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1. EP2955495 - METHOD AND SYSTEM FOR CORRECTING INCIDENT LIGHT FLUCTUATIONS IN ABSORPTION SPECTROSCOPY

Nota: O texto foi obtido por processos automáticos de reconhecimento ótico de caracteres.
Para fins jurídicos, favor utilizar a versão PDF.
Claims

1. A method of correcting for the effects of intensity fluctuations of incident light within an absorption spectroscopy system, comprising the steps of:

controlling a light source to emit a wavelength modulated beam of light;

applying at least one modulation burst signal to perform one or more of modulating the wavelength modulated beam or modulating a separate beam synchronised with the wavelength modulated beam, which at least one modulation burst signal is a tapering signal modulation;

detecting the modulated beam(s) of light after transmission through a sample medium; and

processing the detected beam(s) to obtain at least one detected burst signal and to measure absorption effects of one or more measurands, wherein the processing includes comparing the at least one detected burst signal with the applied at least one modulation burst signal to determine intensity fluctuations of the incident light that are separate from absorption effects of the measurand(s), and correcting for the effects of the determined intensity fluctuations for increased accuracy of measurement of the absorption effects of the measurand(s).


  2. The method of claim 1, comprising selecting at least one wavelength zone and/or selecting a duration for the at least one burst signal to isolate the burst signal from a measured absorption line of the measurand(s).
  3. The method of claim 1 or 2, wherein the light source is a tunable diode laser having an associated laser bias current, and the laser's bias current is repeatedly scanned across a range of values at a scan rate having a period T, for wavelength modulation of the laser's beam of light, and wherein the duration of the burst signal is less than the period T.
  4. The method of any preceding claim, wherein the modulated beam is detected by a photodetector and the processing further comprises:

processing an output signal from the photodetector to obtain a reference signal proportional to the detected burst signal; and

using the reference signal to produce a corrected signal that is proportional to the concentration of one of the one or more measurands.


  5. The method of any one of claims 1 to 4, wherein:

the burst signal is amplitude modulated at fixed phase; or

the burst signal is phase modulated at fixed amplitude; or

the burst signal is both phase and amplitude modulated.


  6. The method of any preceding claim, wherein the frequency of the burst signal is chosen to be equal to an harmonic frequency of the light source modulation frequency used for the spectroscopic measurement of the absorption effects of at least one measurand.
  7. The method of any one of claims 4 to 8, wherein the processing further includes integrating the reference signal over a time period that is an integer multiple of a period of the modulation burst signal.
  8. The method of claim 7, wherein a baseline ramp function is subtracted from the reference signal to correct for selective residual absorption of the measurand and any background chemical species.
  9. The method of any preceding claim, wherein the light source is a diode laser and the step of applying a modulation burst signal includes modulating the bias current of the diode laser to produce the burst signal.
  10. The method of any one of claims 1 to 9, wherein the detecting and processing steps are carried out by a demodulating detector, and the burst signal is applied using one of: an external modulation device synchronised to the demodulating detector, a secondary diode laser synchronised to the demodulating detector, or a light emitting diode synchronised to the demodulating detector.
  11. The method of any preceding claim, wherein at least one of the amplitude and the width of the burst signal is chosen to be substantially larger than any expected natural background fluctuation.
  12. The method according to any preceding claim, wherein multiple burst signals are used in order to determine the light intensity fluctuations and wherein averaging of the measured light intensity is used to minimise a correction error.
  13. The method of claim 12, wherein the corrected light intensity is calculated based on a selected subset of burst signals, the subset including one or more of the multiple burst signals.
  14. The method of claim 3, wherein the position of at least one burst signal is varied between scan cycles.
  15. The method of any preceding claim, wherein the light source is a tunable diode laser having an associated bias current, and the laser's bias current is ramped up and down across a range of values to vary the laser's output beam across a range of wavelengths; and wherein the method further comprises identifying absorption wavelengths of gases in the sample medium and choosing the location of the modulation burst signal within the wavelength range to avoid the identified absorption wavelengths.
  16. The method of any preceding claim, wherein the tapering signal modulation of the burst signal is generated using a window function.
  17. The method of claim 16, wherein the window function is one of a Tukey window function, a Planck-taper window function, a Kaiser-Bessel window function, a Hamming window function, a Hanning window function, a Blackman window function or a triangular window function.
  18. The method of any preceding claim, wherein the burst signal is inverted with respect to at least one absorption feature of the one or more measurands.
  19. The method of any preceding claim, wherein the modulated beam is detected by a photodetector and an optical diffuser is located substantially in front of the photodetector.
  20. An absorption spectroscopy system, comprising:

a light source for emitting a photon beam;

a controller for controlling the light source to emit a wavelength modulated photon beam, wherein the controller is also adapted to apply at least one tapering burst signal modulation to the photon beam;

a photodetector for detecting the modulated photon beam after transmission through a sample medium; and

a signal processing unit for processing the detected beam to obtain at least one detected burst signal and to measure absorption effects of one or more measurands, wherein the processing unit is adapted to compare the at least one detected burst signal with the applied at least one burst signal modulation to determine intensity fluctuations of the incident light that are separate from absorption effects of the measurand(s), and to correct for the effects of the determined intensity fluctuations for increased accuracy of measurement of the absorption effects of the measurand(s).


  21. The system of claim 20, wherein at least one of the amplitude and the width of the tapering burst signal modulation is chosen to be substantially larger than any expected natural background fluctuation.
  22. The system of claim 20 or claim 21, wherein the light source is a tunable diode laser having an associated bias current, and wherein the controller is configured to repeatedly scan the laser's bias current across a range of values at a scan rate having a period T, for wavelength modulation of the laser's beam of light, and wherein the duration of the tapering burst signal modulation is less than the period T.
  23. The system of claim 22, wherein the controller is adapted to apply multiple tapering burst signal modulations to the photon beam within a single scan.
  24. The system of claim 22 or claim 23, wherein the position of at least one tapering burst signal modulation is varied between scan cycles.
  25. The system of claim 22, wherein the corrected light intensity is calculated based on a selected subset of tapering burst signal modulations, the subset including one or more of the tapering burst signal modulations.
  26. The system of any one of claims 20 to 25, wherein the tapering burst signal modulation is one of:

amplitude modulation at fixed phase;

phase modulation at fixed amplitude; or

a combination of phase modulation and amplitude modulation.


  27. The system of any one of claims 20 to 26, wherein the controller is adapted to control one of:

an external modulation device;

a second light source comprising a laser diode;

a light emitting diode; or

the light source bias current;

for applying a tapered burst signal modulation to the photon beam.