Dynamic coded filter gas detection

Patent metadata

Field	Value
Publication number	US-8928879-B2
Application number	US-201213484005-A
Country	US
Kind code	B2
Filing date	May 30, 2012
Priority date	Jun 6, 2011
Publication date	Jan 6, 2015
Grant date	Jan 6, 2015

Abstract

A device for detecting gas concentrations includes a movable coded filter. An optical element is positioned to receive gas filtered light and spectrally separate the gas filtered light. A photo detector is positioned to receive the spectrally separated light through slits in the moveable coded filter to provide an AC signal representative of a selected gas.

First claim

The invention claimed is:

1. A device for detecting gas concentrations comprising:
a movable coded filter;
an optical element positioned to receive gas filtered light and spectrally separate the gas filtered light; and
a photo detector positioned to receive the spectrally separated light through slits in the moveable coded filter to provide an AC signal representative of a selected gas, wherein the slits are positioned to pass at least two AC components of the spectrally separated light corresponding to a gas not of interest such that the AC components cancel out on the photo detector.

2. The device of claim 1 wherein the coded filter comprises an opaque plane having slits.

3. The device of claim 2 wherein the slits are positioned on the opaque plane to pass at least one AC component of the spectrally separated light corresponding to the selected gas.

4. The device of claim 3 wherein a slit in the coded filter corresponding to the AC component of the spectrally separated light corresponding to the selected gas moves about a peak of the selected gas spectra as the coded filter is moved.

5. The device of claim 1 wherein the coded filter comprises an opaque proof mass of a comb drive microelectromechanical oscillator.

6. The device of claim 5 wherein the oscillator has a resonant frequency between 50 to 10000 Hertz.

7. The device of claim 1 wherein the slits have different widths.

8. The device of claim 1 wherein the slits are arranged to cancel AC components of the spectrally separated light from at least two gasses not of interest.

9. The device of claim 1 wherein the coded filter comprises multiple parallel coded filters in a single opaque proof mass and wherein the photodetector comprises a separate photodetector for each of the multiple parallel coded filters.

10. The device of claim 1 and further comprising a first collimator positioned to collimate light received by the coded filter.

11. The device of claim 10 and further comprising a second collimator positioned to collimate light provided to the optical element.

12. The device of claim 1 and further comprising a processor programmed to add a weighting function at a resonant frequency of the moveable coded filter to compensate for red-blue coded filter mis-alignment.

13. The device of claim 1 and further comprising a process programmed to add a weighting function at three times a resonant frequency of the moveable coded filter to compensate for slit width errors.

14. A device for detecting gas concentrations comprising:
a movable coded filter having multiple slits in a proof mass;
an optical element positioned to receive gas filtered light and spectrally separate the gas filtered light onto the coded filter wherein spectral bands run in the same direction as the slits, the slits positioned to cancel AC signals corresponding to at least one gas not of interest;
a photo detector positioned to receive the spectrally separated light through the oscillating slits in the moveable coded filter to provide an AC signal representative of a selected gas; and
a controller coupled to receive the AC signal, convert the AC signal to a digital signal, and to correlate an amplitude of the AC signal to a concentration of the selected gas.

15. A method for detecting a gas, the method comprising:
receiving light from a light source through a plume of gas;
spectrally separating the light;
oscillating a coded filter to selectively pass portions of the spectrally separated light onto a single photo detector; and
detecting an AC signal via the single photo detector representative of a gas of interest, wherein the portions of the spectrally separated light pass through multiple slits of the coded filter such that AC components of light from at least one gas not of interest cancel each other and wherein AC component of light from the gas of interest add to each other.

16. The method of claim 15 wherein the light is spectrally separated via a diffraction grating.

17. The method of claim 15 wherein the slits of the coded filter are configured to cancel AC components of multiple gases not of interest.

18. The method of claim 15 wherein the AC signal at a frequency of twice the frequency of oscillation of the coded filter is representative of the gas of interest.

Assignees

• Youngner Daniel
• Fritz Bernard S
• Liu Yue
• Cox James A
• Honeywell Int Inc

Inventors

• Youngner Daniel
• Fritz Bernard S
• Liu Yue
• Cox James A

Classifications

• G01J3/0208

  using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction · CPC title

• G01N21/3504

  for analysing gases, e.g. multi-gas analysis · CPC title

• G01J3/2803

  using photoelectric array detector · CPC title

• G01J3/0229

  using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters · CPC title

• G01J3/457

  Correlation spectrometry, e.g. of the intensity (G01J3/453 takes precedence) · CPC title