WO2006017644A2 - Commande amelioree d'intensite de lumiere en boucle fermee et procede associe d'application de fluorescence - Google Patents

Commande amelioree d'intensite de lumiere en boucle fermee et procede associe d'application de fluorescence Download PDF

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WO2006017644A2
WO2006017644A2 PCT/US2005/027696 US2005027696W WO2006017644A2 WO 2006017644 A2 WO2006017644 A2 WO 2006017644A2 US 2005027696 W US2005027696 W US 2005027696W WO 2006017644 A2 WO2006017644 A2 WO 2006017644A2
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lamp
fluorescence
emission
loop
intensity
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PCT/US2005/027696
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WO2006017644A3 (fr
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Franek Olstowski
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Franek Olstowski
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/12—Selection of substances for gas fillings; Specified operating pressure or temperature
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/069—Supply of sources
    • G01N2201/0695—Supply to maintain constant beam intensity

Definitions

  • This invention relates to an improved closed-loop control circuit and method intended for stabilized control of light or lamp emission over time.
  • the invention can be utilized in a variety of relevant applications requiring precise control of instantaneous lamp intensity and may be particularly advantageous when specified intensity limits or high-speed control is required.
  • An applied example of beneficial use includes a method for accurately measuring fluorescence of a medium by controlling the emission intensity of the excitation source. More specifically, it relates to utilization of such feedback control with a Krypton-Chloride (KrCl*) Excimer lamp to reliably determine the content or concentration of sulfur dioxide (SO 2 ) by UV Fluorescence in a gaseous medium.
  • KrCl* Krypton-Chloride
  • the varieties of available light sources that are utilized throughout industry are numerous. Frequently, there is a need for accurate and effective control of illumination intensity to compensate for gradual loss of lamp intensity over time, or to correct for more rapid changes in emission in order to achieve a higher instantaneous stability and subsequent signal-to-noise ratio.
  • the number of relevant applications that either requires, or could possibly benefit from, closed-loop control of associated light sources is seemingly endless and rapidly growing.
  • the present invention is directed toward improving present closed-loop control methods utilizing a relatively simple and robust circuit, whose design has inherent flexibility for incorporation in a wide range of potential applications.
  • One application for which there is no current practical solution for control of lamp emission intensity is the analysis of sulfur dioxide (SO 2 ) by UV Fluorescence.
  • excitation sources or lamps that can be used to excite and subsequently detect compounds in a variety of fluorescence methods. These lamps typically require emission of higher-energy UV wavelengths and include, but are not necessarily limited to, both high and low-pressure discharge lamps, spectral line emission lamps, flash lamps, UV light-emitting diodes (LED's) and lasers. Although the spectral content of each light source has its own unique spectrum comprised of characteristic wavelength(s) and spectral distribution, high-pressure discharge lamps and flash lamps are considered to possess broad, continuum-like emission characteristics. Conversely, lasers and spectral line emission lamps contain specific ionized gases or elements and emit either a single, or multitude of individual wavelengths with extremely narrow and highly-monochromatic characteristics or properties.
  • Detecting compounds by UV Fluorescence requires that the measured species of interest first absorb electromagnetic radiation in the region of the UV excitation wavelength. This absorbed energy excites the atoms or molecules and raises them to a higher energy state. This absorbed energy can be released as a secondary electromagnetic emission such as fluorescence or phosphorescence. Wavelengths other than the excitation wavelength are typically rejected by an optical filter to minimize excitation background interference with low-level fluorescence emission. For the purpose of analytical accuracy, it is imperative that the excitation source generate a reliable and stable emission over long periods to minimize the need for frequent instrument calibration.
  • Some of the more common UV excitation sources utilized for detecting compounds by UV Fluorescence are spectral line emission lamps containing a metallic vapor such as mercury, cadmium or zinc. These lamps produce extremely narrow and discrete spectral emission lines, which are beneficial in that they are more easily rejected or eliminated from the induced secondary fluorescence emission spectrum with optical filtration.
  • excitation source commonly utilized for UV Fluorescence applications is the xenon flash lamp, which produces an extremely broad emission continuum from the vacuum UV to infrared region.
  • the spectral profile of a xenon lamp emission that has been filtered with a typical interference filter is approximated by a Gaussian distribution of wavelengths centered about the filters central or peak transmission wavelength. This broader distribution of excitation wavelengths may encompass more fluorophore absorption bands yielding greater subsequent fluorescence intensity, but higher relative background interference from overlapping excitation and adjacent fluorescence emission spectrums is a frequently encountered drawback when utilizing this type lamp.
  • a closed-loop control circuit for a lamp incorporates the use of a photodiode, phototransistor or other light-sensitive device to sense lamp intensity.
  • the detector is connected to circuitry that allows control of lamp current or applied voltage so that variations in light intensity induce a corresponding change in applied lamp power. Therefore, as lamp output decays, increased power is applied to the lamp to correct for any variations in order to maintain a relatively constant level of emission intensity or illumination over time.
  • UV lamps are capable of being easily controlled.
  • xenon flash lamps are capacitive discharge type devices that generate thermal ionization plasmas
  • the resulting emission intensity from individually triggered discharge pulses has an unavoidable statistical variability.
  • improvement in pulse-to-pulse intensity variation or consistency has been achieved over many years of refinement, the physics behind capacitive discharge makes precise control extremely difficult.
  • Many spectral line sources that contain specific metallic vapors are also difficult to control due to the fact that they generate a high-temperature, ionized emission plasma, whose intensity is thermally driven and highly temperature dependent. Any changes in applied current directly impacts resulting internal temperature, and subsequent deviations from optimal operating conditions detrimentally influences plasma stability and resonant line emission distribution.
  • Figure 1 illustrates a preferred embodiment of a closed-loop control circuit encompassed by the present invention.
  • Figure 2 illustrates another preferred embodiment of a closed-loop control circuit similar to that illustrated in Figure 1, but further providing a predictable lamp intensity failure mode range defined by resistance-set voltage boundaries regardless of whether control voltage fails at zero or at amplifier saturation.
  • Figure 3 illustrates another preferred embodiment of a digital control configuration providing even greater application flexibility and optimum utilization of control loop variables.
  • Figure 4 illustrates a prior art device having a light sensing detector in close proximity to the emission aperture. or opposite to the emission aperture.
  • Figure 5 illustrates a prior art device having a light sensing detector opposite to the emission aperture.
  • Figure 6 illustrates a prior art device that uses a partial beam splitter, such as an uncoated piece of glass or quartz, a partially reflecting mirror, a dichroic filter or other optical device between the emission aperture and analytical device, to direct a portion of the lamps incident energy to the photodiode detector.
  • a partial beam splitter such as an uncoated piece of glass or quartz, a partially reflecting mirror, a dichroic filter or other optical device between the emission aperture and analytical device, to direct a portion of the lamps incident energy to the photodiode detector.
  • Figure 7 illustrates intensity versus wavelength where the spectroscopic emission of a new zinc lamp is compared to the emission of the same lamp after an estimated 1000-2000 hours of intermittent operation.
  • Figure 8 illustrates a preferred embodiment of the present invention that uses feedback control of excitation emission within a fluorescence cell utilizing a "through cell" configuration.
  • Figure 9 is a graph of time versus lamp emission that illustrates the emission control precision that was obtained from a KrCl* Excimer lamp with an emission wavelength of 222nm with the disclosed circuit.
  • Figure 10 is a highly magnified representation of that portion of data from Figure 9 ranging from 1000-2000 hours and is plotted at about +/-.4% of average emission.
  • Figure 11 is an expanded portion of the data illustrated in Figures 9 and 10 totaling 100 hours.
  • Figure 12 is a graph of time versus intensity that illustrates the decay of a typical zinc discharge lamp that exhibits a semi-logarithmic diminution of emission that may lose 50% or more of the original intensity over the first 2000 hours of operation.
  • Figure 13 is a graph of time versus lamp emission that illustrates the improved potential long-term stability with this excitation source, even without closed loop control.
  • Figure 14 is a graph of wavelength versus intensity that illustrates
  • Figure 15 is a graph of wavelength versus intensity that illustrates
  • Figure 16 is a graph of wavelength versus intensity that illustrates
  • Figure 17 illustrates UV fluorescence analysis of lng/ul Sulfur in iso- octane utilizing a zinc discharge lamp as the excitation source.
  • Figure 18 illustrates magnified baseline of the above lng/ul sulfur in iso-octane utilizing a zinc discharge lamp as the excitation source.
  • Figure 19 illustrates UV fluorescence analysis of lng/ul sulfur in iso- octane utilizing a KrCl* excimer lamp as the excitation source.
  • Figure 20 illustrates magnified baseline of the above lng/ul sulfur in iso-octane utilizing a KrCl* excimer lamp as the excitation source.
  • Figure 21 illustrates detector response to samples containing sulfur and nitrogen in I-Cg utilizing a zinc lamp excitation source
  • Figure 22 illustrates detector response to samples containing sulfur and nitrogen in i-c 8 utilizing a KrCl* excimer lamp excitation source.
  • More efficient devices such as MOSFETS possess lower resistance current paths and typically yield reduced heat generation in DC current control applications, but careful attention to circuit design and proper clamping is required to avoid increased heat generation when utilized for high frequency switching of inductive loads, such as those found in high voltage and spectral line emission lamp power supplies.
  • the disclosed closed-loop control circuit in Figure 1 utilizes a dual loop configuration; where the primary control loop is a voltage controlled loop containing a DC power source that provides an input voltage (10) to a typical linear type voltage regulator (12). Regulated output voltage from these devices is sensed utilizing a resistive dividing network comprised of a fixed resistor (14) and a second resistor, which may be a variable resistor or potentiometer (16) if an adjustable output is desired.
  • This network provides a small feedback current to the regulator that is proportional to output voltage, which closes the loop (18) and establishes the operating set point or regulated output voltage. Absent any external influence, the primary control loop of the voltage regulator continuously maintains a stable operating voltage independent of any externally applied change in line or load conditions.
  • the voltage regulator (12) can be a common 3-Terminal adjustable type linear regulator, such as a National LM317 or other similar device, but low efficiency makes utilizing a heat sink a probable necessity for all but the lowest of current requirements.
  • An improvement would incorporate use of a Low Drop-Out Regulator or LDO, such as a Linear Technologies LT 1764, as these devices are more efficient than the 3-Terminal voltage regulators.
  • LDO may eliminate the need for a heat sink, or at the very least, reduce the required size thereof.
  • the preferred embodiment of the primary control loop (18) contains a peak- width modulated switching voltage regulator (12), as these devices typically have efficiencies between 85-95%. For higher power applications, utilization generally results in significant reductions to generated heat than the aforementioned linear type voltage regulators, although component application and operational functionality remains essentially unchanged.
  • a specified voltage dividing resistor network may be internally incorporated within the device itself, which sets the regulated output to a predetermined and fixed value.
  • the voltage regulator is capable of providing a stable, regulated output voltage to any lamp, laser, LED or other light source.
  • the regulator output is connected to a power source (20) that converts applied DC voltage to a high-frequency AC or RF voltage necessary to generate emission from an Excimer lamp (24).
  • the internal circuit design of this converter utilizes a resonant oscillating voltage and switching transistors arranged in a typical push-pull configuration.
  • the primary control loop of the voltage regulator is connected to a secondary light control loop, which allows the primary loop control input or value to be influenced and modified.
  • the secondary loop provides a means for either injecting a small current, or providing a leakage current path that essentially alters the perceived or sensed regulator output voltage. This configuration effectively controls the regulator output or applied lamp voltage by trimming the primary loop set point current and essentially changing the relative set point.
  • the secondary loop control signal is obtained when lamp output is first sensed by a photodiode (26), such as a Hamamatsu S1226-8BQ or other light sensitive detector with adequate response to relevant emission wavelength(s) for intended control.
  • the detector signal is then amplified utilizing a current or transimpedance amplifier (28) that generates an output voltage proportional to lamp intensity.
  • This signal is further amplified and inverted in a second stage utilizing a typical instrumentation amplifier (32).
  • the instantaneous light signal must be passed through a low-pass filter (30) to smooth the detected emission profile and establish a DC level representing an integral of all obtained signals within the time constant of the applied filter.
  • the filter may be incorporated as part of the first or second amplification stages, or distributed combination thereof. It should be apparent that the need for this filter and related response or bandwidth is dependent on the utilized light source and associated operational frequency.
  • the amplified and smoothed signal representing near-instantaneous lamp emission is compared to a selected or predetermined reference voltage utilizing a differential instrumentation amplifier (34) in a third stage.
  • the reference voltage provided establishes the selected set point and is preferably obtained utilizing a precision voltage reference (42) powered by a separate voltage source (40) and connected to a potentiometer (44), or alternately provided by any source capable of variable and highly stable voltage.
  • the potentiometer (44) is adjusted to obtain a specified reference voltage on the non-inverting input of the differential amplifier to establish the desired operating set point.
  • the difference between near-instantaneous lamp emission and the applied reference voltage represents deviation from set point, or error.
  • This differential error is amplified by a fourth stage amplifier (50) with sufficient output current drive capability to induce required changes to the primary loop or voltage regulator set point.
  • an optional low pass filter (36) may be necessary or employed.
  • a coupling resistor (52) between the amplifier output and the voltage regulator control loop is selected to obtain an appropriate impedance match and further tune proportional loop response.
  • a simple SPST switch (54) allows the light control loop to be disconnected from the voltage control loop for lamp emission evaluation without feedback control or for troubleshooting purposes.
  • This circuit is capable of highly effective lamp intensity control over a broad operating range of up to +/-50%. Also, when utilizing the preferred switching voltage regulator within the circuit, performance is further characterized by high efficiency that does not require any heat sink or forced air cooling for devices consuming less than 20 watts. Additionally, if the control voltage or signal is lost due to detector or operational amplifier failure in a typical closed loop control circuit, power to the lamp or device would usually be completely shut off. In the disclosed circuit configuration, loss of control signal or voltage from the secondary control loop merely returns the lamp to a predetermined control set point or applied lamp voltage, creating a "fall back position" for complete loss of control voltage signal.
  • the proposed circuit could alternately be designed to incorporate a MOSFET or other voltage controlled resistive device in the primary control loop to establish both minimum and maximum voltage regulator output limits for any control voltage failure.
  • the proposed circuit detailed in Figure 2 is essentially identical to that in Figure 1, with the exception that a
  • MOSFET (56) and resistor (58) are connected to establish a parallel current path to feedback resistor (14).
  • MOSFET impedance is extremely high and acts similar to an open switch, allowing regulator output to be defined by the primary loop voltage drop provided by resistor (14) and potentiometer (16).
  • MOSFET resistance decreases to a minimum ON resistance, typically between 1-10 ohms. This acts similar to a closed switch and essentially sets the lower limit to regulator output voltage established by the resulting parallel resistance value.
  • internal MOSFET resistance varies and allows regulator output voltage to be controlled at any value between the upper and lower voltage limits. Therefore, regardless of whether control voltage fails at zero or at amplifier saturation, a predictable lamp intensity failure mode range defined by resistance-set voltage boundaries can be effectively implemented.
  • Figure 3 discloses a digital control configuration to allow even greater application flexibility and optimum utilization of control loop variables.
  • the amplified and filtered light intensity signal is sampled by an analog-to-digital converter (60) or ADC that digitizes analog samples and serially transfers digitized values to a microcontroller or computer (62).
  • a microcontroller is generally equipped with serial communications interface, internal clock generator, a variety of input/output devices, necessary I/O ports and a small amount of onboard RAM and ROM, usually EPROM or EEPROM memory. If the microcontroller has an onboard ADC included internal to the device, then the external ADC (60) can be eliminated.
  • the microcontroller accumulates sampled data and can generate simple, weighted or exponential moving averages to acquired values. This data can be applied to more complex signal processing, such as Proportional, Integral and Derivative (PID) control algorithms, to further enhance control loop performance.
  • PID Proportional, Integral and Derivative
  • an external memory device (64) may be required to meet the intended data processing application.
  • the microcontroller communicates processed control loop data values to a digital-to-analog converter (66) or DAC.
  • the output from the DAC is connected to a buffer amplifier (68) and series resistor (52) to generate the desired effect on the voltage regulator control loop (18).
  • digital control has the added benefit of allowing a periodic adjustment of the intended control value. This may include inhibiting the transfer of updated values to the DAC (66), effectively suspending applied changes to the voltage regulator control input.
  • the Control/Hold function (70) would either allow normal closed-loop control of lamp intensity, or hold the last control value for any period of time.
  • This function may either be internally generated with imbedded programming or externally triggered utilizing an I/O port configured as an input gate.
  • the externally triggered hold period would be provided to the gate with a TTL or other logic signal, creating a "window" that is timed to coincide with fluorescent compounds passing through the measurement chamber or cell. It may desirable to only adjust or update corrections to light intensity once per hour, once per day or at various and intermittent times during the day. However, a more relevant application for the disclosed feature is effectively applied to closed loop control of an excitation source in UV Fluorescence analysis.
  • the disclosed feature is particularly beneficial when utilizing the preferred digital control configuration in an arrangement where the photodiode is placed such that it detects emission of the excitation source after it passes through the fluorescence chamber or detection cell.
  • the amount of light emitted from trace concentrations of a fluorescing compound would usually be insignificant as compared to the level of excitation emission.
  • the photodiode may sense an increase in detected light that is not due to actual change in emission intensity. Therefore, any resulting control loop correction during presence of a fluorescing compound would create a measurement error that would otherwise be eliminated by holding lamp control constant during this period.
  • Control/Hold Input (70) is particularly advantageous for solving the above problem as intermittently inhibiting updating the control loop variable has negligible impact to relatively slow lamp drift compensation and analytical accuracy is no longer compromised when analyzing high concentrations of fluorescent compounds.
  • the digital control configuration allows additional application flexibility such as compensation of solar radiation interference in outdoor environments where solar radiation can cause significant interference to detected and subsequent control of LED emission.
  • One such application involves adjusting the brightness of LED's utilized in the growing number of advertising signs. Perceived LED brightness can be adjusted for daytime and nighttime viewing levels to reduce potential glare or safety distraction to passing drivers. Intensity can further be differentially adjusted for bright sunshine or cloudy periods during the day.
  • Yet another application example is to provide adjustment of LED brightness in traffic lights to compensate for LED temperature sensitivity and any long-term emission decay related to ageing, without interference from solar radiation.
  • various embodiments typically place a light sensing detector, such as a photodiode, in close proximity to the emission aperture (See, Figure 4), or opposite to the emission aperture (See, Figure 5).
  • a light sensing detector such as a photodiode
  • Other lamp intensity feedback control configurations may alternatively utilize a partial beam splitter, such as an uncoated piece of glass or quartz, a partially reflecting mirror, a dichroic filter or other optical device between the emission aperture and analytical device or instrument, to direct a portion of the lamps incident energy to the photodiode detector (See, Figure 6).
  • a partial beam splitter such as an uncoated piece of glass or quartz, a partially reflecting mirror, a dichroic filter or other optical device between the emission aperture and analytical device or instrument, to direct a portion of the lamps incident energy to the photodiode detector (See, Figure 6).
  • One such device utilizes a temperature controlled housing, photodiode sensor and related control electronics to monitor and stabilize UV emission of a mercury- vapor lamp.
  • metal vapor arc lamps unlike mercury or other gas-filled ionization lamps, effective control of heavier metallic-vapor arc lamps, such as zinc lamps appear to be more challenging.
  • the above patent describes metal vapor arc lamps as being “extremely erratic” in their behavior due to "broad thermal operating conditions", and therefore difficult to effectively control in a precise manner.
  • the photodiode or light sensing detector is often utilized with an interference filter to reduce photodiode sensitivity to any undesired emission wavelengths present.
  • the filter is placed between the light source and photodiode in order to monitor and improve control of the specific excitation emission wavelength of interest.
  • an excitation source when utilized in an analytical device, such as a fluorescence chamber or cell, other optical variables may also interfere with long-term emission intensity that the excited fluorescing medium is subjected to. Since measured or detected fluorescence is directly proportional to photon-flux density, controlling excitation intensity within the fluorescence cell itself would greatly improve analytical results.
  • One such variable known as UV solarization, can cause a gradual decrease in transmission properties of UV-grade quartz and fused silica when exposed to deep UV radiation over time. Fused-silica is most commonly utilized in deep UV applications where depending on product quality, can allow high transmission of wavelengths well into the vacuum UV region.
  • Figure 8 illustrates a preferred embodiment of the present invention that addresses the above issues directly by feedback control of excitation emission within the fluorescence cell utilizing a "through cell" configuration.
  • the resultant excitation intensity the fluorescing medium is subjected to within the fluorescence chamber itself, including variables not directly related to lamp emission, would be sensed by a photodiode or light sensor in this alternative location and subsequently controlled by appropriate electrical means.
  • Various other designs for applied lamp power, feedback control circuitry and optical configurations utilized for the detector or analytical device may be found throughout industry and prior art. It should be clear to those skilled in the arts that any excitation source could be utilized in the preferred embodiment, as well as the location and type of applied circuitry can be changed or altered without deviating from the intended scope of the invention.
  • An advantage of this configuration is that it eliminates the need for any additional interference filter generally required when the photodiode is placed outside of the fluorescence detector or chamber. Since an excitation filter is already incorporated as part of a typical fluorescence detector, placing the photodiode in the configuration of the preferred embodiment subsequently prevents the photodiode or sensor from being exposed to any emission wavelengths other than the excitation wavelength. As previously described in prior art above, a second filter is often placed in front of the photodiode to reject any undesired emission wavelengths so that only the intended wavelength is sensed for control purposes.
  • Figure 9 demonstrates the emission control precision that was obtained from a KrCl* Excimer lamp with an emission wavelength of 222nm with the disclosed circuit. The lamp was run without any control for the first 600 hours to determine initial lamp drift rate. Between 600-1000 hours of operation, a number of circuit revisions were made to optimize control response and performance.
  • Figure 10 is a highly magnified representation of that portion of data from Figure 9 ranging from 1000-2000 hours and is plotted at about +/-.4% of average emission.
  • the data represented in Figure 11 is an expanded portion of the same data totaling 100 hours and reveals that the above mentioned spikes are likely electrical disturbances not associated with lamp emission.
  • Figure 12 represents the decay of a typical zinc discharge lamp that exhibits a semi-logarithmic diminution of emission that may lose 50% or more of the original intensity over the first 2000 hours of operation.
  • UV Fluorescence method involves injection of a sample into a high-temperature oxidation or combustion furnace, which converts all hydrocarbons into water (H 2 O) and carbon dioxide (CO 2 ) by-products.
  • Total sulfur content contained in any molecular-bound hydrocarbon species is similarly oxidized at temperatures in excess of 1000 0 C into sulfur dioxide (SO 2 ) by the reaction:
  • This low-level fluorescence emission is optically filtered to remove undesired wavelengths of the UV source and background scatter within the detector chamber. Detection of the filtered fluorescence emission is usually accomplished with a Photomultiplier Tube (PMT), Channel-Plate Multiplier (CPM) or other high gain, light-sensitive detector.
  • PMT Photomultiplier Tube
  • CPM Channel-Plate Multiplier
  • Cadmium, Zinc and Xenon lamps are continuous type emission sources emitting a spectrum comprised of multiple wavelengths that create a characteristic "fingerprint" whose intensity and distribution is governed by quantum mechanics related to the energy difference between electron transitions within atomic orbital levels of each element.
  • the quasi-monochromatic spectral emission of a KrCl* Excimer lamp has spectral emission continuum like the Deuterium lamp, the resulting profile of UV excitation wavelengths is very similar to that acquired when utilizing either lamp with the same filter.
  • the excitation peak of 214nm for the zinc lamp shows a half-band width (HBW) of about lnm
  • the 222nm peak of the KrCl* Excimer lamp exhibits a noticeably broader HBW of approximately 3nm. It should be noted that this data was obtained at the lnm spectral resolution limit of the 1/8-meter spectrometer utilized and that actual bandwidth of the zinc emission line is considerably narrower.
  • Nitrogen Interference Yet another feature of the proposed invention includes reduced sensitivity or response to nitrogen interference than currently utilized excitation sources for this application. It should be evident that detector response to any compounds other than SO 2 directly affects the analytical accuracy of the intended measurement. In most hydrocarbon-based fuels, particularly heavier products such as diesel fuels, molecular bound nitrogen species can be present in significant concentrations. When sulfur compounds are oxidized in the combustion furnace to produce SO 2 , molecular-bound elemental nitrogen within these species is similarly oxidized to nitric oxide or NO at these elevated temperatures. In addition, any trace concentrations of molecular or diatomic nitrogen (N 2 ) present in the oxidizing gas may also be cracked to form NO resulting from increased localized temperatures during hydrocarbon combustion.
  • N 2 molecular or diatomic nitrogen
  • NO is further oxidized in the presence of air or oxygen to form NO 2 and establishes an NO/NO 2 equilibrium whose ratio is dependent on the ambient gas temperature.
  • this secondary reaction is relatively slow and an insignificant consideration in UV Fluorescence analysis applications since combusted gasses move swiftly through most analytical instruments.
  • the singlet excited state of SO 2 predominantly fluoresces within the wavelength range of about 230-450nm.
  • the fluorescence emission spectrum possesses a pseudo-Gaussian profile, which rises somewhat more rapidly at the shorter wavelengths, reaching a peak or maximum between 320-340nm and tailing more gradually toward the longer fluorescing wavelengths. Consequently, NO also fluoresces within the same region, although its emission covers a narrower wavelength range of about 230-370nm with a peak maximum around 280nm.
  • SO 2 response is typically sacrificed by using a fluorescence rejection filter in front of the PMT to remove some portion of the overlapping NO and SO 2 fluorescence spectrum from the total fluorescence signal.
  • a fluorescence rejection filter in front of the PMT to remove some portion of the overlapping NO and SO 2 fluorescence spectrum from the total fluorescence signal.
  • the greater the portion of NO fluorescence removed by optical means the lower the detector response to remaining SO 2 fluorescence. Therefore, an excitation source that yields reduced nitrogen interference to obtained SO 2 concentration, would be of considerable benefit, particularly in trace sulfur in fuels analysis where both sensitivity and accuracy are of primary concern.
  • the nitrogen interference rejection ratio when utilizing a zinc lamp as the excitation source was calculated to be approximately 386:1. However, when a KrCl* Excimer lamp was substituted as an excitation source, corrected nitrogen response was less than 13% of that obtained with the zinc lamp, yielding a calculated nitrogen interference rejection ratio in excess of 3000:1, or an approximate 8-fold improvement. Further optimization of detector optics achieved nitrogen rejection ratios in excess of 10,000:1.
  • Another feature of the invention is that unlike other excitation sources utilized for SO 2 analysis by UY Fluorescence methods, the KrCl* Excimer lamp has the added flexibility of being utilized in either continuous or pulsed modes of operation.
  • Excitation sources such as Zinc, Cadmium and Deuterium lamps require preheating the envelope to obtain sufficient temperatures to induce ionization and generate the desired emission. This typically requires a warm- up and stabilization period that typically ranges from 10-20 minutes. Once the emission has stabilized, these lamps are usually left on as lamp emission is influenced or governed by the slow thermal response of the envelope. Since temporal emission from these lamps is relatively consistent, fluorescence methods utilizing these lamps are often referred to as continuous type methods. These sources are well suited to rapidly changing or high-speed fluorescence signals since excitation and fluorescence emission signals are continuously present.
  • Pulsed-UV Fluorescence Another widely used approach for sulfur analysis is the Pulsed-UV Fluorescence (PUVF) method, which typically utilizes a xenon flash lamp excitation source and is well documented in current literature.
  • the emission from a xenon flash lamp is a very intense, high-temperature pulse or flash of light.
  • the thermally induced emission is triggered by a capacitive discharge circuit that ionization xenon gas between the electrodes creating an arc or thermal plasma.
  • the temporal emission profile from a single discharge from this type of lamp is characterized by a non-Gaussian curve of extremely short pulse duration.
  • differing lamp and circuit designs can generate light bursts of varying pulse widths, the half- width of these discharges are typically in the range of 1-10 microseconds.
  • this lamp is the first excitation source to demonstrate effective utilization for either continuous, or pulsed mode analysis of SO 2 utilizing the UV Fluorescence analysis method.
  • the inventor believes that he has disclosed a unique closed-loop control loop circuit that has potential benefit to a broad range of light controlled applications.
  • the inventor has disclosed a specific application for utilizing the described light control circuit, as well as an improved optical configuration and means for accurate, long-term excitation emission control of an excitation source for UV Fluorescence analysis.
  • the inventor has disclosed a KrCl* Excimer lamp that was specifically developed for, and ideally suited to, the application of SO 2 analysis by UV Fluorescence, for which there is no practical light control solution utilizing currently applied UV excitation sources documented in prior art. Any changes, modifications, variations or applications of the subject invention may become apparent to those skilled in the art, which do not depart from the spirit and scope of the proposed invention and are only limited by the claims contained herein.

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Abstract

L'invention concerne un double système de rétroaction qui permet de commander l'intensité de la lampe excimère et qui comprend une boucle de réaction primaire destinée à maintenir une tension de fonctionnement stable de la lampe ainsi qu'une boucle de réaction secondaire destinée à commander ou si nécessaire à modifier le point de consigne de la boucle de commande de réaction primaire. L'invention concerne également un système de détection de fluorescence d'UV comprenant une lampe excimère à décharge à barrière électrique, une source d'excitation appliquée destinée à communiquer avec la lampe excimère, une chambre de fluorescence possédant un gaz échantillon contenant du dioxyde de soufre, un détecteur photosensible associé de façon opérationnelle à la chambre d'échantillon, et un dispositif d'analyse et de conditionnement de signal destiné à déterminer le contenu en dioxyde de soufre de l'échantillon.
PCT/US2005/027696 2004-08-03 2005-08-03 Commande amelioree d'intensite de lumiere en boucle fermee et procede associe d'application de fluorescence WO2006017644A2 (fr)

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EP2347246A1 (fr) * 2008-11-13 2011-07-27 Petroleum Analyzer Company, L.P. Système d'analyse d'un échantillon ou d'un composant d'échantillon et procédé de réalisation et l'utilisation de celui-ci
WO2018087279A1 (fr) * 2016-11-11 2018-05-17 Mikrowellen Labor Technik Ag Spectromètre présentant une lampe à décharge à plusieurs trajets de propagation

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US4496946A (en) * 1982-09-28 1985-01-29 Peratron Corporation Programmable electronic display
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US20030020407A1 (en) * 2001-07-30 2003-01-30 Patent-Treuhand-Gesellschaft Fur Elektrische Gluhl Discharge vessel with excimer fill, and associated discharge lamp

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2347246A1 (fr) * 2008-11-13 2011-07-27 Petroleum Analyzer Company, L.P. Système d'analyse d'un échantillon ou d'un composant d'échantillon et procédé de réalisation et l'utilisation de celui-ci
EP2347246A4 (fr) * 2008-11-13 2013-01-16 Petroleum Analyzer Company L P Système d'analyse d'un échantillon ou d'un composant d'échantillon et procédé de réalisation et l'utilisation de celui-ci
WO2018087279A1 (fr) * 2016-11-11 2018-05-17 Mikrowellen Labor Technik Ag Spectromètre présentant une lampe à décharge à plusieurs trajets de propagation
CN110114655A (zh) * 2016-11-11 2019-08-09 微波实验室技术股份公司 具有带多个光路的放电灯的分光计
US20190391072A1 (en) * 2016-11-11 2019-12-26 Mikrowellen Labor Technik Ag Spectrometer Having a Discharge Lamp with a Plurality of Beam Paths
US11085873B2 (en) 2016-11-11 2021-08-10 Mikrowellen Labor Technik Ag Spectrometer having a discharge lamp with a plurality of beam paths

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