Patent Application
20220074850
Exemplary embodiments pertain to the art of gas detection systems and more specifically to a gas detection system employing semi-broadband light and a wavelength modulated band-pass filter.
Gas sensors have been used in various applications such as process monitoring and control and safety monitoring. As certain gases can be flammable, toxic, or explosive, gas detection sensors have also been used for leak detection where such gases are used or manufactured. Various types of sensors and systems have been used or proposed, including but not limited to metal oxide semiconductor (MOS) sensors, non-dispersive infrared detector (NDIR) sensors, pellistor (pelletized resistor) sensors, oxygen ion-permeable high-temperature solid electrolytes, and electrochemical cells. Gas detection systems often utilize sensitive compositional information encoded into infrared absorption signatures. That is to say, light (often infrared light) is passed through a medium suspected of containing a certain type of gas and received by a photodetector. The photodetector provides data associated with the changes to the original light. This data is compared to absorption properties of different gases to determine the presence of a gas and the type of gas as well as other information such as, for example, the concentration of the gas. With these gas detection systems, there is often a compromise between selectivity, sensitivity, and cost.
Disclosed is a method for gas detection. The method includes determining a target gas for detection in the sampling chamber, determining one or more target characteristics of the light based on the target gas, operating a light source to transmit light through a sampling chamber to an objective optical element, operating an optical filter to modulate the light based on the one or more target characteristics of the light, operating a filter to receive the light from the objective optical element and separate the light into a first light portion and a second light portion, operating the photodetector to receive the first light portion from the filter, and analyzing the first light portion to determine a presence of the target gas in the sampling chamber.
Disclosed is a system for gas detection. The system includes a light source operable to transmit light through a sampling chamber to an optical element, an active optical element operable to modulate one or more characteristics of the light, a filter operable to receive the light from the objective optical element, a photodetector, and a controller configured to determine a target gas for detection in the sampling chamber, determine one or more target characteristics of the light based on the target gas, and operate the optical filter to modulate the light based on the one or more target characteristics of the light.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
The diagrams depicted herein are illustrative. There can be many variations to the diagrams or the operations described therein without departing from the spirit of the disclosure. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term “coupled” and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification.
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
Turning now to an overview of the aspects of the disclosure, one or more embodiments provide for a gas detection system with an electrically-tunable band-pass filter which selectively transmits light from a semi-broadband light-source (e.g., light emitting diode (LED)) to a photodetector through a sampling chamber. The spectral position of the peak light emission from the light source and transmission of the filter can be chosen to coincide with an absorbing region of the infrared spectrum of a gas that may or may not be within the sampling chamber. By modulating the filter's transmission wavelength characteristics across a gas-absorption region while synchronously modulating the amplitude of the light (either by current control or as dictated by the spectral properties of the infrared source), the gas detection system can extract sensitive gas concentration measurements of a gas present in the sampling chamber from the amplitude and phase-dependence of the photodetector measurements (i.e., the frequency domain characteristics of the resultant waveform signal). The selectivity for and sensitivity to numerous gasses can be achieved by tuning characteristics of the filter and the light source, i.e., adjusting the wavelength modulation bandwidth, the wavelength peak center, the phase relation, and the source spectrum, for example.
Turning now to a more detailed description of aspects of the present disclosure,
Referring back to
In one or more embodiments, the controller 102 is configured to operate the light source 104 to vary the intensity (amplitude) of the light being emitted. In some embodiments, the light source can be any type of light source such as, for example, an LED, micro-hot-plate, infrared light source, and the like. The light source 104 can be coarsely tunable via temperature control or current control of the light source. The light source 104 emits light over a broad range of wavelengths. The tunable filter 106 is operated by the controller 102 to modulate the transmission wavelength characteristics of the light across a spectrum. That is to say, the controller 102 determines a range of wavelengths for the tunable filter 106 to filter the light from the light source 104. The range of wavelengths is selected based on the target gas 120 absorption characteristics, which are known in the art. When the range of wavelengths is determined, the light passing through the tunable filter 106 is restricted to the wavelengths within that range. For example, when detecting hydrogen sulfide (H2S), the wavelength for detection is known in the art as being a subset of wavelengths between 1550 nm to 1600 nm. The tunable filter 106, in this example, would restrict the light emitted into the sampling chamber to be within a narrow region of this range where H2S, the target gas, absorbs light. The subsets of wavelengths for detection of other gasses are known in the art and thus the tunable filter 106 may be adjusted to detect other target gasses as described herein.
In one or more embodiments, the tunable filter 106 can be any type of electrically tunable filter such as, for example, a bandpass filter, a MEMS Fabry-Perot interferometric filter, a metal-dielectric meta-surface, and the like. In one or more embodiments, the light 110 emitted from the light source 104 and modulated by the tunable filter 106 is transmitted through the sampling chamber 140 and through the target gas 120 (if present) and reflected off the objective optical element 130. The reflected light 112 is then passed back through the sampling chamber 140 and the target gas 120 to the filter 114. In some embodiments, the filter 114 can be an optical filter such as, for example, a notch filter or an out of band filter. The filter 114 is configured to collect the reflected light 112 into the photodiode (a first portion of the light) and filter out any outside light (second portion) that may affect the photodetector 116. That is to say, the filter 114 allows reflected light 112 to pass through if it is within a certain set of wavelengths (e.g., the first portion of the reflected light) and any light outside the set of wavelengths is filtered out (e.g., the second portion of the reflected light). The set of wavelengths is determined based on the target gas 120 selected for the system 100 to detect. The photodetector 116 is utilized to detect the first portion of the reflected light 112. The photodetector 116 is operated by and in communication with the controller 102. The light data collected by the photodetector 116 can be transmitted to the controller 102 for processing and analysis.
In one or more embodiments, the controller 102 may make adjustments to any of the various components of the system 100 to enable detection of a target gas 120. The type of gas set as the target gas 120 can be adjusted based on the gas detection application for the system 100. For example, gas detection operation may be for the detection of benzene. The controller 102 can receive known properties of benzene to determine a set of wavelengths and operational needs for the various components of the system 100 to detect benzene (as the now target gas 120) for detection within the sampling chamber 140. The sampling chamber 140 is typically placed in an area where there is a high probability for the presence of the target gas 120. The controller 102 can adjust the operation of any of the components of the system 100 to determine the presence of the target gas 120 (benzene, in the example) within the sampling chamber 140 and also the concentration and any other characteristics of the target gas (as determined from the data received from the photodetector 116 as explained below). Similarly, if a new target gas, methane for example, is selected for detection, the controller 102 can adjust the components of the system 100 to now detect the new target gas (e.g., methane) based on known properties of the new target gas. In addition, the operation of the various components in the system 100 can be based on the type of gas being determined to be the target gas 120. For certain types of gases (e.g., flammable, toxic, etc.), the sensitivity of the components can be adjusted by the controller 102 for the detection of these dangerous, target gases.
Graph 300b as shown in
Additional processes may also be included. It should be understood that the processes depicted in
In one or more embodiments, the photodetector 116 provides the controller 102 with the signal associated with detected light passing through the sampling chamber 140 and the filters 106 and 114. The controller 102 can analyze this data to determine the presence of a target gas as well as other characteristics. In one or more embodiments, the controller 102 can analyze the measured signal characteristics of the light passing through the target gas 120 at the photodetector 116 as compared to known values of those signal characteristics when the target gas is not present in the sampling chamber. In other embodiments, data collected at the photodetector 116 can be compared to known values of signal characteristics when a pre-calibrated quantity of the target gas is present. This pre-calibration can occur prior to the installing the gas detection system as a way of tuning for a particular target gas. Processing techniques (and extraction of exemplary signal characteristics) include, but are not limited to, comparing a Fourier transform of the light emitted from the light source 104 (after appropriate filtering and signal conditioning; e.g., DC-offset subtraction) to determine the power of the signal at specific frequencies. For example, ratios of specific harmonics of the modulation frequency (i.e., the frequency at which the tunable filter 106 cycles through its wavelength range) can be compared, by the controller 102, against a calibrated look-up table or graph to determine a characteristics of the target gas (e.g., volumetric concentration, partial pressure, parts per million).
Depending on the target gas selected for detection, the desired concentration measurement range, and the accuracy requirements for a given application, adjustments to the system 100 components (e.g., the transmission filter control voltage 300a dictating the properties of tunable filter 106, etc.) can be made to achieve suitable signal-to-noise (e.g., ratio of detection signal to background), sensitivity (e.g., the smallest quantity of target gas detectable) and signal-linearity (e.g., results directly proportional to target gas concentration) as required by the specific gas-detection application (e.g., combustible gas detection, etc.). In low sensitivity applications (in which light is strongly attenuated by the target gas by virtue of suitably high gas concentration), processing techniques may include comparing the amplitude of the modulated light at the modulation frequency with a known zero-gas amplitude (obtained during a calibration procedure). This ratio may be compared to known calibrated look-up values or graphs such that the gas concentration may be expressed in reference to known flammability limits (i.e., percent of lower-flammability-limit).
In some embodiments, gas detection and quantification will be realized via a system-specific variant of wavelength modulation spectroscopy. As shown in
The controller 102 may analyze a waveform output by the photodetector 116. Analyzing the waveform from photodetector 116 in the frequency domain, the change in power concentrated at the first and second harmonic of the modulation frequency F is related to the slope and curvature, respectively, of the absorption spectrum of a target gas. In this manner, one may choose specific wavelength regions for tunable filter 106 modulation such that the gas absorption features impact the signal in robust fashion. At the inflection point near the onset of gas absorption, for instance, the slope of absorbance with respect to wavelength is large while the curvature is small; thus, the majority of signal change would occur in the first modulation frequency harmonic. Monitoring the power in the first harmonic (target-gas-dependent) relative to the second harmonic (largely target-gas-independent) serves as a route to gas quantification that is independent of the total signal—that is, gas concentration may be quantified in such a manner that fluctuations in the amount of light received at the photodetector 116 does not significantly impact the quantification procedure. In this manner, field-environment fluctuations in total light intensity which may result from obscurations in the light path (e.g., dirty optics, etc.) or variations in the light source 104 do not have a substantial impact on the accuracy of gas concentration measurements. In practice, appropriate modulation parameters or sets of modulation parameters for this system-specific variant of wavelength modulation spectroscopy are chosen such that the desired sensitivity and selectivity to a target gas or multiple or other target gasses is achieved.
In one or more embodiments, the system 100 can be operated following the flow diagram outlined in
After setting the detection sequence (
In one or more embodiments, a detection sequence 600a may include numerous sampling intervals with varying modulation parameters such that the pertinent spectral properties of the absorbing gas or gasses are examined in a manner suitable for a given detection application. For instance, one may choose to have a sampling interval corresponding to each of multiple gasses of interest. Each of these sampling intervals would be tuned according to the absorbing features of the multiple gasses of interest (e.g., aligning central wavelength λi with a strongly absorbing feature unique to gas of interest i). Alternatively, one may choose to have multiple sampling intervals pertinent to a single gas but for the purpose of ruling out the presence of a known interfering gas. In this manner, additional confidence in the detection and gas quantification may be achieved without susceptibility to raising false alarms. Additionally, one may choose to have multiple sampling intervals pertinent to a single gas but for the purpose of taking measurements across a wide range of concentrations. One set of sampling intervals may be specific to a low-concentration range (i.e., parts-per-million level) where high sensitivity and selectivity is required (but signal-linearity is compromised at high concentrations), and another set of sampling intervals may be specific to higher concentrations in which signal-linearity is achieved over a larger portion of the measurement range (but may not have adequate sensitivity at the low-end as dictated by the system's signal-to-noise limits). One may also employ a composite metric from signal data acquired over the multiple sampling intervals during a detection sequence such that robust differentiation and quantification of unknown gasses or gas mixtures may take place. For this purpose, a detection sequence can be designed using statistical methods which best differentiate gasses of a given character (e.g. alkanes versus alkenes, aromatics versus aliphatics, etc.).
In one or more embodiments, the controller 102 or any of the hardware referenced in the gas detection system 100 can be implemented by executable instructions and/or circuitry such as a processing circuit and memory. The processing circuit can be embodied in any type of central processing unit (CPU), including a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms as executable instructions in a non-transitory form. Additionally, a network may be in wired or wireless electronic communication with one or all of the elements of the system 100. Cloud computing may supplement, support or replace some or all of the functionality of the elements of the system 100. Additionally, some or all of the functionality of the elements of system 100 may be implemented as a cloud computing node.
A detailed description of one or more embodiments of the disclosed apparatus are presented herein by way of exemplification and not limitation with reference to the Figures.
Various embodiments are described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein.
The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.
Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” may be understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms “a plurality” may be understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term “connection” may include both an indirect “connection” and a direct “connection.”
The terms “about,” “substantially,” “approximately,” and variations thereof, are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
For the sake of brevity, conventional techniques related to making and using aspects of the invention may or may not be described in detail herein. In particular, various aspects of computing systems and specific computer programs to implement the various technical features described herein are well known. Accordingly, in the interest of brevity, many conventional implementation details are only mentioned briefly herein or are omitted entirely without providing the well-known system and/or process details.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.
This application claims the benefit of U.S. Patent Application No. 63/074,686 filed Sep. 4, 2020, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63074686 | Sep 2020 | US |
