transmitted signal  210  has a broader wavelength wherein the organic molecules are detected directly by measuring changes in absorption at a defined target point  212  using a detector such as PTM/Spectrometer  220  measuring at the absorption wavelengths. The target point  212  shown in  FIG. 6  is close to the inside face of a measurement window  202  wherein the angle of measurement of the detector  220  is obtuse. The path link of the transmitted signal  210  and absorbed light  214  through the sample to the target point  212  is fixed. 
         [0056]    A master control board  222  is provided in the invention illustrated in  FIG. 6 . The master control board  222  has signal processing/conditioning  224  which has as a subpart thereof a light control module  226 . The light control module  226  is used to compensate for deviations in the transmitted signal  210 , which are deviations in the light beam from the light source  216 . The signal processing/conditioning unit  224  prepares a signal for the light source  216  and conditions the signal received by detector  220  from the absorbed light  214  via the signal channel  208  from the target point  212 . 
         [0057]    The DAC and PC interface board  228  provides interfacing between the signal processing conditioning unit  224 , the ultrasonic power supply unit  230  and the PC and display module  232 . The PC and display module  232  has an internal display module plus a computer that can either (1) connect to an RS 232 connector or (2) to the Ethernet. The computer within the PC and display module  232  will be appropriately programmed to operate the apparatus shown in  FIG. 6 . The PC and display module  232  may be on location at the site or remotely located. 
         [0058]    A main supply conditioning  234  is used to condition power used to operate the master control board  222 . 
         [0059]    Flow through the measurement chamber  200  is controlled by valve control interface  236  which operates inlet valve  238  or outlet valve  240  to control flow through measurement chamber  200 . By closing both the inlet valve  238  and the outlet valve  240 , a liquid sample may be captured with the measurement chamber  200 . 
         [0060]    Referring now to  FIGS. 6 and 8  in combination, the internal workings of the optical block  218  will be explained in more detail. Light  251  from the light source  216  travels through the beam splitters  242  and  244 . Colminators  246 ,  248 ,  250  and  252  refocus the light into a beam. 
         [0061]    The light source  216  provides light  251  through a colminator  252  to the beam splitter  242 . From the beam splitter  242 , a portion of the light flows through colminator  246  to provide the transmitted signal  210 . The absorbed light  214  is received through colminator  248  before it hits beam splitter  244 . Also transmitted through beam splitter  294  is light  249  that is reflected by beam splitter  242 . Both light  249  and absorbed light  214  give recombined light beam  256  which travels through a colminator  250  to the detector  220  (PTM/Spectrometer). 
         [0062]    Contained within the optical block  218  is a variable optical attenuator  254  to avoid saturation of detector (PMT/Spectrometer)  220 . 
         [0063]    Light  251  from the light source  216  is first colminated in colminator  252  and then sent through beam splitter  242  to divide into two beams. Beam splitter  242  is a long pass dichroic mirror which is highly reflective below the cut-off wavelength and highly transmitted above the cut-off wavelength, whereby the transmitted light is split at a cut-off wavelength such that wavelengths above the cut-off wavelength are transmitted into the measurement chamber  200 , but wavelengths below the cut-off wavelength are reflective to the second beam splitter  244 . The single channel  208  (see  FIG. 6 ) is used both for the transmitted signal  210  and the absorbed light signal  214 . The signal channel  208  is a bifurcated optical filter in a custom bifurcated assembly with blue silicone covered steel Monocoil with two optical legs. One leg is arranged to deliver the transmitted signal  210  from the light source  216  into the measurement chamber  200  and the other leg being arranged to carry absorbed light  214  from the measurement chamber  200  to the detector  220 . 
         [0064]    The secondary beam splitter  244  as shown in  FIG. 8  is a short pass dichroic mirror, which is highly reflective above the cut-off wavelength and highly transmitted below. The secondary beam splitter  244  is used to (1) reflect the absorbed light signal  214  being received from the measurement chamber  200  and (2) transmit there through the light  249  reflected by beam splitter  242  with the two light beams being recombined light beams  256  that are passed to the detector  220 . Detector  220  upon receiving the recombined light beams  256  produces a single spectral output as shown in  FIG. 9  with the part below the cut-off wavelength being area  258  and the part above the cut-off wavelength being area  260 . Variable optical attenuator  254  within the optical block  218  attenuates the light of the recombined light beams  256  to avoid saturation of the detector  220 . 
         [0065]    The light control module  226  shown in  FIG. 6  is programmed to control the deviation from a base light intensity as a result of a change in light output from the light source  216 . The light control module  226  is used in conjunction with the optical block  218  to compensate for deviations in sample measurements due to variations in the optical system components and the environment on a real-time basis. This counteracts variations in output of the light source  216  while matching the principles of traditional absorption measurements. The net result is a stable sample measurement irrespective of the intensity of the light source  216 . 
         [0066]      FIG. 10  shows a flow chart illustrating the operation of the light control module  226 . The light control module  226  determines the value of a sample in a way that counteracts variants in the output of the light source  216 . 
         [0067]    During calibration, a water sample will be placed in the measurement chamber  200 . A blank sample ratio (SR OPPM ) will be set equal to a current sample ratio (SR current ). From this point onward, the light control module will carry out the steps shown in  FIG. 10 . 
         [0068]    Light is generated from the light source  216  at a cut-off wavelength to obtain an absorption response from a water sample within the target point  212  of the measurement chamber  200  to detect light intensities (LI) being received from the secondary and primary optical paths by means of detector  220  to generate a single spectral output as shown in  FIG. 9  with two distinguishable areas for the water sample. This first step is to obtain a reading from the detector  262 . The second step is to calculate base LI and sample LI  264 . This is determined by summing the light intensities between the wavelength mask limits and dividing by the range of each wavelength mask. The wavelength mask is the range of wavelengths used to determined light intensity values from the acquired spectrum.  FIG. 9  shows a spectral output of a recombined light from the optical path, the area below the cut-off wavelength  258  is between 525 and 537.5 nanometers and the area above the cut-off wavelength  260  is between 562.5 and 575 nanometers. 
         [0069]    The third step is to calculate current sample ratio (SR current )  266 . This is done by dividing LI (area above cut-off wavelength  260 ) for different known concentrations of material in a liquid from measurement chamber by the base LI (area below the cut-off wavelength  258 ) from the primary optical path (see  FIG. 10 ). 
         [0000]    
       
         
           
             
               S 
                
               
                   
               
                
               
                 R 
                 current 
               
             
             = 
             
               
                 Sample 
                  
                 
                     
                 
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                 Light 
                  
                 
                     
                 
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                 Intensity 
               
               
                 Base 
                  
                 
                     
                 
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                 Light 
                  
                 
                     
                 
                  
                 Intensity 
               
             
           
         
       
     
         [0070]    In the next step, SR OPPM  is determined by dividing the sample LI (area above cut-off wavelength  260 ) for the blank sample from the measurement chamber  200  by the base LI (area below the cut-off wavelength  258 ) from the primary optical path. 
         [0000]    
       
         
           
             
               S 
                
               
                   
               
                
               
                 R 
                 OPPM 
               
             
             = 
             
               
                 Sample 
                  
                 
                     
                 
                  
                 Light 
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                 Intensity 
               
               
                 Base 
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                 Light 
                  
                 
                     
                 
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                 Intensity 
               
             
           
         
       
     
         [0000]    This step is known as store current sample ratio as zero PPM ratio  268 . 
         [0071]    The light control module  226  determines the SR OPPM , and is stored after which further blank sample readings can be taken and compared against the blank sample SR OPPM . If SR OPPM  is determined, the value stored in these steps can be skipped throughout the remainder of the standard operation. Otherwise, a determination is made of “Is zero PPM sample ratio (SR OPPM ) set”  270 ? If “no,” the cycle is repeated until a current sample ratio at zero PPM ratio  268  is determined. 
         [0072]    If the SR OPPM  is set, then calculate absorption  272  will occur by dividing SR OPPM  by SR current , which is generated for different known concentrations of material in a liquid. 
         [0000]    
       
         
           
             Absorbance 
             = 
             
               
                 Log 
                 10 
               
                
               
                 ( 
                 
                   
                     S 
                      
                     
                         
                     
                      
                     
                       R 
                       OPPM 
                     
                   
                   
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                       current 
                     
                   
                 
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         [0073]    If the output for the light source  216  drops by ten percent, both the base and sample light intensities can be expected to drop by ten percent. As absorption is based on the zero and current sample ratios, the respective ratios will remain constant, negating the effect of varying light output due to the LED fatigue of the light source  216 , changes in environment, or changes in operating temperature. 
         [0074]    The final step is to convert the absorption value (ABS) into a PPM value using a quadratic equation of order  3  by setting y-intercept to zero in the calculate PPM reading  274  step. 
         [0000]      Reading= a *ABS 3   +b *ABS 2   +c *ABS 
         [0075]    The reading value should be zero if the absorption is zero; however, a constant value is not always used. 
         [0076]    Illustrative examples of how the steps in the flow chart ( FIG. 10 ) illustrating the operational logic of the light control module are used to determine readings, and illustrate how the system behaves under different conditions. Any reference to spectrum charts, light intensity counts, wavelengths or any other figures are for demonstrational purposes. 
       EXAMPLE 1 
     Blank Sample 
       [0077]    The first example (Blank Sample), assumes that the system is measuring a blank sample, and the SR OPPM  value has been set at 1.0633. 
         [0078]    1. Spectrum is acquired 
         [0079]    2. Base and sample masks are calculated:
       Base LI: 21,000   Sample LI: 19,750       
 
         [0082]    3. Current Sample ratio is calculated:
       19750/21000=0.9405       
 
         [0084]    4. Absorbance is calculated:
       Log 10 (0.9405/0.9405)=0.00 absorbance       
 
       See FIG.  11 A. 
     EXAMPLE 2 
     Oil in Chamber 
       [0086]    The second example (Oil in Chamber) assumes that oil is placed into the measuring chamber, and that it absorbs a portion of the light intensity on the sample path. The chart below shows that the overall spectral intensity for the sample leg is reduced. Calculating the absorbance assuming that the SR OPPM  is still 1.0633 as mentioned in Example 1. 
         [0087]    1. Spectrum is acquired 
         [0088]    2. Base and sample masks are calculated:
       Base LI: 21,000   Sample LI: 14,000       
 
         [0091]    3. Current Sample ratio is calculated:
       14000/21000=0.6667       
 
         [0093]    4. Absorbance is calculated:
       Log 10 (0.9405/0.6667)=0.1494 absorbance       
 
       See FIG.  11 B. 
     EXAMPLE 3 
     Degraded Light 
       [0095]    Example 3 assumes that the same oil sample is present as for Example 2. However, the light output has decreased by ten percent. 
         [0096]    1. Spectrum is acquired 
         [0097]    2. Base and sample masks are calculated:
       Base LI: 18,900   Sample LI: 12,600       
 
         [0100]    3. Current Sample ratio is calculated:
       12600/18900=0.6667       
 
         [0102]    4. Absorbance is calculated:
       Log 10 (0.9405/0.6667)=0.1494 absorbance—identical to the reading in example 2       
 
       See FIG.  11 C. 
     EXAMPLE 4 
     Blank Sample 
       [0104]    Example 4 assumes that the measuring chamber contains a blank sample, similar to Example 1, with the light source remaining degraded. 
         [0105]    1. Spectrum is acquired 
         [0106]    2. Base and sample masks are calculated:
       Base LI: 18,900   Sample LI: 17,775       
 
         [0109]    3. Current Sample ratio is calculated:
       17775/18900=0.9405       
 
         [0111]    4. Absorbance is calculated:
       Log 10 (0.9405/0.9405)=0.000 absorbance—identical to the reading in example 1       
 
       See FIG.  11 D. 
       [0113]      FIG. 7  is a schematic view of measurements made at the target point  212 , which is just inside of the measurement window  202 . The transmitted signal  210  travels to the target point  212  and the absorbed light  214  is what is furnished to the detector  220 . Light source  216  is what provides the transmitted signal  210 .