# US 9,506,804 B2 · Open path gas detector > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,506,804 B2 - Document ID: US9506804B2 - Status: Granted - Kind: B2 - Application number: 14/760,608 - Filed: 2014-01-10 - Published: 2015-12-10 - Granted: 2016-11-29 - Earliest claimed: 2013-01-17 - Assignees: Detector Electronics Corporation - Applicants: Detector Electronics Corporation - Inventors: Liangju Lu; John King - Web page: https://patentgrep.com/patent/US9506804B2 ## CPC - G01J 3/36: Investigating two or more bands of a spectrum by separate detectors - G01J 3/42: Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry (beam switching arrangements G01J3/08) - G01N 21/3504: for analysing gases, e.g. multi-gas analysis - G01N 21/359: using near infrared light - G01N 21/39: using tunable lasers - G01N 33/0031: {comprising two or more sensors, e.g. a sensor array} - G01J 3/28: Investigating the spectrum (using colour filters G01J3/51) - G01J 3/2823: {Imaging spectrometer} - G01J 2003/423: {Spectral arrangements using lasers, e.g. tunable} - G01N 2021/3513: {Open path with an instrumental source} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract In implementations, an open path gas detector is disclosed that can include imaging or non-imaging optical components. The detector can include components that allow for misalignment of radiation received by the detector of about 1 without causing false alarms. In implementations, the detector can include a beam splitter or a wavelength-division multiplexing filter to allow for more of the radiation received by the detector to be detected by the sensors. ## Claims ### Claim 1 An open path gas detector comprising: an optical element operable to receive radiation from an objective optical element and separate the radiation into a first radiation portion and a second radiation portion; a first beam-shaping optical element operable to receive the first radiation portion; a first photodiode comprising a first active sensing region operable to receive the first radiation portion from the first beam-shaping optical element; a filter operable to receive and filter the second radiation portion to produce a second filtered radiation portion; a second beam-shaping optical element operable to receive the second filtered radiation portion; and a second photodiode comprising a second active sensing region operable to receive the second filtered radiation portion from the second beam-shaping optical element; wherein the first beam-shaping optical element and the second beam-shaping optical element are operable to provide a substantially uniform illumination intensity profile across an entire first active sensing region of the first photodiode and the second active sensing region of the second photodiode. ### Claim 2 (depends on 1) The open path gas detector of claim 1, wherein the optical element comprises a beam splitter. ### Claim 3 (depends on 1) The open path gas detector of claim 1, wherein the optical element comprises a wavelength-division multiplexing (WDM) filter. ### Claim 4 (depends on 1) The open path gas detector of claim 1, further comprising a reference filter operable to receive and filter the first radiation portion to produce a first filtered radiation portion to be provided to the first photodiode. ### Claim 5 (depends on 2) The open path gas detector of claim 2, wherein the beam splitter is operable to produce the first radiation portion and the second radiation portion with substantially equal intensities. ### Claim 6 (depends on 3) The open path gas detector of claim 3, wherein the WDM filter is operable to separate the radiation by wavelength. ### Claim 7 (depends on 1) The open path gas detector of claim 1, wherein any, or combinations of, the optical element, the objective optical element, the filter, the first beam-shaping optical element, and the second beam-shaping optical element comprises a reflective optical component, a refractive optical component, or both a reflective and a refractive optical component. ### Claim 8 An open path gas detector comprising: an optical element operable to receive radiation from an objective optical element and separate the radiation into a first radiation portion and a second radiation portion; a first beam-shaping optical element operable to receive the first radiation portion; a first photodiode comprising a first active sensing region operable to receive the first radiation portion from the first beam-shaping optical element; a filter operable to receive and filter the second radiation portion to produce a second filtered radiation portion; a second beam-shaping optical element operable to receive the second filtered radiation portion; a second photodiode comprising a second active sensing region operable to receive the second filtered radiation portion from the second beam-shaping optical element; a reference field stop positioned near a focal point of the first radiation portion between the optical element and the first beam-shaping optical element; and an active field stop positioned near a focal point of the second radiation portion between the optical element and the second beam-shaping optical element. ### Claim 9 (depends on 8) The open path gas detector of claim 8, wherein the reference field stop comprises an aperture with a diameter smaller than an aperture of the active field stop. ### Claim 10 (depends on 9) The open path gas detector of claim 9, where in the aperture of the active field stop and the aperture of the reference field stop are adjustable to compensate for changes in alignment of the radiation received by the optical element. ### Claim 11 (depends on 1) The open path gas detector of claim 1, wherein the first beam-shaping optical element and the second beam shaping optical comprises any, or combinations of, one or more Kohler lenses, one or more Fly's Eye lenses, one or more Micro-lens arrays, one or more Micro-lens beam homogenizer, one or more faceted tubes, one or more compound parabolic lenses, and combinations thereof. ### Claim 12 An open path gas detector comprising: an optical element operable to receive radiation; a wavelength-division multiplexing (WDM) filter operable to receive the radiation from the optical element and separate the radiation into a first wavelength portion and a second wavelength portion; a first photodiode comprising a first active sensing region operable to receive the first wavelength portion; a filter operable to receive and filter the second wavelength portion to produce a second filtered wavelength portion; and a second photodiode comprising a second active sensing region operable to receive the second filtered wavelength portion from the second filter; wherein the radiation provided to the first active sensing region of the first photodiode and the second active sensing region of the second photodiode comprises a substantially uniform illumination intensity profile across an entire first active sensing region of the first photodiode and the second active sensing region of the second photodiode. ### Claim 13 (depends on 12) The open path gas detector of claim 12, wherein the objective optical element comprises a reflective optical component, a refractive optical component, or both a reflective and a refractive optical component. ### Claim 14 (depends on 12) The open path gas detector of claim 12, further comprising a reference filter operable to receive and filter the first wavelength portion to produce a first filtered wavelength portion to be provided to the first photodiode. ### Claim 15 An open path gas detector comprising: an optical element operable to receive radiation; a wavelength-division multiplexing (WDM) filter operable to receive the radiation from the optical element and separate the radiation into a first wavelength portion and a second wavelength portion; a first photodiode comprising a first active sensing region operable to receive the first wavelength portion; a filter operable to receive and filter the second wavelength portion to produce a second filtered wavelength portion; a second photodiode comprising a second active sensing region operable to receive the second filtered wavelength portion from the second filter; a reference field stop positioned near a focal point of the first radiation portion between the optical element and a first beam-shaping optical element; and an active field stop positioned near a focal point of the second radiation portion between the optical element and a second first beam-shaping optical element. ### Claim 16 (depends on 15) The open path gas detector of claim 15, wherein the reference field stop comprises an aperture with a diameter smaller than an aperture of the active field stop. ### Claim 17 (depends on 16) The open path gas detector of claim 16, where in the aperture of the active field stop and the aperture of the reference field stop are adjustable to compensate for changes in alignment of the radiation received by the optical element. ### Claim 18 (depends on 15) The open path gas detector of claim 15, wherein the first beam-shaping optical element and the second beam-shaping optical element are operable to provide a substantially uniform illumination intensity profile across an entire portion of the first active sensing region of the first photodiode and the second active sensing region of the second photodiode. ### Claim 19 (depends on 12) The open path gas detector of claim 12, wherein the detector comprises a field of view of sufficient size to allow for transmitter-to-receiver misalignments. ### Claim 20 (depends on 12) The open path gas detector of claim 12, wherein additional WDM filters are configured to allow multiple channels at different wavelengths to detect multiple gases. ### Claim 21 (depends on 15) The open path gas detector of claim 15 wherein the first beam-shaping optical element comprises a Kohler lens.