Gas measurement device

Abstract

A gas measurement device 10 comprising: a gas intake module 20 including a gas intake chamber for receiving a gas, a gas sensing chamber 40 including at least one gas sensor 42 for sensing a presence,

Description

The present disclosure relates to a gas measurement device, particularly to a gas measurement device capable of detecting multiple gas species. According to an aspect of the invention, there is provided a gas measurement device comprising: a gas intake module including a gas intake channel for receiving a gas; a gas sensing chamber including at least one gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas; a buffer chamber arranged in fluidic communication between the gas intake module and the gas sensing chamber so that, in use, the gas may flow from the gas intake module to the buffer chamber and from the buffer chamber to the gas sensing chamber. The gas measurement device may further include a gas flow controller operable to control a flow of the gas from the buffer chamber to the gas sensing chamber. The gas flow controller may be operable to modulate a flow of the gas from the buffer chamber to the gas sensing chamber. The gas measurement device may include a pressure controller operable to increase an internal chamber pressure of the buffer chamber. The gas measurement device may further include an evacuation device operable to evacuate the buffer chamber and / or the gas sensing chamber. The gas measurement device may include a heater operable to heat the buffer chamber and / or the gas sensing chamber. The gas measurement device may further include a gas filter arranged to, in use, filter the gas flowing from the buffer chamber to the gas sensing chamber. The gas sensing chamber may include a plurality of gas sensors, each gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas. The plurality of gas sensors may be gas sensors of different types for sensing a presence, at least one parameter and / or at least one component of respective different gas species. The plurality of gas sensors may be gas sensors of the same type with respective different configurations for sensing a presence, at least one parameter and / or at least one component of respective different gas species. The gas sensing chamber may include a plurality of gas sensing submodules, each gas sensing submodule including a respective gas sensor. The gas measurement device may further include a scrubber arranged to, in use, scrub one or more gas species from the gas flowing from the gas intake channel to the gas sensing chamber or to one or more gas-sensing sub-chambers. The gas measurement device may include at least one additional gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas. The at least one additional gas sensor may be arranged in the buffer chamber. The gas intake channel may include a one-way valve configured to facilitate a one-way flow of the received gas from an exterior of the gas measurement device into an interior of the gas measurement device. The gas intake module may include a gas collection chamber. The gas intake channel may be configured to direct a portion of the received gas into the buffer chamber and direct another portion of the received gas into the gas collection chamber. The gas measurement device may include a calibration gas chamber for containing a calibration gas. The calibration gas chamber may be arranged in fluidic communication with the gas sensing chamber so that, in use, the calibration gas may flow from the calibration gas chamber to the gas sensing chamber. The at least one gas sensor may include a carbon dioxide sensor, an alcohol sensor, an oxygen sensor, a water vapour sensor, a biomarker sensor and / or a drug sensor. The at least one gas sensor may include a nitrous oxide sensor. The plurality of gas sensors may include a nitrous oxide sensor and an alcohol sensor. The gas measurement device may include a mouthpiece or mask. At least part of the gas intake channel may form part of the mouthpiece or mask. The gas intake module, the gas sensing chamber and the buffer chamber may be arranged in a portable or hand-held casing. According to a second aspect of the invention, a method of operating the gas measurement device may comprise the steps of: by the gas intake module, collecting a gas; by the buffer chamber, collecting at least part of the gas from the gas intake module; by the gas sensing chamber, collecting at least part of the gas from the buffer chamber; by the at least one gas sensor, sensing a presence, at least one parameter and / or at least one component of the gas. According to a third aspect of the invention, there is provided a gas measurement device comprising: a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component; a first gas sensor for obtaining a measurement of the first gas component; a second gas sensorfor obtaining a measurement of the second gas component; a processor configured to, in use, determine a total volume of gas based on the measurement of the second gas component, wherein the processor is configured to, in use, determine a concentration level of the first gas component based on the measurement of the first gas component and the determined total volume of the gas. According to a fourth aspect of the invention, there is provided a gas measurement device comprising: a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component; a first gas sensor for measuring a combined concentration level of the first gas component and the second gas component; a second gas sensor for measuring an individual concentration level of the second gas component; and a processor configured to, in use, determine an individual concentration level of the first gas component by combining the measured combined concentration level of the first gas component and the second gas component, the measured individual concentration level of the second gas component and a calibration value, wherein the calibration value is a correction factor associated with a response of the first gas sensor to a presence of the second gas component. The first gas sensor may be a non-dispersive infrared sensor. The first gas may be nitrous oxide. The second gas may be carbon dioxide. It will be appreciated that the use of the terms "first" and "second", and the like in this patent specification may be used to help distinguish between similar features (e.g., the first and second gas components), and is not intended to indicate the relative importance of one feature over another feature, unless otherwise specified. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and the claims and / or the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and all features of any embodiments can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Preferred embodiments of the invention will now be described by way of non-limiting examples with reference to the following drawings, in which: Figure 1 shows a schematic diagram of a gas measurement device according to an embodiment of the invention; Figure 2 shows a resulting graph of gas concentration from an experimental implementation; Figure 3 shows a resulting graph comparing the gas concentration measured by an experimental implementation with that of a commercially available gas sensor. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interests of clarity and conciseness. A schematic of an embodiment of the gas measurement device is shown in Figure 1 and is designated generally by the reference numeral 10. In some aspects, the gas measurement device 10 may be used to take a gas sample and determine the concentration of a target gas species in the sample. The sample may be, for example, the breath of a user, a patient or a participant. The gas measurement may be administered by a separate party or by the party whose breath is to be sampled. It is envisioned that the gas measurement device 10 may be used in real-time and in-situ, for instance, in roadside driver capacity assessments. Particularly, the gas measurement device 10 may be ideally configured to test the breath of a driver to assess the concentration of alcohol, nitrous oxide and / or other substances in their breath. It is envisioned that other uses of the gas measurement device 10 are possible and that the invention's utility is not limited to roadside driver capacity assessments, or measurements of human breath or the breath of any animal, and the gas measurement device 10 may be used in a variety of scenarios and may be adapted to test for a variety of gases in different scenarios without departing from the scope of the claims. The gas measurement device 10 includes: a gas intake module 20, which further includes a gas intake channel 22 for receiving a gas; a buffer chamber 30; and a gas sensing chamber 40 which further includes at least one gas sensor 42 for sensing a presence, at least one parameter and / or at least one component of the gas. The buffer chamber 30 is arranged in fluidic communication between the gas intake module 20 and the gas sensing chamber 40 so that, in use, the gas may flow from the gas intake module 20 to the buffer chamber 30 and from the buffer chamber 30 to the gas sensing chamber 40. It will be appreciated that, in other embodiments of the invention, the gas measurement device 10 may include a plurality of buffer chambers 30 and / or a plurality of gas sensing chambers. Gas may flow from the gas intake module 20 to the buffer chamber 30 at atmospheric pressure or higher. A filter may be placed between the gas intake module 20 and the buffer chamber 30. The gas intake module 20 may further include a gas collection chamber 24. The pictured embodiment has a collection chamber 24 in the exemplary form of a collection bag. The valve arrangement and gas flow path in the gas measurement device 10 may enable the user to collect the gas sample in the collection bag 24 and subsequently introduce the gas sample to the buffer volume 30 and gas sensing chamber 40 after a period of time has lapsed following initial sample collection. For example, a user may provide multiple breaths to fill the collection bag, thereby providing a larger sample. Alternatively, the collection bag may be manually compressed to provide a greater pressure when introducing the gas sample to the other chambers and gas flow channels in the gas measurement device. The gas collected in the gas collection chamber 24 may be used for offline validation or calibration. Optionally the gas collection chamber 24 may be omitted or may be replaced by an exhaust vent. In some embodiments, the gas intake channel 22 may be configured to direct a portion of the received gas into the buffer chamber 30 and direct another portion of the received gas into the gas collection chamber 24. This may be achieved, by way of example and not limitation, by a split pipe or gas flow arrangement. The gas intake channel 22 may further include a one-way valve which facilitates a one-way flow of the received gas from the outside towards the gas collection chamber 24 and the buffer chamber 30 so as to prevent backflow. Such prevention of the backflow can beneficially yield sufficient gas flow rate to ensure successful and reliable measurements. The gas measurement device 10 may include a mouthpiece or mask 26 to facilitate sampling of the breath of a user or participant. At least part of the gas intake channel 22 may form part of the mouthpiece or mask. The mouthpiece or mask may be detachable from the rest of the measurement device 10, for example, for storage or hygienic replacement. The mouthpiece or mask may be disposable, or it may be made of a sterilisable material and reused following sterilisation. For optimal operation of the gas measurement device 10, it may be necessary to purge the chambers and gas flow lines to remove any accumulation of residual gas from previous use of the device or from ingress of atmospheric impurities. During each measurement or during use of the device, gas samples can become trapped, for example, in the gas lines, chambers, pumps, valves, filters and other components of the gas measurement device 10. Hence, a purge of gas in the device before or after each use is desirable to ensure that a given measurement run is not affected by a previous measurement run. During a gas purge, the chambers and gas lines are evacuated at a pressure lower than atmospheric pressure. The purging involves configuring any gas flow control device, such as pumps and valves, so that the flow direction of gas is from the buffer chamber 30 or the gas sensing chamber 40 to the outside environment. A heater may also be used to enhance the removal of any adsorbed materials. It is also advantageous to enable control of the direction of flow for maintenance purposes, and control of the pressure and / or velocity of gas flow through the various chambers in the device. Furthermore, a uniform flow of gas from the buffer chamber 30 to the gas sensing chamber 40 is particularly desirable to obtain accurate measurements. To facilitate these operations, the gas measurement device 10 may also include a gas flow controller 50 (e.g. a pump and / or a valve arrangement) operable to control and / or modulate the flow of the gas from the buffer chamber 30 to the gas sensing chamber 40. The pictured embodiment has a gas flow controller 50 exemplarily comprising a pump downstream from the gas sensing chamber 40 which regulates the flow out of the buffer chamber 30 and into the gas sensing chamber 40. Such control and / or modulation of the flow of the gas from the buffer chamber 30 to the gas sensing chamber 40 may be implemented to stabilise gas measurement and / or increase measurement reliability and / or enhance signal sensitivity and / or shorten a measurement period. The gas flow controller 50 may also be operated in a gas purge mode, wherein it operates in cooperation with the evacuation device 54, as detailed below. The gas measurement device 10 includes a pressure controller 52 which is operable to increase an internal chamber pressure of the buffer chamber 30. The pressure controller 52 is preferably in the form of a pump upstream of the buffer chamber 30. In other embodiments, the pressure controller may be or may include other components, such as (for example and not limitation) a pressure sensor, a heater, a gas reservoir, inlet or outlet. The pressure controller 52 may be used to enable storage of the gas sample or breath in the buffer chamber at pressures higher than that of the surrounding atmosphere and / or it may be used to regulate gas flow through the device 10. The gas measurement device may further include an evacuation device 54 operable to evacuate the buffer chamber and / or the gas sensing chamber. The evacuation device may include, for example and not limitation, gas flow lines, pumps, valves, heaters and outlets. In some embodiments the evacuation device may be defined by a change in configuration of the components when the gas measurement device enters a gas purge mode. In the embodiment of Figure 1, the evacuation device 54 is in the form of a bypass line which allows gas to exit the device without being forced backwards through the pump. This may extend the lifetime of the pump and enables a section of the gas flow line to remain one-way. Further embodiments not pictured may also include a heater operable to heat the buffer chamber 30 and / or the gas sensing chamber 40. The heater may contribute to the purging of impurities or residual gas from those chambers and the surrounding gas flow channels. For example, the heater may be configured to heat the buffer and / or gas sensing chamber 30, 40 to remove any adsorbed molecules. It may be used to change the pressure of one or each chamber 30, 40. The pictured embodiment includes a filter 60 arranged so that, in use, gas flowing from the buffer chamber 30 to the gas sensing chamber 40 passes through the filter 60. By passing through the filter 60, gas passing through the gas flow line from the buffer chamber 30 to the gas sensing chamber 40 may be filtered or otherwise processed by the filter before being introduced into the gas sensing chamber 40. The filter may include a particle or particulate filter, moisture and chemical scrubbers, and / or filters which target specific gas species. The filter may be a multi-stage filter comprising one or more filter stages. Each stage of the multi-stage filter may target one of more gas species in one or more concentrations, or they may be targeted at filtering out other components of the gas sample. For example, it may be advantageous to filter out undesirable particulate matter, moisture and gas species in different stages, depending on the requirements of the sensors 42 and the target gas to be detected. This is particularly advantageous in embodiments where the gas sample is taken from human or animal breath which has a high moisture and carbon dioxide content, both of which may negatively impact or interfere with the detection of the target gas. Light-based sensors in particular are sensitive to the presence of dust or moisture in the gas sample due to light being blocked or refracted by dust and / or moisture. In some embodiments the filter 60 may more particularly be a carbon dioxide filter or scrubber. For example and not limitation, the filter 60 may be a limestone filter. In embodiments where a target gas species is nitrous oxide, reducing the concentration of carbon dioxide in the gas which proceeds to the sensing chamber 40 may improve nitrous oxide detection. The presence of carbon dioxide in the gas sample may give a false detection signal for nitrous oxide, depending on the sensing method used. For instance, in embodiments where nitrous oxide is a target gas for detection, a non-dispersive infrared sensor may be used. An absorption line of carbon dioxide is close in wavelength to an absorption line of nitrous oxide and may generate false positives if carbon dioxide is not removed or if the concentration of carbon dioxide is not reduced in the sample. The gas sensing chamber 40 may include a plurality of gas sensors 42, each for sensing a presence, at least one parameter and / or at least one component of the gas. Each of the gas sensors 42 may be gas sensors of different types for sensing a presence, at least one parameter and / or at least one component of respective different gas species. In further embodiments, each of the gas sensors 42 may be gas sensors of the same type for sensing a presence, at least one parameter and / or at least one component of respective different gas species. For example, and not limitation, the gas sensing chamber 40 may include first and second gas sensors wherein the first gas sensor is configured to detect the presence of alcohol, and the second gas sensor is configured to detect the presence of nitrous oxide. The at least one gas sensor 42 may also be, for example, carbon dioxide, oxygen, water vapour, biomarker and / or drug sensors. A single gas sensor may also be configured to detect the presence or at least one property of multiple gas species. It will be appreciated that the gas measurement device may be configured to provide a reading corresponding to a measured concentration level, or provide a 'pass' or 'fail' status. The gas sensors may be the same type of sensor configured for sensing different gas species, or different types of sensors configured to detect different aspects or parameters of different gas species. In addition to detecting different gas species or different aspects of the same gas species, the sensors may be of different construction, operation or type. For instance, one sensor may be an electrochemical sensor, while the other is an infrared sensor, or both sensors may be electrochemical sensors. Further examples of sensors which may be used as the sensor or sensors in the invention include, but are not limited to, optical sensors, acoustic sensors, enzymatic sensors, biosensors, catalytic sensors, semiconductor-based sensors, 2-Dimensional materials-based sensors, non-dispersive infrared sensors, fibre-based evanescent cavity-enhanced optical sensors and photo-ionisation detectors. Non-limiting examples of optical sensors include Raman spectroscopy sensors, fluorescence sensors turbidity sensors and opto-acoustic sensors. Modalities that fall within the measurement of the target gas species may include, but are not limited, to optical absorption, acoustic response, electrochemical response, total gas flow rate, and combined gas flow rate. The measurement of the response of the gas sensor(s) to the target gas species may be used to, for example, determine gas total or partial volume and thereby determine gas concentration level. For example, gas volume is proportional to a gas sensor's optical response, i.e. the surface area under an absorption peak. The choice of sensor(s) is determined by the target gas species and testing environment. Further embodiments may include further gas sensors, etc., which are sensitive to yet further gas species or parameters and / or components of the same gas species as at least one of the other gas sensors. The provision of a plurality of sensors 42 may advantageously allow for the detection of multiple gas species in a single gas sample or breath. Alternatively, the provision of multiple gas sensors targeted at the same gas species may allow for a greater depth or accuracy of testing. The number of gas sensors 42 is not limited to two or three, and the sensing chamber 40 may contain any practicable number of sensors. In the context of a roadside driver capacity assessment, for example, it is desirable that at least one of the sensors 42 is a nitrous oxide sensor and, optionally, at least one is an alcohol sensor. Alternatively, it may be advantageous to provide both a nitrous oxide and carbon dioxide sensor to enable the subtraction of background signal from carbon dioxide in the breath and achieve a more accurate measurement of nitrous oxide concentration. Various combinations of sensors may be provided depending on the measurement requirements and to achieve detection of multiple gas species in one gas measurement device 10. In some aspects, a single gas sample or breath may be used to detect multiple gas species, in other aspects multiple samplings may be used. The gas sensing chamber 40 may be divided into a plurality of gas sensing subchambers. These gas sensing sub-chambers may be in fluidic communication with one another and the buffer chamber 30, or they may be in communication with the buffer chamber 30 and otherwise isolated from communication with one another. Each gas sensing sub-chamber may contain one or more sensors 42 for detecting a presence, at least one parameter and / or at least one component of the gas. The gas sensing sub-chambers may contain the same sensors, for example to perform multiple measurements to obtain an average, or the gas sensing sub-chambers may contain sensors with different target gas species or properties. The gas sensing sub-chambers may provide control measurements to enhance reliability or they may enable simultaneous measurements of multiple target gas species, or a combination. Each gas sensing sub-chamber may function in the same manner as described for the gas sensing chamber 40. Further embodiments of the gas measurement device, not pictured, may include at least one scrubber arranged to, in use, scrub one or more gas species from the gas flowing from the gas intake channel 22 to the gas sensing chamber 40 or, if applicable, one or some of the gas sensing sub-chambers. The or each scrubber may be located in multiple locations along the gas flow path, or may be limited to one location. The scrubber may be, for example and not limitation, a carbon dioxide scrubber comprising soda lime or another form of scrubber. A scrubber may also be located within one or more of the gas sensing sub-chambers, such that only a select portion of the gas sample is scrubbed. Further gas sensors may be arranged in the buffer chamber 30. In some aspects these additional sensors may contribute towards a multi-step measurement, or they may be the only point of measurement for a particular target gas species. The pictured embodiment also includes a calibration gas chamber 70 for containing a calibration gas. The calibration gas chamber 70 is in fluid communication with the gas sensing chamber 40 to facilitate the flow of calibration gas to the gas sensing chamber 40. This allows the plurality of sensors 42 in the gas sensing chamber 40 to be calibrated to, for example, the background atmosphere in the location where the gas sample is being taken. For instance, in roadside driver capacity assessments, the gas sensors 42 may be calibrated to the general atmosphere of the location. The calibration chamber 70 may also contain a gas (or a gas mixture) of known concentration to be used to ensure that there is agreement between the gas sensors 42 and the processing electronics. When the calibration gas flows to the gas sensing chamber 40, the buffer chamber 30 is not used, and fluidic communication between the buffer chamber 30 and the gas sensing chamber 40 is prevented during this operation, for example by using a valve arrangement. The configuration of the gas measurement device 10 of the invention provides an integrated solution for collecting, processing and directing the target gas species to a measurement system in an autonomous fashion. The invention is applicable to a wide range of gas sensing applications that require gas flow sampling and dosing to ensure reliable and accurate gas concentration measurements. It is envisaged, for example, that the gas measurement device 10 is portable and may be used in a variety of environments with differing background gas concentrations. The calibration gas may also be used to clear any potential contaminants and / or reset the device 10 from any background or existing measurement which could introduce noise, false positives or false negatives into the measurement. A portable embodiment of the gas measurement device 10 may also be provided with a portable or handheld casing in which the gas intake module 20, the gas sensing chamber 30 and the buffer chamber 40 are arranged. The gas intake module 20, gas sensing chamber 30 and buffer chamber 40 may be detachable from one another, or the gas measurement device 10 may be configured to disassemble for storage and reassemble for use. In embodiments including further chambers or parts, for example a calibration gas chamber 70 and / or a mouthpiece, the portable or handheld casing will be configured to accommodate these optional components. The method of operating the gas measurement device 10 includes the steps of: 1) collection of gas by the gas intake module 20 through exposure to the relevant gas environment, for example by way of normal or forced exhalation; 2) collection of at least part of the gas from the gas intake module 20 by the buffer chamber 30. As detailed above, a portion of the collected gas may be collected in the gas collection chamber 24; 3) collection of at least part of the gas from the buffer chamber 30 by the sensing chamber 40; 4) sensing, by the at least one gas sensor 42, of a presence, at least one parameter and / or at least one component of the gas. An alternative embodiment of the gas sensing device, not pictured, includes a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component. The gas may be in the form of the breath of a user or participant, but it is envisaged that other methods of gas sampling are possible. The alternative embodiment includes first and second gas sensors for obtaining a measurement of the first and second gas components. The first and second gas sensors may measure the same quality of the gas components, or they may measure different qualities of the gas components. For example, the first gas sensor may measure a volume of the first gas component while the second gas sensor may measure the pressure of the second gas component. Other non-limiting examples of gas qualities which may be measured include the temperature, and presence of the gas component. Included is a processor which is configured, for example by programming, to determine a total volume of the gas based on the measurement of the second gas component. The processor is also configured to determine a concentration level of the first gas component based on the measurement of the first gas component and the determined total volume of the gas. A gas measurement device according to a further embodiment comprises: a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component; a first gas sensor for measuring a combined concentration level of the first gas component and the second gas component; a second gas sensor for measuring an individual concentration level of the second gas component; and a processor configured to determine and individual concentration level of the first gas component by combining the measurement combined concentration level of the first gas component and the second gas component, the measured individual concentration level of the second gas component and a calibration value, wherein the calibration value is a correction factor associated with a response of the first gas sensor to a presence of the second gas component. Some implementations of the present invention may be targeted towards driver capacity assessments, and particularly for determining if the blood alcohol and / or nitrous oxide levels of the driver are within legal tolerances. One example of an appropriate sensor for use in detecting nitrous oxide is a non-dispersive infrared sensor. Such sensors require a steady state exposure to the gas sample during the measurement period, which can be several minutes, in order to return a stable reading. A well-mixed or constant concentration of target species in the gas sample is also advantageous for this mode of sensing. If the rate of flow is not steady and / or the gas sample is not well-mixed then the measurement is more susceptible to errors due to external environmental contamination and / or internal stale gas contamination. Thus, the measured concentration of the target gas will be less reliable. This can be mitigated in the present invention by use of the gas flow controller, which controls flow from the buffer chamber to the gas sensing chamber, providing a stable gas flow rate and thereby enhancing measurement sensitivity and reducing measurement time. In a further implementation of the invention, it is possible to obtain a so-called "zeroflow" measurement wherein the target gas diffuses over time from the buffer chamber to the gas sensing chamber without an active gas flow. This implementation has an advantage in that it does not rely on the use of gas flow controllers, pressure controllers, and the like, but requires a longer measurement time to obtain a stable measurement. The buffer chamber itself provides further stability to the measurement. Samples obtained from the breath of a user or participant may have unsteady or varying flow or pressure. Collecting the gas sample in the buffer chamber enables the gas flow to the sensing chamber to be decoupled from the sampling method. In particular, especially but not exclusively to the use of a gas sensor with a slow temporal response, a, temporally varying gas sample collection profile (e.g. a breath sample collection profile) is decoupled from the uniform flow required by the gas sensor. Further, the buffer chamber may be independently pressurised to a higher than atmospheric pressure, which allows for a greater amount of gas in a small sample space than if at atmospheric pressure. A small device footprint is particularly advantageous in portable and / or handheld implementations. The sensor or sensors in the gas sensing chamber may be used for simultaneous detection of multiple gas species, for instance simultaneous detection of nitrous oxides and / or alcohol and / or carbon dioxide. Simultaneous detection of the carbon dioxide concentration improves the accuracy and precision of a nitrous oxide concentration measurement by compensating for the interference signal, tracking breath beginning and ending phases and providing a temporal profile of the concentration. Carbon dioxide detection may be used as a proxy or approximation for total breath volume detection and contributes to a more reliable nitrous oxide measurement. Simultaneous measurement of nitrous oxide and alcohol in one device and with a single gas sample is particularly advantageous for roadside driver capacity assessments. In some implementations simultaneous measurements of multiple gas species, for example carbon dioxide and nitrous oxide, may occur in separate gas sensing subchambers. At least one of the gas sensing sub-chambers is provided with a gas sample scrubbed of carbon dioxide and configured to perform clean detection of the presence or at least one parameter of nitrous oxide. Another gas sensing sub-chamber would receive a sample of gas without scrubbing and is configured to detect the presence or at least one parameter of carbon dioxide. In further implementations, a single gas sensing chamber without sub-chambers may be used to detect multiple gas species by providing different forms of sensor which are specific to a gas species. In alternative implementations, different scrubbers can be used in respective sensing sub-chambers. A further implementation includes the use of a sensor in the buffer chamber to detect e.g., carbon dioxide, which is then scrubbed from the gas sample as it travels to the gas sensing chamber, enabling more reliable detection of e.g., nitrous oxide in the gas sensing chamber. Yet another implementation includes the use of a single non-dispersive infrared sensor equipped with multiple LED sources at different emission peaks to target different gases, wherein the sensor may be located in the gas sensing chamber. In implementations making use of a low-dispersion infrared sensor the crossover between the carbon dioxide absorption peak at 4.3 pm and the nitrous oxide peak at 4.5 pm can result in false positives for nitrous oxide due to the high concentration of carbon dioxide and proximity of the peaks. Use of a carbon dioxide scrubber or filter upstream of or inside the gas sensing chamber or sub-chamber containing a nitrous oxide sensor reduces the risk of false positives. It possible to use detected carbon dioxide volumes and / or concentration to correct for this interference. Furthermore, detecting carbon dioxide amount may be used as a proxy measurement to determine the temporal breath profile of the user or participant and enable determination of a more accurate accumulated breath volume. The accumulated total breath volume may then be used to determine an accurate nitrous oxide concentration. An experimental implementation of the invention was manufactured for testing the measurement method for nitrous oxide gas. The experimental implementation comprises a gas intake module, a gas sensing chamber with a nitrous oxide sensor, and a buffer chamber according to the invention. A mixture of gases was provided with 30mL / minute of a pre-mixed nitrous oxide and 70 mL / minute of nitrogen gas, achieving a resultant concentration of approximately 600 pm nitrous oxide. A resulting graph is shown in Figure 2. The markers on the graph indicate: a) when gas flow without nitrous oxide is introduced; b) when nitrous oxide was introduced; c) when nitrous oxide flow is stopped; and d) when gas flow is stopped. An ideal measurement period for the experimental implementation was found to be 4 minutes, which is within an acceptable range for roadside driver capacity assessments. It is anticipated that further implementations may have different ideal measurement periods. The experimental test was directed towards assessing the viability of including nitrous oxide sensors in implementations of the gas measurement device. Successful detection of target gas concentration ranges was demonstrated. A further test was performed to measure the response of the experimental implementation to varying controlled concentrations of nitrous oxide mixed with nitrogen. The mixture of nitrous oxide with nitrogen was intended to simulate the expected nitrous oxide concentration present in a human breath. A detected concentration of nitrous oxide according to an embodiment of the invention was compared to the detected concentration of nitrous oxide according to an existing commercial sensor used for trace gas monitoring in industrial or surgical environments. The commercial sensor is not optimised for breath measurements, so a constant gas flow was provided from a gas mixing station to both detectors under laboratory conditions. A resulting graph showing a comparison between the invention and the existing commercial trace gas sensor is shown in Figure 3. The x-axis indicates the nitrous oxide concentration measured by the commercial sensor; the y-axis indicates the nitrous oxide concentration according to the experimental implementation of the invention. The invention was able to determine the concentration of nitrous oxide gas with similar accuracy to the commercial sensor. Similar methods may be employed for simultaneous detection of alcohol, oxygen, water and other substances (such as drugs) which leave markers in the breath. Other sensing techniques, for example electrochemical or biomarker sensing, may be used according to the desired gas species or marker for detection. Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention. The listing or discussion of an apparently prior published document in this specification 5 should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Claims

1. A gas measurement device comprising:a gas intake module including a gas intake channel for receiving a gas;a gas sensing chamber including at least one gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas;a buffer chamber arranged in fluidic communication between the gas intake module and the gas sensing chamber so that, in use, the gas may flow from the gas intake module to the buffer chamber and from the buffer chamber to the gas sensing chamber.

2. A gas measurement device according to Claim 1 including a gas flow controller operable to control a flow of the gas from the buffer chamber to the gas sensing chamber.

3. A gas measurement device according to Claim 2 wherein the gas flow controller is operable to modulate a flow of the gas from the buffer chamber to the gas sensing chamber.

4. A gas measurement device according to any one of the preceding claims including a pressure controller operable to increase an internal chamber pressure of the buffer chamber.

5. A gas measurement device according to any one of the preceding claims including an evacuation device operable to evacuate the buffer chamber and / or the gas sensing chamber.

6. A gas measurement device according to any one of the preceding claims including a heater operable to heat the buffer chamber and / or the gas sensing chamber.

7. A gas measurement device according to any one of the preceding claims including a gas filter arranged to, in use, filter the gas flowing from the buffer chamber to the gas sensing chamber.

8. A gas measurement device according to any one of the preceding claims wherein the gas sensing chamber includes a plurality of gas sensors, each gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas.

9. A gas measurement device according to any one of the preceding claims including a scrubber arranged to, in use, scrub one or more gas species from the gas flowing from the gas intake channel to the gas sensing chamber or to one or more gas sensing sub-chambers of the gas sensing chamber.

10. A gas measurement device according to any one of the preceding claims including at least one additional gas sensor for sensing a presence, at least one parameter and / or at least one component of the gas, wherein the at least one additional gas sensor is arranged in the buffer chamber.

11. A gas measurement device according to any one of the preceding claims wherein the gas intake channel includes a one-way valve configured to facilitate a oneway flow of the received gas from an exterior of the gas measurement device into an interior of the gas measurement device.

12. A gas measurement device according to any one of the preceding claims wherein the gas intake module includes a gas collection chamber, wherein the gas intake channel is configured to direct a portion of the received gas into the buffer chamber and direct another portion of the received gas into the gas collection chamber.

13. A gas measurement device according to any one of the preceding claims including a calibration gas chamber for containing a calibration gas, wherein the calibration gas chamber is arranged in fluidic communication with the gas sensing chamber so that, in use, the calibration gas may flow from the calibration gas chamber to the gas sensing chamber.

14. A gas measurement device according to any one of the preceding claims wherein the at least one gas sensor includes a carbon dioxide sensor, an alcohol sensor, an oxygen sensor, a water vapour sensor, a biomarker sensor and / or a drug sensor.

15. A gas measurement device according to any one of the preceding claims wherein the at least one gas sensor includes a nitrous oxide sensor.

16. A gas measurement device according to Claim 15 when dependent on Claim 8, wherein the plurality of gas sensors includes a nitrous oxide sensor and a carbon dioxide sensor.

17. A gas measurement device according to Claim 15 when dependent on Claim 8, wherein the plurality of gas sensors includes a nitrous oxide sensor and an alcohol sensor.

18. A gas measurement device according to any one of the preceding claims including a mouthpiece or mask, wherein at least part of the gas intake channel forms part of the mouthpiece or mask.

19. A gas measurement device according to any one of the preceding claims wherein the gas intake module, the gas sensing chamber and the buffer chamber are arranged in a portable or hand-held casing.

20. A method of operating a gas measurement device according to any one of the preceding claims, the method comprising the steps of:by the gas intake module, collecting a gas;by the buffer chamber, collecting at least part of the gas from the gas intake module;by the gas sensing chamber, collecting at least part of the gas from the buffer chamber;by the at least one gas sensor, sensing a presence, at least one parameter and / or at least one component of the gas.

21. A gas measurement device comprising:a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component;a first gas sensor for obtaining a measurement of the first gas component;a second gas sensorfor obtaining a measurement of the second gas component;a processor configured to, in use, determine a total volume of the gas based on the measurement of the second gas component, wherein the processor is configured to, in use, determine a concentration level of the first gas component based on the measurement of the first gas component and the determined total volume of the gas.

22. A gas measurement device comprising:a gas intake module including a gas intake channel for receiving a gas including a first gas component and a second gas component;a first gas sensorfor measuring a combined concentration level of the first gas component and the second gas component;a second gas sensor for measuring an individual concentration level of the second gas component; anda processor configured to, in use, determine an individual concentration level of the first gas component by combining the measured combined concentration level of 5 the first gas component and the second gas component, the measured individual concentration level of the second gas component and a calibration value, wherein the calibration value is a correction factor associated with a response of the first gas sensor to a presence of the second gas component.10 23. A gas measurement device according to Claim 22 wherein the first gas sensoris a non-dispersive infrared sensor.

24. A gas measurement device according to any one of Claims 21 to 23 wherein the first gas is nitrous oxide.1525. A gas measurement device according to any one of Claims 21 to 24 wherein the second gas is carbon dioxide.

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