CA1075033A - Sodium light intensity monitor - Google Patents
Sodium light intensity monitorInfo
- Publication number
- CA1075033A CA1075033A CA275,143A CA275143A CA1075033A CA 1075033 A CA1075033 A CA 1075033A CA 275143 A CA275143 A CA 275143A CA 1075033 A CA1075033 A CA 1075033A
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Abstract
Abstract of the Disclosure A method and apparatus are disclosed for measuring the amount of characteristic light produced by a process to be monitored. Light in a waveband characteristic of the process is measured. Light in nearby non-characteristic wavebands is also measured and used an in indication of the amount of background light in the characteristic waveband. The amount of background light is subtracted from the total amount of light in the characteristic waveband, and the result is a measurement of the intensity of light produced by the process. An example of the embodiment applies the invention to the measurement of sodium light produced by burning sodium.
Description
Background of the Invention In Nelson, United States Patent No. 3,870,467, it was : disclosed that the reduction efficiency of a chemical recovery furnace could be monitored by measuring the amount of sodium vapor produced in the process. The Nelson disclosure proposed to do this by measuring the intensity of radiation in the sodium band taround 5890 angstroms) characteristically produced by the sodium vapor that burns as it rises from the char bed.
Though burning sodium is a source of light in the sodium band, other sources of such light typically exist in a recovery furnace. The glow of the char bed and the intermittent flaring that occurs there both give off some light in the same waveband as the light produced by the burning sodium, so the total light in the sodium band is composed of light from several sources other than burning sodium. In more general terms, any , - time a process is monitored by measuring the amount of light occuring in a characteristic waveband, light from sources other than the process are likely to be included in the measurement.
A As a result, the monitoring of a process by merely measuring the - 20 amount of light emitted in a characteristic waveband can lack precision.
Summary of the Invention Accordingly, the present invention is a method and apparatus for producing a measurement of the characteristic light produced by a process. According to the invention, the general level of background light intensity is determined by measuring the light intensityin at least one waveband that is not identical to the characteristic waveband. This background-light intensity is substracted from the total light intensity in the characteristic waveband. The resultant quantity is the ~ -2-i: ' ~075033 intensity of only that part of a characteristic light that is produced by the process.
: In one broad aspect, the invention may be summarized as residing in a method of monitoring a process by measuring the intensity of light occurring in a waveband having wave-lengths characteristic of the process, the light including back-ground light not produced by the process, the improvement com-prising: measuring the intensity of light in at least one of a . plurality of reference wavebands, the intensities in combination 10 being representative of the intensity of the background light in the characteristic waveband; and subtracting a quantity proportional to a weighted average of the intensities of light measured in the reference wavebands from the intensity of light measured in the characteristic waveband, thereby producing an indication of the intensity of that portion of the light in the characteristic waveband that is produced by the process.
In another broad aspect, the invention may be summarized as residing in an apparatus for monitoring a process, which apparatus comprises means for producing an output indic-ative of the intensity of light occurring in a waveband havingwavelengths characteristic of the process, the light including background light not produced by the process, the improvement comprising: means for measuring the intensity of light in each of a plurality of reference wavebands so as to define a curve of .: intensity-wavelength ordered pairs, the intensities in combin-- ation being representative of the intensity of the background light of the characteristic waveband; and means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the -2a-`` 1075033 characteristic-waveband means and a quantity proportional to an intensity value occurring in the characteristic waveband on the curve defined by the intensity-wavelength ordered pairs derived from the outputs of the reference-waveband means. - -Brief Description of the Drawings These and further features and advantages of the invention become evident in the description of the embodiment -shown in the drawings attached, wherein:
-2b-.~
, . . .
; ` 1075033 Figure 1 is the side elevation view of a light-receiving apparatus used in the preferred embodiment of the present invention;
Figure 2 is a front elevation view of the same apparatus;
Figure 3 is a front elevation view of a rotating filter used with the preferred embodiment of the present invention;
Figure ~ is a side sectional view of a rotating-filter assembly;
Figure 5 is a graph of a typical output signal from the rotating-: - filter assembly; and Figure 6 is a block diagram of the signal processing circuitry for use with the preferred embodiment.
Detailed Descri~tion of the Preferred Embodiment Figure 1 is a side elevation view of the light-receiving apparatus used in Nelson. The apparatus has been slightly modified in order to adapt it to use in the preferred embodiment of the present invention. In Nelson, it was the intent to monitor the rate of the reduction reaction in a char bed by measuring the intensity of light characteristic of a related process, namely the burning of sodium. The light-receiving apparatus is one of a plurality aimed at the furnace in which the burning of sodium occurs. A
fiber-optic bundle 32, possibl~ capped with a lens 30 for concentrating 20 light on the bundle, is housed within compartment 34, ~hich is attached - to plate 26. Plate 26 supports slide 28, which holdstwo filters 36, as shown in Figure 2. Plate member 26 includes aperture 38 through which light shines on fiber-optic bundle 32. Slide 28 is arranged so tha~ one window 36 covers aperture 38 while the other window 36 is exposed for 25 cleaning. As can be seen in Figure 1, a tubular section 22 is attached to the front surface of plate 26, and light from the furnace passes through tubular section 22. Connection 24 on tubular section 22 admits purge gas into tubular section 22 in order to prevent blowback from the furnace, which could cause black liquor and ash to deposit on window 36.
30 Air, steam, or another relatively inert gas mignt typically be used for purging. Fiber-optic bundles 32 are led from the viewing assemblies to - a rotating filter assembly, a front vie~ of which is shown in Figure 3.
~ .
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Three filters, 44, 46 and 48 having different pass bands are unevenly spaced about rotating disc 50. One of the filters passes light in a waveband that includes the sodium-light wavelengths. The other two filters pass light in wavebands equally spaced on either side of the sodium band. For example, filter 44 might be a sodium-light filter with half-power wavelengths of 5840 angstroms and 5940 angstroms, while filters 46 and 48 might be filters that admit light in bands equally spaced on either side of the sodium band. Typical pass bands for these filters might be 5540 to 5640 angstroms and 5240 to 5340 angstroms. As can be seen in Figure 4, disc 50 is rotated by shaft 56 within frame 52.
Fiber-optic bundles 32, one from each viewing apparatus, are mounted so that each one is in registration with one of the detectors 54, typically a photo-diode, photo-resistor, or other light-sensitive circuit element.
Rotating disc 50 brings filters 44, 46 and 48 into registration with each of the bundle-detector pairs in succession, and signals indicative of the intensity of light within the chosen waveband are transmitted to associated circuitry. The result of this arrangement is that each detector 54 receives light within each waveband in sequence as the filters pass between it and the fiber-optic bundle from the furnace quadr~nt associated with it.
The signal sent by each detector 54 resembles the example shown in Figure 5. As can be seen in Figure 5, the detector 54 gives a reading of zero intensity during a substantial portion of each revolution. During other periods, B filter is situated between the detector and its fiber-optic bundle, permitting light of wavelengths within the waveband passed by the filter to strike the detector, ~hich sends a signal indicative o~ the intensity of light within the passed waveband to associated circuitry. For example, the peak 58 could be a signal sent when filter 44, the sodium-light filter, passes between a detector 54 and its associated fiber-optic bundle 32. The signal rises as the filter comes more directly in front of detector 54. A narrow plateau occurs during the time when detector 54 recei~-es light from the entire face of the fiber-optic bundle 32, and the signal falls off ' 1075033 as the filter passes on to the next detector. Assuming that di3c 50 rotates in a clockwise direction, peak 60 is indicative of the intensity of light passed by ~ilter 46, and peak 62 is indicative of the intensity of light passed by filter 48. Tnus, the combination with the apparatus of Figures 1 and 2 of one of the filters 44 and any of the detectors 54 constitutes means for producing an output indicative of the indensity of light occurring in a waveband having wavelengths characteristic of the process of burning sodium. Similarly, the combination with the apparatus of Figures 1 and 2 of filters 46 and 48 and any of the detectors 54 constitutes means for producing an output indicative of the intensity of light in at least one reference waveband, which intensity is representative of the intensity of background light in the characteristic waveband that was not produced by the process of burning sodium.
The uneven spacing of the filters would be desirable if signal-processing circuitry were to be operated in a synchronous manner, that is, with no direct connection between rotating disc 50 and the synchronizing circuitry.
Peaks 60 and 62 are of importance because they give an indication of the general level of background light. The light hitting fiber-optic bundle 32 and being transmitted by it to the filter assembly is, of course, composed of light occurring in a whole spectrum of wavelengths, the light of some wavelengths being more intense than the light of other wavelengths. Even though the intensities vary, however, most sources of light have fairly continuous intensity-versus- wavelength characteristics through most regions of their spectra. In other words, the light intensity at one wavelength will typically be close to the light intensity at nearby wa~elengths. At certain character1stic wavelengths, though, the light intensity greatly exceeds the intensity of light at nearby wavelengths.
The present invention takes advantage of this phenomenon. Since background sources have relatively smooth intensity-versus-wavelength characteristics at and near the sodium-light wavelengths, an indication of the background intensity at the sodium-light wavelengths can be produced by interpolating between the intensities o~ light occurring at nearby reference wavelengths. Accordingly, the signal-processing circuitry shown in block-diagram form in Figure 6 averages the values of peaks 60 and 62 and uses the resultant quantity as the intensity of the - background light at the sodium-light wavelengths. This background intensity is subtracted from peak 58 to determine what portion of the sodium-light radiation intensity is caused by the sodium burning above the char bed. me resultant intensity has been found to be a measure of the sodium concentration above the char bed. Since the amount of sodium produced by the process in the char bed is an indication of reduction efffciency, the output of the Figure 6 circuitry (described below) is a ~-more exact indication of reduction efffciency than is the total intensity of all radiation within the sodium band.
e preferred embodiment employs an averaging circuit to generate a quantity that represents the background-light intensity, but it is apparent that many modifications of the preferred embodiment could be designed that wo-~;d use the basic principal of the present invention without using a circuit for producing an unweighted average. The averaging circuit is merely one example of any number of embodiments that could be used in the present invention. A simpler embodiment, for instance, might generate the background-intensity indication by producing a signal proportional to the intensity of light in only one waveband. A slightly more complicated apparatus might use a weighted average of two wavelengths to make up for different reference-waveband wiaths or for the fact that i one reference waveband is closer than the other to the characteristic wavelength. A weighted-average embodiment, of course, is only a more general case of the ordinary average used in the preferred embodiment described below. Accordingly, the term wei~hted average is used in the claims to refer to the addition of the outputs of any number of reference-waveband filters, each of which output may be multiplied by an appropriate ~075033 coefficient before the addition. Wei~hted svera~e therefore includes the use of only one reference intensity, the use of the ordinary average of two or more rePerences, and the use of differing coefficients in the computation of the average of two or more reference intensities.
An even more elaborate setup might employ one of the curve-fitting methods known to mathemstics. Such sn embodiment would perform a function having the effect of finding a curve in the intensity-wavelength two-space that fits the dats taken at the reference wavelengths, and it would use a value of thst curve occurring in the charscteristic wsveband ss the background-light intensity. This would differ from the weighted-sverage embodiment in that the formuls for producing the background-intensity v~lue would not in general be a linesr function of the reference intensities. Whichever of these embodiments is used, the bssic principle is the same--using nearby wavelengths to give an indication of what the background-radiation intensity is at the characteristic wavelengths.
Block 64 of Figure 6 represents the rotating-filter assembly of Figures 3 and 4, and signal line 65 represents the signal from one of the detectors 54 of Figure 4. Lines 81 represent the signals from the other thr~e detectors 54. Since signal line 65 contains indications of the intensities of radistion in all these wsvebands, it is fed to synchronizer 66, which is a cir-cuit for separsting those intensities from each other. Synchronizer 66 typicallyconsists of three sample-and-hold circuits, one for each filter, and the sample-and-hold circuits are triggered either through a connection to the di~c, therebyproviding synchronization, or by an internally generated trigger signal that employs the uneven spacing of the filters to determine the orientation of the disc. Of course, if it is desired to synchronize the sample-and-hold circuits by means of a direct connection to disc 50, uneven spacing of the filters is - not necessary.
The intensity indication from the sodium-light filter is fed to block 58, which represents an amplifier that may or may not be used depending on the buffering and amplification requirements of the C751650 ~7~
~ 1075033 particular design. Signals indicative of the intensities of the light passed by the two reference filters 46 and 48 are fed to block 70, which represents an averaging circuit, typically an amplifier, that produces a signal indicative of the average of the intensities indicated by the reference-filter signals.
; 5 A signal is thereby produced that represents the background-light level at the sodium wavelengths. The resulting signal is fed, along with the output of block 68, to block 72. Block 72 is typically a difference amplifier, and it subtracts the reference signal from the char&cteristic-wavelength signal. From the above definition of weighted averaOEe, it can be appreciated that blocks 70 and 72 in combination constitute means for producing a signal indicative of the differencebetween the intensity indicated by the characteristic-waveband means and a quan-tity proportional to a weighted average of the intensities indicated by the reference-waveband means. Block 74 is a linear or logarithmic amplifier whose purpose is to drive a monitor, represented by block 78, in case the output of the subtraction circuit is not appropriate for that function. Block 78 would be a DC meter in the typical case.
Block 82 represents parallel signal-processing paths that perform the same function as blocks 56, 58, 70, 72, 74 and 76 on the other three sigr~lsproduced by block 64. The result is that the light produced by the burning sodium above the char bed is monitored by, typically, four DC meters, one of which is represented by block 78, and the other three of which are part of block 84. In addition, the signal produced by the circuits represented by block 74 and their corresponding parts of block 82 are averaged to give an indication of the reduction efficiency of the entire furnace. This averaging function is included in block 84. Finally, it may be desired to monitor the level of background light in order, for instance, to inform the operator of unwanted flames or flaring around the viewing ports or in the char bed. This background-light level would be indicated by block 80 and corresponding parts of block 84, typically DC meters.
~0 The circuit just described could easily be operated at disc speeds of around 1000 RPM. Sampling would then occur approximately once every 60 C751650 -ô-~075033 milliseconds. Thls would reduce to insignificance any inaccuracies produced by the fact that different reference-light levels are not measured simultan-eously, since light-intensity variations would occur at a rate that is much slower than the sampling rate.
While the invention has been described in con~unction with a specific embodiment, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing descrip-tion. Accordingly, it is intended to cover all such alternatives as fall withi~
the spirit and broad scope of the appended claims.
What is claimed is:
Though burning sodium is a source of light in the sodium band, other sources of such light typically exist in a recovery furnace. The glow of the char bed and the intermittent flaring that occurs there both give off some light in the same waveband as the light produced by the burning sodium, so the total light in the sodium band is composed of light from several sources other than burning sodium. In more general terms, any , - time a process is monitored by measuring the amount of light occuring in a characteristic waveband, light from sources other than the process are likely to be included in the measurement.
A As a result, the monitoring of a process by merely measuring the - 20 amount of light emitted in a characteristic waveband can lack precision.
Summary of the Invention Accordingly, the present invention is a method and apparatus for producing a measurement of the characteristic light produced by a process. According to the invention, the general level of background light intensity is determined by measuring the light intensityin at least one waveband that is not identical to the characteristic waveband. This background-light intensity is substracted from the total light intensity in the characteristic waveband. The resultant quantity is the ~ -2-i: ' ~075033 intensity of only that part of a characteristic light that is produced by the process.
: In one broad aspect, the invention may be summarized as residing in a method of monitoring a process by measuring the intensity of light occurring in a waveband having wave-lengths characteristic of the process, the light including back-ground light not produced by the process, the improvement com-prising: measuring the intensity of light in at least one of a . plurality of reference wavebands, the intensities in combination 10 being representative of the intensity of the background light in the characteristic waveband; and subtracting a quantity proportional to a weighted average of the intensities of light measured in the reference wavebands from the intensity of light measured in the characteristic waveband, thereby producing an indication of the intensity of that portion of the light in the characteristic waveband that is produced by the process.
In another broad aspect, the invention may be summarized as residing in an apparatus for monitoring a process, which apparatus comprises means for producing an output indic-ative of the intensity of light occurring in a waveband havingwavelengths characteristic of the process, the light including background light not produced by the process, the improvement comprising: means for measuring the intensity of light in each of a plurality of reference wavebands so as to define a curve of .: intensity-wavelength ordered pairs, the intensities in combin-- ation being representative of the intensity of the background light of the characteristic waveband; and means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the -2a-`` 1075033 characteristic-waveband means and a quantity proportional to an intensity value occurring in the characteristic waveband on the curve defined by the intensity-wavelength ordered pairs derived from the outputs of the reference-waveband means. - -Brief Description of the Drawings These and further features and advantages of the invention become evident in the description of the embodiment -shown in the drawings attached, wherein:
-2b-.~
, . . .
; ` 1075033 Figure 1 is the side elevation view of a light-receiving apparatus used in the preferred embodiment of the present invention;
Figure 2 is a front elevation view of the same apparatus;
Figure 3 is a front elevation view of a rotating filter used with the preferred embodiment of the present invention;
Figure ~ is a side sectional view of a rotating-filter assembly;
Figure 5 is a graph of a typical output signal from the rotating-: - filter assembly; and Figure 6 is a block diagram of the signal processing circuitry for use with the preferred embodiment.
Detailed Descri~tion of the Preferred Embodiment Figure 1 is a side elevation view of the light-receiving apparatus used in Nelson. The apparatus has been slightly modified in order to adapt it to use in the preferred embodiment of the present invention. In Nelson, it was the intent to monitor the rate of the reduction reaction in a char bed by measuring the intensity of light characteristic of a related process, namely the burning of sodium. The light-receiving apparatus is one of a plurality aimed at the furnace in which the burning of sodium occurs. A
fiber-optic bundle 32, possibl~ capped with a lens 30 for concentrating 20 light on the bundle, is housed within compartment 34, ~hich is attached - to plate 26. Plate 26 supports slide 28, which holdstwo filters 36, as shown in Figure 2. Plate member 26 includes aperture 38 through which light shines on fiber-optic bundle 32. Slide 28 is arranged so tha~ one window 36 covers aperture 38 while the other window 36 is exposed for 25 cleaning. As can be seen in Figure 1, a tubular section 22 is attached to the front surface of plate 26, and light from the furnace passes through tubular section 22. Connection 24 on tubular section 22 admits purge gas into tubular section 22 in order to prevent blowback from the furnace, which could cause black liquor and ash to deposit on window 36.
30 Air, steam, or another relatively inert gas mignt typically be used for purging. Fiber-optic bundles 32 are led from the viewing assemblies to - a rotating filter assembly, a front vie~ of which is shown in Figure 3.
~ .
.
Three filters, 44, 46 and 48 having different pass bands are unevenly spaced about rotating disc 50. One of the filters passes light in a waveband that includes the sodium-light wavelengths. The other two filters pass light in wavebands equally spaced on either side of the sodium band. For example, filter 44 might be a sodium-light filter with half-power wavelengths of 5840 angstroms and 5940 angstroms, while filters 46 and 48 might be filters that admit light in bands equally spaced on either side of the sodium band. Typical pass bands for these filters might be 5540 to 5640 angstroms and 5240 to 5340 angstroms. As can be seen in Figure 4, disc 50 is rotated by shaft 56 within frame 52.
Fiber-optic bundles 32, one from each viewing apparatus, are mounted so that each one is in registration with one of the detectors 54, typically a photo-diode, photo-resistor, or other light-sensitive circuit element.
Rotating disc 50 brings filters 44, 46 and 48 into registration with each of the bundle-detector pairs in succession, and signals indicative of the intensity of light within the chosen waveband are transmitted to associated circuitry. The result of this arrangement is that each detector 54 receives light within each waveband in sequence as the filters pass between it and the fiber-optic bundle from the furnace quadr~nt associated with it.
The signal sent by each detector 54 resembles the example shown in Figure 5. As can be seen in Figure 5, the detector 54 gives a reading of zero intensity during a substantial portion of each revolution. During other periods, B filter is situated between the detector and its fiber-optic bundle, permitting light of wavelengths within the waveband passed by the filter to strike the detector, ~hich sends a signal indicative o~ the intensity of light within the passed waveband to associated circuitry. For example, the peak 58 could be a signal sent when filter 44, the sodium-light filter, passes between a detector 54 and its associated fiber-optic bundle 32. The signal rises as the filter comes more directly in front of detector 54. A narrow plateau occurs during the time when detector 54 recei~-es light from the entire face of the fiber-optic bundle 32, and the signal falls off ' 1075033 as the filter passes on to the next detector. Assuming that di3c 50 rotates in a clockwise direction, peak 60 is indicative of the intensity of light passed by ~ilter 46, and peak 62 is indicative of the intensity of light passed by filter 48. Tnus, the combination with the apparatus of Figures 1 and 2 of one of the filters 44 and any of the detectors 54 constitutes means for producing an output indicative of the indensity of light occurring in a waveband having wavelengths characteristic of the process of burning sodium. Similarly, the combination with the apparatus of Figures 1 and 2 of filters 46 and 48 and any of the detectors 54 constitutes means for producing an output indicative of the intensity of light in at least one reference waveband, which intensity is representative of the intensity of background light in the characteristic waveband that was not produced by the process of burning sodium.
The uneven spacing of the filters would be desirable if signal-processing circuitry were to be operated in a synchronous manner, that is, with no direct connection between rotating disc 50 and the synchronizing circuitry.
Peaks 60 and 62 are of importance because they give an indication of the general level of background light. The light hitting fiber-optic bundle 32 and being transmitted by it to the filter assembly is, of course, composed of light occurring in a whole spectrum of wavelengths, the light of some wavelengths being more intense than the light of other wavelengths. Even though the intensities vary, however, most sources of light have fairly continuous intensity-versus- wavelength characteristics through most regions of their spectra. In other words, the light intensity at one wavelength will typically be close to the light intensity at nearby wa~elengths. At certain character1stic wavelengths, though, the light intensity greatly exceeds the intensity of light at nearby wavelengths.
The present invention takes advantage of this phenomenon. Since background sources have relatively smooth intensity-versus-wavelength characteristics at and near the sodium-light wavelengths, an indication of the background intensity at the sodium-light wavelengths can be produced by interpolating between the intensities o~ light occurring at nearby reference wavelengths. Accordingly, the signal-processing circuitry shown in block-diagram form in Figure 6 averages the values of peaks 60 and 62 and uses the resultant quantity as the intensity of the - background light at the sodium-light wavelengths. This background intensity is subtracted from peak 58 to determine what portion of the sodium-light radiation intensity is caused by the sodium burning above the char bed. me resultant intensity has been found to be a measure of the sodium concentration above the char bed. Since the amount of sodium produced by the process in the char bed is an indication of reduction efffciency, the output of the Figure 6 circuitry (described below) is a ~-more exact indication of reduction efffciency than is the total intensity of all radiation within the sodium band.
e preferred embodiment employs an averaging circuit to generate a quantity that represents the background-light intensity, but it is apparent that many modifications of the preferred embodiment could be designed that wo-~;d use the basic principal of the present invention without using a circuit for producing an unweighted average. The averaging circuit is merely one example of any number of embodiments that could be used in the present invention. A simpler embodiment, for instance, might generate the background-intensity indication by producing a signal proportional to the intensity of light in only one waveband. A slightly more complicated apparatus might use a weighted average of two wavelengths to make up for different reference-waveband wiaths or for the fact that i one reference waveband is closer than the other to the characteristic wavelength. A weighted-average embodiment, of course, is only a more general case of the ordinary average used in the preferred embodiment described below. Accordingly, the term wei~hted average is used in the claims to refer to the addition of the outputs of any number of reference-waveband filters, each of which output may be multiplied by an appropriate ~075033 coefficient before the addition. Wei~hted svera~e therefore includes the use of only one reference intensity, the use of the ordinary average of two or more rePerences, and the use of differing coefficients in the computation of the average of two or more reference intensities.
An even more elaborate setup might employ one of the curve-fitting methods known to mathemstics. Such sn embodiment would perform a function having the effect of finding a curve in the intensity-wavelength two-space that fits the dats taken at the reference wavelengths, and it would use a value of thst curve occurring in the charscteristic wsveband ss the background-light intensity. This would differ from the weighted-sverage embodiment in that the formuls for producing the background-intensity v~lue would not in general be a linesr function of the reference intensities. Whichever of these embodiments is used, the bssic principle is the same--using nearby wavelengths to give an indication of what the background-radiation intensity is at the characteristic wavelengths.
Block 64 of Figure 6 represents the rotating-filter assembly of Figures 3 and 4, and signal line 65 represents the signal from one of the detectors 54 of Figure 4. Lines 81 represent the signals from the other thr~e detectors 54. Since signal line 65 contains indications of the intensities of radistion in all these wsvebands, it is fed to synchronizer 66, which is a cir-cuit for separsting those intensities from each other. Synchronizer 66 typicallyconsists of three sample-and-hold circuits, one for each filter, and the sample-and-hold circuits are triggered either through a connection to the di~c, therebyproviding synchronization, or by an internally generated trigger signal that employs the uneven spacing of the filters to determine the orientation of the disc. Of course, if it is desired to synchronize the sample-and-hold circuits by means of a direct connection to disc 50, uneven spacing of the filters is - not necessary.
The intensity indication from the sodium-light filter is fed to block 58, which represents an amplifier that may or may not be used depending on the buffering and amplification requirements of the C751650 ~7~
~ 1075033 particular design. Signals indicative of the intensities of the light passed by the two reference filters 46 and 48 are fed to block 70, which represents an averaging circuit, typically an amplifier, that produces a signal indicative of the average of the intensities indicated by the reference-filter signals.
; 5 A signal is thereby produced that represents the background-light level at the sodium wavelengths. The resulting signal is fed, along with the output of block 68, to block 72. Block 72 is typically a difference amplifier, and it subtracts the reference signal from the char&cteristic-wavelength signal. From the above definition of weighted averaOEe, it can be appreciated that blocks 70 and 72 in combination constitute means for producing a signal indicative of the differencebetween the intensity indicated by the characteristic-waveband means and a quan-tity proportional to a weighted average of the intensities indicated by the reference-waveband means. Block 74 is a linear or logarithmic amplifier whose purpose is to drive a monitor, represented by block 78, in case the output of the subtraction circuit is not appropriate for that function. Block 78 would be a DC meter in the typical case.
Block 82 represents parallel signal-processing paths that perform the same function as blocks 56, 58, 70, 72, 74 and 76 on the other three sigr~lsproduced by block 64. The result is that the light produced by the burning sodium above the char bed is monitored by, typically, four DC meters, one of which is represented by block 78, and the other three of which are part of block 84. In addition, the signal produced by the circuits represented by block 74 and their corresponding parts of block 82 are averaged to give an indication of the reduction efficiency of the entire furnace. This averaging function is included in block 84. Finally, it may be desired to monitor the level of background light in order, for instance, to inform the operator of unwanted flames or flaring around the viewing ports or in the char bed. This background-light level would be indicated by block 80 and corresponding parts of block 84, typically DC meters.
~0 The circuit just described could easily be operated at disc speeds of around 1000 RPM. Sampling would then occur approximately once every 60 C751650 -ô-~075033 milliseconds. Thls would reduce to insignificance any inaccuracies produced by the fact that different reference-light levels are not measured simultan-eously, since light-intensity variations would occur at a rate that is much slower than the sampling rate.
While the invention has been described in con~unction with a specific embodiment, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing descrip-tion. Accordingly, it is intended to cover all such alternatives as fall withi~
the spirit and broad scope of the appended claims.
What is claimed is:
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of monitoring a process by measuring the intensity of light occurring in a waveband having wavelengths characteristic of the process, the light including background light not produced by the process, the improvement comprising:
a. measuring the intensity of light in at least one of a plurality of reference wavebands, the intensities in combination being representative of the intensity of the back-ground light in the characteristic waveband; and b. substracting a quantity proportional to a weighted average of the intensities of light measured in the reference wavebands from the intensity of light measured in the charac-teristic waveband, thereby producing an indication of the inten-sity of that portion of the light in the characteristic waveband that is produced by the process.
a. measuring the intensity of light in at least one of a plurality of reference wavebands, the intensities in combination being representative of the intensity of the back-ground light in the characteristic waveband; and b. substracting a quantity proportional to a weighted average of the intensities of light measured in the reference wavebands from the intensity of light measured in the charac-teristic waveband, thereby producing an indication of the inten-sity of that portion of the light in the characteristic waveband that is produced by the process.
2. A method as recited in claim 1 wherein the process is that of burning sodium.
3. A method as recited in claim 2 wherein the charac-teristic waveband includes wavelengths in the region of 5890 angstroms.
4. A method as recited in claim 3 wherein the reference wavebands are a waveband including wavelengths in the region of 5590 angstroms and a waveband including wavelengths in the re-gion of 6290 angstroms.
5. A method as recited in claim 1 wherein the step of measuring the intensity of radiation occurring in reference wavebands comprises measuring the light intensity in each of a plurality of reference wavebands and wherein the step of sub-tracting a quantity from the intensity of radiation in a characteristic waveband comprises substracting a quantity pro-portional to an intensity value occurring in the characteristic waveband on a curve defined by the intensity-wavelength ordered pairs derived from the step of measuring the intensity of light within the reference wavebands.
6. A method as recited in claim 5 wherein the process is that of burning sodium.
7. A method as recited in claim 6 wherein the character-istic waveband includes wavelengths in the region of 5890 angstroms.
8. In an apparatus for monitoring a process, which apparatus comprises means for producing an output indicative of the intensity of light occurring in a waveband having wavelengths characteristic of the process, the light including background light not produced by the process, the improvement comprising:
a. means for producing an output indicative of the intensity of light in at least one reference waveband, which intensity is representative of the intensity of background light in the characteristic waveband; and b. means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the characteristic-waveband means and a quantity proportional to a weighted average of the intensities indicated by the reference-waveband means.
a. means for producing an output indicative of the intensity of light in at least one reference waveband, which intensity is representative of the intensity of background light in the characteristic waveband; and b. means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the characteristic-waveband means and a quantity proportional to a weighted average of the intensities indicated by the reference-waveband means.
9. An apparatus as recited in claim 8 wherein the pro-cess is that of burning sodium.
10. An apparatus as recited in claim 9 wherein the charac-teristic waveband includes wavelengths in the region of 5890 angstroms.
11. An apparatus as recited in claim 10 wherein the means for producing outputs indicative of the intensity of light in at least one reference waveband comprises a means for producing outputs, one of which is indicative of the intensity of light having wavelengths in the region of 5590 angstroms and the other which is indicative of the intensity of light having wavelengths in the region of 6290 angstroms.
12. In an apparatus for monitoring a process, which apparatus comprises means for producing an output indicative of the intensity of light occurring in a waveband having wave-lengths characteristic of the process, the light including back-ground light not produced by the process, the improvement com-prising:
a. means for measuring the intensity of light in each of a plurality of reference wavebands so as to define a curve of intensity-wavelength ordered pairs, the intensities in com-bination being representative of the intensity of the background light of the characteristic waveband; and b. means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the characteristic-waveband means and a quantity proportional to an intensity value occurring in the characteristic waveband on the curve defined by the intensity-wavelength ordered pairs derived from the outputs of the reference-waveband means.
a. means for measuring the intensity of light in each of a plurality of reference wavebands so as to define a curve of intensity-wavelength ordered pairs, the intensities in com-bination being representative of the intensity of the background light of the characteristic waveband; and b. means, receiving as its inputs the outputs of the reference-waveband means and the characteristic-waveband means, for producing a signal indicative of the difference between the intensity indicated by the characteristic-waveband means and a quantity proportional to an intensity value occurring in the characteristic waveband on the curve defined by the intensity-wavelength ordered pairs derived from the outputs of the reference-waveband means.
13. An apparatus as recited in claim 12 wherein the characteristic-waveband means is a means for producing an output indicative of the intensity of light occurring in a waveband having wavelengths characteristic of the burning of sodium.
14. An apparatus as recited in claim 13 wherein the characteristic-waveband means is a means for measuring the intensity of light having wavelengths in a region of 5890 angstroms.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US71901676A | 1976-08-30 | 1976-08-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075033A true CA1075033A (en) | 1980-04-08 |
Family
ID=24888458
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA275,143A Expired CA1075033A (en) | 1976-08-30 | 1977-03-30 | Sodium light intensity monitor |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5329785A (en) |
| CA (1) | CA1075033A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5009099A (en) * | 1989-05-09 | 1991-04-23 | Varian Associates, Inc. | Background correction method for use in gas chromatography |
| US5022755A (en) * | 1989-05-09 | 1991-06-11 | Varian Associates, Inc. | Photodiode configurations for simultaneous background correction and specific wavelength detection |
| US6341890B1 (en) * | 1998-01-20 | 2002-01-29 | Auxitrol S.A. | Sensor for measuring temperature and/or concentration |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3588252A (en) * | 1969-09-17 | 1971-06-28 | Baird Atomic Inc | Background suppression system for optical spectrometer |
| JPS5425436B1 (en) * | 1970-07-04 | 1979-08-28 | ||
| GB1353024A (en) * | 1970-07-24 | 1974-05-15 | Nat Res Dev | Tanning |
-
1977
- 1977-03-30 CA CA275,143A patent/CA1075033A/en not_active Expired
- 1977-08-29 JP JP10277577A patent/JPS5329785A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5009099A (en) * | 1989-05-09 | 1991-04-23 | Varian Associates, Inc. | Background correction method for use in gas chromatography |
| US5022755A (en) * | 1989-05-09 | 1991-06-11 | Varian Associates, Inc. | Photodiode configurations for simultaneous background correction and specific wavelength detection |
| US6341890B1 (en) * | 1998-01-20 | 2002-01-29 | Auxitrol S.A. | Sensor for measuring temperature and/or concentration |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5329785A (en) | 1978-03-20 |
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