Enhanced gas sensor selectivity

Systems and apparatus for gas sensing including: a sample inlet; a first sorbent tube and a second sorbent tube each in fluidic communication with the sample inlet, wherein the first sorbent tube is sensitive to a first set of gas analytes and the second sorbent tube is sensitive to a second, different set of gas analytes; an array of gas sensors housed in a chamber that is in fluidic communication with the first sorbent tube and the second sorbent tube; and a desorption system configured to selectively desorb and direct contents from each of the first sorbent tube and the second sorbent tube into the chamber housing the array of gas sensors at different times. Methods for gas sensing are also disclosed.

BACKGROUND

Gas sensor arrays can be used to detect the presence of analytes in ambient environments surrounding the gas sensors. Detecting particular analytes in an ambient environment, e.g., volatile organic compounds can be useful for safety, manufacturing, and/or environmental monitoring applications. Individual gas sensors can be differently sensitized to a particular subset of analytes and nonreactive to other analytes.

SUMMARY

This specification describes systems, methods, devices, and other techniques relating to pre-filtering gas samples for a gas sensing apparatus. Specifically, implementations are directed to a sorbent tube array for a gas sensing apparatus and operations of the gas sensing apparatus for employing the sorbent tube array to pre-filter gas samples. For example, a gas sensing apparatus can employ an array of different sorbent tubes to enhance the selectivity of electronic gas sensors in the apparatus to distinguish between different analytes in gas samples. In some examples, a gas sensing apparatus can improve the selectivity of electronic gas sensors by passing a gas sample through several different sorbent tubes. Each sorbent tube is sensitive to a different set of gas analytes. The gas sensing apparatus individually desorbs the contents (e.g., desorbed analytes) of each sorbent tube and passes the desorbed contents to gas sensors. The array of sorbent tubes serves as an analyte selective pre-filter for the gas sensing apparatus. The contents of each sorbent tube are individually desorbed and passed to an array of gas sensors, which reduces the likelihood of one type of analyte masking another. The sorbent tubes can be removable from the gas sensing apparatus, allowing for in-situ configuration of a pre-filter to particular sets of analytes, for example.

In general, in a first aspect, the disclosure features a gas sensing apparatus including: a sample inlet; a first sorbent tube and a second sorbent tube each in fluidic communication with the sample inlet, wherein the first sorbent tube is sensitive to a first set of gas analytes and the second sorbent tube is sensitive to a second, different set of gas analytes; an array of gas sensors housed in a chamber that is in fluidic communication with the first sorbent tube and the second sorbent tube; and a desorption system configured to selectively desorb and direct contents from each of the first sorbent tube and the second sorbent tube into the chamber housing the array of gas sensors at different times.

Implementations of the gas sensing apparatus can include one or more of the following features and/or features of other aspects. For example, the desorption system can include a first flow path between the first sorbent tube and the chamber housing the array of gas sensors, and a second flow path between the second sorbent tube and the chamber containing the array of gas sensors, and wherein the gas sensing system further includes: a pump in fluidic communication with the first sorbent tube and the second tube; and a processing system configured to control operations of the gas sensing system and to perform operations that include: causing the pump to draw a gas sample through the first sorbent tube and the second sorbent tube; causing the desorption system to open the first flow path; causing the desorption system to desorb a content of the first sorbent tube into the chamber through the first flow path; obtaining, from the array of gas sensors, first sensor response data responsive to the content of the first sorbent tube; causing the desorption system to isolate the first flow path; causing the desorption system to open the second flow path; causing the desorption system to desorb a content of the second sorbent tube into the chamber; and obtaining, from the array of gas sensors, second sensor response data responsive to the content of the second sorbent tube. The operations can further include: obtaining data identifying the first set of gas analytes that the first sorbent tube is sensitive to; and identifying, based on the data identifying the first set of gas analytes and the first sensor response data, at least one analyte present in the gas sample. Identifying the at least one analyte present in the gas sample can include comparing the first sensor response data with training data from sensor response curves associated with the first set of gas analytes.

Causing the desorption system to desorb the content of the first sorbent tube can include activating a desorption mechanism associated with the first sorbent tube. Activating a desorption mechanism associated with the first sorbent tube can include activating a heater proximate to the first sorbent tube.

In some embodiments, the array of gas sensors includes a multi-modal array of gas sensors of different types.

The array of gas sensors can include a first array of gas sensors housed in a first chamber and a second array of different gas sensors house in a second chamber, and wherein the desorption system is configured to direct contents from the first sorbent tube to the first chamber and to direct contents from the second sorbent tube to the second chamber.

The desorption system can be configured to flush the chamber after desorbing and directing the contents from one of the first or second sorbent tube into the chamber.

The the first sorbent tube can be removable from the gas sensing system.

In general, in another aspect, the disclosure features a method of detecting analytes in gas, the method including: drawing a gas sample through a first sorbent tube and a second sorbent tube of a gas sensing system, wherein the first sorbent tube is sensitive to a first set of gas analytes and the second sorbent tube is sensitive to a second, different set of gas analytes; opening a first flow path between the first sorbent tube and a chamber containing an array of gas sensors; desorbing a content of the first sorbent tube into the chamber through the first flow path; obtaining, from the array of gas sensors, first sensor response data responsive to the content of the first sorbent tube; isolating the first flow path; opening a second flow path between the second sorbent tube and the chamber containing the array of gas sensors; desorbing a content of the second sorbent tube into the chamber through the second flow path; and obtaining, from the array of gas sensors, second sensor response data responsive to the content of the second sorbent tube.

Implementations of the method can include one or more of the following features and/or features of other aspects. For example, the array of gas sensors can include a multi-modal array of gas sensors of different types.

The array of gas sensors can include a first array of gas sensors housed in a first chamber and a second array of different gas sensors house in a second chamber, and wherein the first flow path directs the content from the first sorbent tube to the first chamber and the second flow path directs contents from the second sorbent tube to the second chamber.

The method can include flushing the chamber after desorbing the content of the first sorbent tube into the chamber through the first flow path.

The first sorbent tube can be removable from the gas sensing system.

The method can include: obtaining data identifying the first set of gas analytes that the first sorbent tube is sensitive to; and identifying, based on the data identifying the first set of gas analytes and the first sensor response data, at least one analyte present in the gas sample. Identifying the at least one analyte present in the gas sample can include comparing the first sensor response data with training data from sensor response curves associated with the first set of gas analytes.

Desorbing the content of the first sorbent tube can include activating a desorption mechanism associated with the first sorbent tube. Activating a desorption mechanism associated with the first sorbent tube can include activating a heater proximate to the first sorbent tube.

In general, in another aspect, the disclosure features a gas sensing system including: a sorbent tube array including a first sorbent tube and a second sorbent tube, each in fluidic communication with one or more gas sensors, wherein the first sorbent tube is sensitive to a first set of gas analytes and the second sorbent tube is sensitive to a second, different set of gas analytes; at least one processor in communication with the gas sensors; and a data store coupled to the at least one processor having instructions stored thereon which, when executed by the at least one processor, causes the at least one processor to perform operations comprising: causing a gas sample to be drawn through the first sorbent tube and the second sorbent tube; opening a first flow path between the first sorbent tube and a chamber containing the gas sensors; causing a content of the first sorbent tube to be desorbed into the chamber through the first flow path; obtaining, from the gas sensors, first sensor response data responsive to the content of the first sorbent tube; causing the first flow path to be isolated; opening a second flow path between the second sorbent tube and the chamber containing the gas sensors; causing a content of the second sorbent tube to be desorbed into the chamber through the second flow path; and obtaining, from the gas sensors, second sensor response data responsive to the content of the second sorbent tube.

Implementations of the gas sensing system can include one or more features of other aspects.

Particular embodiments of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. For example, an advantage of this technology is that it can improve the selectivity of gas sensors to distinguishing between different analytes in a gas sample. Another advantage of this technology is that it allows for the development of fully-customizable gas sensor arrays for a particular set of gases unique to a use-case by using an automated simulation of environmental variables in a controlled laboratory setting. The custom “e-nose” system can be generated from a multi-modal system generic to many different use cases and using automated sample collection and analysis, where a machine-learned model for a particular use-case is trained in the controlled environment. Additionally, a custom sub-set of gas sensors can be selected from the multi-modal generic system to create a best-fit e-nose for the particular use-case. Rather than requiring the creation of the custom device prior to collecting the data and training the model for the particular use-case, a custom sensor array can be created in real-time using the generic multi-modal sensor array and custom software feedback loops. An automated high-throughput system allows for the collection of massive amounts of pertinent odor data for the particular use-case and enables the e-nose system to properly classify odors automatically in the field.

DETAILED DESCRIPTION

Overview

The technology of this patent application utilizes a pre-filtering sorbent tube array in a gas sensing apparatus to enhance the selectivity of the apparatus's electronic gas sensor(s). A gas sensing system employs an array of different sorbent tubes to enhance the selectivity of electronic gas sensors in distinguishing between different analytes in a gas sample. For example, a gas sensing system can improve the selectivity of electronic gas sensors by passing a gas sample through several different sorbent tubes, each being sensitive to a different set of gas analytes. The sorbent tubes can serve as a pre-filter for the gas sample. The gas sensing system individually desorbs the contents (e.g., desorbed analytes) of each sorbent tube and passes the desorbed contents to gas sensors. The array of sorbent tubes forms an analyte selective pre-filter to the gas sensing system. The tubes can be selected to pre-filter and concentrate particular sets of analytes. The contents of each sorbent tube are individually desorbed and passed to an array of gas sensors, which reduces the likelihood of one type of analyte masking another.

The sorbent tubes can be removable. For example, the sorbent tubes can be readily replaced when exhausted. The removable sorbent tubes also permits the array to be reconfigured to pre-filter specific sets of analytes and improve the selectivity of an array of gas sensor to the particular analytes of interest in a given situation.

In one example, a gas sensing system includes an array of at least two different sorbent tubes positioned between a gas sample inlet and a chamber housing the gas sensors. The gas sensing system also includes a desorption system that is configured to control the desorption of the contents from each sorbent tube and individually provide the desorbed contents into the chamber housing the gas sensors. For example, the desorption system can include an array of controllable valves separating the sorbent tube outlets from the sensor chamber. The controllable values are controlled to selectively open individual flow paths between each sorbent tube and the chamber, allowing the contents of each sorbent tube to be separately desorbed and passed into the chamber of gas sensors. In some examples, the analyte array and desorption system can be implemented as a separate attachment to a gas sensing system.

E-Nose Multi-Modal Gas Sensing Array Training Environment

FIG. 1is a block diagram of an example system100for training an e-nose gas sensing apparatus102. The system100for training an e-nose gas sensing apparatus102can include a controlled environment, e.g., a laboratory setting, where external environmental factors, e.g., temperature, humidity, presence of chemicals/gases, is highly controlled and/or regulated.

The gas sensing apparatus102includes a housing104including an environment regulator106and sorbent tube pre-filter140. Environmental regulator106can include a heat-exchange component, e.g., cylindrical heaters inserted into the housing, and/or heat transfer fins for controlling the temperature of gases that are introduced through the gas inlet110. The heat-exchange component can be configured to interact with the gas and regulate a temperature of the gas to the particular temperature and prior to entering the gas inlet.

Environmental regulator106can be configured to control a temperature within the housing104, gas sensors108, and a gas within the housing104, for example, to a temperature between 40-45° C., to a temperature above dew point >16° C., or at a temperature relevant to an environment of interest (e.g., room temperature 23° C.). In some implementations, environmental regulator106can be configured to regulate a relative humidity within the housing104, gas sensors108, and a gas within the housing104, e.g., to a relative humidity below 10%, to a relative humidity between 10-30%, or to a relative humidity relevant to an environment of interest.

The housing104and environmental regulator106can be in thermal contact such that the gas introduced through the gas inlet110, the gas sensors108, and the housing104are all maintained at a same temperature during operation of the apparatus102.

Sorbent tube pre-filter system140can be configured to pre-filter various different analyses or sets of analytes from a test gas sample prior to passing the test gas to a set of gas sensors108for analysis. Sorbent tube pre-filter system140can be integrated into the housing104of a gas sensing apparatus102(as illustrated). In some examples, sorbent tube pre-filter system140can be implemented as a separate pre-filtering apparatus. In such examples, sorbent tube pre-filter system140can be installed between the gas manifold126and the gas inlet110, for example. As discussed in more detail below, sorbent tube pre-filter system140includes an array of multiple different sorbent tubes and a desorption system to individually desorb and pass the content of each sorbent tube to the gas sensors108. Gas sensors108are disposed inside a chamber. In some implementations, the housing104can serve as the chamber. In some implementations, the gas sensors108are disposed in a chamber separate from the housing104. For example, different sets of sensors108can each be disposed in one of multiple separate chambers within the housing104. Such a configuration may allow for separate analysis of the content from two different sorbent tubes at a time.

Sorbent tube pre-filter system140is configured to separate different analytes or sets of analytes from a gas into an array of different sorbent tubes, and separately desorb and pass the individual analytes (or sets of analytes), i.e., the content of each sorbent tube, to the gas sensors108. In other words, the sorbent tube pre-filter system140forms an analyte selective pre-filter for the gas sensing apparatus that can serve to disambiguate output from gas sensor(s)108that might be responsive to multiple different analytes. For example, a particular one of the gas sensors108may produce a similar output when in the presence of two different analytes (e.g., methanol and ethanol). The sorbent tube pre-filter system140may permit disambiguation between methanol and ethanol without changing the operation of the sensor. For instance, sorbent tube pre-filter system140can include a first sorbent tube that adsorb methanol and a second sorbent tube that adsorb ethanol. A test gas is passed through both sorbent tubes and the content of each tube is then separately desorbed and passed to the gas sensor108. If the gas sensor108generates a positive response when in the presence of the desorbed content from the first sorbent tube and a negative response when in the present of the desorbed content from the second sorbent tube, the gas sensing apparatus can determine that the test gas contains methanol and does not contain ethanol. If the gas sensor108generates a negative response when in the presence of the desorbed content from the first sorbent tube and a positive response when in the present of the desorbed content from the second sorbent tube, the gas sensing apparatus can determine that the test gas contains ethanol and does not contain methanol. If the gas sensor108generates a positive response when in the presence of the desorbed content from the first sorbent tube and a positive response when in the present of the desorbed content from the second sorbent tube, the gas sensing apparatus can determine that the test gas contains both methanol and ethanol. The sorbent tube pre-filter system140is discussed in more detail below with reference toFIGS. 5 and 6.

Housing104can be composed of various materials that are selected to be non-reactive to a set of analytes to which the housing104will be exposed. Materials for the housing104can include, for example, Teflon, Teflon-coated aluminum or stainless steel, Delrin, or other materials that are resistant to the set of analytes.

Housing104includes fixtures to hold a set of gas sensors108within the housing104. The fixtures can be configured to accommodate particular dimensions of the gas sensors, and a layout of the fixtures within the housing104can be configured to designate particular locations for different types of gas sensors108within the housing104.

Housing104further includes a gas inlet110and a gas outlet112, where the gas inlet110is configured to allow for the introduction of gases into the housing104and to flow gas across the gas sensors108. Gas outlet112is configured to allow for the purge of the gases from the housing104.

Gas inlet110and gas outlet112can be configured for gas flow rates ranging between 0-10 cubic feet/hour, e.g., 5 cubic feet/hour. A particular flow rate for a gas into the gas inlet110can be selected, for example, based on an amount of time it takes for the environmental regulator106to bring a gas introduced at the gas inlet110to a test temperature, e.g., how long the gas will have to be in the fins to get it to the temperature of the housing104.

In some implementations, gas sensing apparatus102includes a fan114configured to generate a negative pressure at the gas inlet110and within the housing104which can draw a gas into the housing104via the gas inlet110, move the gas across the gas sensors108, and purge the gas from the gas outlet112. One or more operating parameters of the fan114, e.g., a rotational speed of the fan, can be selected to regulate a desired flow rate of the gas through the gas sensing apparatus102.

Gas sensors108include a multi-modal array of gas sensors that can be sensitive to various different organic and/or inorganic compounds. In other words, the multi-modal array of gas sensors108can include gas sensors that are responsive to certain analytes in a test gas and not sensitive to others. Types of gas sensors108can include gas sensors having different sensing mechanisms, e.g., metal oxide (MOx) sensors, photoionization detector (PID) sensors, electrochemical sensors, nondispersive infrared (NDIR) sensors, or other types of gas sensors. For example, gas sensors included in a gas sensing apparatus102include MOx sensors108a-c, PID sensors108d-f, electrochemical sensor108g, and NDIR sensor108h.

In some implementations, types of gas sensors108include gas sensors having a same sensing mechanism, e.g., oxidation-based, resistivity-based, optical-based, etc., but can have different sensitivities to the multiple analytes. In other words, a first type of gas sensor108aand a second type of gas sensor108bhave a same mechanism for gas sensing, e.g., MOx sensors that make resistivity-based measurements, but are configured to have different performance parameters, e.g., a MOx sensor operating at a first voltage bias and a MOx sensor operating at a second voltage bias, such that the respective sensitivities to certain analytes are different.

The multi-modal array of gas sensors108can include multiple gas sensors, e.g., 38 total gas sensors, 25 total gas sensors, greater than 40 total gas sensors. A number of each type of gas sensor relative to respective numbers of each other type of gas sensor included in the multi-modal array of gas sensors108can depend in part on dimensional/size considerations, cost-benefit of each type of sensor, responsivity, signal-to-noise ratio of each sensor, or the like. A field of application of the sensor array, e.g., agricultural, industrial, etc., can determine a number of each time of gas sensor relative to a respective number of each other type of gas sensor in the multi-modal array of gas sensors108. For example, for applications that may have a fainter signal-to-noise ratio, e.g., more background analytes not of interest, more sensors will be included overall in the multi-modal array of gas sensors108.

In some implementations, multiple different gas sensors can each have a same sensitivity to a particular analyte, e.g., a first type of gas sensor and a second type of gas sensor can each be sensitive to the particular analyte. For example,

The array of gas sensors108can be configured within the house104such that a test gas introduced via an inlet110can be sampled simultaneously by all of the gas sensors108in the array of gas sensors. In other words, the test gas is exposed to the multiple gas sensors in the array of gas sensors simultaneously such that data collection from each of the multiple gas sensors108can be performed in parallel.

In some implementations, the multi-modal array of gas sensors can include multiple MOx sensors108a-cthat are each configured to operate at a different temperature, e.g., biased at a different operating voltage, such that they have different responses to particular analytes based on the operating parameters.

Each gas sensor108is connected to a data processing apparatus116which is configured to collect data from the gas sensors108, e.g., response data118. Response data118can include a time-dependent response of each of the gas sensors108to a test gas. Additionally, the data processing apparatus116can be configured to collect time-dependent measurements of operating conditions of the plurality of sensors108, gas inlet110, environmental controller124, and desorption controller142, e.g., temperature and relative humidity, gas flow rate, gas pressure, and the like.

In some implementations, response data118includes a measure of the resistivity of the gas sensor108versus time. Further discussion of the response data is discussed with reference toFIGS. 3A-Cbelow.

Data processing apparatus116can be hosted on a server or multiple servers in data communication with the gas sensors over a network. The network may include, for example, one or more of the Internet, Wide Area Networks (WANs), Local Area Networks (LANs), analog or digital wired and wireless telephone networks (e.g., a public switched telephone network (PSTN), Integrated Services Digital Network (ISDN), a cellular network, and Digital Subscriber Line (DSL)), radio, television, cable, satellite, or any other delivery or tunneling mechanism for carrying data. The network may include multiple networks or subnetworks, each of which may include, for example, a wired or wireless data pathway. The network may include a circuit-switched network, a packet-switched data network, or any other network able to carry electronic communications (e.g., data or voice communications). For example, the network may include networks based on the Internet protocol (IP), asynchronous transfer mode (ATM), the PSTN, packet-switched networks based on IP, X.25, or Frame Relay, or other comparable technologies and may support voice using, for example, VoIP, or other comparable protocols used for voice communications. The network may include one or more networks that include wireless data channels and wireless voice channels. The network505may be a wireless network, a broadband network, or a combination of networks including a wireless network and a broadband network.

Data processing apparatus116can be configured annotate the response data118received from the gas sensors108responsive to a test gas. In some implementations, annotation data120includes timestamps, e.g., a start time label, a stop time label, and/or respective composition data122of the test gases, e.g., a set of known analytes of interest and set of known analytes not of interest, being evaluated using the gas sensing apparatus102. In some implementations, the composition data122includes concentrations of the analytes of interest, concentrations of the analytes not of interest, or concentrations of both.

In some implementations, the data processing apparatus116is configured to generate annotation data120before, during, and after exposure of a test gas to the gas sensors108, where the annotation data120includes recording a first label describing a first state of the multi-modal gas sensing array, e.g., a start time of the gas exposure. The gas manifold126can provide a first test gas to the multi-modal array of gas sensors108, where the first test gas includes a first concentration of a known analyte of interest and a second concentration of a known analyte that is not of interest, e.g., a confounding gas. The data processing apparatus116can then collect a set of sample data118from each of the gas sensors108of the multi-modal gas sensing array responsive to the first test gas and then record annotation data120, e.g., a second label, describing a second state of the multi-modal gas sensing array, e.g., a stop time of gas exposure. Further details of processes for the gas sensing apparatus102are discussed with reference toFIGS. 7A-8below.

In some implementations, the data processing apparatus116further generates, from the response data118, the annotation data120, and the composition data122for the known test gases, training data for a machine-learned model. Details described in further detail below with reference toFIG. 8.

In some implementations, the data processing apparatus116is in data communication with an environmental controller124. The environmental controller124may be a part of the data processing apparatus116. For example, environmental controller124can be implemented as a software routine executed by data processing apparatus116. The environmental controller124can be configured to provide operating instructions to the environmental regulator106, gas sensors108, data processing apparatus116, and gas manifold126. In some implementations, the environmental controller124can be configured to receive operational feedback, e.g., solenoid valve status, temperature control, etc., from one or more of the environmental regulator106, gas sensors108, data processing apparatus116, and gas manifold126.

In some implementations, the environmental controller124can receive operating conditions feedback, e.g., temperature, humidity readings, from a temperature and/or humidity gauge128. The gauge128, e.g., a thermocouple, hygrometer, or the like, can be in physical contact with the housing104or gas sensors108to measure a temperature and/or relative humidity. The gauge128can additionally or alternatively measure a temperature and/or relative humidity of the gas present within the housing104.

In some implementations, the operating conditions feedback received by the environmental controller124can be provided to the data processing apparatus116and recorded as annotation data120. For example, temperature of the housing104, gas sensors108, and test gas can be recorded as annotation data120and included with the response data118for the particular test gas.

In some implementations, the data processing apparatus116is in data communication with a desorption controller142. The desorption controller142may be a part of the data processing apparatus116. For example, desorption controller142can be implemented as a software routine executed by data processing apparatus116. The desorption controller142can be configured to provide operating instructions to sorbent tube pre-filter system140and data processing apparatus116. The desorption controller142can control the sorbent tube pre-filter system140to separately desorb the content of sorbent tubes in the sorbent tube pre-filter system140and to pass the desorbed content to the gas sensors108for analysis. In some implementations, the desorption controller142can be configured to receive operational feedback, e.g., sorbent tube pre-filter status data, sorbent tube information, etc., from one or more of the sorbent tube pre-filter system140and data processing apparatus116. Sorbent tube pre-filter status data can include, but is not limited to, operational status of sorbent tube pre-filter valves, heaters, pumps, fans, purge systems, or a combination thereof. Sorbent tube information can include, but is not limited to, data identifying a type of a sorbent tube (e.g., the analyte or set of analysts that a tube is sensitive to), a position of the tube within a sorbent tube array, a number of times that a sorbent tube has been activated (e.g., the number of times that content has been desorbed from the sorbent tube), or a combination thereof.

In some implementations, the operating conditions feedback received by the pressurization controller142can be provided to the data processing apparatus116and recorded as annotation data120. For example, sorbent tube information associated with a sorbent tube from which a test gas sample was desorbed can be recorded as annotation data120and included with the response data118for the particular test gas.

The system100further includes a gas manifold126having multiple gas sources130. The multiple gas sources130can each include multiple known analytes of interest and multiple known analytes not of interest. For example, gas manifold126can include gas source130a,130beach having analytes of interest and gas sources130cand130deach having analytes not of interest (e.g., confounding gases).

Gas manifold126can be a closed-loop system, where no external compounds are present within the gas manifold126that could interfere with the test gases provided by the gas manifold to the gas sensing apparatus102via the gas inlet110. The test gases provided by the gas manifold126to the gas sensing apparatus102can be composed only of the known analytes of interest and known analytes not of interest from the one or more gas sources130.

Gas manifold126can further include regulatory components132which can be operable to selectively allow a controlled flows (e.g., 0-5 cubic feet/hour) of one or more of the gas sources130from the gas manifold126and into the gas inlet110to generate a particular test gas for the gas sensing apparatus102. Further details of the gas manifold126are discussed with reference toFIG. 2.

FIG. 2is a block diagram of another example system200for training the e-nose gas sensing apparatus102. As described with reference toFIG. 1, the gas manifold126can include one or more regulatory components132for each gas source130that are configured to determine which of the gas sources130are selected to flow from the gas manifold126to the gas inlet110and further into the gas sensing apparatus102. Referring now toFIG. 2, the system200depicts in further detail the gas manifold126that can be used to provide test gases to the e-nose gas sensing apparatus102. Additional configurations of the gas manifold are possible, where a gas manifold126can include additional or fewer elements than those described with reference toFIG. 1andFIG. 2.

As depicted inFIG. 2, each gas source130of the gas manifold126includes a pressure regulator202, a solenoid valve204, an adjustable orifice206, and a check valve208, which can be utilized in combination to control the flow of gas for each gas source130. One or more of the components of each gas source130mentioned can be electronically controllable, e.g., an electronically adjustable orifice206, by the environmental controller124.

One or more of the gas sources130, e.g., gas source130b, can further include a mixing vessel210. Mixing vessel210can be a vessel containing an item, e.g., coffee grounds, or a secondary gas source (e.g., a methane tank) that provides an analyte to the gas source130.

Pressure regulator202can regulate a pressure from a purge gas source212, e.g., a compressed gas cylinder, from a high pressure to a low pressure to generate a desired flow rate of the purge gas into the gas sources130, e.g., into a mixing vessel210. The purge gas source212can include a compressed air source, e.g., clean dry air, and/or an inert gas source, e.g., nitrogen, argon, or the like. The purge gas source212can be regulated by an electronic flow meter214which controls a flow rate of the purge gas source212into the various gas sources130, where pressure regulator202for each gas source130can further regulate a flow of the purge gas into the particular gas source130.

In some implementations, a gas source130ais only composed of purge gas from gas source212, e.g., compressed air and/or inert gas, which is provided to a gas inlet110without any analytes of interest or analytes not of interest present.

In some implementations, a gas source, e.g., gas source130b, is a first gas source, where the first gas source is generated by mixing at least the purge gas source212with an analyte present in the mixing vessel210b, e.g., coffee grounds, soil, methane, etc. A gas source, e.g., gas source130b, can be a second gas source, where the second gas source is generated by mixing at least the purge gas source212with an analyte present in the mixing vessel210c, e.g., ethanol, apples, charcoal, etc.

In some implementations, the gas manifold126further includes a solenoid valve216and a gas stream mixer218. Solenoid valve216can be configured to control the flow of gases from the gas manifold126prior to entering the gas inlet110. Solenoid valves216can receive operational instructions from the environmental controller124and/or from the data processing apparatus116.

In some implementations, gas stream mixer218can be used to mix gases from multiple gas sources130. For example, a first gas source130band a second gas source130ccan be allowed to flow to the gas stream mixer218and blended together to form a test gas that is provided to the gas inlet110. Operation of the gas stream mixer218can be controlled by the environmental controller124and/or the data processing apparatus116. Other methods for blending gases from multiple gas sources130prior to the test gas being provided to the gas inlet110are possible.

In some implementations, some or all of the pressure regulators202, solenoid valves204, adjustable orifices206, mixing vessels210, check valves208, solenoid valve216, electronic flow meter214, and gas stream mixer218can be operated automatically and/or semi-automatically by the environmental controller124. For example, the environmental controller124can be configured to provide process control instructions to the gas manifold126to provide, at the gas inlet110, a particular test gas including a composition of analytes.

In some implementations, the environmental controller124can open and close solenoid valves204and216to determine which gas sources130flow into the gas inlet110. The environmental controller124can control a flow rate for each pressure regulator202to establish a concentration of the particular analyte present in the mixing vessel210for the gas source130. For example, mixing vessels130band130ccan include a same analyte (e.g., coffee grounds) and the environmental controller124can set pressure regulator202bto a first flow rate and pressure regulator202cto a second flow rate to achieve a gas source130bwith a first concentration of a given analyte and a gas source130cwith a second, different concentration of the given analyte.

Referring back toFIG. 1, for a particular test gas provided by the gas manifold through the gas inlet110of the e-nose gas sensing apparatus102, response data118is collected from each of the gas sensors108of the gas sensing array. The gas sensors108can be a multi-modal array of gas sensors having a variety of response characteristics to a range of analytes. Different types of gas sensors108can be more or less responsive to a particular analyte, and a subset of the gas sensors108can be identified as optimally responsive to the particular analyte based in part on the response data118collected.

In some implementations, response of a gas sensor108to a test gas including one or more analytes can be measured as a change in gas sensor electrical resistivity before, during, and after exposure to the particular test gas (e.g., as in MOx sensors). In some implementations, response of a gas sensor108can be measured as an electrical signal generated by one or more analytes of interest that are present in the test gas (e.g., as in PID sensors).FIGS. 3A-3Care example plots of gas sensor responses for the e-nose gas sensing apparatus.

FIG. 3Adepicts an example plot300of a response of a gas sensor A to a particular test gas including one or more analytes. Gas sensor A, e.g., gas sensor108a, exhibits a response302to a particular test gas over time. The response302can be plotted versus time and annotation data, e.g., annotation data120, can be recorded for the response302. Annotation data120can include one or more timestamps, where T1indicates a timestamp beginning the introduction of the test gas to the gas sensor A, T2is a timestamp where the exposure to the test gas is terminated (e.g., the solenoid valve216is closed or the purge gas source130aflows into the gas inlet110), and T3is a timestamp associated with the response of the gas sensor A reaching a baseline response Ro.

A baseline response Ro can be a response measurement for the gas sensor A prior to providing the first test gas, where T3is the time stamp after termination of the gas exposure when the response302of the gas sensor A matches the baseline response measurement Ro. The baseline response measurement Ro can be a resistivity measurement for the gas sensor, where the resistivity of the gas sensor A is below a minimum threshold resistivity.

Additional timestamps can be recorded in the annotation data120for the plot300, for example, a timestamp for threshold time Tt, when the response302of the gas sensor A reaches a threshold response Rt. In another example, a timestamp can be annotated when the response302of the gas sensor A reaches a saturation point Ts, in other words, when the response302of the gas sensor A saturates to the exposure of the test gas.

Threshold response Rt can be selected based in part on a concentration of the one or more analytes of interest in the test gas, e.g., for very low concentrations of analytes the threshold response Rt can be set lower than for relatively higher concentrations of analytes. Threshold response Rt can be selected based in part on the characteristics of the particular analytes in the test gas, e.g., a lower threshold response can be set for a highly dangerous and/or toxic analyte versus a higher threshold response can be set for a non-toxic analyte.

In some implementations, a threshold response Rt can depend in part on the one or more types of gas sensors of the multiple gas sensors108that are exposed to the test gas. For example, if all of the gas sensors have some amount of sensitivity to a particular analyte in the test gas, the threshold response may be set at a higher threshold response to select only the gas sensor(s) with a highest relative sensitivity to the particular analyte.

In some implementations, a threshold response Rt can depend in part on a type of gas sensor, for example, depending on a mechanism of detection for the type of gas sensor, in order to normalize the sensitivities of each type of gas sensor relative to each other type of gas sensors in the multi-modal array of gas sensors108. A minimum response threshold can be defined as a lowest detectable limit of a particular analyte. For example, a threshold of detectability can be 1 part per million (ppm) for most MOx sensors when detecting acetone vapor.

As depicted inFIG. 3A, response302of the gas sensor A to the particular test gas reaches a threshold response Rt prior to the timestamp T2where the gas sensor A exposure to the test gas is terminated, e.g., a solenoid204bis closed and a solenoid204afor the purge gas source130ais opened. A second set of response data118can include a time-dependent recovery response P2of the gas sensor A after terminating exposure at T2of the gas sensor A to the test gas.

In some implementations, one or more of the gas sensors in the array of gas sensors108, e.g., gas sensor108b, do not meet a threshold response Rt to the particular test gas.FIG. 3Bdepicts an example plot310of a gas sensor B, e.g., gas sensor108b, that has a response312to the particular test gas including the one or more analytes of interest over time. In contrast to the plot300depicted inFIG. 3A, the response312of the gas sensor B to the particular test gas does not reach the threshold response Rt prior to T2where the gas sensor exposure to the test gas is terminated.

In some implementations, gas sensor B can have negligible response R to a test gas, where the response312of the gas sensor B is not measurable, e.g., below the sensitivity of the sensor. Gas sensor B can have zero response to a test gas, where the gas sensor130is nonreactive to analytes of interest in the test gas, e.g., an inorganic gas sensor130can have zero reactivity to an organic compound being tested.

In some implementations, multiple gas sensors108can have at least a threshold response Rt to a particular test gas, where a first gas sensor can have an optimized response to the particular test gas versus a second gas sensor. An optimized response can be defined as a shorter period of time between exposure to the test gas T1and a time to reach a threshold response Rt. Referring toFIG. 3A, a period of time between the exposure to the test gas T1and the time to reach the threshold response Tt is P1. A range of time for P1can be, for example, 5-120 seconds.

In some implementations, an optimized response can be a period of recovery time for the gas sensor between the exposure of the gas being terminated T2and the gas sensor reaching the baseline responsivity Ro, T3. Referring toFIG. 3A, a period of time between the timestamp when exposure of the gas is terminated T2and the timestamp when the gas sensor reaches the baseline responsivity T3is P2. A range of time for P2can be, for example, 5-120 seconds.

Referring now toFIG. 3C, plot320depicts a response322of gas sensor C, e.g., gas sensor108c, to the particular test gas. Gas sensor C has a period of time P3between a timestamp marking the exposure to test gas T1and a timestamp marking when the gas sensor C reaches the threshold response Rt at Tt. Gas sensor C also has a period of time P4between the timestamp marking the exposure of the gas being terminated T2and the timestamp marking when gas sensor C reaches the baseline responsivity Ro at T3. As depicted inFIGS. 3A and 3C, the period of time P3for gas sensor C is greater than the period of time P1for gas sensor A.

In some implementations, selecting a particular gas sensor with an optimized response is based on the particular gas sensor exhibiting a shorter period of time to reach a threshold response after exposure to the particular test gas and/or a shorter period of time to recover a baseline response Ro, e.g., selecting gas sensor A instead of gas sensor C because P1is less than P3and/or because P2is less than P4.

In some implementations, each gas sensor having at least a threshold response Rt to the particular test gas can be compared to each other gas sensor having at least the threshold response to the particular test gas, and a particular gas sensor or set of two or more gas sensors of the multiple gas sensors can be selected based in part on the respective responses, e.g., response302and322, of each gas sensor. The response data118, e.g., including plots300,310,320of responses302,312,322respectively, for each gas sensor108of the multiple gas sensors can be analyzed and gas sensors having at least a threshold response Rt recorded in the set of response data118can be selected. A proper subset of gas sensors can include the gas sensors that have a difference between the third timestamp and first timestamp, e.g., between T3and T1that is less than a threshold time. A range of time for T3-T1can be, for example, 5-120 seconds. Further discussion of the selection of the subset of gas sensors is discussed with reference toFIGS. 4 and 5.

FIG. 4is a block diagram of an e-nose gas sensing apparatus402. As discussed above with reference toFIG. 1, the e-nose gas sensing apparatus402includes a housing104including a gas inlet110configured to receive an unknown gas mixture404and a gas outlet112through which the unknown gas mixture404is purged from the e-nose gas sensing apparatus402.

The gas inlet110is coupled to the housing104and configured to expose the multiple gas sensors108to an unknown gas mixture404that is introduced through the gas inlet110. Unknown gas mixture404can be introduced passively via the environment surrounding the gas inlet110. For example, the unknown gas mixture404can be introduced via the gas inlet110when the gas sensing apparatus402is deployed in a testing environment, e.g., in a factory setting, Passive introduction of the unknown gas mixture404into the gas inlet110can be, for example, by diffusion of the unknown gas mixture into the gas inlet110.

In some implementations, the unknown gas mixture404can be introduced actively into the gas inlet110, for example, by generating a negative pressure within the housing104using a fan114or other similar device. In another example, the unknown gas mixture404can be introduced actively to the gas inlet110by a positive pressure of the gas at the gas inlet, e.g., by a person blowing into the gas inlet110, a gas exhaust from a piece of equipment, or the like.

Multiple gas sensors108including a first type of gas sensor, e.g., gas sensor108a, and a second type of gas sensor, e.g., gas sensor108b, that is different from the first type of gas sensor are located within the housing104where each of the first type of gas sensor and second type of gas sensor is sensitive to a respective set of analytes. The first type of gas sensor108aand the second type of gas sensor108bcan have different methods for gas sensing, e.g., where the first type of sensor is a MOx sensor and the second type of sensor is a PID sensor.

In some implementations, the first type of gas sensor108aand the second type of gas sensor108bhave a same method for gas sensing but are configured to have different performance parameters, e.g., a MOx sensor operating at a first operating temperature and a MOx sensor operating at a second operating temperature. Operating the MOx sensors at different temperatures can cause each respective MOx sensor to respond differently to analytes in a test gas, even when sensing a same test gas at a same concentration.

Gas sensing apparatus402further includes an environmental controller124coupled to the housing104and configured to regulate temperatures of the housing104, gas inlet110, and gas sensors108to a particular temperature. The environmental controller124can include an environmental regulator106, for example, a heating source and heat-transfer fins, embedded into the housing104where gas introduced at the gas inlet110passes through heating channels within the heat-transfer fins of the housing104to stabilize a temperature of the gas404to the particular temperature. In some implementations, the environmental controller124can include temperature and/or humidity gauges128to measure a temperature and/or relative humidity of the unknown gas mixture404that is received at the gas inlet110.

Gas sensing apparatus402includes a data processing apparatus116in data communication with the gas sensors108and the environmental controller124. The data processing apparatus116can be an onboard computer that is affixed to the housing104of the apparatus402. In some implementations, a portion or all of the data processing apparatus116can be hosted on a cloud-based server that is in data communication with the gas sensing apparatus402over a network.

Data processing apparatus116can include a user device410, where a user can interact with the gas sensing apparatus402via the user device410, e.g., receive data, provide testing instructions, receive testing information, or the like. User device410can include, for example, a mobile phone, tablet, computer, or another device including an application environment through which a user can interact with the gas sensing apparatus402. In one example, user device410is a mobile phone including an application environment configured to display gas mixture test results for the unknown gas mixture404, allow for user interaction with the gas sensing apparatus402, and the like.

In some implementations, the apparatus402includes a display406configured to communicate information408to a user of the gas sensing apparatus402and/or allow for user interaction with the gas sensing apparatus402. Information408can include, for example, the operational status of the apparatus402, e.g., on/off, testing, processing, etc.

In some implementations, information408includes test results for the unknown gas mixture404. Information408can be presented to a user based on user preferences, e.g., to highlight a particular set of analytes that the user is interested in discovering in the unknown gas mixture404. Information408can be additionally or alternatively provided to one or more user devices410in data communication with the apparatus402.

In some implementations, display410is configured to respond to user interaction, e.g., a touch-screen functionality. Display410can further include audio feedback, e.g., an alert, to notify a user of the status of the apparatus402. For example, the apparatus402can provide an audio and/or visual update to the user of a testing status. In another example, the apparatus402can provide an audio and/or visual alarm to the user, e.g., if a particular analyte is detected above/below a preset threshold, e.g., a threshold concentration of the analyte is detected in the ambient.

In some implementations, imaging data can be captured of an environment surrounding the apparatus402, e.g., using a camera or video recording device. The imaging data of the surrounding environment can be displayed on display410to identify, to a user, one or more objects in the surrounding environment that may be included in the unknown gas mixture404being sampled by the apparatus402. A blend ratio of the various analytes that are being sensed in the unknown gas mixture404can be displayed on display410.

Gas sensing apparatus402can also include a sorbent tube pre-filter system140and desorption controller142. Sorbent tube pre-filter system140is configured to separate different analytes or sets of analytes from a gas into an array of different sorbent tubes, and separately desorb and pass the individual analytes (or sets of analytes), i.e., the content of each sorbent tube, to the gas sensors108. In other words, the sorbent tube pre-filter system140forms an analyte selective pre-filter for the gas sensing apparatus that can serve to disambiguate output from gas sensor(s)108that might be responsive to multiple different analytes (e.g., as discussed above in reference toFIG. 1). In some implementations, the desorption controller142is configured to control the sorbent tube pre-filter system140in coordination with data processing apparatus116to obtain sensor response measurements of analytes contained in the gas404. For example, desorption controller142can be configured to control the sorbent tube pre-filter system140to separately desorb the content of the sorbent tubes in the sorbent tube pre-filter system140and to pass the desorbed content to the gas sensors108for analysis (e.g., as discussed above in reference toFIG. 1). The sorbent tube pre-filter system140is discussed in more detail below with reference toFIGS. 5 and 6.

Further details of the gas sensing apparatus402are discussed with reference toFIGS. 10A-10Dbelow.

Example Sorbent Tube Pre-Filter for a Multi-Modal Gas Sensing Apparatus

FIG. 5is a block diagram of one example sorbent tube pre-filter system140for an e-nose gas sensing apparatus. Sorbent tube pre-filter system140includes an array of sorbent tubes504a-504d(referred to collectively as sorbent tube array504) and multiple flow paths510a-510dproviding fluidic communication between the sorbent tubes504a-504dand a sensor chamber502in which the gas sensors108are disposed. Sorbent tubes504a-504dcan be sensitive to a different sets of gas analytes. That is, sorbent tubes504a-504din sorbent tube array504can be configured to adsorb different sets of gas analytes. For example, sorbent tube504acan include an adsorbent material (i.e., a sorbent) that traps one particular gas analyte (or set of gas analytes) (e.g., methanol) and sorbent tube504bcan include a different sorbent material that traps a different gas analyte (or set of gas analytes) (e.g., ethanol). Although the sorbent tubes504a-504dare illustrated as being connected in parallel flow paths, in some implementations, one or more sorbent tubes can be coupled in series along a common flow path. For instance, a second sorbent tube can be installed in series with sorbent tube504aalong flow path510a.

The sorbent tube array504can include fixtures to hold the sorbent tubes504a-504din position within the array. In some implementations, the sorbent tubes504a-504dare removable. For example, the fixtures can be configured to allow the sorbent tubes504a-504dto be removed and replaced with different sorbent tubes. For example, the sorbent tubes504a-504dcan be replaced when the sorbent material becomes used up, e.g., less effective over time. As another example, the sorbent tubes504a-504dcan be swapped for sorbent tubes that are sensitive to different analytes, e.g., permitting users to reconfigure the sorbent tube array504to a particular use.

The sorbent tube pre-filter system140includes sorbent tube inlet and outlet isolation valves508,509. Isolation values508,509can be controlled by desorption controller142to selectively isolate each sorbent tubes504a-504dfrom its respective flow path510a-510d. The isolation values508,509can be implemented as individual valves or as value manifolds (represented by508mand509m).

A desorption device506is positioned proximate to each sorbent tube504a-504d. Each desorption device506can be independently controlled by the desorption controller142to cause its associated sorbent tube to desorb, e.g., to release, analyte contents adsorbed by the sorbent material in the sorbent tube. Mechanisms for desorbing the content of a sorbent tube504can include, but are not limited to, heat, reductive/oxidative desorption, electron-stimulated desorption, or passing a carrier gas with higher affinity to a sorbent in the sorbent tube relative to the analyte. For example, desorption devices506can be, but are not limited to, heaters, electrodes configured to reverse an electrical bias on the sorbent tube (e.g., affecting reductive/oxidative desorption), an electron source configured to perform electron-stimulated desorption, or desorption carrier gas source.

The sorbent tube pre-filter system140can include a flow control device512such as a pump or fan. The flow control device512can be used for drawing gas through the sorbent tubes504a-504dto collect analytes and/or to draw desorbed contents from a sorbent tube into the chamber502that contains the gas sensors108. In some implementations, the sorbent tube pre-filter system140can use the gas sensing apparatus's102fan114(seeFIGS. 1 and 4) as the flow control device512.

In some implementations, the sorbent tube pre-filter system140can include an exhaust flow path514with an exhaust isolation valve516and a chamber isolation valve517. The exhaust flow path514can be used when drawing test gas through the sorbent tube array504without exposing the gas sensors108to the test gas, e.g., by closing valve517. For instance, in some implementations, it may be desirable to only expose the gas sensors108to the individually desorbed contents from the sorbent tube array504. In some implementations, it may be useful to draw an initial test gas sample through the sorbent tube array504and then pass the filtered gas sample into the chamber (e.g., by isolating or not including exhaust flow path514), e.g., to detect analytes that will not be adsorbed by the sorbent tube array504.

In some implementations, the sorbent tube pre-filter system140can include flush gas source518. The clean gas source518can be isolated by an isolation valve520. The clean gas source can be configured to provide a clean gas for flushing the desorbed content of the sorbent tubes504a-504dinto the chamber502and/or for purging the chamber502between the desorption of content from different sorbent tubes. For purging the chamber502between the desorption of content from different sorbent tubes the clean gas source518can be passed to the chamber502through a flow path that bypasses the sorbent tube array504(e.g., a bypass path (not shown)). The clean gas source518can be a reserve volume air, e.g., clean dry air, and/or an inert gas, e.g., nitrogen, argon, or the like. In some implementations, the clean gas source518be a high purity filter coupled to a gas inlet524. The gas inlet110can also include an isolation valve522, e.g., to isolate the gas inlet110during operations when the clean gas is being applied to the sorbent tube array504.

In some implementations, the sorbent tube pre-filter system140includes sensor(s) configured to read sorbent tube information from a sorbent tube. For example, the sorbent tubes can include machine readable information, e.g., a machine readable code applied to a label on the sorbent tube. The sensors can be configured to detect the machine readable code and send the data to the desorption controller or the data processing apparatus116to interpret the code/decode the information. The machine readable code can identify the sorbent tube type, e.g., the analyte(s) that the sorbent tube is sensitive to. Example machine readable codes can include, but are not limited to, bar codes, QR codes, and radio frequency identification codes (e.g., RFID tags). The machine readable code sensors can be positioned to detect the machine readable code applied to the sorbent tubes504a-504dwhen the tubes are installed within the sorbent tube array504. In some implementations, the sorbent tube information, e.g., sorbent tube type or analytes that the sorbent tube is sensitive to, can be received from user input. For example, the data processing apparatus116can provide a user interface, through which the user can provide input identifying which types of sorbent tubes are installed in various locations of the sorbent tube array504.

Chamber502can be composed of various materials that are selected to be non-reactive to a set of analytes to which the chamber502will be exposed. Materials for the chamber502can include, for example, Teflon, Teflon-coated aluminum or stainless steel, Delrin, or other materials that are resistant to the set of analytes.

Chamber502can include fixtures to hold an array of gas sensors108within the chamber502. The fixtures can be configured to accommodate particular dimensions of the gas sensors, and a layout of the fixtures within the chamber502can be configured to designate particular locations for different types of gas sensors108within the chamber502.

FIG. 6is a block diagram of another example sorbent tube pre-filter system140for an e-nose gas sensing apparatus. The sorbent tube pre-filter system140depicted inFIG. 6is similar to that depicted inFIG. 5, but includes multiple flow paths602,604for desorbing the content of sorbent tubes of the sorbent tube array504into separate chambers502a,502b. For example, the gas sensing apparatus102can include multiple gas sensor chambers502a,502b, each containing a separate group of gas sensors108,108′. In such implementations, the sorbent tube pre-filter140can include additional flow paths602,604to transfer desorbed contents from the sorbent tube array504to any of the chambers502aor502b. Each flow path602and604is directed to a different one of the chambers502a,502band can include a separate set of isolation valves509mand609mand a separate flow control device512,612.

The operations of the sorbent tube pre-filter system140depicted inFIG. 6are similar to that depicted inFIG. 5, with the additional ability to selectively direct desorbed content from the sorbent tube array504to any of the different gas sensor chambers502a,502b. For example, gas sensor array108can contain gas sensors that respond to different analytes than the gas sensors in gas sensor array108′. In operation, the gas sensing device102(e.g., as controlled by data processing apparatus116) can direct the desorption controller to desorb and transfer content from sorbent tube504ato the gas sensors108in chamber502aand to desorb and transfer content from sorbent tube504bto the gas sensors108′ in chamber502b. The data processing apparatus116can direct the desorption into appropriate chambers502a,502bbased on sorbent tube type. For instance, the data processing apparatus116can select to desorb and transfer the content of sorbent tube504ainto the chamber502acontaining gas sensors108because the sensors108are more responsive to the type of analytes adsorbed by sorbent tube504athan gas sensors108′.

Example Operation of E-Nose Multi-Modal Gas Sensing Apparatus

The e-nose multi-modal gas sensing apparatus can operate in various modes, including a configuration mode, e.g., determining a subset of gas sensors to include in the gas sensing apparatus for a particular environment including a set of analytes of interest, a training mode, e.g., training a machine-learned model to identify various analytes of interest, and detection mode, e.g., where the e-nose multi-modal gas sensing apparatus is deployed in a testing environment.

FIG. 7Ais a flow diagram of an example process700of the e-nose gas sensing apparatus. E-nose gas sensing apparatus, e.g., gas sensing apparatus102, can be configured to detect a particular set of analytes of interest utilizing process700, where configuring the apparatus102can include determining a subset of gas sensors of a set of multiple gas sensors108from which to gather response data, e.g., response data118.

In a first step, multiple gas sensors are provided, where the multiple gas sensors include multiple types of gas sensors, e.g., a first type of gas sensor and a second type of gas sensor different from the first type of gas sensor (702). As depicted inFIG. 1, multiple gas sensors108including a first type of gas sensor108aand a second type of gas sensor108bcan be different types of sensors. For example, gas sensor108acan be a MOx sensor and gas sensor108bcan be an electrochemical gas sensor. In another example, gas sensor108acan be a MOx sensor operated at a first voltage bias and gas sensor108bcan be a MOx sensor operated at a second, different voltage bias.

In some implementations, the first type of gas sensor can be an organic-type gas sensor and the second type of gas sensor can be an inorganic-type gas sensor. For example, a volatile organic compound (VOC) sensor is sensitive to organic compounds, e.g., hydrogen, carbon dioxide, etc. In another example, PID sensors are sensitive to inorganic compounds, e.g., chlorine, tin oxide, etc.

A test gas is provided to the multiple gas sensors, where the test gas includes multiple known analytes (704). The test gas can be produced using a gas manifold, e.g., gas manifold126, including multiple gas sources, e.g., gas sources130. Each of the multiple gas sources130can include a different analyte, where the analytes can be mixed together using gas manifold126to generate a particular composition of known analytes in the test gas. The test gas can include a first concentration of a known analyte of interest and a second concentration of a known analyte not of interest. For example, 0.01% of methane and 0.99% of nitrogen or air.

The analytes of interest can be selected based on an intended environment for the apparatus with the selected set of gas sensors. For example, an industrial setting may have an interest in solvent analytes or processing gases. In another example, in an agricultural setting, analytes of interest are methane, pesticide compounds, or other agricultural by-products. In yet another example, in a laboratory setting, an analyte of interest can be a toxic or hazardous gas, e.g., chlorine gas. The analytes not of interest, or “confounding” gases can be selected to be inert gases, e.g., nitrogen, or as gases that are typically present in the intended environment for the apparatus with the selected set of gas sensors. For example, in a laboratory environment, an analyte not of interest can be nitrogen, solvent, e.g., isopropyl alcohol, or carbon dioxide. In another example, in an agricultural setting, analytes not of interest can be carbon dioxide, equipment exhaust, e.g., vehicle exhaust, or gasoline.

In some implementations, providing the test gas of known analytes to the multiple gas sensors108includes providing the test gas in a controlled environment including a particular temperature and a particular relative humidity. An environmental regulator, e.g., environmental regulator106including heat transfer fins, can be used to alter a temperature and/or relative humidity of the test gas prior to the test gas reaching the multiple gas sensors108. Temperature and humidity of the test gas can be regulated, for example, to room temperature and a relative humidity below dew point. In some implementations, the test gas is a sample of gas from a surrounding environment with unknown analyte concentrations.

In some implementations, providing the test gas to the gas sensors108includes providing the test gas at a flow rate of less than 5 cubic feet per hour for a known period of time. A flow rate can be, for example, as low as 1 cubic centimeter per minute. In another example, a flow rate can be up to 2 liters per minute. A particular flow rate can be selected based in part on a desired temperature and/or relative humidity of sampling and a temperature and/or relative humidity of the test gas prior to entering the gas inlet110. In other words, an amount of time required to regulate the temperature and/or relative humidity of the test gas prior to exposure to the gas sensors108by the environmental regulator106, e.g., heating fins, can determine a flow rate of the test gas within the environmental regulator106.

In some implementations, providing the test gas to the gas sensors108includes providing the test gas through a sorbent tube pre-filter system140.FIG. 7Bis a flow diagram of an example process704A of the e-nose gas sensing apparatus for controlling operations of a sorbent tube pre-filter system140. For example, process704A can be performed by desorption controller142ofFIGS. 1 and 4-6. In some implementations, process704A can be directed by data processing apparatus116, e.g., data processing apparatus can provide desorption controller142with instructions that coordinate desorption of content from individual sorbent tubes. For example, data processing apparatus can provide desorption controller142with instructions indicating which sorbent tube content to desorb into which sensor chamber or an order for desorbing content from the sorbent tubes. Process704A is described with periodic reference to elements of the sorbent tube pre-filter systems140depicted inFIGS. 5 and 6.

The test gas is drawn through an array of different sorbent tubes (720). For example, a desorption controller can control isolation valves and a flow control device in the sorbent tube pre-filter system to direct the test gas through an array of sorbent tubes. For example, the desorption controller can open appropriate isolation valves to provide a flow path from an inlet of the sorbent tube pre-filter system (e.g., an inlet of the gas sensing apparatus102) through an array of sorbent tubes. The desorption controller can control the operation of the flow control device (e.g., pump or fan) to obtain a desired flow rate of the test gas through the sorbent tube array. For example, the desorption controller can open inlet valve522, open all of the sorbent tube inlet and outlet isolation valves508,509, and turn on flow control device512.

In some implementations, the desorption controller can direct the test gas through a subset of sorbent tubes in the array that includes fewer than all of the sorbent tubes in the array. For example, the desorption controller can open only the isolation valves508,509associated with the sorbent tubes that are to be used for analysis of a particular test gas. Or, in some circumstances, sorbent tubes may be missing from the array, e.g., the entire array may not be filled with sorbent tubes if some are being replaced or the sorbent tube array has the capacity to accept more sorbent tubes than are needed for a particular analysis. In such situations, empty sorbent tube fixtures may remain isolated.

In some implementations, the desorption controller directs the test gas out an exhaust outlet after passing through the sorbent tube array. For example, the desorption controller can close chamber isolation valve517and open exhaust isolation valve516. In some implementations, the desorption controller directs the test gas into a chamber containing the gas sensors after passing through the sorbent tube array. In such implementations, the process704A would proceed to Step726below to obtain response data from the gas sensors to the sorbent tube filtered test gas.

Once a desired volume of the test gas has been passed through the sorbent tube array, the desorption controller can isolate the sorbent tubes, e.g., by closing the respective isolation valves508,509associated with each sorbent tube and turning off the flow control device512.

A flow path from a first one of the sorbent tubes to a chamber containing gas sensor(s) is opened (722). The desorption controller establishes a flow path from a selected one of the sorbent tubes to a chamber containing the gas sensors. For example, the desorption controller opens appropriate isolation valves to established a flow path between the selected sorbent tube and the chamber. For instance, if sorbent tube504ais the selected sorbent tube, the desorption controller can open its inlet and outlet isolation valves508,509and open (if needed) the chamber isolation valve517. In implementations in which the gas sensing apparatus102contains multiple gas sensor chambers, a flow path is established between the outlet of the selected sorbent tube and the appropriate chamber. For example, if the selected chamber is chamber502ainFIG. 6, sorbent tube504a's outlet isolation valve in valve manifold509mwould be opened. If the selected chamber is chamber502binFIG. 6, sorbent tube504a's outlet isolation valve in valve manifold609mwould be opened.

In some implementations, the desorption controller obtains sorbent tube information from sensors in the sorbent tube array and passes the sorbent tube information to the data processing apparatus. Sorbent tube information can include, but is not limited to, data identifying a type of a sorbent tube (e.g., the analyte or set of analytes that a tube is sensitive to), a position of the tube within a sorbent tube array, a number of times that a sorbent tube has been activated (e.g., the number of times that content has been desorbed from the sorbent tube), or a combination thereof. The data processing apparatus can use the sorbent tube information to select which sorbent tube to align with which gas sensor chamber and pass appropriate instructions to the desorption controller.

Content from the first one of the sorbent tubes is desorbed and passed into the chamber (724). The desorption controller activates the desorption device associated with the selected sorbent tube to initiate desorption of any analytes adsorbed by the selected sorbent tube from the test gas. For example, the desorption controller activate a desorption mechanism of the desorption device506that is associated with sorbent tube504a, e.g., the desorption device can turn a heater proximate to sorbent tube504ato desorb analytes from sorbent material within the sorbent tube. The desorption controller can also control the operation of the flow control device512to pass the desorbed content (e.g., desorbed analytes from the test gas) along the established flow path and into the chamber containing the gas sensors. In some implementations, the desorption controller can control the operation of the flow control device to obtain a desired flow rate of the desorbed analytes into the chamber.

The desorption controller can open a flow path between the inlet of the selected sorbent tube and clean gas source (e.g., clean gas source518ofFIGS. 5 and 6) in which to entrain and transport the desorbed analytes into the chamber. For example, the desorption controller can close an inlet isolation valve of the sorbent tube pre-filter system (e.g., valve522) and open an isolation valve to the clean gas source (e.g., valve520).

In some implementations, the desorbed analytes from the selected sorbent tube can be passed through the environmental regulator, e.g., environmental regulator106, prior to being passed into the chamber. For example, the can be used to alter a temperature and/or relative humidity of the desorbed analytes prior to the desorbed analytes reaching the multiple gas sensors108. Temperature and humidity of the desorbed analytes can be regulated, for example, to room temperature and a relative humidity below dew point.

Response data is obtained from the gas sensor(s) in the chamber (726). For example, data processing apparatus collects data generated by each gas sensor of the multiple gas sensors in response to the desorbed content of the sorbent tube, where the generated data from each gas sensor of the multiple gas sensors includes a response of the gas sensor to one or more analytes of the multiple known analytes in the desorbed content of the sorbent tube. Data processing apparatus116can collect response data118, annotation data120, and composition data122for each gas sensor108in response to desorbed content of the sorbent tube.

In some implementations, response data includes a response of the gas sensor108over a period of time. In one example, response data includes a measure of a change in electrical resistivity of the gas sensor over time. Each of a first type of gas sensor and the second type of gas sensor can have a different response to the multiple known analytes of desorbed content of the sorbent tube. For example, an organic-type gas sensor may react to an organic analyte, e.g., methane, in the test gas and not react to an inorganic analyte, e.g., tin oxide, in the test gas, and an inorganic-type gas sensor may not react to the organic analyte in the test gas and react to the inorganic analyte in the test gas.

As described above with reference toFIGS. 3A-3C, a gas sensor can have no response or a response below a threshold response to a particular analyte. A gas sensor can have a threshold response to a particular analytes. In some implementations, a change in electrical resistivity of a gas sensor108is measured prior to exposure to the test gas, e.g., timestamp T1, during exposure to the test gas, e.g., timestamp Tt, and after termination of exposure to the test gas, e.g., timestamp T2. A plot of the response of the gas sensor versus time of collection can be recorded for each gas sensor by the data processing apparatus, e.g., plots300,310,320as depicted inFIGS. 3A, 3B, and 3C, respectively.

In some implementations, the data processing apparatus can identify a particular analyte contained in the test gas based on the sorbent tube information associated with the selected sorbent tube and a sensor response from at least one of the gas sensors. For example, the data processing apparatus can distinguish analytes based on a gas sensor response and information indicating the set of analytes that a selected sorbent tube is sensitive to. In one example, if a particular gas sensor that is responsive to methanol generates a positive sensor response (e.g., a response equal to or above the sensor's threshold response Rt) when the content of a sorbent tube that adsorbs methanol is desorbed and passed to the gas sensors for analysis, the data processing apparatus can determine the test gas includes methanol.

The flow path from a first one of the sorbent tubes to a chamber containing gas sensor(s) is isolated (728). The desorption controller can isolate the selected sorbent tube and turn off the flow control device. For example, after a predetermined time has elapsed to ensure that a sufficient amount of the adsorbed analytes of the selected sorbent tube have been desorbed, the desorption controller can turn off the flow control device512and isolate the selected sorbent tube, e.g., by shutting its associated inlet and outlet isolation valves508and509.

Steps722-728can be repeated to desorb content from another sorbent tube in the sorbent tube array and pass the desorbed analytes into the gas sensor chamber for analysis (730). In some implementations, the desorption controller can purge the gas sensor chamber prior to desorbing and providing the content from another sorbent tube into the gas sensor chamber. For example, the desorption controller can direct clean gas from the clean gas source518directly into the gas sensor chamber through a bypass path to purge the chamber.

Once the content of each sorbent tube in the sorbent tube array504(for which analysis is desired) has been desorbed and analyzed by the gas sensors, the process returns to step706ofFIG. 7A.

Referring back toFIG. 7A, a proper subset of gas sensors is selected from the multiple gas sensors to include in an optimized gas sensor array (706). The proper subset of gas sensors108can include fewer than the full set of gas sensors. For example, a full set of gas sensors can include gas sensors108a-108h, as depicted inFIG. 1, while the proper subset can include108a,108c,108d, and108h.

In some implementations, the proper subset of gas sensors108can include sensors that are responsive to at least one of the multiple analytes of the test gas. Each of the gas sensors of the proper subset of gas sensors108can be responsive to one or more of the multiple analytes of the test gas. For example, gas sensor108acan be responsive to a first analyte, gas sensor108ccan be responsive to the first analyte and a second analyte, gas sensors108dand108hcan both be responsive to the second analyte and a third analyte.

In some implementations, the proper subset of gas sensors108can include sensors that are unresponsive to one or more of the multiple analytes of the test gas. Sensors that are unresponsive may have zero response to a particular analyte or can have a response to an analyte below a threshold responsivity, e.g., Rt as discussed with reference toFIG. 3B. One or more of the gas sensors of the proper subset of gas sensors108can be unresponsive to one or more of the multiple analytes of the test gas. Continuing the example from above, gas sensor108acan be unresponsive to the second and third analyte, gas sensor108ccan be unresponsive to the third analyte, and gas sensors108dand108hare unresponsive to the first analyte.

A proper subset is selected including selecting a particular gas sensor from the multiple gas sensors based on the response of the particular sensor to the one or more analytes in the multiple known analytes in the test gas meeting a threshold response (708). As described with reference toFIGS. 3A-3C, a gas sensor can have at least a threshold response Rt to one or more of the multiple analytes in the test gas. For example, gas sensor A and gas sensor C, as depicted inFIGS. 3A and 3C, respectively, both exhibit at least a threshold response to one or more of the analytes of the multiple analytes of the test gas. The proper subset can be selected to include the gas sensors that each meet a threshold response to one or more analytes of the multiple analytes of the test gas.

In some implementations, the subset of gas sensors that each meet the threshold response can include meeting a threshold reactivity to one or more analytes of the multiple analytes in the test gas. In one example, the threshold reactivity includes a threshold change in resistivity of the gas sensor in response to the one or more analytes, e.g., for a MOx sensor. In another example, the threshold reactivity includes a threshold oxidation or reduction of the one or more analytes at an electrode of the sensor, e.g., for an electrochemical sensor.

In some implementations, the threshold reactivity can be defined by a change of at least 0.1% relative to a total response range of a particular gas sensor. The threshold reactivity can be defined in part by what is considered a standard detectable signal for the particular gas sensor and can be different depending on the total response range of the particular gas sensor, e.g., can be different between a MOx sensor and an electrochemical sensor.

Selecting a proper subset further includes determining to include the selected gas sensor in the proper subset of gas sensors based on the selected gas sensor meeting a threshold temporal response (710). A threshold temporal response can include an amount of time between exposure of a particular gas sensor to the test gas and the particular gas sensor reaching the threshold response Rt. In one example, as depicted inFIGS. 3A and 3C, each of the gas sensor A and gas sensor C has a different amount of time, P1and P3, respectively, to reach the threshold response Rt. A threshold temporal response can be greater than P1but less than P3, such that gas sensor A is selected to be included in the proper subset but gas sensor C is not selected to be included in the proper subset as result.

As depicted inFIGS. 3A-C, the threshold temporal response can further include an amount of recovery time for the particular gas sensor to reach a baseline reading after termination of exposure to the test gas. In other words, an amount of time it takes for the gas sensor to recover from exposure to the test gas before it can be exposed again to another test gas.

In some implementations, a first gas sensor and a second gas sensor can be selected for inclusion in the proper subset of gas sensors based on the respective responses of the gas sensors, where the first gas sensor and the second gas sensor are determined to have similar responses to a same set of analytes of the plurality of analytes, e.g., both meet a threshold response Rt within a period P1. A first temporal response of the first gas sensor can be determined to be less than a second temporal response of the second gas sensors, where only the first gas sensor is then determined to be utilized in the subset of gas sensors. In one example, as depicted inFIGS. 3A and 3C, each of the gas sensor A and gas sensor C has a different amount of recovery time, P2and P4, respectively, to reach the baseline response at timestamp T3. The threshold temporal response can be less than P4but greater than P2, such that gas sensor A is selected to be included in the proper subset but gas sensor C is not selected to be included in the proper subset as result. In one example, if a gas sensor of the array of gas sensors108does not respond to an analyte of interest or does not have a response that is at least 0.1% of its total response range, the gas sensor can be excluded from the proper subset.

In some implementations, a threshold temporal response and threshold response for selecting the proper set of sensors depends in part on the subset of sensors of the multiple sensors that have non-zero responsivity to the test gas. For a test gas with a very low concentration of analytes of interest and/or analytes that are relatively difficult to detect, the subset of sensors that have a non-zero sensitivity to the test gas may have a low sensitivity and long temporal response, e.g., sampling time to reach threshold response Rt is relatively long. In this example, the threshold temporal response may be set to a relatively long period of time and threshold response may be set to a relatively low response R. In contrast, for a test gas with high concentrations of analytes of interest and/or analytes that are relatively simple to detect, the subset of sensors that have a non-zero sensitivity may be a large subset of the multiple gas sensors, where at least some of the subset of gas sensors have high sensitivity to the test gas and quick temporal response, e.g., sampling time to reach threshold response Rt is relatively short. In this example, the threshold response may be set to a relatively short period of time and threshold response may be set to a relatively high response R.

In some implementations, the proper subset of gas sensors is selected by selecting an optimized set of gas sensors that collectively have a best response to the multiple analytes of the test gas. Each individual gas sensor may be nonresponsive to one or more analytes of the multiple analytes, but overall can have a best response to a particular analyte of the multiple analytes.

In some implementations, selecting the proper subset of gas sensors depends in part on cost considerations, reliability of each type of gas sensors of the gas sensing array, and a repeatability requirement of the particular environment and application. In one example, an environment having safety critical aspects, e.g., toxic gases, redundancy of sensing can factor into a selection of the proper subset of gas sensors, where multiple sensors having a same sensor response can be selected.

In some implementations, selecting the proper subset of gas sensors includes selecting only the gas sensors of the proper subset of gas sensors to be included in a gas sensing apparatus, e.g., gas sensing apparatus402, that is deployed in a particular test environment, e.g., a factory setting. Fewer than the total available number of gas sensors, e.g., the multi-modal array of gas sensors discussed inFIG. 1, are physically incorporated into the gas sensing apparatus402that is deployed in a test environment.

In some implementations, selecting the proper subset of gas sensors includes collected data from only the gas sensors of the proper subset of gas sensors for a gas sensing apparatus, e.g., gas sensing apparatus402, that is deployed in a particular test environment, e.g., a factory setting. The total available number of gas sensors, e.g., the multi-modal array of gas sensors108discussed inFIG. 1, are physically incorporated into the gas sensing apparatus402that is deployed in the test environment, but sensing data, e.g., response data118, is only collected from the proper subset of gas sensors.

FIG. 8is a flow diagram of an example process800of the e-nose gas sensing apparatus. The e-nose gas sensing apparatus102can be trained using system100including multiples test gases each including multiple known analytes from multiple gas sources in gas manifold126.

Training data can be generated using system100and provided to train a machine-learned model which can then be deployed in a test environment to detect one or more analytes. Multiple sets of training data can be generated, where each set of training data can be customized for a particular test environment, e.g., a factory environment, an agricultural environment, a home environment, etc., such that the machine-learned model is trained to recognize a set of analytes that are relevant to the environment, e.g., process gases to a fabrication environment, and of importance to the particular environment, e.g., detecting toxic chemicals rather than inert chemicals. The process800described with reference toFIG. 8is flexible such that the training data can be generated using a same gas sensing apparatus102for multiple different environments using a different set of known analytes and known concentrations of the analytes from gas sources130.

Training data is generated for multiple test gases, where each test gas includes multiple analytes and is representative of a first environment (802). The first environment, e.g., an industrial environment, an agricultural environment, a residential environment, etc., can have a particular set of relevant analytes of interest and analytes not of interest, depending on the particulars of the environment. The test gases each include a particular composition of the set of multiple analytes, where the particular composition can include known concentrations of a subset of analytes of interest and analytes not of interest.

Training data is generated for each test gas including exposing the multi-modal gas sensor array including multiple gas sensors to the test gas at a first set of operating conditions, where the multiple gas sensors include a first type of gas sensor and a second type of gas sensor different from the first type of gas sensor (804). The first set of operating conditions includes a first concentration of a first analyte of interest of the multiple analytes and a second concentration of a second analyte not of interest of the multiple analytes. For example, the first concentration of the first analyte that is of interest is 0.2% of coffee and the second concentration of the second analyte that is not of interest is 1% of ethanol, where the first analyte and the second analyte are mixed with an inert gas, e.g., nitrogen, in the test gas.

Exposing the multi-modal gas sensor array includes flowing the test gas from the gas manifold126through gas inlet110into the environmental regulator106. Within the environmental regulator106, e.g., heating/cooling fins, the test gas is regulated to a particular temperature, e.g., as measured by temperature gauge128and monitored by environmental controller124. The test gas is then provided to the array of gas sensors108and exhausted through gas outlet112. A flow of the test gas within house104can be controlled by the environmental controller124and regulated in part using regulatory components of the gas manifold126, e.g., flow meter214, pressure regulator202, by a negative pressure generated by fan114within the housing104, or a combination thereof.

For each test gas, a first set of sample data including response data for each of the multiple gas sensors responsive to the test gas at the first set of operating conditions is collected by a data processing apparatus and from each of the multiple gas sensors (806). Response data118can be collected by data processing apparatus116from each of the multiple gas sensors108of the gas sensing apparatus102. In some implementations, process704A ofFIG. 7Bcan be used to employ a sorbent tube pre-filter system140to analyze each test gas and obtain gas sensor response data.

The response data118can include multiple different formats of responses depending in part on a type of gas sensor108of the multiple different types of gas sensors. Formats of response data can include optical response data, e.g., from PID sensors, electrical resistivity data, e.g., from MOx sensors, and oxidation/reduction response data, e.g., from electrochemical sensors. In some implementations, the response data118includes a measure of electrical resistivity of the gas sensor over a period of time during the exposure to the test gas, e.g., for MOx gas sensors.

Additionally, annotation data120, e.g., timestamps, temperature/humidity data, etc., delineating when the test gas is exposed to the gas sensors108can be recorded, e.g., when the test gas is provided from the environmental regulator106to the array of gas sensors108. Further details of annotation data120are described in further detail with reference toFIGS. 3A-3Cabove.

Composition data122describing a particular composition of the test gas including the respective concentrations of one or more analytes of interest and one or more analytes not of interest in the test gas can be recorded for each test gas. The known analytes of interest and known analytes not of interest can be associated with the response data118generated by each gas sensor of the multi-modal array of gas sensors108.

In some implementations, the known concentrations of known analytes can be used to label the response data118, e.g., response outputs, of the multiple gas sensors. The labeled response data118can be provided to a machine-learned model for training. The labeled response data118can be processed, e.g., calibrated to a standard baseline, to ensure consistency between different sensing apparatuses102having a same design.

A subset of gas sensors from the multiple gas sensors is selected from the first set of sample data for the test gas, where the response data collected for each gas sensor of the subset of gas sensors meets a threshold response (808). As described above with reference toFIG. 7B, the subset of gas sensors can be selected, for example, based in part on each selected sensor meeting threshold of responsivity to the test gas. Additionally, the subset of gas sensors can be selected based in part on each selected sensor being below a threshold recovery period after termination of exposure of the selected gas sensor to the test gas.

In some implementations the multiple gas sensors are 38 or more gas sensors in the multi-modal array of gas sensors108, where the subset of gas sensors includes fewer than all of the total number of gas sensors in the gas sensing apparatus102. For example, the total number of gas sensors in the gas sensing apparatus102is 30 gas sensors of multiple different types, e.g., MOx sensors, PID sensors, electrochemical sensors, and the subset of selected gas sensors are 15 gas sensors, 20 gas sensors, or 8 gas sensors. The subset of gas sensors that is selected represents an optimized subset of the total available gas sensors in the gas sensing apparatus102for responding to the particular test gas under the first set of operating conditions.

The multiple gas sensors of the multi-modal gas sensing array are exposed to the test gas under a second set of operating conditions (810). The second set of operating conditions can differ from the first set of operating conditions based on sampling conditions, e.g., temperature/relative humidity, relative concentrations of the analytes in the test gas, and/or the set of one or more analytes of interest and analytes not of interest included in the test gas.

In some implementations, the second set of operating conditions includes a first concentration of a second analyte of interest of the multiple analytes and the second concentration of the analyte not of interest of the multiple analytes. Continuing the example from above, the second set of operating conditions can include a first concentration of a second analyte of interest, e.g., 0.1% vanilla, combined with 1% of ethanol as the analyte not of interest and mixed with the inert gas, e.g., nitrogen.

In some implementations, the second set of operating conditions includes a third concentration of the analyte of interest of the multiple analytes and a fourth concentration of the analytes not of interest of the multiple analytes, where the third concentration is different than the first concentration. Continuing the example from above, the third concentration of the analyte of interest can be 0.5% coffee and the fourth concentration of the analyte not of interest can be 5% of ethanol, where the two analytes are then mixed with an inert gas, e.g., nitrogen, to generate the test gas.

In another example, the third concentration of the analyte of interest can be 0.5% coffee and the fourth concentration of the analyte not of interest can be the same as the second concentration, e.g., 1% of ethanol, where the two analytes are then mixed with a purge gas, e.g., nitrogen, to generate the test gas.

In some implementations, prior to exposing the gas sensors to the test gas under the second set of operating conditions, the multiple gas sensors108are exposed to a purge gas, e.g., nitrogen or compressed clean dry air, for a period of time. The purge gas, e.g., gas source130adepicted inFIG. 2, can be used to assist in shortening a recovery time of the sensors after exposure to the test gas, e.g., shorten P2for gas sensor A inFIG. 3A, and/or to ensure that no remaining test gas is present within the housing104or gas manifold126.

In some implementations, the period of time of exposure of the multiple gas sensors108to the purge gas can be an amount of time for each of the sensors to reach a baseline resistivity reading. The period of time of exposure can be selected based on a longest recovery time of all the respective recovery times for the multiple gas sensors108. The period of time exposure of the multiple gas sensors108to the purge gas can be, for example, 1 minute, 5 minutes, 30 seconds, or the like.

A second set of sample data including response data is collected by the data processing apparatus and from each of the subset of gas sensors responsive to the test gas under the second set of operating conditions (812). Response data118can be collected by data processing apparatus116from only the selected subset of gas sensors108of the multiple gas sensors of the gas sensing apparatus102that were selected as responsive to the test gas under the first set of operating conditions in Step808. The gas sensors108of the multiple gas sensors108not selected for inclusion in the subset of gas sensors108can be, for example, switched “off” during the sampling process. In another example, the gas sensors108not selected for inclusion in the subset of gas sensors108can be active, e.g., “on”, during the sampling process but the data generated by those particular gas sensors may not be collected by the data processing apparatus116.

Training data is generated for the test gas representative of the first environment from the first set of sample data and the second set of sample data from each of the subset of gas sensors (814). In some implementations, training data is generated by recording the captured response for each sensor to the test gas, an amount of time that the response was captured, e.g., a “sniff” time, as well as an amount of time that a baseline measurement of no gas exposure was recorded prior to exposure of the test gas and an amount of time that the response was captured after termination of the exposure to the test gas. In other words, training data includes sensor response as well as labeled timestamps denoting baseline measurement, exposure to test gas, and recovery measurement, e.g., as described with reference toFIGS. 3A-3C. Each labeled sensor response is produced for various test gases including varying compositions of analytes and concentrations of each analyte.

The process described with reference to Steps802-814can be repeated for multiple test gases, where each test gas is representative of the test environment. The multiple test gases can be selected based on a range of compositions and/or environmental conditions, e.g., temperature, over which the response of the gas sensors108are measured to generate the training data.

The training data is provided to a machine-learned model (816). A machine-learned model can be trained for each intended test environment using a particular set of test gases and environmental conditions. For example, a machine-learned model for an industrial applications can be different that a machine-learned model for a food production facility, where both sets of training data are generated using system100described with reference toFIG. 1.

In some implementations, training the machine-learned model using the training data can further include providing, to the subset of gas sensors, a particular test gas of the multiple test gasses under a third set of operating conditions. A third set of sample data is collected from each of the subset of gas sensors and provided to the machine-learned model. The machine-learned model determines characteristics descriptive of the particular test gas under the third set of operating conditions, e.g., determines the analytes included in the test gas and relative concentrations of each of the analytes included in the test gas. For example, the third set of operating conditions can include a fifth concentration of the analyte of interest, e.g., 0.6% of coffee, and a sixth concentration of the analyte not of interest, e.g., 1% of ethanol, where the two analytes are mixed with an inert gas, e.g., nitrogen, to generate the test gas under the third set of operating conditions.

In some implementations, the operating conditions of the first set of operating conditions, the second set of operating conditions, and the third set of operating conditions are defined as a particular temperature and relative humidity of the test gas and the gas sensors108when the test gas is exposed to the subset of gas sensors108. For example, the first set of operating conditions can be 20 degrees C. at 10% humidity, the second set of operating conditions can be 40 degrees C. at 33% humidity, and the third set of operating conditions can be 35 degrees C. at 33% humidity.

In some implementations, determining characteristics descriptive of the test gas under the third set of operating conditions includes identifying, by the machine-learned model, a first concentration of a first analyte in the test gas under the third set of operating conditions.

FIG. 9A-9Dare schematics of example views of e-nose gas sensing apparatuses.FIG. 9Adepicts an example exterior of an e-nose gas sensing apparatus900, e.g., gas sensing apparatus402. The gas sensing apparatus900can include housing902, e.g., housing104, enclosing the various components of the gas sensing apparatus900. A gas inlet904, e.g., gas inlet110, can receive an unknown gas mixture, e.g., unknown gas mixture404, and provide the unknown gas mixture to a multi-modal gas sensing array, e.g., a multi-modal array of gas sensors108, within the housing902. Gas sensing apparatus900can include a display906, e.g., display406, which can include a touchscreen. Display906can provide an intuitive user interface for receiving user instructions, e.g., run test, testing parameters, etc., and display information, e.g., information408, to a user viewing the display906.

A footprint, e.g., width and length, of the gas sensing apparatus900can be, for example, smaller than 2×4 inches, smaller than 10×12 inches, smaller than 20×20 inches, or the like. Though depicted inFIG. 9Aas having a rectangular form factor, other form factors are possible, e.g., cylindrical form factor. In one example, the gas sensing apparatus900can have dimensions similar to a standard shoebox, e.g., 14×8×5 inches. In some implementations, a footprint of the gas sensing apparatus900can be fit to the dimensions of a silicon chip, e.g., on the order of 1 mm×1 mm×0.1 mm or smaller.

FIG. 9Bdepicts a perspective view, another example of an e-nose gas sensing apparatus920where a portion of the house922of the gas sensing apparatus920is transparent to view an interior of the apparatus920. Gas sensing apparatus920including a multi-modal array of gas sensors924, e.g., a multi-modal array of gas sensors108. As depicted inFIG. 9B, a multi-modal array of gas sensors924includes multiple types of gas sensors924a,924b,924c, and924d. The multiple types of gas sensors can have different form factors, gas sensing mechanisms, operating parameters, or the like. The multi-modal array of gas sensors is described in further detail above with reference toFIGS. 1-6.

Gas sensing apparatus920includes a gas inlet926, e.g., gas inlet110, to receive an unknown gas mixture, e.g., unknown gas mixture404, and provide the unknown gas mixture to a multi-modal gas sensing array924. Gas sensing apparatus920can route the unknown gas mixture from the gas inlet926via internal tubing and/or fins to regulate the flow of the unknown gas mixture across the gas sensors924. In some implementations, the gas sensing apparatus920includes heating fins or another temperature control component, e.g., as described with reference to the environmental regulator106inFIGS. 1 and 4.

In some implementations, gas sensing apparatus920includes a display1028

FIG. 9Cdepicts a side view of gas sensing apparatus920along axis A-A. Housing922is depicted as transparent to display the interior components of the gas sensing apparatus920. Gas sensors924include respective circuitry930, e.g., contacts or pins, and can be in physical and electrical contact with additional circuitry of a printed circuit board (PCB)932. Additional electrical connections to the gas sensors924via circuitry930to a data processing apparatus, e.g., data processing apparatus116, can be included (not shown).

FIG. 9Ddepicts another side view of gas sensing apparatus920along axis B-B. Housing922is depicted as transparent to display the interior components of the gas sensing apparatus920. Unknown gas mixture introduced at gas inlet926flows into the housing922and over the gas sensors924, following a flow path indicated by934. Gas mixture is purged through gas outlet936, e.g., gas outlet112. In some implementations, a fan, pump, or blower938, e.g., fan114, can provide a negative pressure within the housing922to facilitate a flow from the gas inlet926to a gas outlet (not pictured), e.g., gas outlet112.

FIG. 10is a block diagram of an example computer system1000that can be used to perform operations described above. The system1000includes a processor1010, a memory1020, a storage device1030, and an input/output device1040. Each of the components1010,1020,1030, and1040can be interconnected, for example, using a system bus1050. The processor1010is capable of processing instructions for execution within the system1000. In one implementation, the processor1010is a single-threaded processor. In another implementation, the processor1010is a multi-threaded processor. The processor1010is capable of processing instructions stored in the memory1020or on the storage device1030.

The memory1020stores information within the system1000. In one implementation, the memory1020is a computer-readable medium. In one implementation, the memory1020is a volatile memory unit. In another implementation, the memory1020is a non-volatile memory unit.

The storage device1030is capable of providing mass storage for the system1000. In one implementation, the storage device1030is a computer-readable medium. In various different implementations, the storage device1030can include, for example, a hard disk device, an optical disk device, a storage device that is shared over a network by multiple computing devices (for example, a cloud storage device), or some other large capacity storage device.

The input/output device1040provides input/output operations for the system1000. In one implementation, the input/output device1040can include one or more network interface devices, for example, an Ethernet card, a serial communication device, for example, a RS-232 port, and/or a wireless interface device, for example, a 802.11 card. In another implementation, the input/output device can include driver devices configured to receive input data and send output data to other input/output devices, for example, keyboard, printer and display devices1060. Other implementations, however, can also be used, such as mobile computing devices, mobile communication devices, set-top box television client devices, etc.

The processes and logic flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by special purpose logic circuitry, for example, an FPGA or an ASIC, or by a combination of special purpose logic circuitry and one or more programmed computers.

Computers suitable for the execution of a computer program can be based on general or special purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a central processing unit for performing or executing instructions and one or more memory devices for storing instructions and data. The central processing unit and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, for example, magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, for example, a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device, for example, a universal serial bus (USB) flash drive, to name just a few.

Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, for example, EPROM, EEPROM, and flash memory devices; magnetic disks, for example, internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

Data processing apparatus for implementing machine learning models can also include, for example, special-purpose hardware accelerator units for processing common and compute-intensive parts of machine learning training or production, that is, inference, workloads.

Machine learning models can be implemented and deployed using a machine learning framework, for example, a TensorFlow framework, a Microsoft Cognitive Toolkit framework, an Apache Singa framework, or an Apache MXNet framework.

Embodiments of the subject matter described in this specification can be implemented in a computing system that includes a back-end component, for example, as a data server, or that includes a middleware component, for example, an application server, or that includes a front-end component, for example, a client computer having a graphical user interface, a web browser, or an app through which a user can interact with an implementation of the subject matter described in this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, for example, a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), for example, the Internet.

The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. In some embodiments, a server transmits data, for example, an HTML page, to a user device, for example, for purposes of displaying data to and receiving user input from a user interacting with the device, which acts as a client. Data generated at the user device, for example, a result of the user interaction, can be received at the server from the device.