WO1996024833A1 - Method and system for monitoring a test material - Google Patents

Method and system for monitoring a test material Download PDF

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Publication number
WO1996024833A1
WO1996024833A1 PCT/US1996/001758 US9601758W WO9624833A1 WO 1996024833 A1 WO1996024833 A1 WO 1996024833A1 US 9601758 W US9601758 W US 9601758W WO 9624833 A1 WO9624833 A1 WO 9624833A1
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WO
WIPO (PCT)
Prior art keywords
test
signals
signal
predetermined
detector
Prior art date
Application number
PCT/US1996/001758
Other languages
French (fr)
Inventor
Daniel Jonathan Seeman
Hassan Modaress-Razavi
Original Assignee
Daniel Jonathan Seeman
Modaress Razavi Hassan
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Daniel Jonathan Seeman, Modaress Razavi Hassan filed Critical Daniel Jonathan Seeman
Priority to AU49195/96A priority Critical patent/AU4919596A/en
Publication of WO1996024833A1 publication Critical patent/WO1996024833A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G01N21/274—Calibration, base line adjustment, drift correction

Definitions

  • the present invention relates generally to monitoring systems and methods and, more particularly, to systems and methods for monitoring changes in at least one characteristic of a test material.
  • a conventional monitoring system includes a broadband light source which illuminates the test material, such as the mixture under test.
  • a conventional monitoring system also generally includes a detector, such as a photodetector, for detecting the light following the interaction of the light with the test material, such as after the light has passed through the test material. Based upon the intensity of the detected light, the monitoring system can determine if the test material is within specifications.
  • a conventional monitoring system will detect light of a second predetermined intensity if the light has passed through a mixture of the proper proportions.
  • a mixture of the proper proportions will generally attenuate the light passing therethrough by a predetermined amount such that the second predetermined intensity detected by the monitoring system is less than the first predetermined intensity by a predetermined amount. If, however, the mixture is not properly formulated and, as a result, includes more or less of the components than desired, the resulting intensity of the light detected by the monitoring system will not equal the second predetermined intensity. Instead, the intensity detected by the monitoring system will be greater or less than the second predetermined intensity since the variations in the respective proportions of the components will effect the attenuation of the light passing therethrough.
  • Conventional monitoring systems can also include various means for altering the proportions at which the respective components are mixed, based upon the detected intensity of the light, in an attempt to correct or cure the mixture. However, during the time expended in an attempt to correct or cure the mixture, additional quantities of the improperly formulated mixture will be produced.
  • the broadband light source of such conventional monitoring systems generally emits light which may fluctuate in intensity due to, for example, a fluctuation in the energy supplied to the light source, temperature changes within the light source or light detector or degradation of the light source.
  • some monitoring systems observe the light and, more particularly, the fluctuations in the intensity of the light in order to separate those variations in the intensity of the light detected by the photodetector which are due to variations in the mixture itself from variations in measured intensity which are due to fluctuations by the light or the light detectors.
  • these monitoring systems include a separate detector to detect a portion of the light emitted by the broadband light source which has not been attenuated by the test material, generally termed the reference beam.
  • These conventional monitoring systems generally process the signals generated by the detection of the reference beam separately from the signals generated by the detection of the light following its interaction with the test material. For example, conventional monitoring systems may separately filter, amplify and/or convert these signals from analog to digital. As known to those skilled in the art, the performance of each distinct electrical component can very due to a number of factors, such as electronic noise, drift or temperature fluctuations. Thus, the electrical components which separately process the signals generated by detection of the reference beam and the signals generated by detection of the light beam which has interacted with the test material may vary differently during the monitoring process, thereby potentially skewing the results. In addition, conventional monitoring systems generally include separate detectors for detecting the reference beam and the light beam which has interacted with the test material.
  • each detector has a specific response curve which establishes the relationship between the input and output of the detector.
  • the response curve of a photodetector relates the output voltage produced by the photodetector to the corresponding intensity of the light received and detected by the photodetector.
  • each photodetector of a conventional monitoring system may respond quite differently to fluctuations in the intensity of the detected light. As a result, it may be difficult, if not impossible, to accurately compare the variations in the output voltages of the different detectors of a conventional monitoring system in order to determine if the composition of the test material has changed.
  • monitoring system which precisely monitors variations in at least one predetermined characteristic of a test material.
  • a monitoring system which detects variations in the predetermined characteristic of the test material independent of fluctuations in the signal source, such as fluctuations in the intensity of a light source, or variations in the performance of the electrical components which process the various signals.
  • a method and apparatus for monitoring a test material which includes a signal source for providing signals to the test material, a reference detector for detecting a portion of the signals provided by the signal source and for generating a reference signal based upon the detected portion of the signals, and a test detector for detecting the signals provided by the signal source following interaction of the signals with the test material and for generating a test signal based upon the detected signals.
  • the monitoring apparatus also includes a monitor for monitoring at least one characteristic of the test material based upon an evaluation of the test signal.
  • the monitor is a common monitor positioned immediately downstream of and operably connected to both the test and reference detectors.
  • the monitoring apparatus of this embodiment of the present invention will process the test and reference signals under the same conditions and in the same fashion. Accordingly, the monitoring method and apparatus of the present invention precisely and reliably monitors the desired characteristic of the test material.
  • the monitor includes evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween.
  • the monitoring apparatus includes notification means for providing a notification signal, such as an alarm, if the difference between the reference signal and the test signal is at least as great as a predetermined difference.
  • the signal source provides signals having at least one predetermined property.
  • the signal source can include a light source for emitting light having a predetermined intensity.
  • the reference and test detectors preferably generate the reference and test signals, respectively, in response to the predetermined property of the detected signals.
  • the reference and test detectors can include photodetectors for generating reference and test signals, respectively, in response to the intensity of the detected light.
  • the common monitor includes a common controller, operably connected to both the test and reference detectors, and a multiplexer, disposed immediately downstream of the test and reference detectors and between the common controller and the test and reference detectors. The multiplexer alternately passes the test and reference signals from the test and reference detectors, respectively, to the common controller.
  • the test and reference signals are processed by the same controller. Consequently, the common monitor will process both the test and reference signals in a like fashion, notwithstanding temporary variations in the performance of the elements which form the common monitor.
  • the monitoring apparatus can also include signal control means disposed between the signal source and the reference detector.
  • the signal control means controls the portion of the signals provided by the signal source which is detected by the reference detector.
  • the signal control means is a shutter, such as a mechanical shutter which defines an aperture having a predetermined size, or a timed shutter which defines an aperture which alternately opens and closes.
  • the reference detector generates the reference signal in response to a first predetermined response curve.
  • the test detector of this embodiment generates the test signal in response to a second predetermined response curve and, more particularly, in response to a portion of the second predetermined response curve which has a second predetermined slope.
  • the signal control means controls the portion of the signals provided by the signal source which is detected by the reference detector such that the reference detector generates the reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope.
  • the difference between the first and second predetermined slopes is preferably less than a predetermined difference.
  • the reference detector and the test detector will respond similarly to fluctuations in the signals provided by the signal source, thereby further increasing the precision with which the monitoring system and method of the present invention monitors the test material. Therefore, the monitoring method and apparatus of one embodiment of the present invention commonly processes both the reference signal and the test signal to eliminate processing variations, such as the varying drift of different electrical components or variations induced by temperature fluctuations or electronic noise between the components. In addition, the monitoring method and apparatus of another embodiment of the present invention controls the portion of signals received by the reference detector such that both the reference detector and the test detector respond similarly to variations in the signal source. Accordingly, the method and apparatus for monitoring a test material according to the present invention can precisely and reliably monitor the test material and can notify an operator if a desired characteristic of the test material does not meet the predetermined specifications of the test material.
  • Figure 1 is a schematic perspective view of one embodiment of the monitoring apparatus of the present invention which includes a mechanical shutter which defines an aperture of a predetermined size.
  • FIG. 2 is a schematic perspective view of another embodiment of the monitoring apparatus of the present invention which includes a timed shutter which defines an aperture which alternately opens and closes.
  • Figure 3 is a graphical representation of the intensity of light detected by both the reference and test detectors over time.
  • Figure 4 is a graphical representation of the exemplary response curves of the reference detector and test detector of a monitoring apparatus according to one embodiment of the present invention.
  • test material refers to any natural or manmade material, including materials in a gaseous, liquid or solid state and materials in a transitional state between a gaseous liquid or solid state.
  • the test material can include a mixture, such as a soft drink or sealant, which is formed of a plurality of different components mixed in predefined proportions according to a predetermined recipe.
  • the monitored characteristic of the test material 14 can include any characteristic, aspect, or condition of a test material irrespective of whether the test material is undergoing any transformation, such as a mixing process with another material, or is being subjected to any treatment, handling, or other processing.
  • the characteristic of the test material may be of the type which is relatively temporary or relatively permanent and may be of the type which exists on an exterior or interior surface of the material.
  • the characteristic of the test material can be the transmissivity or reflectivity of the test material which, in turn, is related to the transmissivity or reflectivity of the respective components of the test material and to the relative proportions of the components.
  • the monitoring method and apparatus 10 of the present invention can effectively monitor the composition of the test material and the relative proportions of the components of the test material.
  • the monitoring apparatus 10 includes a signal source 20 for providing signals 16 to the test material 14.
  • the signal source provides signals having at least one predetermined property.
  • the signal source can include a light source, such as a broadband light source which includes a conventional filament bulb, which provides light having a predetermined intensity. While a light source is illustrated and will be described in more detail herein, the signal source can include a number of other types of signal sources for producing a variety of signals without departing from the spirit and scope of the present invention.
  • the signals produced by the signal source can include sound, radioactivity or temperature.
  • the signal source is selected such that the signal produced thereby has either a characteristic which is to be monitored, such as a signal source producing signals of a predetermined temperature for monitoring the temperature of a test material, or a characteristic which varies in response to the particular characteristic of the test material which is to be monitored, such as light source which emits light having an intensity which changes based upon the transmissivity or reflectivity of a test material and, more specifically, based upon the composition of the test material.
  • a characteristic which is to be monitored such as a signal source producing signals of a predetermined temperature for monitoring the temperature of a test material, or a characteristic which varies in response to the particular characteristic of the test material which is to be monitored, such as light source which emits light having an intensity which changes based upon the transmissivity or reflectivity of a test material and, more specifically, based upon the composition of the test material.
  • the signal source 20 provides signals 16 to the test material 14.
  • the monitoring apparatus 10 can also include an optical fiber 15 extending between the light source and the test material to receive and transmit the light signals provided by the light source to the test material without significant attenuation.
  • the subsequent interaction of the signals 16 provided by the signal source 20 with the test material 14 will alter or affect the signals, such as by attenuating the signals.
  • the signals may be at least partially reflected by the test material as shown by reflected beam 12 of Figure 1.
  • the portion of the signals reflected by the test material will depend upon the predetermined reflectivity of the test material, among other things.
  • the signals may be refracted by and transmitted through the test material.
  • the refraction and/or transmission of the signals through the test material will depend upon the index of refraction and the resulting transmissivity of the test material, among other things.
  • the signals which are reflected from and/or transmitted through the test material will generally have a reduced or lessened intensity due to the interaction of the signals with the test material.
  • the monitoring apparatus 10 also includes a test detector 18 for detecting the signals originally provided by the signal source 20 following interaction of the signals with the test material 14.
  • the test detector also generates a test signal based upon the detected signals. As illustrated in Figure 1, the test detector can detect the signals 12 reflected from the test material. Although not illustrated, the test detector could also detect the signals refracted by and/or transmitted through the test material in addition to or instead of the reflected signals.
  • the test detector 18 preferably generates test signals in response to the predetermined property of the detected signals 12.
  • the test detector is preferably a photodetector or photodiode which generates test signals in response to the intensity of the detected light.
  • the test detector can be a digital detector which produces output signals or pulses which have a frequency which varies in a predetermined relationship to the intensity of the detected light.
  • the monitoring apparatus of this embodiment can also include an optical fiber 17 disposed between the test material and the test photodetector to receive and transmit the signals from the test material to the test detector without significant attenuation.
  • the test detector 18 also generates the test signals in response to a predetermined response curve as shown in Figure 4 which defines the relationship between the detected signals and the corresponding voltage of the test signals.
  • the test detector preferably generates the test signals in response to a portion of the predetermined response curve, as indicated by point T of Figure 4, which has a predetermined slope m-.
  • the test detector will generate a test signal having an increased voltage level in response to detected signals having an increased intensity.
  • the test detector will generate test signals having a reduced voltage level in response to detected signals having a lesser or decreased intensity.
  • the monitoring apparatus 10 of the present invention also includes a monitor 22 for monitoring at least one characteristic of the test material 14 based upon an evaluation of the test signal. For example, by monitoring the reflectivity or transmissivity of the test material, the monitoring apparatus of the present invention can determine if the test material is formed of the proper components in the desired proportions as described above. As a more specific example, one exemplary test material is preferably formed of 10% by weight of material A, 50% by weight of material B and 40% by weight of material C. Upon exposure to a signal 16 having a predetermined intensity and a predetermined wavelength or frequency, the test material will have a predetermined reflectivity and, as a result, will reflect a predetermined percentage of the original signal. Accordingly, by monitoring the intensity of the signal 12 reflected by the test material, the monitoring apparatus of the present invention can determine if the test material is properly formed by comparing the intensity of the reflected light to the intensity of the light reflected by a properly formulated test material.
  • the monitoring system 10 and method of the present invention is designed to isolate the fluctuations in the test signal which are created by variations of the test material, as opposed to variations in the components of the monitoring apparatus.
  • the monitoring apparatus also includes a reference detector 34 for detecting fluctuations in the signals provided by the signal source 20 which are independent of the test material.
  • the reference detector detects a portion of the signals provided by the signal source and generates a reference signal based upon the detected portion of the signals.
  • the reference detector preferably generates a reference signal in response to the predetermined property of the detector signals.
  • the reference detector is preferably a photodetector or photodiode which detects at least a portion of the light emitted by the light source and which generates a reference signal in response to the intensity of the detected light.
  • the reference detector can be a digital detector which produces output signals or pulses which have a frequency which varies in a predetermined relationship to the intensity of the detected light.
  • the monitor 22 includes evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween. As illustrated in Figures 1 and 2, the monitor, including the evaluation means, is immediately downstream of and operably connected to both test and reference detectors 18 and 34, respectively. Thus, the monitor can commonly monitor both the reference and test signals to eliminate variations in the processing of the reference and test signals and to further increase the monitoring precision of the apparatus- 10 of this embodiment of the present invention. In particular, any variations in the performance of the various components of the monitor, such as those performance variations introduced by electronic noise, drift or temperature fluctuations, will affect the processing of both the reference and test signals in a like manner and to the same degree.
  • the common monitor 22 includes a multiplexer 26 directly electrically connected to both the test and reference detectors 18 and 34, respectively.
  • the multiplexer is adapted to alternately pass the test and reference signals from the test and reference detectors, respectively.
  • the common monitor also preferably includes a common controller 24, such as a microprocessor or microcontroller, operably connected to the multiplexer for alternately receiving the test and reference signals.
  • the common controller preferably includes the common evaluation means for repeatedly comparing the reference signals and the test signal and for determining the difference therebetween at a number of discrete instants in time.
  • the common controller also monitors the predetermined characteristic of the test material 14 based upon an evaluation of the test signal. In particular, the common controller can compare the test signal to a predetermined desired value or to a predetermined range of desired values which are representative of an acceptable test material as described hereinbelow.
  • the common monitor 22 can also include common means for conditioning the signals, such as a filter 30 and a signal amplifier 32 disposed between the multiplexer 26 and the common controller 24 in order to appropriately filter and amplify, respectively, the test and reference signals.
  • the common monitor and, more particularly, the common signal conditioning means can include an analog-to-digital convertor 28 disposed between the multiplexer and the common controller in order to convert the test and reference signals from analog to digital for subsequent processing by the common controller.
  • the common monitor of the illustrated embodiment includes a number of distinct electrical components
  • the common controller can include internal circuitry and/or software for performing the desired signal conditioning.
  • the common monitor 22 can detect a variation or change in the test material 14, independent of variations or fluctuations in the signal source 20.
  • fluctuations in the signals provided by the signal source such as variations in the intensity of the light emitted by a light source, affects both the test signal and the reference signal in the same manner. For example, if the signal source emits signals of increased intensity, both the test signal and the reference signal will increase. As described below, fluctuations in the signals provided by the signal source preferably also affect both the reference signal and the test signal to the same degree.
  • the monitoring apparatus 10 of the present invention can determine if changes in the test signal are due to fluctuations by the signal source 20 or detectors or to changes in the test material 14.
  • the test detector 18 As graphically illustrated in Figure 3 and for a light source which emits light of a predetermined intensity, the test detector 18 generates a test signal having a predetermined voltage V- , in response to the detection of light 12 which has reflected from a properly formulated test material.
  • the reference detector 34 generates a reference signal which differs from the test signal generated by the test detector by no more than a predetermined difference C in response to the detection of the light of the predetermined intensity.
  • the intensity of light emitted by the light source will typically vary over time due to environment and/or power supply fluctuations. As shown in the leftmost portion of Figure 3 between t 0 and t for purposes of example, the respective intensity of light detected and, correspondingly, the output signal generated by both the test detector 18 and the reference detector 34 in response to a sinusoidally varying light source will also vary in the same manner and to the same degree over time so long as the predetermined characteristic of the test material 14, such as the reflectivity and, therefore, the composition of the test material, remains constant. If the predetermined characteristic of the test material does change, however, the light received by and the corresponding output signals generated by the test detector and the reference detector will vary in different manners and to different degrees.
  • the monitoring method and apparatus 10 and, more particularly, the common controller 24 defines a predetermined maximum difference D between the test and reference signals generated by the test detector 18 and the reference detector 34, respectively.
  • the common monitor 22 and, more particularly, the common controller repeatedly compares the reference and test signals to determine if the difference therebetween exceeds the predetermined maximum difference D. For example, the common monitor would determine that the difference between the reference and test signals exceeds the predetermined maximum difference D for that time after, or the right of, t 2 in Figure 3. Once the common monitor detects that the test and reference signals differ by more than the predetermined maximum difference D, the monitoring apparatus of the present invention determines or recognizes that the predetermined characteristic of the test material has changed.
  • the monitoring apparatus 10 can also include notification means 42 for providing a notification signal if the difference between the reference and the test signals is at least as great as a predetermined maximum difference D.
  • the notification means can include a light emitting diode ("LED") which is illuminated as shown in Figure 2 if the difference between the reference and test signals exceeds the predetermined maximum difference D.
  • a notification means can also include an audible alarm for other devices for alerting an operator of the monitoring apparatus of the detected change in the predetermined characteristic of the test material 14.
  • the monitoring system 10 of one embodiment of the present invention can be operatively connected to the processing equipment for providing signals to, for example, a microprocessor or other controller of the processing equipment to automatically stop or adjust the mixing process based upon the detected change in the test material.
  • the reference detector 34 preferably generates the reference signal in response to a predetermined response curve.
  • the predetermined response curve of the reference detector defines the output voltage generated by the reference detector in response to detected signals of varying intensity.
  • the monitoring apparatus 10 also includes signal control means 38, disposed between the signal source 20 and the reference detector, for controlling the portion of the signals provided by the signal source which is detected by the reference detector.
  • the signal control means is a shutter for controlling the portion of the signals, such as light signals, provided by the signal source which is detected by the reference detector.
  • the shutter 38 is a mechanical shutter having an adjustable aperture.
  • the mechanical shutter defines an aperture 36 having a predetermined size and a predetermined shape, such as circular.
  • the mechanical shutter can include a plate 40 for slidably covering a portion of the aperture in order to selectively reduce the size of the aperture.
  • the resulting size of the aperture defined by the mechanical shutter and, correspondingly, the amount of light provided by the light source 20 to the reference detector 34 can be controlled. For example, by slidably raising the plate to expose a greater percentage of the aperture, the portion of the signals provided by the signal source which are detected by the reference detector is increased. Likewise, by slidably lowering the plate so as to cover additional portions of the aperture, the portion of the signals provided by the signal source which are detected by the reference detector is decreased.
  • the shutter 38 can include a timed shutter which alternately opens and closes.
  • the operation of the timed shutter is preferably controlled, such as by the controller 24 or, alternatively, by a separate shutter controller 37, such as a microprocessor or microcontroller, which is operably connected to the timed shutter.
  • a separate shutter controller 37 such as a microprocessor or microcontroller, which is operably connected to the timed shutter.
  • the portion of the signals provided by the signal source 20 which is detected by the reference detector 34 can be controlled. While an iris-type timed shutter is illustrated in Figure 2, the timed shutter can include other types of electronic shutters which alternately open and close in a controlled fashion without departing from the spirit and scope of the present invention.
  • the signal control means 38 controls the portion of the signals provided by the signal source 20 which is detected by the reference detector 34 such that the reference detector generates a reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope. Moreover, the signal control means preferably controls the portion of the signals detected by the reference detector such that the difference between the first and second predetermined slopes is less than a predetermined difference, such as less than 10%. As a result, the reference detector and the test detector will respond similarly, i.e., in the same manner and to the same degree, to fluctuations in the signals provided by the signal source.
  • the monitoring apparatus 10 of the present invention can more precisely monitor changes in the test material and can distinguish the changes in the test material from fluctuations in performance by the signal source or the other components of the monitoring apparatus.
  • the monitoring apparatus of this embodiment provides increased precision during monitoring operations.
  • the signal control means 38 preferably controls the portion of the signals detected by the reference detector 34 such that the reference detector operates at or near point R of a portion of the respective predetermined response curve which has a first predetermined slope m.. .
  • the first predetermined slope ⁇ I R is the same or similar to the second predetermined slope ⁇ L- of the respective response curve of the test detector 18.
  • the monitoring method and apparatus 10 of the present invention provides signals 16, such as light signals, to the test material 14.
  • a first portion of the signals are detected by the reference detector 34 prior to interaction with the test material so as to generate a reference signal.
  • a test signal is also generated by the test detector 18 based upon a second portion of the signals 12 following interaction of the second portion of the signals with the test material, such as following the reflection of the second portion of the signals from the test material.
  • the test material 14 can be a mixture, such as a soft drink or a sealant, which is formed of a number of components in predetermined proportions.
  • a mixture such as a soft drink or a sealant, which is formed of a number of components in predetermined proportions.
  • the monitoring method and apparatus 10 of the present invention can determine if the test material, such as the soft drink or sealant mixture, is formed of the proper components and mixed in the proper proportions.
  • the monitoring method and apparatus 10 of the present invention monitors at least one characteristic of the test material 14 based upon the differences between the reference signal and the test signal.
  • the monitoring method and apparatus 10 of the present invention prevents undesirable processing errors arising due to changes in the performance of the components of the monitor 22, such as due to electronic noise, drift or temperature fluctuations.
  • the precision with which the monitoring method and apparatus of the present invention can monitor a test material is significantly enhanced.
  • the monitoring system and method can precisely monitor relatively minute changes in the composition of the test material. Consequently, the monitoring method and apparatus of the present invention is particularly applicable to precision monitoring applications, such as chemical, medical, industrial and food and beverage processing applications in which it is desirable or critical to detect changes in the test material which are so small or slight that a variation in the operation of a conventional monitoring system would "mask" or otherwise prevent or inhibit detection of these changes.

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Abstract

A monitoring apparatus and method for monitoring a test material (14) includes a signal source (20) for providing signals to the test material, a reference detector (34) for detecting a portion of the signals provided by the signal source and for generating a reference signal based upon the detected portion of the signals, and a test detector (18) for detecting the signals provided by the signals source following interaction of the signals with the test material and for generating a test signal based upon the detected signals. The monitoring apparatus can also include a common monitor (22) for monitoring at least one characteristic of the test material based upon an evaluation of the test signal. The common monitor is positioned immediately downstream of and operably connected to both the test and reference detectors in order to process the test and reference signals under the same conditions and in the same fashion. The monitoring apparatus can also include a shutter (38) for controlling the portion of the signals provided by the signal source which is detected by the reference detector such that both the reference detector and the test detector will respond similarly to fluctuations in the signals provided by the signal source, thereby further increasing the precision with which the monitoring system and method monitors the test material.

Description

METHOD AND SYSTEM FOR MONITORING A TEST MATERIAL
Field of the Invention The present invention relates generally to monitoring systems and methods and, more particularly, to systems and methods for monitoring changes in at least one characteristic of a test material.
Background of the Invention It is desirable in many instances to monitor one or more characteristics of a test material. For example, it is desirable to monitor the processing of a mixture, such as a soft drink, to ensure that the different components of the mixture are mixed in the proper proportions. Accordingly, a number of monitoring systems have been developed to monitor a variety of processes, such as industrial, chemical, medical, food and beverage processes.
Conventional monitoring systems include a broadband light source which illuminates the test material, such as the mixture under test. A conventional monitoring system also generally includes a detector, such as a photodetector, for detecting the light following the interaction of the light with the test material, such as after the light has passed through the test material. Based upon the intensity of the detected light, the monitoring system can determine if the test material is within specifications.
For example, for a broadband light source which emits light of a first predetermined intensity, a conventional monitoring system will detect light of a second predetermined intensity if the light has passed through a mixture of the proper proportions. In particular, a mixture of the proper proportions will generally attenuate the light passing therethrough by a predetermined amount such that the second predetermined intensity detected by the monitoring system is less than the first predetermined intensity by a predetermined amount. If, however, the mixture is not properly formulated and, as a result, includes more or less of the components than desired, the resulting intensity of the light detected by the monitoring system will not equal the second predetermined intensity. Instead, the intensity detected by the monitoring system will be greater or less than the second predetermined intensity since the variations in the respective proportions of the components will effect the attenuation of the light passing therethrough.
Conventional monitoring systems can also include various means for altering the proportions at which the respective components are mixed, based upon the detected intensity of the light, in an attempt to correct or cure the mixture. However, during the time expended in an attempt to correct or cure the mixture, additional quantities of the improperly formulated mixture will be produced.
The broadband light source of such conventional monitoring systems generally emits light which may fluctuate in intensity due to, for example, a fluctuation in the energy supplied to the light source, temperature changes within the light source or light detector or degradation of the light source. Thus, some monitoring systems observe the light and, more particularly, the fluctuations in the intensity of the light in order to separate those variations in the intensity of the light detected by the photodetector which are due to variations in the mixture itself from variations in measured intensity which are due to fluctuations by the light or the light detectors. Thus, these monitoring systems include a separate detector to detect a portion of the light emitted by the broadband light source which has not been attenuated by the test material, generally termed the reference beam.
These conventional monitoring systems generally process the signals generated by the detection of the reference beam separately from the signals generated by the detection of the light following its interaction with the test material. For example, conventional monitoring systems may separately filter, amplify and/or convert these signals from analog to digital. As known to those skilled in the art, the performance of each distinct electrical component can very due to a number of factors, such as electronic noise, drift or temperature fluctuations. Thus, the electrical components which separately process the signals generated by detection of the reference beam and the signals generated by detection of the light beam which has interacted with the test material may vary differently during the monitoring process, thereby potentially skewing the results. In addition, conventional monitoring systems generally include separate detectors for detecting the reference beam and the light beam which has interacted with the test material. As known to those skilled in the art, each detector has a specific response curve which establishes the relationship between the input and output of the detector. For example, the response curve of a photodetector relates the output voltage produced by the photodetector to the corresponding intensity of the light received and detected by the photodetector. Thus, each photodetector of a conventional monitoring system may respond quite differently to fluctuations in the intensity of the detected light. As a result, it may be difficult, if not impossible, to accurately compare the variations in the output voltages of the different detectors of a conventional monitoring system in order to determine if the composition of the test material has changed. Thus, although a number of monitoring systems have been developed, it is nevertheless desirable to develop a monitoring system which precisely monitors variations in at least one predetermined characteristic of a test material. In addition, it is desirable to develop a monitoring system which detects variations in the predetermined characteristic of the test material independent of fluctuations in the signal source, such as fluctuations in the intensity of a light source, or variations in the performance of the electrical components which process the various signals.
Summary of the Invention It is therefore an object of the present invention to provide an improved method and apparatus for precisely monitoring at least one characteristic of a test material.
It is another object of the present invention to provide an improved method and apparatus for monitoring at least one characteristic of a test material independent of fluctuations in the signal source or in the performance of the electrical components which process the various signals.
These and other objects are provided, according to the present invention, by a method and apparatus for monitoring a test material which includes a signal source for providing signals to the test material, a reference detector for detecting a portion of the signals provided by the signal source and for generating a reference signal based upon the detected portion of the signals, and a test detector for detecting the signals provided by the signal source following interaction of the signals with the test material and for generating a test signal based upon the detected signals. The monitoring apparatus also includes a monitor for monitoring at least one characteristic of the test material based upon an evaluation of the test signal.
According to one embodiment, the monitor is a common monitor positioned immediately downstream of and operably connected to both the test and reference detectors. Thus, the monitoring apparatus of this embodiment of the present invention will process the test and reference signals under the same conditions and in the same fashion. Accordingly, the monitoring method and apparatus of the present invention precisely and reliably monitors the desired characteristic of the test material.
The monitor includes evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween. According to one embodiment, the monitoring apparatus includes notification means for providing a notification signal, such as an alarm, if the difference between the reference signal and the test signal is at least as great as a predetermined difference. Thus, the operator of the monitoring apparatus can take appropriate remedial action in response to the notification signal to correct or cure the test material, thereby minimizing the quantity of undesirable test material which is produced.
The signal source provides signals having at least one predetermined property. For example, the signal source can include a light source for emitting light having a predetermined intensity. As a result, the reference and test detectors preferably generate the reference and test signals, respectively, in response to the predetermined property of the detected signals. For example, the reference and test detectors can include photodetectors for generating reference and test signals, respectively, in response to the intensity of the detected light. According to one advantageous embodiment, the common monitor includes a common controller, operably connected to both the test and reference detectors, and a multiplexer, disposed immediately downstream of the test and reference detectors and between the common controller and the test and reference detectors. The multiplexer alternately passes the test and reference signals from the test and reference detectors, respectively, to the common controller. Thus, the test and reference signals are processed by the same controller. Consequently, the common monitor will process both the test and reference signals in a like fashion, notwithstanding temporary variations in the performance of the elements which form the common monitor.
The monitoring apparatus can also include signal control means disposed between the signal source and the reference detector. The signal control means controls the portion of the signals provided by the signal source which is detected by the reference detector. In one embodiment, the signal control means is a shutter, such as a mechanical shutter which defines an aperture having a predetermined size, or a timed shutter which defines an aperture which alternately opens and closes.
According to one advantageous embodiment, the reference detector generates the reference signal in response to a first predetermined response curve. Likewise, the test detector of this embodiment generates the test signal in response to a second predetermined response curve and, more particularly, in response to a portion of the second predetermined response curve which has a second predetermined slope. According to this embodiment, the signal control means controls the portion of the signals provided by the signal source which is detected by the reference detector such that the reference detector generates the reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope. Further, the difference between the first and second predetermined slopes is preferably less than a predetermined difference. Thus, the reference detector and the test detector will respond similarly to fluctuations in the signals provided by the signal source, thereby further increasing the precision with which the monitoring system and method of the present invention monitors the test material. Therefore, the monitoring method and apparatus of one embodiment of the present invention commonly processes both the reference signal and the test signal to eliminate processing variations, such as the varying drift of different electrical components or variations induced by temperature fluctuations or electronic noise between the components. In addition, the monitoring method and apparatus of another embodiment of the present invention controls the portion of signals received by the reference detector such that both the reference detector and the test detector respond similarly to variations in the signal source. Accordingly, the method and apparatus for monitoring a test material according to the present invention can precisely and reliably monitor the test material and can notify an operator if a desired characteristic of the test material does not meet the predetermined specifications of the test material.
Brief Description of the Drawings Figure 1 is a schematic perspective view of one embodiment of the monitoring apparatus of the present invention which includes a mechanical shutter which defines an aperture of a predetermined size.
Figure 2 is a schematic perspective view of another embodiment of the monitoring apparatus of the present invention which includes a timed shutter which defines an aperture which alternately opens and closes.
Figure 3 is a graphical representation of the intensity of light detected by both the reference and test detectors over time.
Figure 4 is a graphical representation of the exemplary response curves of the reference detector and test detector of a monitoring apparatus according to one embodiment of the present invention.
Detailed Description of the Preferred Embodiments The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, this embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
Referring now to Figure 1, a monitoring system 10 according to one embodiment of the present invention is illustrated. As described hereinafter, the monitoring system and method of the present invention is designed to monitor a test material 14 and, more particularly, at least one characteristic of a test material. As used herein, the term "test material" refers to any natural or manmade material, including materials in a gaseous, liquid or solid state and materials in a transitional state between a gaseous liquid or solid state. For example, the test material can include a mixture, such as a soft drink or sealant, which is formed of a plurality of different components mixed in predefined proportions according to a predetermined recipe. In addition, the monitored characteristic of the test material 14 can include any characteristic, aspect, or condition of a test material irrespective of whether the test material is undergoing any transformation, such as a mixing process with another material, or is being subjected to any treatment, handling, or other processing. Additionally, the characteristic of the test material may be of the type which is relatively temporary or relatively permanent and may be of the type which exists on an exterior or interior surface of the material. For example, the characteristic of the test material can be the transmissivity or reflectivity of the test material which, in turn, is related to the transmissivity or reflectivity of the respective components of the test material and to the relative proportions of the components. Thus, by monitoring the transmissivity or reflectivity of the test material, the monitoring method and apparatus 10 of the present invention can effectively monitor the composition of the test material and the relative proportions of the components of the test material.
As shown in Figures 1 and 2, the monitoring apparatus 10 includes a signal source 20 for providing signals 16 to the test material 14. Preferably, the signal source provides signals having at least one predetermined property. For example, the signal source can include a light source, such as a broadband light source which includes a conventional filament bulb, which provides light having a predetermined intensity. While a light source is illustrated and will be described in more detail herein, the signal source can include a number of other types of signal sources for producing a variety of signals without departing from the spirit and scope of the present invention. For example, the signals produced by the signal source can include sound, radioactivity or temperature. Preferably, the signal source is selected such that the signal produced thereby has either a characteristic which is to be monitored, such as a signal source producing signals of a predetermined temperature for monitoring the temperature of a test material, or a characteristic which varies in response to the particular characteristic of the test material which is to be monitored, such as light source which emits light having an intensity which changes based upon the transmissivity or reflectivity of a test material and, more specifically, based upon the composition of the test material.
As shown in Figures 1 and 2, the signal source 20 provides signals 16 to the test material 14. In the illustrated embodiment in which the signal source is a light source, the monitoring apparatus 10 can also include an optical fiber 15 extending between the light source and the test material to receive and transmit the light signals provided by the light source to the test material without significant attenuation. As known to those skilled in the art, the subsequent interaction of the signals 16 provided by the signal source 20 with the test material 14 will alter or affect the signals, such as by attenuating the signals. For example, the signals may be at least partially reflected by the test material as shown by reflected beam 12 of Figure 1. As known to those skilled in the art, the portion of the signals reflected by the test material will depend upon the predetermined reflectivity of the test material, among other things. In addition, at least a portion of the signals may be refracted by and transmitted through the test material. As also known to those skilled in the art, the refraction and/or transmission of the signals through the test material will depend upon the index of refraction and the resulting transmissivity of the test material, among other things. Thus, for a light source which provides signals of a predetermined intensity to the test material, the signals which are reflected from and/or transmitted through the test material will generally have a reduced or lessened intensity due to the interaction of the signals with the test material.
The monitoring apparatus 10 also includes a test detector 18 for detecting the signals originally provided by the signal source 20 following interaction of the signals with the test material 14. The test detector also generates a test signal based upon the detected signals. As illustrated in Figure 1, the test detector can detect the signals 12 reflected from the test material. Although not illustrated, the test detector could also detect the signals refracted by and/or transmitted through the test material in addition to or instead of the reflected signals.
For a signal source 20 which provides signals having at least one predetermined property, the test detector 18 preferably generates test signals in response to the predetermined property of the detected signals 12. For example, for a light source which emits light of a predetermined intensity, the test detector is preferably a photodetector or photodiode which generates test signals in response to the intensity of the detected light. While an analog detector is described below, the test detector can be a digital detector which produces output signals or pulses which have a frequency which varies in a predetermined relationship to the intensity of the detected light. In addition, the monitoring apparatus of this embodiment can also include an optical fiber 17 disposed between the test material and the test photodetector to receive and transmit the signals from the test material to the test detector without significant attenuation.
According to one advantageous embodiment, the test detector 18 also generates the test signals in response to a predetermined response curve as shown in Figure 4 which defines the relationship between the detected signals and the corresponding voltage of the test signals. In particular, the test detector preferably generates the test signals in response to a portion of the predetermined response curve, as indicated by point T of Figure 4, which has a predetermined slope m-. Thus, for a test detector which generates a test signal in response to the predetermined response curve of Figure 4, the test detector will generate a test signal having an increased voltage level in response to detected signals having an increased intensity. Similarly, the test detector will generate test signals having a reduced voltage level in response to detected signals having a lesser or decreased intensity.
The monitoring apparatus 10 of the present invention also includes a monitor 22 for monitoring at least one characteristic of the test material 14 based upon an evaluation of the test signal. For example, by monitoring the reflectivity or transmissivity of the test material, the monitoring apparatus of the present invention can determine if the test material is formed of the proper components in the desired proportions as described above. As a more specific example, one exemplary test material is preferably formed of 10% by weight of material A, 50% by weight of material B and 40% by weight of material C. Upon exposure to a signal 16 having a predetermined intensity and a predetermined wavelength or frequency, the test material will have a predetermined reflectivity and, as a result, will reflect a predetermined percentage of the original signal. Accordingly, by monitoring the intensity of the signal 12 reflected by the test material, the monitoring apparatus of the present invention can determine if the test material is properly formed by comparing the intensity of the reflected light to the intensity of the light reflected by a properly formulated test material.
In order to precisely measure the desired characteristic of the test material 14, the monitoring system 10 and method of the present invention is designed to isolate the fluctuations in the test signal which are created by variations of the test material, as opposed to variations in the components of the monitoring apparatus. Thus, the monitoring apparatus also includes a reference detector 34 for detecting fluctuations in the signals provided by the signal source 20 which are independent of the test material. In particular, the reference detector detects a portion of the signals provided by the signal source and generates a reference signal based upon the detected portion of the signals. For a signal source which provides signals having at least one predetermined property, the reference detector preferably generates a reference signal in response to the predetermined property of the detector signals. For example, for a monitoring system which includes a light source, the reference detector is preferably a photodetector or photodiode which detects at least a portion of the light emitted by the light source and which generates a reference signal in response to the intensity of the detected light. While an analog detector is described below, the reference detector can be a digital detector which produces output signals or pulses which have a frequency which varies in a predetermined relationship to the intensity of the detected light.
The monitor 22 includes evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween. As illustrated in Figures 1 and 2, the monitor, including the evaluation means, is immediately downstream of and operably connected to both test and reference detectors 18 and 34, respectively. Thus, the monitor can commonly monitor both the reference and test signals to eliminate variations in the processing of the reference and test signals and to further increase the monitoring precision of the apparatus- 10 of this embodiment of the present invention. In particular, any variations in the performance of the various components of the monitor, such as those performance variations introduced by electronic noise, drift or temperature fluctuations, will affect the processing of both the reference and test signals in a like manner and to the same degree.
In the illustrated embodiment, the common monitor 22 includes a multiplexer 26 directly electrically connected to both the test and reference detectors 18 and 34, respectively. The multiplexer is adapted to alternately pass the test and reference signals from the test and reference detectors, respectively. The common monitor also preferably includes a common controller 24, such as a microprocessor or microcontroller, operably connected to the multiplexer for alternately receiving the test and reference signals. The common controller preferably includes the common evaluation means for repeatedly comparing the reference signals and the test signal and for determining the difference therebetween at a number of discrete instants in time. The common controller also monitors the predetermined characteristic of the test material 14 based upon an evaluation of the test signal. In particular, the common controller can compare the test signal to a predetermined desired value or to a predetermined range of desired values which are representative of an acceptable test material as described hereinbelow.
The common monitor 22 can also include common means for conditioning the signals, such as a filter 30 and a signal amplifier 32 disposed between the multiplexer 26 and the common controller 24 in order to appropriately filter and amplify, respectively, the test and reference signals. In addition, the common monitor and, more particularly, the common signal conditioning means can include an analog-to-digital convertor 28 disposed between the multiplexer and the common controller in order to convert the test and reference signals from analog to digital for subsequent processing by the common controller. While the common monitor of the illustrated embodiment includes a number of distinct electrical components, the common controller can include internal circuitry and/or software for performing the desired signal conditioning.
By comparing the reference signal and the test signal, the common monitor 22 can detect a variation or change in the test material 14, independent of variations or fluctuations in the signal source 20. As shown in Figure 3, fluctuations in the signals provided by the signal source, such as variations in the intensity of the light emitted by a light source, affects both the test signal and the reference signal in the same manner. For example, if the signal source emits signals of increased intensity, both the test signal and the reference signal will increase. As described below, fluctuations in the signals provided by the signal source preferably also affect both the reference signal and the test signal to the same degree.
Thus, if both the test signal and the reference signal vary in the same manner and to the same degree, the monitoring apparatus 10 of the present invention and, more particularly, the common monitor 22, can determine if changes in the test signal are due to fluctuations by the signal source 20 or detectors or to changes in the test material 14. As graphically illustrated in Figure 3 and for a light source which emits light of a predetermined intensity, the test detector 18 generates a test signal having a predetermined voltage V-, in response to the detection of light 12 which has reflected from a properly formulated test material. In addition, for a light source which emits light of the predetermined intensity, the reference detector 34 generates a reference signal which differs from the test signal generated by the test detector by no more than a predetermined difference C in response to the detection of the light of the predetermined intensity.
As known to those skilled in the art, the intensity of light emitted by the light source will typically vary over time due to environment and/or power supply fluctuations. As shown in the leftmost portion of Figure 3 between t0 and t for purposes of example, the respective intensity of light detected and, correspondingly, the output signal generated by both the test detector 18 and the reference detector 34 in response to a sinusoidally varying light source will also vary in the same manner and to the same degree over time so long as the predetermined characteristic of the test material 14, such as the reflectivity and, therefore, the composition of the test material, remains constant. If the predetermined characteristic of the test material does change, however, the light received by and the corresponding output signals generated by the test detector and the reference detector will vary in different manners and to different degrees. See, for example, the portion of Figure 3 to the right of tx. More specifically, changes in the predetermined characteristic of the test material will alter the light received by the test detector and, correspondingly, the test signal generated by the test detector since the test material will interact differently with the light 16. However, changes in the test material will not alter the amount of light received by the reference detector or the reference signals generated by the reference detector since such signals are not dependent upon the characteristics of the test material.
According to the present invention, the monitoring method and apparatus 10 and, more particularly, the common controller 24 defines a predetermined maximum difference D between the test and reference signals generated by the test detector 18 and the reference detector 34, respectively. The common monitor 22 and, more particularly, the common controller repeatedly compares the reference and test signals to determine if the difference therebetween exceeds the predetermined maximum difference D. For example, the common monitor would determine that the difference between the reference and test signals exceeds the predetermined maximum difference D for that time after, or the right of, t2 in Figure 3. Once the common monitor detects that the test and reference signals differ by more than the predetermined maximum difference D, the monitoring apparatus of the present invention determines or recognizes that the predetermined characteristic of the test material has changed. For example, for a monitoring system adapted to monitor a mixture, such as a soft drink, a significant increase in the difference between the test and reference signals may indicate that the components which are mixed to form the mixture have changed or that the ratio or proportions of the components forming the mixture have changed. The monitoring apparatus 10 can also include notification means 42 for providing a notification signal if the difference between the reference and the test signals is at least as great as a predetermined maximum difference D. For example, the notification means can include a light emitting diode ("LED") which is illuminated as shown in Figure 2 if the difference between the reference and test signals exceeds the predetermined maximum difference D. A notification means can also include an audible alarm for other devices for alerting an operator of the monitoring apparatus of the detected change in the predetermined characteristic of the test material 14. Upon notification, the operator can halt further production of the test material and can correct or cure the formulation of the test material. Thus, the quantity of test material which does not meet specifications can be significantly reduced by the precision monitoring method and apparatus of the present invention. In addition, the monitoring system 10 of one embodiment of the present invention can be operatively connected to the processing equipment for providing signals to, for example, a microprocessor or other controller of the processing equipment to automatically stop or adjust the mixing process based upon the detected change in the test material.
In a like manner to the test detector 18, the reference detector 34 preferably generates the reference signal in response to a predetermined response curve. As shown in Figure 4, the predetermined response curve of the reference detector defines the output voltage generated by the reference detector in response to detected signals of varying intensity. As illustrated in Figures 1 and 2, the monitoring apparatus 10 also includes signal control means 38, disposed between the signal source 20 and the reference detector, for controlling the portion of the signals provided by the signal source which is detected by the reference detector. Preferably, the signal control means is a shutter for controlling the portion of the signals, such as light signals, provided by the signal source which is detected by the reference detector.
In a first embodiment illustrated in Figure 1, the shutter 38 is a mechanical shutter having an adjustable aperture. In particular, the mechanical shutter defines an aperture 36 having a predetermined size and a predetermined shape, such as circular. The mechanical shutter can include a plate 40 for slidably covering a portion of the aperture in order to selectively reduce the size of the aperture. Thus, by selectively covering a portion of the aperture, the resulting size of the aperture defined by the mechanical shutter and, correspondingly, the amount of light provided by the light source 20 to the reference detector 34 can be controlled. For example, by slidably raising the plate to expose a greater percentage of the aperture, the portion of the signals provided by the signal source which are detected by the reference detector is increased. Likewise, by slidably lowering the plate so as to cover additional portions of the aperture, the portion of the signals provided by the signal source which are detected by the reference detector is decreased. In an alternative embodiment illustrated in
Figure 2, the shutter 38 can include a timed shutter which alternately opens and closes. The operation of the timed shutter is preferably controlled, such as by the controller 24 or, alternatively, by a separate shutter controller 37, such as a microprocessor or microcontroller, which is operably connected to the timed shutter. By controlling the frequency and speed at which the timed shutter opens and closes, as well as the duty cycle of the shutter, i.e., the percentage of time that the shutter is open in comparison to the percentage of time that the shutter is closed, the portion of the signals provided by the signal source 20 which is detected by the reference detector 34 can be controlled. While an iris-type timed shutter is illustrated in Figure 2, the timed shutter can include other types of electronic shutters which alternately open and close in a controlled fashion without departing from the spirit and scope of the present invention.
According to one advantageous embodiment of the present invention, the signal control means 38 controls the portion of the signals provided by the signal source 20 which is detected by the reference detector 34 such that the reference detector generates a reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope. Moreover, the signal control means preferably controls the portion of the signals detected by the reference detector such that the difference between the first and second predetermined slopes is less than a predetermined difference, such as less than 10%. As a result, the reference detector and the test detector will respond similarly, i.e., in the same manner and to the same degree, to fluctuations in the signals provided by the signal source. By responding similarly to fluctuations in the signals provided by the signal source, the monitoring apparatus 10 of the present invention can more precisely monitor changes in the test material and can distinguish the changes in the test material from fluctuations in performance by the signal source or the other components of the monitoring apparatus. Thus, the monitoring apparatus of this embodiment provides increased precision during monitoring operations.
As illustrated in Figure 4, for example, the signal control means 38 preferably controls the portion of the signals detected by the reference detector 34 such that the reference detector operates at or near point R of a portion of the respective predetermined response curve which has a first predetermined slope m.. . As shown, the first predetermined slope ΠIR, is the same or similar to the second predetermined slope ΠL- of the respective response curve of the test detector 18. In operation, therefore, the monitoring method and apparatus 10 of the present invention provides signals 16, such as light signals, to the test material 14. A first portion of the signals are detected by the reference detector 34 prior to interaction with the test material so as to generate a reference signal. A test signal is also generated by the test detector 18 based upon a second portion of the signals 12 following interaction of the second portion of the signals with the test material, such as following the reflection of the second portion of the signals from the test material.
For example, the test material 14 can be a mixture, such as a soft drink or a sealant, which is formed of a number of components in predetermined proportions. By measuring the intensity of the signals 12 reflected from the test material, at least one characteristic of the test material, such as the reflectivity of the test material, can be determined. Based upon this characteristic of the test material, the monitoring method and apparatus 10 of the present invention can determine if the test material, such as the soft drink or sealant mixture, is formed of the proper components and mixed in the proper proportions. In particular, the monitoring method and apparatus 10 of the present invention monitors at least one characteristic of the test material 14 based upon the differences between the reference signal and the test signal. If the difference between the reference signal and the test signal is at least as great as a predetermined maximum difference D, a notification signal is provided to alert the operator of the detected change in the test material. Thus, the operator can cure or correct the test material prior to the production of large quantities of improperly mixed test material. In addition, by commonly processing the test and reference signals, the monitoring method and apparatus 10 of the present invention prevents undesirable processing errors arising due to changes in the performance of the components of the monitor 22, such as due to electronic noise, drift or temperature fluctuations. Moreover, by separating the variations in the reference and test signals which are caused by changes in the test material 14 from the variations in the reference and test signals which are due to fluctuations in the performance of the signal source or other components of the monitoring apparatus, the precision with which the monitoring method and apparatus of the present invention can monitor a test material is significantly enhanced. Thus, the monitoring system and method can precisely monitor relatively minute changes in the composition of the test material. Consequently, the monitoring method and apparatus of the present invention is particularly applicable to precision monitoring applications, such as chemical, medical, industrial and food and beverage processing applications in which it is desirable or critical to detect changes in the test material which are so small or slight that a variation in the operation of a conventional monitoring system would "mask" or otherwise prevent or inhibit detection of these changes.
In the drawings and the specification, there has been set forth preferred embodiments of the invention and, although specific terms are employed, the terms are used in a generic and descriptive sense only and not for purpose of limitation, the scope of the invention being set forth in the following claims.

Claims

THAT WHICH IS CLAIMED IS:
1. An apparatus for monitoring a test material comprising: a signal source for providing signals to the test material; a reference detector, responsive to said signal source, for detecting a portion of the signals provided by said signal source and for generating a reference signal based upon the detected portion of the signals; a test detector for detecting the signals provided by said signal source following interaction of the signals with the test material and for generating a test signal based upon the detected signals; a common monitor, immediately downstream of and operably connected to both said test and reference detectors, for monitoring at least one characteristic of the test material based upon an evaluation of the test signal, said common monitor comprising common evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween; and notification means, responsive to said common evaluation means, for providing a notification signal if the difference between the reference signal and the test signal is at least as great as a predetermined difference.
2. A monitoring apparatus according to Claim 1 wherein said signal source provides signals having at least one predetermined property, and wherein said reference and test detectors generate the reference and test signals, respectively, in response to the predetermined property of the detected signals.
3. A monitoring apparatus according to Claim 2 wherein said signal source comprises a light source for emitting light having a predetermined intensity, and wherein said reference and test detectors are photodetectors for detecting at least a portion of the light emitted by said light source and for generating the reference and test signals, respectively, in response to the intensity of the detected light.
4. A monitoring apparatus according to
Claim 1 wherein said common monitor comprises : a common controller operably connected to both said test and reference detectors; and a multiplexer, disposed immediately downstream of said test and reference detectors and between said common controller and said test and reference detectors, for alternately passing the test and reference signals from the test and reference detectors, respectively, to said common controller.
5. A monitoring apparatus according to
Claim 1 further comprising signal control means, disposed between said signal source and said reference detector, for controlling the portion of the signals provided by said signal source which is detected by said reference detector.
6. A monitoring apparatus according to Claim 5 wherein said signal control means comprises a shutter selected from the group consisting of a mechanical shutter which defines an aperture having a predetermined size and a timed shutter which defines an aperture which alternately opens and closes.
7. A monitoring apparatus according to Claim 1 wherein said reference detector generates the reference signal in response to a first predetermined response curve, wherein said test detector generates the test signal in response to a portion of a second predetermined response curve which has a second predetermined slope, and wherein said signal control means controls the portion of the signals provided by said signal source which is detected by said reference detector such that said reference detector generates a reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope, wherein the difference between the first and second predetermined slopes is less than a predetermined difference such that said reference detector and said test detector respond similarly to variations in the signals provided by said signal source.
8. An apparatus for monitoring a test material comprising: a signal source for providing signals to the test material; a reference detector, responsive to said signal source, for detecting a portion of the signals provided by said signal source and for generating a reference signal based upon the detected portion of the signals in response to a first predetermined response curve; a test detector for detecting the signals provided by said signal source following interaction of the signals with the test material and for generating a test signal based upon the detected signals in response to a portion of a second predetermined response curve which has a second predetermined slope; a monitor, operably connected to said test detector, for monitoring at least one characteristic of the test material based upon an evaluation of the test signal, said monitor comprising evaluation means for comparing the reference signal and the test signal and for determining the difference therebetween; and signal control means, disposed between said signal source and said reference detector, for controlling the portion of the signals provided by said signal source which is detected by said reference detector such that said reference detector generates a reference signal in response to a portion of the first predetermined response curve which has a first predetermined slope, wherein the difference between the first and second predetermined slopes is less than a predetermined difference such that said reference detector and said test detector respond similarly to variations in the signals provided by said signal source.
9. A monitoring apparatus according to Claim 8 wherein said signal source provides signals having at least one predetermined property, wherein said reference and test detectors generate the reference and test signals, respectively, in response to the predetermined property of the detected signals, and wherein the first and second predetermined response curves define the relationship between the predetermined property of the detected signals and the reference and test signals generated by said reference and test detectors, respectively.
10. A monitoring apparatus according to Claim 9 wherein said signal source comprises a light source for emitting light having a predetermined intensity, and wherein said reference and test detectors are photodetectors for detecting at least a portion of the light emitted by said light source and for generating the reference and test signals, respectively, in response to the intensity of the detected light, and wherein the first and second predetermined response curves define the relationship between the intensity of the detected light and the reference and test signals generated by said reference and test detectors, respectively.
11. A monitoring apparatus according to Claim 8 wherein said signal control means comprises a shutter for controlling the portion of the signals provided by said signal source which is detected by said reference detector.
12. A monitoring apparatus according to Claim 11 wherein said shutter is selected from the group consisting of a mechanical shutter which defines an aperture having a predetermined size and a timed shutter which defines an aperture which alternately opens and closes.
13. A method for monitoring a test material comprising the steps of: providing signals to the test material; generating a reference signal based upon a first portion of the signals prior to interaction of the first portion of the signals with the test material; generating a test signal based upon a second portion of the signals following interaction of the second portion of the signals with the test material; commonly processing both the reference signal and the test signal, said commonly processing step comprising the steps of monitoring at least one characteristic of the test material based upon the test signal and determining the difference between the reference signal and the test signal; and providing a notification signal if the difference between the reference signal and the test signal is at least as great as a predetermined difference.
14. A method according to Claim 13 wherein said providing step comprises the step of providing signals having at least one predetermined property, and wherein the method further comprises the steps of: detecting the predetermined property of the first portion of the signals prior to said step of generating a reference signal; and detecting the predetermined property of the second portion of the signals following interaction of the second portion of the signals with the test material.
15. A method according to Claim 14 wherein said providing step comprises the step of providing signals having a predetermined intensity, wherein said step of detecting the predetermined property of the first portion of the signals comprises the step of detecting the intensity of the first portion of the signals, and wherein said step of detecting the predetermined property of the second portion of the signals comprises the step of detecting the intensity of the second portion of the signals.
16. A method according to Claim 14 further comprising the step of controlling the first portion of the signals which is detected.
17. A method according to Claim 16 wherein said step of generating a reference signal comprises the step of generating the reference signal in response to a first predetermined response curve, wherein said step of generating a test signal comprises the step of generating the test signal in response to a portion of a second predetermined response curve which has a second predetermined slope, wherein said controlling step comprises the step of controlling the first portion of the signals such that the reference signal is generated in response to a portion of the first predetermined response curve which has a first predetermined slope, and wherein the difference between the first and second predetermined slopes is less than a predetermined difference.
PCT/US1996/001758 1995-02-08 1996-02-07 Method and system for monitoring a test material WO1996024833A1 (en)

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