WO2014143049A1

WO2014143049A1 - Gas sensing with tunable photonic radiation filter element

Info

Publication number: WO2014143049A1
Application number: PCT/US2013/032577
Authority: WO
Inventors: Gary Francis MURJADA
Original assignee: Draeger Safety, Inc.
Priority date: 2013-03-15
Filing date: 2013-03-15
Publication date: 2014-09-18

Abstract

Using a gas detector, photonic radiation is emitted over a first range of frequencies and through a pathway. The gas detector includes at least one broadband light source, at least one detector, and an electronically tunable filter element disposed in the pathway and between the at least one light source and the at least one detector. The electronically tunable filter element allows a window of radiation frequencies to pass through the filter and suppresses other radiation frequencies. The electronically tunable filter element is tuned to allow different windows of radiation frequencies to pass through the filter. Photonic radiation energy that passes through the tuned electronically tunable filter element and impinges on the detector is measured to form a spectral absorption signature characterizing constituents of gas in the pathway. Related apparatus, systems, techniques, and articles are also described.

Description

Gas Sensing with Tunable Photonic Radiation Filter Element

TECHNICAL FIELD

[0001] The subject matter described herein relates to gas sensing and gas detection.

BACKGROUND

[0002] Hazardous situations can exist due to the presence of toxic and/or combustible gases and vapors e.g. in oil and gas exploration and storage, transportation and storage of flammable liquids and gases, in processes involving the use of solvents, in the plastics processing industry, underground environments like mining operations or subway transit systems, production facilities, warehouses, and the like. In such environments, protection measures are desirable to protect personnel and property and may be required by statute. Many hazardous and harmful gases are hydrocarbon gases. Toxic and flammable gas leaks should be detected early, when concentrations are so low that a dangerous condition, such as an explosion or exposure of personnel to toxic environments can be avoided.

[0003] Pellistor sensor (or catalytic bead sensor) are a flameproof sensor based on a chemical reaction with oxygen and thus needs at least 12 % v/v. The pellistor sensor cannot operate without oxygen, (but also because of oxygen deficiency, there is no danger of an explosion). The pellistor sensor can measure multiple gases and vapors, but with different sensitivity. If the sensitivity for a substance is too low, however, the pellistor sensor may not reliably detect a presence of the substance, potentially leading to unsafe conditions.

[0004] Infrared absorption sensors are used to measure an optical energy absorption characteristic of an environment to detect individual gases. Gas optical absorption characteristics vary over frequency and this variation is the absorption spectrum (or signature). Photonic radiation is transmitted through a gas and the energy absorption is measured at a specific frequency known to be a peak absorption frequency for a particular gas. However, environments often have the potential to contain many different potential hazardous gases, and a single detector may not be sufficient to provide reliable hazardous gas detection and avoidance.

SUMMARY

[0005] In one aspect, using a gas detector, photonic radiation is emitted over a first range of frequencies and through a pathway. The gas detector includes at least one broadband light source, at least one detector, and an electronically tunable filter element disposed in the pathway and between the at least one light source and the at least one detector. The electronically tunable filter element allows a window of radiation frequencies to pass through the filter and suppresses other radiation frequencies. The window pass through range of frequencies is less than the first range of frequencies. The electronically tunable filter element is tuned to allow different windows of radiation frequencies to pass through the filter. By at least one detector, photonic radiation energy that passes through the tuned electronically tunable filter element and impinges on the detector is measured to form a spectral absorption signature characterizing constituents of gas in the pathway. A signal is provided characterizing the spectral absorption signature.

[0006] In another aspect, a system includes a a broadband light source, a detector, an electronically tunable filter element, and a controller. The broadband light source transmits radiation over a range of frequencies and through a pathway. The pathway is between the illumination source and the detector. The electronically tunable filter element is in the pathway and limiting to a window the frequencies of radiation that impinges on the detector. The controller is configured to tune the electronically tunable filter element to a plurality of predetermined windows and measure the intensity of filtered radiation at a plurality of frequency bands.

[0007] In yet another aspect, data comprising a spectral absorption spectral signature of constituents of gas having a peak and one or more side lobes is received. The spectral absorption signature was measured using a gas detector comprising at least one broadband light source, at least one detector, a controller, and an electronically tunable filter element disposed in a pathway and between the at least one light source and the at least one detector. The spectral absorption signature being acquired by emitting, using the broadband light source, photonic radiation over a range of frequencies and through the pathway, tuning the electronically tunable filter element to allow different windows of radiation frequencies to pass through the filter, and measuring the radiation energy that passes through the tuned electronically tunable filter. Using the controller, a signature feature is computed including one or more peak to side lobe ratios. Using the controller, the signature feature is compared to a set of predetermined signature features. Each predetermined signature feature corresponds to a known target gas. Using the controller a presence likelihood of one or more of the known target gas constituents in the gas is computed based on the comparison. A signal is provided characterizing the presence likelihood.

[0008] One or more of the following features can be included. For example, the electronically tunable filter element can include a Fabry-Perot filter. Tuning the electronically tunable filter element can include varying a control voltage applied to the filter element. Tuning the electronically tunable filter element can include scanning over a set of predetermined control voltage levels, each control voltage level corresponding to a window center frequency. Tuning the electronically tunable filter element can further include using a stepping voltage supply circuit.

[0009] One or more features of the spectral absorption signature can be compared to a database of features associated with gas identities to identify one or more of the constituents of gas in the pathway. Absorption peaks and peak frequencies can be determined from the spectral absorption signature. The absorption peaks and peak frequencies can be compared to a database of gasses with known absorption peaks and peak frequencies to identify one or more of the constituents of gas in the pathway.

[0010] Information can be provided about the identified gas. Providing can include recalling gas specific information from a database and transmitting the information. The information about the identified gas can include at least gas name, alarm threshold settings, and high and low alarm level trigger points.A concentration of one or more of the constituents of gas in the pathway can be determined based on at least the absorption signature.

[0011] The transmitted photonic radiation can include infrared radiation. Providing the signal can include at least one of persisting, loading, displaying, and transmitting the signal. A presence of constituents of target gas in the pathway can be detected for using the measured radiation energy and using a single measurement.

[0012] Using a second gas detector, photonic radiation can be emitted over a second range of frequencies and through a second pathway. The second gas detector can include at least one second broadband light source, at least one second detector, and a second electronically tunable filter element disposed in the second pathway and between the at least one second light source and the at least one second detector. The second electronically tunable filter element can allow a second window of radiation frequencies to pass through the second filter and suppress other radiation frequencies. The second window pass through range of frequencies can be less than the second range of frequencies. The second electronically tunable filter element can be tuned to allow different windows of radiation frequencies to pass through the second filter. By at least one second detector, photonic radiation energy that passes through the second tuned electronically tunable filter element and impinges on the second detector can be measured to form a second spectral absorption signature characterizing constituents of gas in the second pathway. A presence of oxygen can be measured using an oxygen sensor. A signal characterizing the second spectral absorption signature and the oxygen presence can be provided.

[0013] The controller can be further configured to tune at least a center frequency of the window of the electronically tunable filter element. The controller can tune the window center frequency of the electronically tunable filter element by varying a voltage applied to the electronically tunable filter element. The system can further include an adjustable supply module capable of varying a voltage applied to the electronically tunable filter element. The system can further include a second filter element and a corresponding reference detector. The controller can be configured to detect a spectral absorbance signature of one or more gas constituents in the pathway and identify the gas constituents.

[0014] The system can further include a second broadband light source transmitting radiation over a second range of frequencies and through a second pathway, a second detector, the second pathway being between the second light source and the second detector, a second electronically tunable filter element in the second pathway and limiting to a window the frequencies of radiation that impinges on the second detector, and a second controller configured to tune the second electronically tunable filter element to a plurality of predetermined windows and measure the intensity of filtered radiation at a plurality of frequency bands.

[0015] The signature feature can include a peak to side lobe ratio for each non-zero side lobe. The absorbance spectral signature can contain samples spaced apart in frequency by at least 25 nanometers. The absorbance spectral signature can include values characterizing a percent absorption of photonic radiation by the constituents of gas. A side lobe can be a non-peak and non-zero value in the absorbance spectral signature. Providing the signal can include at least one of persisting, loading, displaying, and transmitting signal.

[0016] Using the controller, the absorbance spectral signature peak and corresponding frequency can be compared to a set of predetermined absorbance spectral signature peaks and corresponding frequencies, each predetermined absorbance spectral signature corresponding to a known target gas. Using the controller, a subset of known target gas constituents that have a likelihood of being present in the gas can be determined based on the comparison. The set of predetermined signature features used in the comparison can correspond to the subset of known target gas constituents.

[0017] Information about the known target gas constituents can be provided. Providing can include recalling gas specific information from a database and transmitting the information. The information about the identified gas can include at least gas name, alarm threshold settings, and high and low alarm level trigger points. A concentration of one or more of the known target gas constituents in the gas can be determined.

[0018] Computer program products are also described that comprise non- transitory computer readable media storing instructions, which when executed by at least one data processors of one or more computing systems, causes at least one data processor to perform operations herein. Similarly, computer systems are also described that may include one or more data processors and a memory coupled to the one or more data processors. The memory may temporarily or permanently store instructions that cause at least one processor to perform one or more of the operations described herein. In addition, methods can be implemented by one or more data processors either within a single computing system or distributed among two or more computing systems.

[0019] The subject matter described herein provides many advantages. For example, the current subject matter reduces cost by reducing the number of required parts, complexity of parts, and number of required devices to achieve the same detection objectives. For example, static band pass filter elements required for each specific gas species or detector are no longer required and multiple gases can be detected with a single inexpensive and portable sensor. Additionally, using the current subject matter unknown types, and unknown quantities of gas can be analyzed, and specific gas species can be discriminated. Appropriate measurement and/or alarm signaling based on the measurement parameters can be provided to relevant human operators or control modules.

[0020] The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a process flow diagram illustrating a method of measuring or estimating a spectral absorption signature (i.e., absorption spectrum) of gas constituents; [0022] FIG. 2 is a process flow diagram illustrating a method of using a gas sensor to detect for a presence of target gas constituents in a gas;

[0023] FIG. 3 is a system diagram illustrating an example gas detector;

[0024] FIG. 4 is a system diagram illustrating a gas detector configured in an open path configuration where the light source is remote from the detector;

[0025] FIG. 5 is a plot illustrating the transmission characteristics of an example electronically tunable filter element and detector;

[0026] FIG. 6 is a plot of two hydrocarbon based gases (acetylene and ethylene) showing a separation of approximately 200 nanometers between the peak absorption bands for each gas;

[0027] FIG. 7 is a process flow diagram illustrating a method of determining a presence likelihood of one or more target gas constituents in the gas by utilizing off peak absorption values;

[0028] FIG. 8 is a plot illustrating a spectral absorption signal of constituents of gas containing methane (CH₄) and pentane (C H₆) measured by an example gas detector with a window center-frequency-shift of 50 nanometers;

[0029] FIG. 9 is a process flow diagram illustrating an example scan algorithm utilized by a gas detector with an electronically tunable filter element; and

[0030] FIG. 10 is a system diagram illustrating an example implementation of a gas detector system 1000 capable of detecting a broad range of potentially harmful gases.

[0031] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION

[0032] FIG. 1 is a process follow diagram illustrating a method 100 of measuring or estimating a spectral absorption signature (i.e., absorption spectrum) of constituents of a gas. Using a gas detector photonic radiation is emitted at 1 10. The photonic radiation is emitted at least over a range of frequencies that are to be measured and through a pathway, which contains at least the gas constituents. The gas detector includes at least one light source, at least one detector, and an electronically tunable filter element disposed in the pathway between the light source and the detector. The electronically tunable filter element is an adjustable band pass filter that allows certain frequencies of photonic radiation to pass through the filter while suppressing others. The gas detector can modify the band pass or window characteristics, such as center frequency, electronically. The electronically tunable filter element can include, for example, a Fabry-Perot Interferometer, which has partially transmitting mirrors arranged in parallel at a distance such that only radiation that satisfies resonance conditions transmits through the filter. Applying a voltage to the example Fabry-Perot

Interferometer changes the distance between the partially transmitting mirrors thereby causing the window of frequencies (i.e., band pass frequencies) of the interferometer to change.

[0033] The broadband light source can include, for example, a glass bulb or solid-state emitter that simultaneously emits light over a portion of the visible and/or infrared (IR) spectrum. The visible and IR spectrum can include photonic radiation with wavelengths between 380 nanometers (violet light) and 10500 nanometers (IR light). The light source can include multiple light sources transmitting light over different frequency bands. The light source transmits at least over a range of frequencies that are being measured. As used here, broadband refers to a band of frequencies that includes at least a range of frequencies that are being measured, and can include additional frequencies. The detector can include photo detectors or other photo sensors capable of measuring photonic radiation energy content at a wide range of frequencies. [0034] The gas detector tunes the electronically tunable filter element at 120 to allow different windows of radiation frequencies to pass through the filter and impinge the detector. The detector measures the radiation energy that passes through the tuned electronically tunable filter element at 130. Each measurement characterizes the photonic radiation absorption characteristics of the gas constituents at a particular window of frequencies (e.g., the measurement can be expressed as a percentage of emitted light that is absorbed or transmitted by the gas constituents at a particular window of frequencies). By taking measurements of different windows of frequencies, the gas detector can form a spectral absorption signature of the gas constituents. The spectral absorption signature of the gas constituents characterizes absorption characteristics of the constituents of gas across a plurality of frequency windows.

[0035] Tuning the electronically tunable filter element can include the gas detector varying a control voltage applied to the filter element. The tuning can include scanning the control voltage over a set of predetermined control voltage levels, with each control voltage level corresponding to a window center frequency. The gas detector can include a stepping voltage supply circuit for varying the voltage. For example, the voltage can step from 0 to 33 Volts in predetermined increments. The window center frequencies can correspondingly step from 4300 nanometers to 3000 nanometers in, for example, 25, or 50 nanometer steps.

[0036] The spectral absorption signature is provided at 140. The providing can include, for example, persisting, loading, displaying, or transmitting data

characterizing the spectral absorption signature or providing a signal that characterizes the spectral absorption signature.

[0037] The spectral absorption signature can be used to identify particular target gas constituents in a gas. This can be accomplished by, for example, comparing one or more features of the measured spectral absorption signature to a database of features associated with gas identities. The features can include peak absorbance values and frequencies. The gas can be identified when the measured spectral absorption signature peak values and frequencies are similar to one or more of the known gases in the database. Once a gas constituent is identified, information about the gas (e.g., name, alarm threshold settings, toxicity levels, high and low alarm level trigger points, or other associated data stored in a database) can be provided.

[0038] FIG. 2 is a process flow diagram illustrating a method 200 of using a gas detector to detect for a presence of target gas constituents in the gas. A gas detector is used to tune a tunable filter element to allow a preselected window of radiation frequencies to pass through the filter at 210. A broadband light source of a gas detector emits photonic radiation through a pathway; the tunable filter element is in the pathway and between the broadband light source and a detector. Photonic radiation in the preselected window of frequencies pass through the filter and the detector measures the radiation energy at 230. Based on the measurement, the gas detector detects for a presence of target gas constituents in the pathway at 240. The detection can be based on a measurement at a single window center frequency. The target gas constituents can be predetermined and the detection can include comparing the measured radiation energy to a database of predetermined radiation values for the selected window of frequencies. A characterization of the presence of the target gas constituents is provided at 250.

[0039] The gas detector can tune the tunable filter to allow different windows of radiation frequencies to pass through the filter at 260. For each of the different windows, the gas detector can detect for a present of different target gas constituents in the pathway at 270. A characterization of the presence of the different target gas constituents can be provided.

[0040] FIG. 3 is a system diagram illustrating an example gas detector 300. The gas detector 300 includes at least a broadband light source 305, a detector 310, an optical pathway 315 between the illumination source 305 and the detector 310, an electronically tunable filter element 320 in the optical pathway 315, and a controller 325.

[0041] The broadband light source 305 can include an emitter that simultaneously emits light over a portion of the visible and/or infrared (IR) spectrum. The detector 310 can include photo detectors or other photo sensors capable of measuring photonic radiation energy content at a wide range of frequencies. The broadband light source 305 can be remote from the detector 310. The length of the optical pathway 315 can vary among implementations. For example, the optical pathway 315 can be a few centimeters in length in some implementations to hundreds of feet in other

implementations. A reflector 330 can be included in the optical path to redirect light emitted by the broadband light source 305 towards the electronically tunable filter element 320 and detector 310.

[0042] The controller 325 can include data processing capability such as at least one processor coupled to memory. The controller 325 can further include an analogue to digital converter (ADC), input/output (I/O), and signal processing modules. The controller 325 can enable the measurement of the spectral absorption signature and analysis thereof to discriminate gas constituents in the pathway and provide information related to the identified gas constituents.

[0043] The electronically tunable filter element 320 can be controlled (i.e., tuned) by the controller 325 and/or adjustable power supply 335. The example implementation shown in FIG. 3 also has a reference detector 340 with second filter element 345 that allows the gas detector 300 to measure losses and converts the detector 310 measurements into gas value readings. The reference detector with second filter element 345 enables measurement of radiation transmission at predetermined

frequencies, for example, at 4400 nm. At the predetermined frequencies, little or no absorption occurs in any constituent of gas, and the measurement made by the reference detector with second filter element 345 can be used to estimate other pathway

transmission losses (e.g., contamination of the optical system by dust or mud causes intensity attenuation). The estimate can be applied to the measurements made by the electronically tunable filter element 320 to isolate the gas constituent transmission losses. The example implementation also has a power supply 350, source controller 355, and a window 365. [0044] The window 365 is in the optical pathway 315 between the broadband light source 305 and the detector 310. The window is used as a protective element in an explosion proof detector head and as a frequency selective pass element for a given range of photonic radiation frequencies. As an example, for a gas detector 300 capable of measuring spectrums between 2800 nanometers and 4300 nanometers (e.g., to measure for hydrocarbon combustible gases), the window material used can include Sapphire. For a gas detector 300 capable of measuring between 3900 nanometers and 5000 nanometers (e.g., to measure carbon monoxide, Nitrogen Dioxide, Sulfur Dioxide, Hydrogen Sulfide, and non-hydrocarbon gases) the window material can include Zinc Selenide (ZnSe2). Zinc Selenide can also be used for a gas detector 300 capable of measuring between 8000 nanometers and 10500 nanometers (e.g., to measure refrigerant gases such as

chlorofluorocarbons, hydro fluorocarbons, Rl 1, R12, R22, HFC132, and HFC134A).

[0045] FIG. 4 is a system diagram 400 illustrating a gas detector 300 configured in an open path configuration where the broadband light source 305 is remote from the detector 310. The distance between the broadband light source 305 and the detector 310 is limited by the intensity of the broadband light source 305. In FIG. 4, the optical pathway 315 is shown as being 300 feet in length, although different lengths are possible depending on the applications. The open path configuration could be used in an application where the detector may be looking or observing an area above a series of delivery pipes or storage containers. This could also be used in outdoor storage facilities that require large area monitoring.

[0046] In one implementation, the detector 310 and electronically tunable filter element 320 can include a pyroelectric detector with tunable Fabry-Perot filter (for example, part no. LFP-3041L-337 by InfraTec, Dresden Germany). FIG. 5 is a plot 500 illustrating the transmission characteristics of an example electronically tunable filter element 320 and detector 310. Five separate band pass windows are illustrated for different control voltages. The detector 310 and electronically tunable filter element 320 can have a window aperture of +/- 200 nanometers around center frequency. The tuning voltage range is 0 to 33 volts (direct current), corresponding to a scanning range of 3000 to 4300 nanometers. Scan step sizes are voltage dependent. When the voltage step is 1.5 volts, the window-center-frequency shift is 50 nanometers. When the voltage step is 0.75volts, the window-center-frequency shift is 25 nanometers. Window step and settle time is 5 milliseconds when the voltage step is 1.5 volts. Peak window transmissivity is 65% in reflective mode of operation with peak signal to noise ratio.

[0047] The gas constituents may not be limited to a single gas component but may contain several different target gas constituents, each with a different absorption signature. FIG. 6 is a plot 600 of two hydrocarbon based gases (acetylene and ethylene) showing a separation of approximately 200 nanometers between the peak absorption bands for each gas. Ethylene's peak absorption 610 occurs at approximately 3100 cm^"1 while acetylene's peak absorption 620 occurs at approximately 3300 cm^"1. Thus, a gas detector 300 with a 50-nanometer window spacing that was measuring constituents of gas comprising both acetylene and ethylene would detect both the peak 610 at 3100 cm^"1 and the peak 620 at 3300 cm^"1. By comparing measured peak values and frequencies to a database containing peak values and frequencies of potential target gas constituents, the identity of one or more of the present gas constituents may be determined.

[0048] However, not all gases have a large separation between peak absorption frequencies. FIG. 7 is a process flow diagram 700 illustrating a method of determining a presence likelihood of one or more target gas constituents in the gas by utilizing off peak absorption values to better discriminate constituent gases. A spectral absorption signature is received at 710. The spectral absorption signature is measured using a gas detector including at least one broadband light source, at least one detector, a controller, and an electronically tunable filter element disposed in a pathway and between the light source and detector. The spectral absorption signature can be measured using, for example, a 25 or 50 nanometer window center frequency shift. The spectral absorption signature has a peak value and one or more non-zero side lobe values. A signature feature is computed at 720 that includes peak to side lobe ratios. A peak to side lobe ratio is a proportional ratio between the peak value and one side lobe value. The signature feature is compared at 730 to a set of predetermined signature features. Each predetermined signature features corresponds to a known target gas. By incorporating information from some or all of the measured spectrum into the signature feature, as opposed to using just the peak value, gas constituents with overlapping or close to overlapping absorption signatures can be discriminated. Based on the comparison, a presence likelihood of one or more of the known target gas constituents in the gas can be determined at 740. The presence likelihood is provided at 750.

[0049] FIG. 8 is a plot 800 illustrating a spectral absorption signal of a constituents of gas containing methane (CH₄) and pentane (C₆H₆) measured by an example gas detector 300 with a window center-frequency-shift of 50 nanometers.

Methane's peak absorption can be seen at 810 (12% transmission) and pentane's peak absorption can be seen at 820 (75% transmission). An example side lobe of methane would be the minimum absorbance band having 96% transmission and an example side lobe of pentane would be the minimum absorbance band having 90% transmission. An example peak to side lobe ratio (e.g., peak / side lobe) would then be .12 / .96 = 0.125 for methane and .75 / .90 = 0.833 for pentane. Additional peak to side lobe ratios could be computed for this example, however, even using only these two values (i.e., signature features), a comparison of the signature features to a database of predetermined signature features for known target gas constituents could discriminate both methane and pentane in the measured absorption spectrum signature.

[0050] FIG. 9 is a process flow diagram 900 illustrating an example scan algorithm utilized by a gas detector 300 with an electronically tunable filter element 320. The light source 305 is enabled at 905 and the electronically tunable filter element 320 control voltage is initially set to 0 volts. The light source, in this implementation, is continuously transmitting. The gas detector 300 then performs a scan acquisition phase 910, which includes waiting for control voltage to settle, taking three 1 ms readings or measurements from the detector 310, and placing those three measurements into an array 915. The three measurements are averaged to minimize any transient artifacts or noise and the average is placed into a table 920. During the scan acquisition phase 910, after the three readings have occurred, the electronically tunable filter element 320 control voltage is shifted by 1.5 volts, which corresponds to a 50 nanometer window center frequency shift. A peak reading is compared against past peak readings and stored for future use. The scan acquisition phase 910 repeats until the entire measurable spectrum is acquired. In this example, with a 50 nanometer window center frequency shift, 28 shifts will occur to acquire measurements from 4300 nanometers to 3000 nanometers.

[0051] When the scan acquisition phase 910 is completed, the peak reading is compared at 925 against a table 930 of peak spectral values for known target gas constituents. The table 930 also includes signature features comprising peak to side lobe ratios, as well as other data associated with the known gas constituents such as alarm values, and other information. Based on the comparison performed at 925, a list or subset of known target gas constituents 932 are identified as possible matches at 935. The subset of known target gas constituents are compared with the data in the table 920 for possible matches at 940 and peak to side lobe ratios are calculated at 945. The list or subset of possible known target gas constituents 932 can be further reduced to a second subset 960 by comparing the measured spectral values with the stored spectral values at 950. This comparison can eliminate potential target gas constituents that do not express similar peak values at similar frequencies. The peak to side lobe ratio comparison can also be performed at 955 to further reduce the list of possible gas constituents to one or more gases that are likely to be present in the target gas or the comparison 960 can confirm the identity of the potential target gas constituent. One or more present gas constituents can be identified at 965. Once one or more gas constituents have been identified, additional information about the gas constituents can be extracted from the table 930. The additional information can include or be used to determine, for example, gas name, toxicity level data, alarm threshold settings, high and low alarm level trigger points, etc. The additional information can be provided at 975, and can be used to perform other operations such as calculating a concentration of the identified gas constituents, or for signaling of alarm state conditions. The implementation described in FIG. 9 can complete two detection cycles in less than 1 second, which allows it to meet or exceed safety criteria under several agency testing standards. The implementation described in FIG. 9 can be varied to meet additional timing or accuracy requirements. [0052] Alternatively, or in addition to the above, if a number of gases are identified as potential present gas constituents, then the gas detector 300 can tune the window-center-frequency to each potential present gas known peak frequency and measure the absorption characteristics. This known peak frequency may be different from a frequency previously measured. For example, if the gas detector 300 steps through a range of frequencies and performs a measurement every 50 nanometers, including 3600 nanometers and 3650 nanometers, and it is known that a potential present gas has a peak frequency at 3620 nanometers, then the gas detector 300 can tune the window-center- frequency to 3620 nanometers. This measurement can be used to verify or confirm a presence of the gas.

[0053] Detecting for specific gas constituents has many applications. For example, the current subject matter can be used in semiconductor manufacturing, chemical warfare detection (e.g., in subways), for monitoring drill heads, fracking ponds, and fracking fluid tanks. The current subject matter can be used in, for example, plastics manufacturing, hydrocarbon gas cracking operations, open air refining, garbage processing facilities, recycling plants, gas drilling rigs, deep-ocean drilling rigs, refrigeration plants, and generally anywhere there is a need to measure gases such as hydrocarbons and carbon dioxide. The current subject matter could be used to monitor gas bottle filing stations, where hydrocarbon gases are being used in cylinder refilling operations (e.g., refilling welding gas cylinders).

[0054] The gas detector 300 can be configured to detect for generally dangerous or toxic target gases or can be configured to detect for a single or small set of target gas constituents. Depending on the application, there may be only two or three target gas constituents that are of a particular concern. The current subject matter can be configured by a user or in the factory to detect for only those limited gas constituents. For example, comparisons of the measured spectral absorption signature to the table 930 in the example implementation described in FIG. 9 could be limited to only those target gas constituents of interest. [0055] FIG. 10 is a system diagram illustrating an example implementation of a gas detector system 1000 capable of detecting a broad range of potentially harmful gases. The gas detector system 1000 includes two gas detectors 300 at 1005 and 1010 (configured as described above and shown in FIG. 4), and an oxygen sensor 1015. Gas detector 1005 includes a sapphire window, and a light source and electronically tunable filter element and detector suited for transmitting and detecting photonic radiation between at least 3000 nm and 4300 nm. Gas detector 1005 is suited to detect hydrocarbon gases. Gas detector 1010 includes a zinc selinide window and a light source and electronically tunable filter element and detector suited for transmitting and detecting photonic radiation between at least 3900 nm to 5000 nm. Gas detector 1010 is suitable to detect toxic gases. Gas detectors 1005 and 1010 are integrated into one common housing with oxygen sensor 1015.

[0056] The gas detector system 1000 is a single packed solution for detecting a wide range of hazardous and harmful gases. For example, mineworkers and operations must monitor many CH4 gases species, carbon dioxide, sulfur dioxide, hydrogen sulfide, and oxygen depletion levels. The gas detector system 1000 can provide gas detection for each gas of interest instead of having numerous individual gas sensors to detect for each gas. Furthermore, the gas detector system 1000 can replace catalytic combustible sensors (electrochemical sensors), which are susceptible to heavy molecule poisoning and are thus less reliable than a photonic radiation gas sensor.

[0057] Various implementations of the subject matter described herein may be realized in digital electronic circuitry, integrated circuitry, specially designed ASICs (application specific integrated circuits), computer hardware, firmware, software, and/or combinations thereof. These various implementations may include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. [0058] These computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and may be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. As used herein, the term "machine-readable medium" refers to any computer program product, apparatus and/or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine- readable signal. The term "machine-readable signal" refers to any signal used to provide machine instructions and/or data to a programmable processor.

[0059] To provide for interaction with a user, the subject matter described herein may be implemented on a system having a display device (e.g., a OLED (Organic Light Emitting Diode display ), CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and devices by which the user may provide input to the system. Other types of devices may be used to provide for interaction with a user as well; for example, feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form, including acoustic, speech, or tactile input.

[0060] Although a few variations have been described in detail above, other modifications are possible. For example, the logic flow depicted in the accompanying figures and described herein do not require the particular order shown, or sequential order, to achieve desirable results. Other embodiments may be within the scope of the following claims.

Claims

WHAT IS CLAIMED IS

1. A method comprising :

receiving data comprising a spectral absorption spectral signature of constituents of gas having a peak and one or more side lobes, the spectral absorption signature measured using a gas detector comprising at least one broadband light source, at least one detector, a controller, and an electronically tunable filter element disposed in a pathway and between the at least one light source and the at least one detector, the spectral absorption signature acquired by emitting, using the broadband light source, photonic radiation over a range of frequencies and through the pathway, tuning the electronically tunable filter element to allow different windows of radiation frequencies to pass through the filter, and measuring the radiation energy that passes through the tuned electronically tunable filter;

computing, using the controller, a signature feature comprising one or more peak to side lobe ratios;

comparing, using the controller, the signature feature to a set of predetermined signature features, each predetermined signature feature corresponding to a known target gas;

determining, using the controller and based on the comparison, a presence likelihood of one or more of the known target gas constituents in the gas; and

providing a signal characterizing the presence likelihood.

2. The method of any of the preceding claims, wherein the signature feature includes a peak to side lobe ratio for each non-zero side lobe.

3. The method of any of the preceding claims, wherein the absorbance spectral signature contains samples spaced apart in frequency by at least 25 nanometers.

4. The method of any of the preceding claims, wherein the absorbance spectral signature comprises values characterizing a percent absorption of photonic radiation by the constituents of gas.

5. The method of any of the preceding claims, wherein a side lobe is a non-peak and non-zero value in the absorbance spectral signature.

6. The method of any of the preceding claims, wherein providing the signal includes at least one of persisting, loading, displaying, and transmitting signal.

7. The method of any of the preceding claims, further comprising:

comparing, using the controller, the absorbance spectral signature peak and corresponding frequency to a set of predetermined absorbance spectral signature peaks and corresponding frequencies, each predetermined absorbance spectral signature corresponding to a known target gas; and

determining, using the controller and based on the comparison, a subset of known target gas constituents that have a likelihood of being present in the gas;

wherein the set of predetermined signature features used in the comparison correspond to the subset of known target gas constituents.

8. The method of any of the preceding claims, further comprising providing information about the known target gas constituents.

9. The method of claim 8, wherein providing includes recalling gas specific information from a database and transmitting the information.

10. The method of claim 8, wherein the information about the identified gas includes at least gas name, alarm threshold settings, and high and low alarm level trigger points.

11. The method of any of the preceding claims further comprising determining a concentration of one or more of the known target gas constituents in the gas.

12. A non-transitory computer program product storing instructions, which when executed by at least one data processor of at least one computing system, implement a method according to any of the preceding claims.

13. A system comprising: at least one data processor; and memory storing

instructions, which when executed by the at least one data processor, implement a method according to any of claims 1 to 11.

14. The system of claim 13, wherein the method is performed using a gas detector comprising at least one broadband light source, at least one detector, a controller, and an electronically tunable filter element disposed in a pathway and between the at least one light source and the at least one detector, the spectral absorption signature acquired by emitting, using the broadband light source, photonic radiation over a range of frequencies and through the pathway, tuning the electronically tunable filter element to allow different windows of radiation frequencies to pass through the filter, and measuring the radiation energy that passes through the tuned electronically tunable filter;