Spectrometer-based open path gas detector

Abstract

An open path gas detection system includes a transmitter and a receiver. The emitter is configured to generate illumination through an open path, the illumination having a broadband spectrum. The receiver is positioned to detect the illumination from the transmitter after the illumination has traveled through the open path. The receiver includes at least one spectrometer configured to determine spectral information of the illumination, to identify at least one gas of interest based on the spectral information, and to provide an output based on the at least one gas of interest.

Description

[0001] This application is a divisional application of patent application No. 202210996446.9, entitled "Open Path Gas Detector Based on Spectrometer", filed on August 18, 2022.

[0002] Cross-references to related applications

[0003] This application is based on and claims the benefit of U.S. Provisional Patent Application No. 63 / 234,839, filed on August 19, 2021, the contents of which are incorporated herein by reference in their entirety. Background Technology

[0004] Open-path gas detectors (OPGDs) are line-of-sight gas monitors typically installed for long-range monitoring of gas presence. OPGDs offer high-speed responses, operate under extreme conditions, and require fewer instruments to monitor large areas or regions. These detectors generally detect the unique spectral fingerprints of individual chemical substances. Such gas detectors typically consist of a pair of devices: a source unit and a detector unit. The source unit generates a high-energy beam that travels through the open path. The target gas absorbs some of the radiated energy and transmits the remainder. The detector unit then detects the transmitted energy within a specific spectral range based on the target gas.

[0005] The use of nondispersive infrared spectroscopy to detect hydrocarbon gases and UV spectroscopy to detect toxic and / or flammable gases is known. It essentially involves transmitting broadband radiation along a path through the area being monitored. The wavelengths of the radiation are chosen in two different ranges; one is absorbed by the gas of interest and is referred to as the signal (the “signal” wavelength is in…). Figure 1A (As shown in block 10). And a reference is selected from different wavelength ranges in which the target gas does not exhibit significant absorption (the "reference" wavelength is...). Figure 1A (As shown in block 20). The intensity of the radiation traveling along the path in the monitored area and the attenuation of the ratio of that radiation (signal and reference) provide a measurement of the amount of target gas in the monitored area. However, factors other than absorption by the target gas can also cause radiation attenuation, including interference or obstruction by rain, fog and / or vapor, atmospheric scattering of radiation, contamination of the lens surface (e.g., dirt or condensation), and component aging. In these cases, false alarms may occur. Therefore, the reliability of current open-path gas detectors is limited.

[0006] Current open-path gas detectors typically use imaging systems that include beamsplitters for each detector (signal and reference). Each detector has a dedicated bandpass interferometer filter to allow the appropriate wavelength to be transmitted to the intended detector. In this arrangement, the maximum number of channels is limited to two using beamsplitters. Summary of the Invention

[0007] An open-path gas detection system includes a transmitter and a receiver. The transmitter is configured to generate illumination that travels through an open path, the illumination having a broadband spectral wavelength. The receiver is positioned to detect the illumination from the transmitter after the illumination has traveled through the open path. The receiver includes at least one spectrometer configured to determine spectral information of the illumination in order to identify at least one gas of interest based on the spectral information and to provide an output based on the at least one gas of interest. Attached Figure Description

[0008] Figure 1A This is a graph of transmittance versus wavelength used in open gas detectors.

[0009] Figure 1B It is a graph of transmittance versus wavelength in a pair of wavelength bands for methane and water.

[0010] Figure 2A and Figure 2B This is a graph showing the transmittance versus wavelength of an open gas detector using a variety of different wavelengths according to one embodiment.

[0011] Figure 3 This is a schematic diagram of an open-path gas detector based on a spectrometer, according to one embodiment.

[0012] Figure 4A and Figure 4B These are, respectively, a measured transmittance versus wavelength curve according to one embodiment and a theoretical transmittance versus wavelength curve.

[0013] Figure 5 This is a system block diagram of an open path gas detection system according to an embodiment of the present invention.

[0014] Figure 6 This is a flowchart of a method for operating an open-path gas detection system according to an embodiment of the present invention. Detailed Implementation

[0015] The embodiments described herein provide novel optical open-path gas detectors using low-resolution spectrometers for gas detection (such as toxic gases and / or hydrocarbons) in the ultraviolet (UV) and / or short-wave infrared / mid-infrared (SWIR / MIDIR) ranges. While current open-path gas detectors offer acceptable sensitivity, they have relatively low immunity to false alarms and limited gas selectivity. To overcome these limitations, the embodiments described herein provide an autonomous, miniaturized, low-resolution spectrometer UV and IR version specifically tailored for diagnosing a variety of gases with high immunity to false alarms.

[0016] According to the embodiments described herein, radiometric measurements are performed with more than one signal wavelength and more than one reference wavelength to significantly improve performance and reduce false alarms, while also expanding gas selectivity and reading accuracy. The embodiments described herein measure the spectral fingerprint of a gas and then calculate the ratios and correlations at different wavelengths at which the target gas is absorbed.

[0017] Figure 1B It is a graph of transmittance versus wavelength in a pair of wavelength bands for methane and water. Figure 1B The illustration shows the limitations of current open-path gas detectors that use two channels (i.e., a single signal and a reference). Figure 1B The diagram illustrates the transmittance versus wavelength in a pair of wavelength bands 22 and 24 for an open path containing both methane 26 and water vapor 28. In the case of methane and water vapor, for mid-infrared radiation, water and water vapor act as particles that absorb specific electromagnetic radiation, which is a common cause of attenuation. This situation can prevent false alarms. Furthermore, scattering, diffraction, and other processes can also contribute to and affect the signal. In this case, although the signal band must be insensitive to substances other than gases to avoid false alarms, this aspect can introduce errors when only two channels are used.

[0018] Figure 2A and Figure 2B This is a graph showing the transmittance versus wavelength of an open gas detector using various different wavelengths according to an embodiment of the present invention. Figure 2A It shows the relationship with Figure 1A Compared to the two-channel approach shown, multiple wavelength bands of interest (30, 40, 50, 60, 70, 80) are available when determining the presence and / or concentration of various gases. Similarly, Figure 2B It shows the relationship with Figure 1B Compared to the two-channel approach shown, multiple wavelength bands of interest are available when determining the presence and / or concentration of various gases. More specifically, Figure 2AThe illustration shows six different wavelength bands with a bandwidth of approximately 0.15 µm between 2.0 µm and 3.0 µm in the near-infrared region. In another embodiment, Figure 2B The diagram illustrates eighteen different wavelength bands (90-1, 90-2, ..., 90-18) between 1.9 µm and 2.6 µm, each with a bandwidth of approximately 0.038 µm. Utilizing this increasing number of wavelength bands, such as... Figure 2A and Figure 2B As shown, this allows for the detection of only the gas of interest and reduces false alarms.

[0019] Figure 3 This is a schematic diagram of a spectrometer-based open-path gas detector according to one embodiment. The open-path gas detector 100 includes an emitter or source 102 and a receiver or detector 104. The source 102 includes a light source that generates illumination of multiple wavelengths. In some embodiments, the illumination wavelengths can range from IR wavelengths to UV wavelengths. In other embodiments, the wavelength range is within a smaller region, such as IR pulses. Collimating optics 106 in the source 102 are used to project a collimated beam 108 from the emitter 102 through the open path to the receiver 104. The receiver 104 includes telescope optics 110 that captures the incident light and focuses the energy to a spectrometer (i.e., a detector capable of real-time spectral detection) for analysis. As light travels through the open path of air, it is affected by any compounds present in the beam path (e.g., gases or water vapor). In the case of gases in the open path, the unique combination of various detection wavelengths provides a “spectral fingerprint.” In one embodiment, the receiver / detector 104 with the spectrometer also includes a memory containing a list of spectral fingerprints for each gas of interest. This stored spectral fingerprint information associated with the gas of interest allows the receiver / detector to analyze the received illumination to identify each gas. Accordingly, the illumination collected by detector 104 from the beam after beam 108 has traveled through an open path is compared with a library reference of stored gases, and pattern matching techniques are used for analysis. Furthermore, gas readings may be affected by a correlation factor threshold, such that a reading is reported only if the correlation factor is sufficiently high or otherwise exceeds the threshold. According to the embodiments described herein, multiple ratios of illumination levels of various different signal bands to various different reference bands can be employed to provide higher resolution.

[0020] According to an embodiment of the invention, receiver 104 includes a spectrometer. This device detects spectral information directly from the light beam. Therefore, the spectrometer differs from a simple photodetector, or even from detectors that use Fourier transform to derive spectral information (such as open-path Fourier transform infrared spectroscopy (OP-FTIR) systems). Spectrometers allow for the simultaneous capture of a large number of wavelength bands (such as…). Figure 2B (The 18 or more wavelength bands shown) can then be analyzed by a receiver as signal bands or reference bands to be compared with a stored spectral fingerprint stored in the detector.

[0021] An example of a spectrometer that can be used according to embodiments of the invention is a multichannel spectrometer, such as a one-dimensional (1D) (linear array) or two-dimensional (2D) silicon-based charge-coupled device (CCD). A 2D CCD is a spectrometer having thousands of elements (pixels) generally arranged in a rectangular shape. Some 2D CCDs offer high responsivity from the near-infrared (NIR) region to 1.1 micrometers. At longer wavelengths, photon energies are lower, and specific materials should be used in 2D CCD spectrometers. For example, indium gallium arsenide (InGaAs) provides suitable detection in the range of 0.9 µm to 1.7 µm, and spectrometers using this material are available in configurations providing detection up to 2.0 µm. Other multichannel detectors using different materials (such as HgCdTe or InSb) are also available for detection at longer wavelengths. Other multichannel detectors include, but are not limited to, PbS sensors and / or PbSe sensors. According to the embodiments described herein, the receiver may include an NIR spectrometer and / or a UV spectrometer. 2D CCD arrays capable of spectral detection are commercially available.

[0022] Figure 4A and Figure 4B These are, respectively, a measured transmittance versus wavelength curve according to one embodiment and a theoretical transmittance versus wavelength curve. Figure 4A and Figure 4BThe illustration shows that the measured response of an open gas detector may deviate from the theoretical response. The receiver signal may be affected by the presence of other materials (i.e., materials other than the gas of interest (one or more) between the radiation source and the receiver). For example, water vapor and / or particles (such as dust) may require special attention for infrared radiation. Signal attenuation may be caused by absorption of electromagnetic radiation in the gas of interest, but it may also be due to scattering or obstruction caused by dust or contamination on the optical elements in the path. If the beam is attenuated, for example by water vapor, the wavelength of the spectral fingerprint will differ from the wavelength of the gas and will be rejected and will not pass pattern matching analysis. In this way, the embodiments described herein provide high immunity to false alarms while still providing high selectivity for the gas of interest.

[0023] Figure 5 This is a system block diagram of an open path gas detection system according to an embodiment of the present invention. The open path gas detection system 200 includes a transmitter 202 and a receiver 204. Each of the transmitter 202 and the receiver 204 is housed within a respective housing 206, 208.

[0024] Many environments in which open-path gas detectors operate are highly volatile or explosive and can be ignited by sparks or elevated surface temperatures within the gas detection system. Therefore, it is highly desirable for such gas detection systems to meet explosion protection standards. These standards require that any explosion or flame generated within the compliant equipment will not ignite the environment in which the equipment is located. These standards drive design constraints such as enclosure wall thickness and materials, and the configuration of flame quenching paths from the inside of the equipment to the external environment. An example of explosion protection standards is the ATEX certification of Ex-d standards EN60079-0 and EN60079-1 for potentially explosive air. Generally, explosion-proof enclosures are relatively large to be mechanically robust enough to contain an internal explosion without fracturing. Typically, such explosion-proof containers are very robust metal enclosures designed to withstand explosion pressures. However, for optical equipment, the enclosure must accommodate some type of window to allow light to travel through the environment.

[0025] Another method for protecting hazardous environments is to require equipment operating in those environments to meet intrinsically safe requirements. When electronics are intrinsically safe, even under fault conditions, the electronics themselves cannot generate the necessary temperature or spark to cause an explosion. An example of an intrinsically safe specification is the standard issued by Factory Mutual Research in October 1998, entitled "APPROVAL STANDARD INTRINSICALLY SAFEAPPARATUS AND ASSOCIATED APPARATUS FOR USE IN CLASS I, II, AND III, DIVISION 1 HAZARDOUS (CLASSIFIED) LOCATIONS, CLASS NUMBER 3610". Intrinsically safe requirements generally specify such low energy levels that compliance is simply impossible for circuits involving high voltage, high current, and / or high power (such as AC circuits). In at least some of the embodiments described herein, the circuit is designed and configured to meet intrinsic safety requirements such as those set forth above.

[0026] The embodiments described herein preferably include intrinsically safe circuitry within explosion-proof housings 206, 208 and / or transmitter 202 and / or receiver 204.

[0027] The transmitter 202 includes a controller 210 coupled to the source laser driver module 212. The source laser driver module 210 may include power processing components and frequency control and pulse generation logic, such that upon receiving a signal from the controller 210, the source laser driver module 212 is configured to cause the illuminator module 214 to generate a suitable pulse or signal 216 toward the receiver 204 through the housing window 217. The illuminator 214 may include one or more individual illuminators, such as a xenon lamp and / or a laser source. The controller 210 may be any suitable circuitry or logic arrangement capable of causing the laser driver module 212 to generate the pulse or signal 216. In one embodiment, the controller 210 is a microprocessor.

[0028] Receiver 204 includes one or more spectrometers 218 positioned within housing 208 near window 219. The one or more spectrometers 218 may be of the type described above and are coupled to controller 220. Each spectrometer is capable of simultaneously capturing spectral information from a pulse or signal 216 after the pulse or signal 216 has traveled through an open path. One spectrometer may be configured to acquire spectral information in a specific region (e.g., 1.9 µm to 2.6 µm), while another spectrometer is configured to acquire spectral information in another region (e.g., UV). The one or more spectrometers 218 are coupled to controller 220 to provide their spectral information to controller 220. Controller 220 may be any suitable circuitry or logic arrangement capable of receiving spectral information from the one or more spectrometers 218 and generating useful gas detection information and providing such gas detection information to output module 222. In one embodiment, controller 220 is a microprocessor. The output module may include a local display, a local alarm output device, and / or a wireless communication module configured to interact with one or more remote systems to provide output.

[0029] Controller 220 includes a spectral fingerprint storage device 224 containing spectral fingerprint information for at least one type of gas to be detected. Such spectral fingerprint information generally includes wavelengths at which a specific gas has absorption lines(s) at that wavelength. Storage device 224 may include multiple absorption wavelengths for each gas and may store such information for a large number of different gases. Additionally or alternatively, fingerprint storage device 224 may include a digital representation of the transmittance of each gas of interest in various frequency regions (e.g., NIR, MIDIR, SWIR, and / or UV) against wavelength. Controller 220 is configured to provide a pattern matching engine 226 via hardware, software, or a combination thereof. Pattern matching engine 226 receives spectral information from one or more spectrometers and applies known pattern matching techniques to identify one or more gases having spectral fingerprints that match the detected spectral information. In one embodiment, the output of the pattern matching engine is a list of potentially detected gases along with an indication of confidence or probability. In this embodiment, the output of the pattern matching engine 226 is provided to threshold setting logic 228 to select one or more gas detection outputs based on whether the confidence or probability exceeds a threshold, such as a predefined threshold or a threshold based on a statistical function (e.g., standard deviation) of the probability within the most recent (e.g., 1 hour) time window.

[0030] Figure 6This is a flowchart of a method for operating an open-path gas detection system according to an embodiment of the present invention. Method 300 begins at block 302, where an open-path gas emitter and receiver are configured. In one example, this configuration simply requires the installation of two devices to define an open optical path along which gas detection is desired. However, other initial setup operations can also be performed, such as selecting one or more gases for detection from a large set of all known gases having spectral fingerprints stored in the receiver. When a subset of gases is selected, pattern matching and threshold setting are simplified and potentially more accurate. Next, at block 304, the emitter generates illumination along the open path. This illumination may be from one or more lasers with defined spectral characteristics, or alternatively, the illumination may be a relatively broad-spectrum pulse, such as a flash from a xenon lamp. As explained above, this illumination interacts with the molecules of the gas along the open path, which affects the spectral composition of the illumination reaching the receiver. At block 306, the receiver uses one or more spectrometers located within the receiver to receive the illumination that has traveled through the open path. The spectrometers generate spectral information based on the amplitude of the illumination at various wavelengths. As described above, such spectrometers may include one or more two-dimensional CCD arrays. At box 308, one or more spectrometers provide their respective spectral information to the controller (e.g., by reading out the CCD arrays). At box 310, the controller uses the received spectral information and one or more spectral fingerprints stored in or in memory coupled to the controller to perform a pattern matching process. The controller uses the results of the matching process to generate an output, as indicated at box 312. The output may be provided locally and / or wirelessly communicated to a remote device (e.g., a process controller). As shown in dashed box 314, because method 300 iterates by returning to box 304, the method may optionally include learning and / or adjusting the spectral detection and / or matching process over time. Examples of such adjustments include changing the intensity and / or wavelength distribution of the initial illumination provided by the source. For example, in the case of using a broadband source, such adjustments may include switching to a laser illumination source. Another example of adjustment includes changing the matching process or parameters within threshold setting logic 228 in response to environmental changes (such as disturbances from water vapor, steam, or rain).

[0031] Although the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention.

Claims

1. An open-path gas detection system, comprising: An emitter configured to generate illumination through an open path, the illumination having a broadband spectrum having multiple non-overlapping wavelength bands; and A receiver, positioned to detect the illumination from the transmitter after the illumination has traveled through the open path, the receiver including at least one spectrometer configured to determine spectral information of the illumination in order to identify at least one gas of interest based on the spectral information and to provide an output based on the at least one gas of interest, wherein the receiver stores multiple spectral fingerprints associated with the gas of interest; The determination of the spectral information includes: obtaining the ratio of the intensity of the first signal wavelength to the intensity of the first reference wavelength, and obtaining the ratio of the intensity of the second signal wavelength to the intensity of the second reference wavelength; The receiver further includes: A memory storing multiple spectral fingerprints associated with the gas of interest, wherein the multiple spectral fingerprints include wavelengths in which the specific gas has absorption lines at that wavelength; and A controller configured to match the spectral information with at least one of the plurality of spectral fingerprints to detect the at least one gas of interest.

2. The open-path gas detection system according to claim 1, wherein, The controller's detector is configured to compare the identifier of the at least one gas of interest with a threshold to provide the output.

3. The open-path gas detection system according to claim 1, wherein, The at least one spectrometer includes an NIR spectrometer.

4. The open-path gas detection system according to claim 1, wherein, The at least one spectrometer includes a MIR spectrometer.

5. The open-path gas detection system according to claim 1, wherein, The at least one spectrometer includes a SWIR spectrometer.

6. The open-path gas detection system according to claim 1, wherein, The at least one spectrometer includes a UV spectrometer.

7. The open-path gas detection system according to claim 1, wherein, The at least one spectrometer includes multiple spectrometers.

8. The open-path gas detection system according to claim 1, wherein, The detector includes an explosion-proof housing, and the at least one spectrometer is positioned near a window of the explosion-proof housing.

9. The open-path gas detection system according to claim 1, wherein, The detector is configured to perform adjustments based on the spectral information.

10. The open-path gas detection system according to claim 1, wherein, The output is provided locally.

11. The open-path gas detection system according to claim 1, wherein, The detector is configured to wirelessly provide the output to a remote device.

12. The open-path gas detection system according to claim 1, wherein, The transmitter includes a collimating optics device that collimates the light traveling through the open path.

13. A method for detecting at least one gas, the method comprising: A beam of light is emitted toward a receiver through an open path, the light having a broadband spectrum having multiple non-overlapping wavelength bands; After the light has traveled through the open path, the spectral components of the light are detected using the receiver; The detected spectral components are compared with spectral fingerprints associated with multiple gases of interest to detect at least one gas of interest, wherein the spectral fingerprints include wavelengths in which a specific gas has an absorption line, and wherein the spectral fingerprints are stored within the receiver, and the comparison of the detected spectral components with the spectral fingerprints is performed by a controller within the receiver; and Provides an output indicating the detected gas of interest.

14. The method according to claim 13, wherein, The spectral components are detected using a spectrometer within the receiver.

15. The method according to claim 14, wherein, The spectrometer is an NIR spectrometer, and the gas of interest is a hydrocarbon.

16. The method of claim 14, wherein, The spectrometer is a UV spectrometer, and the gas of interest is a toxic gas.

Images