Using pressure waves to detect blockages in porous components

Abstract

A method for detecting at least a blockage state in a porous component, wherein the porous component separates a measuring chamber of a device, the device includes a gas sensor positioned in the measuring chamber, the gas sensor responding to an analyte in an ambient environment to be sampled, the method comprising: emitting a pressure wave from a pressure wave source, the pressure wave propagating in the measuring chamber; measuring a first response by a first sensor responding to the pressure wave, the first sensor being located at a first position in the measuring chamber, measuring a second response by a second sensor at a second position, the second position being different from the first position, and the second sensor being connected to the pressure wave source fluid; and determining the blockage state of the porous component based on a functional relationship between the first response and the second response.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 847,705, filed on May 14, 2019, and U.S. Patent Application No. 16 / 874,018, filed on May 14, 2020, the disclosures of which are incorporated herein by reference. Background Art

[0003] The following information is provided to help the reader understand the technology disclosed below and the environment in which these technologies can generally be used. Unless otherwise clearly stated in this document, the terms used are not intended to be limited to any specific narrow interpretation. The references set forth herein can promote understanding of the technology or its background. The disclosures of all references cited are incorporated herein by reference.

[0004] Many gas sensors include gas porous components / barriers or diffusion barriers, which separate or partition the analysis components of the sensor from the environment that the sensor is intended to monitor. Such porous components are generally used to reduce or eliminate the entry of pollutants that may hinder the operation of the sensor analysis component and / or isolate the analysis component (such as ignition sources in the environment, to which the sensor is exposed). When using such porous components, the analyte gas (multiple) to be detected / monitored by the sensor must pass through the porous component to reach the analysis component of the sensor. The ability and effectiveness of analyte transmission through the porous component directly affect the speed, precision and accuracy of the relative concentration changes of the analyte in the external surrounding environment that the sensor responds to be monitored. Therefore, the porous component is designed and / or selected to make the analyte transmission through the porous component, consistent with the analysis component of the sensor, so that the sensor can be defined with the nominal or minimum rate, precision and accuracy of the sensing application, to respond to the level of the analyte in the monitored environment and / or the change of the relative level. Once the sensor is deployed, foreign contaminants that contact or penetrate the porous component (generated in the normal operating environment or caused by unusual events or maintenance activities) can directly (or as a result of reaction with the porous component) inhibit the transmission of analytes between the environment and the analytical components of the sensor. This inhibition of analyte transmission through the porous component results in a deviation in the target sensor response rate with the analyte and / or a deviation in the assessment precision / accuracy of the absolute or relative change in analyte concentration, which is termed "blockage" or "blocking". In addition, the contaminants or conditions that cause blockage are generally referred to as "blockage". A common example of blockage occurs in an industrial environment, in which the sensor's response to the analyte may be partially or completely inhibited by heavy spray, water, dust / mud, insect or animal deposits, or other foreign substances that hinder diffusion. Failure to identify transmission barriers through the sensor porous component can result in under-detection or non-detection of analyte concentration levels exceeding safe environmental limits.

[0005] In addition to diffusion or clogging of other sensor porous components, the performance of the sensor itself may degrade over time. Therefore, it is prudent to decide to test the functionality of the gas detection instrument on a regular basis. For example, it is common practice to perform a "bump check" or functional check on a portable gas detection instrument every day. The purpose of this test is to ensure that the entire gas detection system (commonly referred to as the instrument) is functioning properly. Periodic bump checks or functional checks can also be performed on permanent gas detection instruments, for example, to extend the time between full calibrations. A gas detection system includes at least one gas sensor, electronic circuitry, and a power supply for driving the sensor, interpreting its response, and displaying its response to the user. The system also includes a housing to enclose and protect these components. A bump check typically includes: a) applying a gas of interest (usually a target gas or analyte gas that the instrument is intended to detect); b) collecting and interpreting the sensor response; and c) indicating the functional status of the system to the end user (i.e., whether the instrument is functioning properly).

[0006] As described above, for portable gas detection instruments, such collision tests are performed regularly (usually daily). The collision check provides the user with a relatively high assurance that the gas detection device is working properly. The collision check implements all necessary functions of all components of the gas detection device in the same manner as required to detect the alarm level of dangerous gases. In this regard, the collision check ensures that the gas is effectively delivered from the outside of the instrument, through any transmission path (including, for example, any protection and / or diffusion member or membrane) to contact the active sensor assembly. The collision check also ensures that the detection aspects of the sensor itself are working properly and that the sensor provides the correct response function or signal. The collision check also ensures that the sensor is properly connected to the associated power supply and electronic circuit and correctly interprets the sensor signal. In addition, the collision check ensures that the indicator (multiple) or user interface (multiple) (e.g., display and / or notification function) of the gas detection instrument operates as expected.

[0007] However, periodic / daily bump checking requirements have a number of significant disadvantages. For example, such bump checking is very time consuming, particularly in facilities that include many gas detection systems or instruments. Bump checking also requires the use of expensive and potentially hazardous calibration gases (i.e., the analyte gas or simulant to which the sensor responds). In addition, bump checking requires a dedicated gas delivery system, typically consisting of a pressurized gas cylinder, a pressure reducing regulator, and tubing and adapters for properly supplying the calibration gas to the instrument. The requirement for a dedicated gas delivery system often means that opportunities to bump check individual gas detection equipment are limited by the location and temporal availability of the gas delivery equipment.

[0008] Recently, a number of systems and methods have been proposed to reduce the number of bump tests required. For example, such systems may include electronic interrogation of the sensor and / or testing of the transmission path to the sensor, including through diffusion or other barriers (without the application of the analyte gas or its simulant). Nevertheless, there remains a need to develop improved testing systems and methods to reduce the number of bump checks required for sensors. Summary of the invention

[0009] In one aspect, a method of detecting at least a blockage state in a porous member that separates a measurement chamber of a device, the device including a gas sensor located in the measurement chamber, the gas sensor responding to an analyte in an ambient environment to be sampled, the method comprising: emitting a pressure wave from a pressure wave source that propagates in the measurement chamber, measuring a first response by a first sensor in response to the first pressure wave, measuring a second response by a second sensor at a second location that is different from the first location and the second sensor is fluidly connected to the pressure wave source, and determining the blockage state of the porous member based on a functional relationship between the first response and the second response. In various embodiments, the second sensor is operated or used as a reference sensor.

[0010] The pressure wave source may for example comprise a speaker, and emitting pressure waves propagating within the measurement chamber may comprise activating the speaker to emit sound waves within the measurement chamber.For example, the first sensor may comprise a first microphone, and the second sensor may for example comprise a second microphone.

[0011] For example, the second position of the second sensor can be in a reference chamber that is separate from the measurement chamber but fluidly connected to the speaker. In many embodiments, the reference chamber is separated from the measurement chamber by the speaker. Alternatively, the second position of the second sensor can be in the measurement chamber.

[0012] In various embodiments, the first response and the second response are measured in the time domain over a period of time, and the measured time domain responses are transformed to the frequency domain.

[0013] For example, at least one of an amplitude and a phase may be determined at a frequency for each of the first sensor and the second sensor. The method may also include determining a ratio of at least one of an amplitude and a phase measured by the first sensor and the second sensor. In various embodiments, the ratio of each of an amplitude and a phase measured by the first sensor and the second sensor is determined.

[0014] In various embodiments, the method further comprises comparing the two-dimensional map of the determined ratio of amplitude and phase to a previously determined reference map to determine a blockage state of the porous member.

[0015] In various embodiments, determining the blockage state includes determining at least one of a blockage degree or a blockage type in the porous member. In various embodiments, the method further includes driving the pressure level of the pressure wave source to the determined level in a closed loop control method using a feedback signal from the second sensor.

[0016] In another aspect, a gas sensor device for detecting an analyte gas in an ambient environment includes a housing including a measurement chamber and a port, a porous member operatively connected to the port to separate the measurement chamber from the ambient environment, a sensor responsive to an analyte gas located in the measurement chamber, a source of pressure waves located in the measurement chamber, a first sensor for the pressure waves at a first position in the measurement chamber, responsive to the pressure waves, a second sensor responsive to the pressure waves at a second position, the second position being different from the first position, and the second sensor being fluidically connected to the source of pressure waves, and a circuit operatively connected to the first sensor and the second sensor to determine a blockage state of the porous member based on a functional relationship between the response of the first sensor and the response of the second sensor. For example, the second sensor can be operated or used as a reference sensor.

[0017] In various embodiments, the pressure source comprises a speaker that emits sound waves when activated. In various embodiments, the first sensor comprises a first microphone, and the second sensor comprises a second microphone.

[0018] In many embodiments, the second position of the second sensor is in a reference chamber that is separate from the measurement chamber but fluidly connected to the speaker. For example, the reference chamber can be separated from the measurement chamber by a speaker. Alternatively, the second position of the second sensor can be in the measurement chamber.

[0019] In various embodiments, a plurality of first responses and second responses are measured in a time domain by a circuit over a period of time, and the measured time domain responses are transformed into a frequency domain.

[0020] In various embodiments, at least one of an amplitude and a phase is determined for each of the first sensor and the second sensor at a frequency. For example, a ratio of the responses of the first sensor and the second sensor may be determined by the circuit. In various embodiments, the circuit determines a ratio of at least one of the measured amplitude and the measured phase of the first sensor and the second sensor. In various embodiments, the circuit determines a ratio of each of the measured amplitude and the measured phase of the first sensor and the second sensor.

[0021] In various embodiments, the circuit compares the determined ratio of the measured amplitude and the measured phase to a previously determined reference map to determine the blockage state of the porous member.

[0022] In various embodiments, determining the blockage state includes determining at least one of a degree of blockage or a type of blockage in the porous member.

[0023] For example, the circuit may include a processor system operatively connected to a memory system. In various embodiments, the circuit is further configured to drive the pressure level of the pressure wave source to a determined level in a closed-loop control method using a feedback signal from the second sensor.

[0024] In another aspect, a method for detecting at least a partial blockage in a porous member that separates a first volume of a device from another volume includes emitting a pressure wave from a pressure wave source that propagates within the first volume; measuring a first response by a first sensor in response to the pressure wave at a first position within the first volume; measuring a second response by a second sensor at a second position that is different from the first position and that is fluidly connected to the pressure wave source; and determining an operating state of the porous member based on a functional relationship between the first response and the second response. For example, the second sensor can be operated or used as a reference sensor. In multiple embodiments, the pressure wave source includes a speaker, and emitting the pressure wave propagating within the first volume includes activating the speaker to emit a sound wave within the first volume. In multiple embodiments, the first sensor includes a first microphone, and the second sensor includes a second microphone.

[0025] On the other hand, an apparatus includes: a housing having a first volume and a port; a porous member operatively connected to the port to separate the first volume from another volume; a pressure wave source located in the first volume; a first sensor at a first position in the first volume that responds to the pressure wave; a second sensor at a second position that responds to the pressure wave, the second position being different from the first position, and the second sensor being fluidly connected to the pressure wave source; and a circuit operatively connected to the first sensor and the second sensor to determine an operating state of the porous member based on a functional relationship between a response of the first sensor and a response of the second sensor. For example, the second sensor can be operated or used as a reference sensor. In many embodiments, the pressure wave source includes a speaker that emits sound waves when activated. In multiple embodiments, the first sensor includes a first microphone and the second sensor includes a second microphone.

[0026] Thus, embodiments of multiple devices, systems, and methods herein include a pressure wave source (such as a speaker), a first sensor (e.g., a first microphone), and a second reference sensor (e.g., a second microphone). The sound guide can be divided into two sound chambers: a measurement chamber including the first sensor and a reference chamber including the second sensor. Alternatively, the sound guide can include only the measurement chamber, in which the first sensor and the second reference sensor are positioned. The pressure wave source / speaker can emit one or more tones / frequencies that are directed to the first and second sensors.

[0027] In another embodiment, a method of detecting at least a blockage state in a porous member, the porous member separating a measurement chamber of a device, the device including a gas sensor located in the measurement chamber, the gas sensor responsive to an analyte in an ambient environment to be sampled, the method comprising emitting a pressure wave from a pressure wave source, the pressure wave propagating in the measurement chamber; measuring a first response by a response of a first sensor to the pressure wave, the first sensor being located at a first position in the measurement chamber; measuring at least one reference variable associated with a change in output of the pressure wave source, the output change being caused by a condition other than a control input; and determining a blockage state of the porous member based on a functional relationship between the first response and the at least one reference variable. For example, the input to the pressure wave source may be monitored and / or the response estimated. In various embodiments, the pressure wave source is a speaker, and the reference variable is determined by directly measuring at least one of a speaker driving voltage or current, or in combination with a predictive model utilizing predetermined, estimated, or measured electrical and mechanical parameters of the speaker. In various embodiments, at least one reference variable is measured by a response of a second sensor, the second sensor responsive to the pressure wave at a second position, the second position being different from the first position, and the second sensor being fluidically connected to the pressure wave source.

[0028] In another aspect, an apparatus includes a housing having a first volume and a port; a porous member operably connected to the port to separate the first volume from another volume; a pressure wave source located in the first volume; a first sensor at a first location in the first volume that is responsive to the pressure wave; and a circuit operatively connected to the first sensor and the pressure wave source. The circuit is configured to determine at least one reference variable related to a change in the output of the pressure wave source, the change being caused by a condition other than a control input, and to determine an operating state of the porous member based on a functional relationship of the response of the first sensor to the at least one reference variable.

[0029] The devices, systems and methods herein do not require precise control of the output level of the speaker, and provide a more uniform response grouping from unit to unit, thereby making detection of a blockage state or condition easier, while also making the system more immune to false detections. When a second reference sensor (e.g., a microphone) is used to provide a reference measurement of the pressure wave source / speaker output, the blockage state or status determination becomes more reliable. Without such a reference measurement, the true or actual output of the pressure wave source / speaker and output changes caused by conditions such as environmental changes or material fatigue may be confused with changes caused by blockage of the porous member. Reference measurements also help to generate a more uniform response for blockage types between units.

[0030] The present apparatus, systems and methods, and their attributes and attendant advantages, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1A An embodiment of a gas sensor device herein is illustrated which comprises a first of the measuring microphones and a second or reference microphone.

[0032] Figure 1B Another embodiment of a gas sensor device herein is illustrated, which comprises a first of the measuring microphones and a second or reference microphone.

[0033] Figure 2 Another embodiment of a gas sensor device herein is illustrated wherein a drive signal is monitored or the response of a pressure wave source or speaker is estimated.

[0034] Figure 3 A two-dimensional graph or frequency response function (FRF) determined from a Fourier transform of the time domain responses of the first and second (reference) microphones is illustrated, illustrating regions associated with a plugged state of the porous member.

[0035] Figure 4 An embodiment of the Goertzel Discrete Fourier Transform (DFT) algorithm used in various embodiments herein is illustrated.

[0036] Figure 5 Illustrated herein are embodiments of frequency response function (FRF) congestion classification maps illustrating polygons and regions of boundary-related congestion conditions, such as congestion percentages and / or congestion locations.

[0037] Figure 6 A two-dimensional graph or magnitude and phase diagram based on the Fourier transform of the time domain response of a single (measurement channel) microphone is illustrated. DETAILED DESCRIPTION

[0038] In addition to the representative embodiments described, it is readily understood that the components (as generally described and illustrated in the figures herein) may be arranged and designed in a variety of different configurations. Therefore, the following more detailed description of the representative embodiments, as illustrated in the accompanying drawings, is not intended to limit the scope of what is claimed, but is merely an illustration of the representative embodiments.

[0039] References throughout this specification to "one embodiment" or "an embodiment" etc. mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in at least one embodiment. Thus, the phrases "in one embodiment" or "in an embodiment" etc. that appear in various places in this specification do not necessarily all refer to the same embodiment.

[0040] In addition, the described features, structures or characteristics may be combined in one or more ways in any suitable manner. In the following description, specific details are provided to provide a thorough understanding of the various embodiments. However, those skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details or using other methods, components, materials, etc. In other cases, well-known structures, materials or operations are not shown or described in detail to avoid confusion.

[0041] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural forms unless the context clearly dictates otherwise. Thus, for example, reference to "a sensor" includes a plurality of such sensors and equivalents thereof known to those skilled in the art, and reference to "the sensor" is a reference to one or more such sensors and equivalents thereof known to those skilled in the art, and so forth. References herein to ranges of values ​​are merely used as a shorthand method of individually referring to each individual value falling within the range. Unless otherwise indicated, each individual value, as well as intermediate ranges, are incorporated into the specification as if individually recited herein. All methods described herein may be performed in any suitable order unless otherwise indicated in the text or otherwise expressly prohibited.

[0042] As used herein, the term "circuit" or "circuitry" includes, but is not limited to, hardware, firmware, software, or a combination thereof for performing function(s) or action(s). For example, based on desired features or needs. A circuit may include a software controlled microprocessor, discrete logic (such as an application specific integrated circuit (ASIC)), or other programmed logic device. A circuit may also be fully embodied in software.

[0043] As used herein, the term "control system" or "controller" includes, but is not limited to, any circuit or device that coordinates and controls the operation of one or more input or output devices. For example, a controller may include a device having one or more processors, microprocessors, or central processing units (CPUs) that can be programmed to perform input or output functions.

[0044] As used herein, the term "processor" includes, but is not limited to, one or more processor systems or independent processors, such as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors (DSPs), or any combination thereof. The processor may be associated with various other circuits that support the operation of the processor, such as a memory system (e.g., random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable memory), programmable read-only memory (EPROM), clocks, decoders, storage controllers, or interrupt controllers, etc. These support circuits may be internal or external to the processor or its associated electronic package. The support circuits are in operable communication with the processor. The support circuits are not necessarily shown separately from the processor in block diagrams or other diagrams.

[0045] As a metric, blockage can directly specify the impedance of the analyte transmission through the porous member and / or specify the corresponding change in sensor performance caused by the transmission impedance. For example, blockage can be measured in a continuous measure. For example, blockage can be measured as a percentage, ranging from 0% to 100% when the analyte transmission through the porous member is normal or nominal, 100% marking the complete inhibition of the transmission of the analyte between the sensor analysis component and the monitored environment. Blockage can also be measured as a discrete state, specifying such as unblocked (indicating that the analyte is usually or normally transmitted through the porous member) or partially blocked (indicating that the impedance of the analyte transmission exceeds the usual or normal but is less than the complete transmission inhibition) or completely blocked (indicating that the analyte transmission is completely inhibited through the porous member). Alternatively, blockage can be attributed to a Boolean state, wherein the unblocked state indicates that the inhibition of the analyte transmission through the porous member is below the specified acceptable limit, and the blocked state indicates that the analyte transmission inhibition exceeds the specified limit. Appropriate measures for detecting and specifying blockage (and / or the resulting sensor performance impairment) are important for ensuring sensor function. Failure to identify barriers to transport through the sensor's porous components can result in under- or non-detection of analyte concentration levels exceeding safe environmental limits.

[0046] In a number of embodiments, many devices, systems and methods herein are used to detect the flow of a porous member, membrane or barrier (e.g., diffusion barrier) through a sensor (e.g., for detecting a target or analyte gas). For example, in many representative embodiments, such a porous member may be a porous metal frit or a porous polymer membrane. In a number of embodiments, a source, generator or transmitter (e.g., speaker) of a pressure wave or sound wave is activated in an interior or measurement volume or chamber (i.e., on the sensor side and relative to the environment side) behind a porous member (porous frit or porous membrane). The response to the generated sound wave / pressure wave (e.g., sound) is measured by a first pressure wave sensor, an acoustic sensor or a receiver (e.g., a microphone), and the response is related to gas transmission through the membrane. A second pressure wave sensor or receiver (e.g., a microphone) is provided at a position different from the first pressure wave sensor or receiver to provide a reference signal. Typically, any sensor or receiver that responds to a pressure change or a pressure wave propagating in a medium (e.g., air) can be used. Such a sensor or receiver is sometimes commonly referred to as an acoustic sensor or receiver.

[0047] In many representative embodiments, the present apparatus, systems, and methods may be used, for example, in fixed or portable gas instruments. For fixed (as opposed to portable) gas instruments, the instrument is calibrated when placed in service. As described above, after being placed in service, it is recommended that the instrument be "bump tested" frequently to check that the gas flow into the sensor and the sensor's response are as expected. As also described above, to bump test the instrument, the user applies a known concentration of a target / analyte gas (or a simulated gas to which the sensor responds) to the instrument and checks the instrument for an expected or acceptable response. If the sensor response is acceptable (e.g., using a predetermined threshold), the user may then calibrate the instrument to the known concentration of the target gas.

[0048] By using, for example, U.S. Patent Nos. 7,413,645, 7,959,777 and U.S. Patent Application Publication Nos. 2014 / 0273263, 2013 / 0193004, 2013 / 0192332, 2013 / 0186776, 2013 / 0186777 and U.S. Patent Application No. 15 / 012,919, the disclosures of which are incorporated herein by reference, one has the ability to electronically interrogate the sensor to determine changes in sensor performance, and compensate the sensor output so that the sensor response is acceptable, thereby extending the time period between collision checks (or eliminating collision checks). Electronic interrogation of the sensor can, for example, include applying electrical energy to an electrode or sensor element and measuring the response to the applied electrical energy and / or the electrical characteristics of the electrode or sensor element to determine the state of the sensor. However, electronically interrogating the sensor cannot account for or detect blockage of a porous member that separates / protects the sensor from the surrounding environment or the outside world. Combining electronic interrogation of sensors with systems, apparatus and methods for detecting blockage of such porous members provides the ability to further reduce or eliminate crash testing of the instrument.

[0049] In many representative embodiments herein, in order to detect the blockage of the porous member separating the gas sensor from the surrounding environment (where the concentration of the analyte gas is to be determined), one or more sound waves transmitted from the source / speaker interact with the porous member and any blockage thereof. The signal is received by a first sensor (pressure wave or acoustic sensor / microphone) located in the measurement chamber to be excited by both the output of the pressure wave source / speaker and the reflection from the porous member. The second sensor (pressure wave or acoustic sensor / microphone; located at a position different from the first sensor) is used as a reference sensor and can be excited by only one or both of the output of the pressure wave source / speaker and the reflection from the porous member. The response of the first sensor and the response of the second reference sensor are processed and associated with the flow loss through the porous member (i.e., the blockage state) and / or (in the case of a gas sensor) with the gas response loss at the gas sensor. There are multiple methods to analyze and / or process the data to determine the presence and / or extent of the blockage. In various embodiments, the source / speaker and the first sensor are positioned or located on the same side of the porous member as the gas sensor (i.e., within a measurement volume or chamber that includes the gas sensor, which is fluidically connected to the porous member). In various embodiments, the pressure wave source (e.g., a speaker) is located within the chamber, separated from the porous member. Typically, substantially all or all of the pressure waves emitted from the pressure wave source and transmitted out of the chamber are transmitted through the porous member in the manner of these embodiments. For example, in the manner of these embodiments, less than 10%, less than 5%, or less than 2% of the pressure waves emitted from the pressure wave source may be transmitted outside the chamber instead of through such a porous member. The second sensor may be positioned in a reference volume or chamber that is isolated from reflections from the porous member or within the measurement volume of the chamber (but located at a different location therein than the first sensor).

[0050] Figure 1A , Figure 1B and Figure 2 Several embodiments of the devices herein are illustrated in FIG. In several embodiments herein, a combustible gas sensor device such as (see Figure 1A) device 100, the device including a sensor 110 in an interior or measuring volume or chamber, the interior or measuring volume or chamber being formed by an explosion-proof housing 130 and a porous member (in the form of a porous frit 140 (frit)). Catalytic combustible gas sensor devices and electronic interrogation thereof are described, for example, in U.S. Patent Application Publication No. 2014 / 0273263, the disclosure of which is incorporated herein by reference. Although combustible gas sensors are studied in several representative embodiments herein, the devices, systems, and methods herein may be used with any sensor (e.g., an electrochemical sensor, a photoacoustic sensor, etc.) or other device (in which a porous member or membrane separates an interior chamber or volume from another volume (e.g., an outside environment)). In an embodiment of the device 100, a pressure wave source in the form of a speaker 150 (i.e., an electric transducer that converts electrical energy into pressure waves) and a first pressure wave sensor (first sensor) in the form of a first microphone 160 are also located within the chamber 120. Although it is not necessary to acoustically separate the speaker 150 and the first microphone 160 from the rest of the chamber 120 and sensor 110 or to narrowly direct the propagation of sound / pressure waves therebetween, separation / isolation of, for example, microphone 160 from the second (reference) microphone 160a of the chamber 120, and / or directing to preferentially couple microphone 160 to the porous member or frit 140 (and / or preferentially couple second microphone 160a to speaker 150), may, for example, help provide differentiation between various blockage states of the porous member or frit 140, as further discussed below.

[0051] In the illustrated embodiment, the sensor 110, the speaker 150, the first microphone 160 and the second (reference) microphone 160a (discussed further below) are electrically connected to an electrical or electronic circuit 180 (e.g., via a printed circuit board or PCB (not shown)), which may include a control circuit including, for example, a processor system 190 (including one or more processors, such as microprocessors) and a memory system 192 operably connected to the processor system 190. The memory system 192 may, for example, include one or more algorithms / software stored therein and executable by the processor system 190. Data / information may be provided to a user and / or a user may communicate via a user interface system 194 (including, for example, a visual display system, an audio system, and / or a tactile system for providing data / information to a user and one or more data input systems (e.g., a touch screen, a keyboard, a mouse, etc.) for inputting data / information). A communication system 196 (including, for example, a receiver and / or a transmitter) may be provided for communication (e.g., data / information communication) between the device 100 and a remote device or system. The data communication system 196 may, for example, provide wired and / or wireless communication. A power system 198 may be provided to the power circuit 180, which may include one or more batteries in the case of a portable device or may include line power in the case of a stationary device.

[0052] For example, as described in U.S. Patent Application Publication No. 2017 / 0227498 and U.S. Patent Application Publication No. 2017 / 0227499, the disclosures of which are incorporated herein by reference, acoustic waves propagate within the chamber 120 toward the frit 140. Without limitation to any mechanism, some acoustic waves enter the frit 140, and some pressure / acoustic waves are reflected back into the interior chamber 120. In this regard, of the acoustic waves that enter the frit 140, some are absorbed by the frit 140, some are reflected back into the measurement chamber 120 (from which the acoustic waves were emitted), and some pass through the frit 140 into the surrounding environment outside the explosion-proof enclosure 130. The acoustic waves that pass through the frit 140 and outside the explosion-proof enclosure 130 are "lost" acoustic waves, which are related to the degree of blockage of the frit 140. When the frit 140 is blocked, fewer acoustic waves (e.g., acoustic waves) are lost, and more acoustic waves are reflected back into the chamber 120. In many studies, one or more frequencies 150 can be generated by a speaker. In many studies, sound is emitted from the speaker 150 at a single frequency.

[0053] A pressure wave source (e.g., a speaker) exhibits significant variability in output signals (e.g., amplitude and / or phase) that results from a given or determined applied input signal / input energy from one speaker to another (even at the time of manufacturing). In addition, for a given input signal, the output may vary over time due to changes in the components of the pressure wave source / speaker. One cannot generate an output signal for a given input signal / energy, and cannot predict with certainty what the resulting amplitude and phase will be. In addition, the speaker output will vary with environmental conditions (such as temperature, pressure, etc.). In addition, changes in the blockage state of the porous member or frit 140 will also affect the output of the speaker for a given applied input signal / energy. In other words, the output of the speaker 150 will vary with the variable to be measured (i.e., the blockage state frit 140). Therefore, applying the same voltage to the speaker 150 over time will result in different outputs due to the conditions.

[0054] In various embodiments herein, speaker output variations caused by variations other than input signal / energy variations are compensated (e.g., variations due to differences in speakers, changes in environmental conditions, and / or changes in the clogging state of a porous member (e.g., frit 140)). For example, speaker impedance or back EMF determined from measured values ​​of speaker drive voltage and / or current may be used directly, or in combination with, for example, a predictive model that utilizes predetermined, estimated, or measured electrical and mechanical parameters of the speaker, to account for such variations in speaker output. However, accurate or repeatable correlation of speaker output with monitored speaker drive voltage and / or current or a predictive model that uses these monitored signals is difficult. Although difficult, the measured back EMF or speaker input impedance or the functional relationship between the directly measured input voltage and / or current and the output of a measured speaker (such as speaker 150) can be used to compensate for the above-described variations in speaker output. As further described below, in some cases, an amplitude and / or phase determined from a measured speaker drive current or voltage or an estimated back EMF or speaker impedance may be used instead, such as the amplitude and phase of a second reference microphone in a frequency response function (FRF) relationship. However, the provision of a second reference microphone provides a significantly improved measurement, enabling the desired differentiation in the devices, systems, and methods herein.

[0055] In this regard, to account for variations in output for a given energy input between different speakers and variations in a variety of conditions in the various embodiments herein, a second reference sensor is provided in the form of a reference microphone 160a at a different location in the device 100 than the first microphone 160. The clogging state of the porous member is determined by a functional relationship between the response of the microphone 160 and the response of the reference microphone 160a.

[0056] In an embodiment of the device 100, the second microphone 160a is located within a reference volume or chamber 170. The reference chamber 170 is fluidically or acoustically connected to the speaker 150 (via air or other gas in the chamber). In this regard, pressure waves or sounds output from the speaker 150 reach the second microphone 160a. However, the reference chamber 170 and the second microphone 160a therein are isolated from the measurement chamber 120 and the porous frit or member 140. Although the blockage state of the porous member 140 still affects the output of the speaker 150 measured by the second microphone 160a, the second microphone 160a only monitors the speaker output. The second microphone 160a is not excited by reflections from the porous frit or member 140. Figure 1A In an embodiment of the present invention, the reference volume or chamber 170 is isolated from the measurement volume or chamber 120 and the porous frit 140 by the speaker 150. The measurement chamber 120 may, for example, be sealed to a first output of the front of the speaker 150 and be fluidically or acoustically connected thereto, while the reference chamber 170 may be fluidically or acoustically connected to a second output or rear of the speaker 150. The reference chamber 170 may, for example, be connected to the rear side of the speaker 150 and be sealed therewith.

[0057] The analysis of the responses of the first sensor and the second reference sensor herein can be performed, for example, in the time domain or the frequency domain. In the frequency domain, for example, the amplitude and / or phase of the response can be analyzed. In the time domain, for example, the amplitude and / or time delay of the response can be analyzed. The various analysis techniques discussed in U.S. Patent Application Publication No. 2017 / 0227498 and U.S. Patent Application Publication No. 2017 / 0227499 can be modified, for example, to be used in conjunction with the output / response from the second reference sensor herein.

[0058] In various embodiments, the response data is converted from the time domain to the frequency domain using a Fourier transform (e.g., a fast Fourier transform or FFT). Other transforms may be used. In various embodiments, the data from the first microphone 160 and the second microphone 160a are co-sampled over samples of a predetermined length. Co-sampling is an analysis method that uses the phase from the Fourier transform. Co-sampling means that samples are collected at the same rate and fixed time intervals between the two sensors. A Fourier transform is performed on the data at the frequency of interest. A frequency response function (FRF) is determined using a functional relationship (e.g., a ratio) of the two Fourier terms. In various embodiments, the ratio of the measured amplitudes from the first microphone 160 and the second microphone 160a is determined. In Figure 3In the illustrated embodiment, the amplitude from the first microphone 160 is in the numerator and the amplitude from the second reference microphone 160a is in the denominator). The numerator and denominator can be reversed to determine the inverse FRF. Likewise, the offset of the measured phase of the first microphone 160 relative to the second microphone 160a is determined. Figure 3 In the illustrated embodiment, the complex phase from the first microphone 160 is in the numerator, and the complex phase from the second reference microphone 160a is in the denominator. The phase ratio is equivalent to the difference of the phase in the numerator minus the phase in the denominator. Figure 3 In , the amplitude ratio and phase shift / difference are plotted on a two-dimensional map. Figure 3 The locus or area of ​​points on the map (phase ratio / difference, amplitude ratio data pairs) provides information about the congestion status. Figure 3 In the data of , three different blocking states are studied. Figure 3 As shown, distributions that may overlap in amplitude do not overlap in phase, allowing for differentiation in a two-dimensional plot. Thus, a range of values ​​for the determined data pairs of phase ratio / difference and amplitude ratio can be associated with various blockage states. As a representative example, the following is discussed for generating Figure 3 Methods and calculations for each FRF point mapped in .

[0059] In various embodiments, a sine wave Sig_spkr is generated using a digital-to-analog converter or DAC with a sampling frequency Fs of 8k Samp / sec to drive a speaker using fone=200Hz to create a tone as mic1 (measurement microphone) and mic2 (reference microphone), which are sampled simultaneously at 8k Samp / sec. In various embodiments, the selection of the frequency fone is primarily based on the sensitivity of the acoustic response to occlusion conditions, so that an integer 2*π period of fone sampled at Fs at the microphone will fit into a discrete buffer of length N, which is related to the Fourier Transform or DFT calculation of the microphone signal. Sig_spkr[nspk]=A*sin(2*π*ftone / Fs*nspk), which creates a period each time the integer sample index nspk reaches an increment of Fs / ftone samples. The amplitude A can be selected to provide sufficient margin for background noise while not saturating the speaker or microphone.

[0060] In multiple embodiments, at nspk=1780, recording of samples from mic1 and mic2 is initiated into corresponding 8k sample buffers, i.e., n=1 samples captured and recorded by the microphones are synchronized with the speaker playback samples of nspk=1780. After the corresponding microphone data buffers are filled with 8000 samples (nspkr=9780 and n=8000), recording and speaker drive signal generation are stopped. This results in 40 complete 200Hz sine wave data cycles being recorded in the corresponding microphone buffers. The buffer size of 8000 samples is selected to achieve a resolution bandwidth (=Fs / N) of 1Hz for the discrete Fourier transform (DFT), so that fone is located in the center of the DFT transform bin. Furthermore, the buffer size N is selected to capture an integer 2*π cycles of fone at the sampling rate Fs to simplify and reduce the computation of the DFT by eliminating the need for a window function, such as a Hamming or Hanning window, which is multiplied with each sample in the buffer applied to the DFT to reduce or eliminate information spectrum from fone to other DFT bins and information from other frequencies to the fone bin.

[0061] The sampled data from each microphone buffer is converted to a single-frequency discrete Fourier transform using the computationally efficient Goertzel algorithm, as Figure 4 , and described below. While any computational form of the DFT can be used to compute the frequency transform of the microphone signal, the Goertzel implementation of the DFT is suitable for this application because the microphone signal x[n] is real-valued. Unlike the direct DFT, which uses complex-valued coefficients and computes the DFT, the Goertzel algorithm is more efficient and applies a single real-valued coefficient at each iteration, using real-valued arithmetic for real-valued input sequences.

[0062] The Goertzel algorithm utilizes three constants that are pre-computed and stored in the UC memory. All three of these constant terms come from a common phase term 2πk / N, which is unique to the single frequency fone on which the DFT is calculated. Here N is the number of samples applied to the DFT, and k is an integer such that k=(ftone / Fs)*N, where Fs is the sampling frequency at which the microphone samples x[n] are obtained. The real-valued filter coefficient term α=2Cos(2πk / N). The two basis function terms (twist factor terms) used in the final non-recursive stage are used to separate the real and imaginary output terms of the DFT as shown below:

[0063] W1=Cos(2πk / N)(DFT(I) real part coefficient)

[0064] W2=Sin(2πk / N)(DFT(Q)imaginary part coefficient)

[0065] use Figure 4 The Goertzel algorithm identified in computes the DFT of mic1 (the measurement microphone) and mic2 (the reference microphone) separately. The computation first proceeds through a recursive partitioning of the algorithm described in the rectangular region on the left, using the following recursive state-space computation, processing all N samples of the buffer:

[0066]

[0067] At each sample n in the corresponding microphone signal x[n], Figure 4 The values ​​of the state variables y1dot, y2dot, y1, and y2 depicted in are recursively updated N times, that is, n is incremented from 1 to N, as shown below:

[0068] For n=1 to N

[0069] y1dot=y1*α-y2+x[n];

[0070] y2dot=y1;

[0071] y1=y1dot;

[0072] y2=v2dot;

[0073] It is not necessary to record N samples of each microphone signal x[n] into a buffer, since the above calculations can be performed as each sample x[n] is acquired. The use of a buffer simply allows the sampling and calculations to be performed at different times. After the Nth iteration, the values ​​of y1dot and y2dot are passed to the non-recursive part of the calculation to calculate the real (I) and imaginary (Q) parts of the DFT (described below). Figure 4 In the example, y1f=y1dot and y2f=y2dot come from the Nth iteration of the recursive calculation.

[0074] I=W1*y1f-y2f=Cos(2πk / N)*y1f-y2f;

[0075] Q=W2*v2f=Sin(2πk / N)*y2f.

[0076] For mic 1(x mic 1 [n]) and mic 2(x mic2 The above calculations are performed on the data sampled by [n] to generate the following discrete frequency transform X mic 1 and X mic2 :

[0077] X mic1 =I1+i*Q1where for the imaginary part Q, i=sqrt (-1)

[0078] X mic2=I2*i*Q2

[0079] Mapping to a classification graph (such as Figure 3 The frequency response function of the DFT (shown in Figure 1) is calculated as the ratio of the measurement microphone (mic1) to the reference microphone (mic2) in the DFT.

[0080] FRF=X micl / X mic2 .

[0081] To calculate the FRF, it is convenient to convert the X calculated in rectangular form (I+i*Q) mic1 and X mic2 Convert to exponential polar coordinate form r*e iθ , where r = sqrt(I 2 +Q 2 ) and θ=tan -1 (Q / I), where tan -1 In this case the four-quadrant inverse tangent atan2(Q, I) is expressed to return a single value θ such that −π<θ≤π such that I=r*Cos(θ) and Q=r*Sin(θ).

[0082] X mic1 =I mic1 +i*Q mic1 =M*e iθM

[0083] X mic2 =I mic2 +i*Q mic2 =R*e iθR

[0084] Using this formula, the magnitude and phase terms of the FRF mapped to the classification map can be calculated as follows:

[0085] FRF=X mic1 / X mic2

[0086] =M*e iθM / (R*e iθR )

[0087] =M / Re i(θM-θR)

[0088] FRF amplitude = M / R;

[0089] FRF phase = θM-θR;

[0090] Thus, the FRF amplitude represents the ratio of the amplitude of the signal M from the measurement microphone (mic1) positioned and connected to acoustically couple with the porous member to the amplitude of the signal R from the reference microphone (mic2) positioned and connected to acoustically couple with and track the sound produced by the loudspeaker. By this ratio, changes in the signal received at mic 1 due to changes in the loudspeaker acoustic output level measured at mic 2 are effectively cancelled, which allows the FRF amplitude to distinguish the amplitude of the signal amplitude caused by changes in the clogging of the porous member due to changes in the loudspeaker output level at mic 1.

[0091] Likewise, the FRF phase represents the difference between the phase θM of the signal from microphone 1, which is connected to monitor the combined response of the speaker and the reflection from the porous member, and the phase θR of microphone 2, which is positioned and connected to respond to the speaker output. Thus, using FRF phase = θM-θR, changes in the speaker phase can be separated from changes in the phase θM at mic1 caused by changes in the acoustic response of the porous member due to clogging.

[0092] As another aspect of identifying and / or detecting clogging of a porous component, it is convenient to project the FRF calculated after each acoustic interrogation of the system onto a clogging classification map, with the FRF magnitude mapped as the x-axis coordinate and the FRF phase mapped as the y-axis coordinate, such as Figure 3 As the differences in loudspeaker acoustic output are effectively tracked and eliminated by the FRF, the FRFs from different interrogations are mapped to areas on the map, which (e.g. Figure 3 The rectangular area in the figure is uniquely related to the blockage of the porous component. Using such a correlation plot, the blockage of the porous frit can be classified by identifying the area of ​​the plot where the FRF is located. For example, Figure 3 In the correlation plot, the FRFs that fall on or within the borders of the middle rectangular box are associated with blockage type 1, while the FRFs that fall in the large rectangle are associated with blockage type 2.

[0093] like Figure 5 As shown, the tracking provided by FRFs and the ability to remove loudspeaker amplitude and phase variations facilitates the creation of extensive blockage classification maps containing polygons and regions that identify aspects such as blockage percentage and blockage location. Using such a correlation map, where each polygon or unique map region represents a discrete blockage condition, each FRF can be evaluated for blockage by determining to which polygon or region the FRF is mapped.

[0094] For comparison, Figure 6 A two-dimensional plot or map of data pairs of the measured channel phase and the measured channel amplitude is illustrated. Again three different blocking states or conditions are investigated. Figure 6No data from the reference channel is used in this analysis. Instead, the magnitude M and phase θM(X mic1 =M*e iθM ) are used as the x and y coordinates of the points plotted on the graph, instead of Figure 3 The FRF amplitude and phase used in . In this case, it is found that the distributions of both phase and amplitude for the two blocking states (unblocked state and type 1 blocking state) overlap. Therefore, an erroneous determination that an unblocked porous member or frit is blocked may be made, or worse, an erroneous determination that the frit of a blocked porous member is not blocked may be made. This confusion in the evaluation of the blocking condition may occur because the amplitude and / or phase of the signal at mic1 may be affected by both the blocking condition of the porous component and / or the acoustic loading of the speaker caused by the blocking of the porous component and / or the change in the acoustic output of the speaker due to wear and environmental factors. The use of the amplitude (multiple) and / or phase (multiple) of one or more microphone signals (measured separately according to a specified threshold or reference value) is one of the significant limitations of the system as a blocking detection method. If it is not possible to track and remove the components of the measured microphone signal caused by the change in speaker output caused by the blocking condition response, it is difficult or impossible to establish a threshold value that clearly or uniquely separates the amplitude and / or phase of the blocking condition of the porous member. This limitation is effectively removed when the FRF ratio of the two microphone signals specified in the embodiments herein is used. The method herein eliminates the effects of changing loudspeaker outputs, which results in a more consistent and repeatable mapping of the response (FRF) to the same region of the classification map, where the region is more unique to a particular occlusion situation. The improved consistency and uniqueness of the FRF magnitude and / or phase mapping overcomes the limitations inherent in the single microphone method, which allows the use of prescribed magnitude and phase boundaries (e.g., defined by Figure 3 It is less practical and reliable to correlate and identify jams using individual microphone signal methods (represented by rectangular polygons on a map).

[0095] In such Figure 1A In the illustrated embodiment of the apparatus 100, many different arrangements of the first microphone 160 in the measurement chamber 120 and the second microphone 160a in the reference chamber 170 may be used in conjunction with the frequency response functions and their correlation to porous member clogging (as described herein). In all cases, the first microphone 160 and the second microphone 160a are positioned so that the magnitude and / or phase coordinates of the resulting FRF ratio fall in different and distinguishable regions or tracks on the FRF, facilitating classification or identification of clogging conditions as needed or desired for a particular application, such as Figure 3 shown.

[0096] Although not required, it is advantageous in embodiments of the apparatus 100 to design and use the wave propagation characteristics through the measurement chamber 120. In this regard, the acoustic impedance ZL Significantly higher than air Z Air The material of the acoustic impedance forms a channel connecting the first microphone 160, the speaker 150 and the measurement chamber 120 and the second microphone 160a and the speaker 150, so that the acoustic transmission T through the air channel Air =1-(Z Air -Z Air ) / (Z Air +Z Air )~=1 is significantly higher than the material T L =1-(Z L -Z Air ) / (Z L +Z Air )~=0, so the amplitude of the acoustic signal reaching the first and second microphones through the air in the channel is significantly stronger than the signal reaching the first and second microphones through the material in which the air channel is formed.

[0097] Figure 1B Another embodiment of a device 100' is illustrated herein. In many respects, device 100' is manufactured similarly to device 100 and its components are numbered similarly to similar components of device 100 except that the reference numeral "'" is added after the reference numeral. In an embodiment of device 100', a pressure wave source in the form of a speaker 150' and a first pressure wave sensor (first sensor - measurement channel data) in the form of a first microphone 160' are also located within the measurement volume or chamber 120'. Again, it is not necessary to acoustically isolate the speaker 150' and the first microphone 160' from the rest of the chamber 120' and sensor 110', or to narrowly direct the propagation of sound / pressure waves therebetween. Similar to device 100, device 100' includes a second reference microphone 160a' (second sensor - reference channel data) located at a different location than the first microphone 160. However, in Figure 1B In the embodiment of the present invention, each of the first microphone 160' and the second reference microphone 160a' microphones are located at different locations within the measurement volume or chamber 120'.

[0098] In the device 100', the reference microphone is influenced or excited by the output of the speaker 150' and the blockage state of the porous member or frit 150'. Figure 1BIn an embodiment of the present invention, the first microphone 160' and the second microphone 160a' are in the same volume of gas within the measurement chamber 120', but are located or positioned at different locations / positions therein such that the responses therefrom are distinguishable in time, phase and / or amplitude. Many different arrangements of the first microphone and the second microphone can be used in conjunction with the frequency response functions and their correlation to porous member blockage (as described herein). In all cases, it is advantageous to position the first microphone 160' and the second microphone 160a' so that the amplitude and / or phase coordinates of the resulting FRF ratio fall in different and distinguishable regions or tracks on the FRF blockage correlation map, facilitating classification or identification of blockage conditions as needed or required for a particular application, such as Figure 3 In various embodiments, it is advantageous to position the first microphone 160' so that its response changes with changes in the clogging of the porous member 140', while the second microphone 160a' is positioned to respond more significantly to the output of the speaker 150'. Those skilled in the art can readily determine the positioning of the first microphone 160' and / or the second microphone 160a' through known engineering principles and / or routine experimentation to provide discrimination of various clogging states for a particular sensor geometry.

[0099] exist Figure 1B In the embodiment of the present invention, the wave propagation characteristics through the measurement chamber 120' are used. In this regard, the acoustic impedance Z L Significantly higher than air Z Air A material with an acoustic impedance of 100° is used, in which a channel connecting the first microphone, the second microphone, the speaker and the measurement chamber is formed, so that the acoustic transmission T through the air channel is Air =1-(Z Air -Z Air ) / (Z Air +Z Air )~=1 is significantly higher than the acoustic transmission T through the material L =1-(Z L -Z Air ) / (Z L +Z Air )~=0, which makes the amplitude of the acoustic signal reaching the first and second microphones through the air in the channel significantly stronger than the signal reaching the first and second microphones through the material forming the air channel. In many embodiments, it is advantageous to form the air channel connected to the first microphone 160' so that its response changes significantly with the change of the blockage of the porous member 140', while the air channel connected to the second microphone 160a' is designed so that the microphone 160' responds more significantly to the output of the speaker 150'.

[0100] In the device 100', the second microphone 160a' is positioned in a port extending from the measurement chamber 120'. Again, in various embodiments, it is advantageous to form an air passage connected to the first microphone 160' so that its response varies significantly with changes in blockage of the porous member 140', and the air passage connected to the second microphone 160a' is designed so that the microphone 160' is more responsive to the output of the speaker 150'. However, such a port is not required. The first microphone 160' and the second microphone 160a' need only be located at different locations within the measurement chamber 120'. Again, in all cases, it is advantageous to position the first microphone 160' and the second microphone 160a' so that the amplitude and / or phase coordinates of the resulting FRF ratio fall in different and distinguishable regions or tracks on the FRF blockage correlation diagram, facilitating the classification or identification of blockage conditions as needed or required for a particular application, such as Figure 3 shown.

[0101] Figure 2 Another embodiment of the device 100 herein is illustrated. In many respects, the device 100" is manufactured similarly to the device 100 and its components are numbered similarly to similar components of the device 100, except that the reference number is marked with a """. In the embodiment of the device 100", a pressure wave source in the form of a speaker 150" and a first pressure wave sensor (first sensor - measuring channel data) in the form of a first microphone 160" are also located within the measurement volume or chamber 120". Again, it is not necessary to acoustically isolate the speaker 150" and the first microphone 160" from the rest of the chamber 120" and the sensor 110", or to narrowly guide the propagation of sound / pressure waves between them. Compared to the device 100, the device 100" replaces the second reference microphone output with element 160a" (block, which schematically represents a component for monitoring the speaker drive voltage and / or current and calculating an estimate of the speaker response (such as a back EMF, impedance or related estimate of the speaker acoustic output)). The location of the components and calculators included in 160a" is not critical and may be distributed throughout the device 100" herein. Methods for estimating loudspeaker response parameters (e.g., back EMF, impedance, and / or correlations of these estimates or measurements of loudspeaker drive voltage and / or loudspeaker acoustic output current) are numerous and established, and the particular method of determining these parameters herein is not specific or critical. Figure 2 In the context of an embodiment of the present invention, the parameter estimated or measured by block 160a", whether it is a loudspeaker voltage or current, or a parameter estimated from these, such as back EMF, impedance or related loudspeaker output level, can be sampled at the same time interval or together with the signal obtained from the measurement microphone 160". Using the methods described herein, such as DFT, the parameter x estimated by block 160a" paris, for example, one of the speaker drive current, drive voltage, back EMF, impedance, speaker velocity, or sound output estimate, which is converted to a frequency domain representation X par =I par +i*Q par =X mag *e iθX In various embodiments, this value uses the response (X) from the measurement microphone 160″ in the FRF ratio mic1 =M*e iθM ) replaces the reference microphone frequency response (combined with Figure 1A and Figure 1B Embodiments of the apparatus 100 and 100' identified by X mic2 =R*e iθR ). Using this formula, the magnitude and phase terms of the FRF mapped to the classification map can be calculated as follows:

[0102] FRF=X mic1 / X par

[0103] =M*e iθM / (X par *e iθX )

[0104] =M / X par e i(θM-θX)

[0105] FRF Amplitude = FRF mag =M / X par ;

[0106] FRF Phase = FRF phase =θM-θX;

[0107] exist Figure 2 In the embodiment of the present invention, the first microphone 160" is in the same volume of gas within the measurement chamber 120". Many different arrangements of the first microphone can be used in conjunction with the frequency response function and its correlation with porous member clogging described herein. In general, it is advantageous to position the first microphone 160" so that the resulting FRF ratio is consistent with X par The magnitude and / or phase coordinates of the FRF point fall into different and distinguishable regions or tracks on the FRF blockage correlogram, which facilitates the classification or identification of blockage conditions according to the needs or requirements of a particular application, which is similar to the FRF point Figure 3In various embodiments, it is advantageous to position the first microphone 160" so that its response changes significantly with changes in blockage of the porous member 140". As with other embodiments herein, the positioning of the first microphone 160" can be readily determined by those skilled in the art through known engineering principles and / or routine experimentation to provide discrimination of various blockage states for a particular sensor geometry.

[0108] exist Figure 2 In the embodiment of the present invention, the wave propagation characteristics through the measurement chamber 120" are used. In this regard, the acoustic impedance Z L Significantly higher than air Z Air A material with an acoustic impedance of 100° is used, in which a channel connecting the first microphone, the second microphone, the speaker and the measurement chamber is formed, so that the acoustic transmission T through the air channel is Air =1-(Z Air -Z Air ) / (Z Air +Z Air )~=1 is significantly higher than the acoustic transmission T through the material L =1-(Z L -Z Air ) / (Z L +Z Air )~=0, which makes the amplitude of the acoustic signal reaching the first microphone through the air in the channel significantly stronger than the signal reaching the first microphone through the material forming the air channel. In many aspects, it is advantageous to form an air channel connected to the first microphone 160", so that its response changes significantly with the change of blockage of the porous member 140'. In all embodiments herein, those skilled in the art can easily determine the appropriate materials and channel designs used herein using knowledge in the art and / or routine experiments.

[0109] The use of a second reference microphone in the present device eliminates the need for careful, repeatable manufacturing of the speaker or speaker driver. In addition, the second reference microphone provides compensation for changes in speaker output caused by changes in speaker components over time, changes in environmental conditions and / or changes in the clogging state or state of the porous member. In addition, the use of a second reference microphone allows people to operate the system with a more open-loop control architecture or method. For example, the sound pressure level or SPL of the speaker can be driven to a specific level in a closed-loop control manner using feedback from a reference signal. Such a closed-loop control system is generally referred to as automatic gain control (AGC). However, using data from a second reference microphone and analysis techniques (e.g., as described herein), the output level of the speaker can be allowed to float or change. The relationship between the measurement channel data and the reference channel data (e.g., using the above ratio and FRF analysis) remains sufficiently consistent without the need for feedback control. Although feedback control is not necessary and increases complexity, it can be used and can provide improved or more stringent determination specifications in certain embodiments. In such feedback control, for example, a reference channel microphone output may be monitored as a variable, and the speaker drive signal modified as a variable to drive the reference channel signal to the same or consistent output level over time. In various embodiments, closed-loop control may be used to monitor the amplitude and / or distortion of the reference microphone output, and modify the speaker drive level to keep the response at the reference microphone within specified amplitude and / or distortion limits. For example, such control may be useful and necessary to prevent the speaker output from stalling or distorting due to changes in speaker compliance caused by environmental factors (such as temperature) or changes in the acoustic load of the speaker.

[0110] Although the FRF (or other function, e.g., a function of the outputs of the first (measurement) and second (reference) microphones) alleviates the need to tightly control the speaker output level, in various embodiments, it is advantageous to utilize feedback control to monitor both the reference and measurement microphones, and to modify the speaker drive signals to keep the responses of both microphones above their corresponding noise floors and below corresponding saturation or clipping levels. In various embodiments, feedback control may be utilized in which the reference and measurement microphone signals are monitored, and the speaker drive is modified to keep the responses in both microphones within their respective linear or undistorted regions.

[0111] Using the parameters estimated in functional block 160a" of the device 100", the need to rely on careful, repeatable manufacturing of the speaker or speaker driver can be eliminated. In addition, the speaker response parameters estimated or measured by functional block 160a" provide compensation for changes in the speaker output caused by changes in the speaker assembly over time, changes in environmental conditions, and / or changes in the blockage state or state of the porous member. In addition, using the speaker response parameters estimated or measured by functional block 160" allows one to operate the system in a more open-loop control architecture or method. For example, the sound pressure level or SPL of the speaker can be driven to a specific level in a closed-loop control manner using an estimate of the speaker sound pressure level derived from or related to the parameters estimated or measured by functional block 160a". However, using data or estimates of the speaker response factors estimated by functional block 160a" and analysis techniques (e.g., FRF described herein), the output level of the speaker can be allowed to float or vary. The measured microphone channel X estimated in block 160a" mic1 and parameter X par The relationship between (e.g., using the above ratio and FRF analysis) remains sufficiently consistent that feedback control is not required. Although feedback control is not required and adds complexity, it can be used and can provide improved or tighter determination specifications in some cases. In such feedback control, for example, the variable x measured or estimated by the function block 160a" can be monitored. par or X par , and the speaker drive signal is modified to a variable to achieve a more consistent speaker output level over time. In various embodiments, a closed-loop control may be used in which the variable x measured or estimated by the function block 160a" par or X par The output from and / or measurement microphone 160" is monitored and the speaker drive level is modified to keep the response at the measurement microphone and / or the speaker output within specified amplitude and / or distortion limits. For example, such control may be beneficial and necessary to prevent the speaker output from ceasing or distorting due to changes in speaker compliance caused by environmental factors (such as temperature) or changes in the acoustic loading of the speaker.

[0112] While the FRF (or other function of the output of the first (measured) and measured or estimated variable Xpar from functional block 160a" of device 100") alleviates the need to tightly control the speaker output level, in various embodiments it may be advantageous to monitor the measurement microphone and modify the speaker drive signal to keep the microphone's response above its corresponding noise floor and below its corresponding saturation or clipping level. In various embodiments, feedback control may be utilized in which the measurement microphone signal is monitored and the speaker drive is modified to keep the response of microphone 1 within its linear or undistorted region. In various embodiments, the response of the measurement microphone and / or the measured or estimated parameter x from block 160a" may be used to determine the response of the microphone 1. par or X pa Can be used to monitor the speaker output for distortion or clipping, and modify the speaker drive signal to avoid these conditions.

[0113] In various embodiments, the pressure wave / acoustic interrogation devices, systems, and methods herein utilize correlations of amplitude and / or phase changes of transmitter acoustic energy returned to the measurement sensor and the reference sensor, or correlations of amplitude and / or phase changes of the transmitter response monitored by the microphone and the response variable X monitored or estimated by functional block 160a″. par Gas permeation through a porous member or frit (and / or a combined porous member and external obstruction) is used (in a measurement situation similar to that of apparatus 100') to infer / determine changes in gas transport restriction (blockage) from the external environment to / from the measurement chamber side of the porous member. For example, the percentage of blockage may be inferred / determined or a Boolean blockage condition declared based on changes in amplitude and / or phase relative to a reference amplitude and / or phase for an unblocked system. Figure 5 The use of this correlation is illustrated by using discrete congestion conditions and locations indicated by regions and polygons on the congestion FRF correlation diagram. Figure 5 In the congestion correlation diagram of FIG. 1 , a Boolean congestion state may be evaluated as an unblocked state based on FRF points falling on or within a polygon marked as "unblocked", while FRF points falling outside of the polygon are evaluated as a blocked state.

[0114] In various embodiments, a multi-dimensional thresholding scheme for discerning the blockage state of a porous member is created by utilizing both amplitude and phase variations of a received signal at single or multiple frequencies to significantly improve blockage detection.

[0115] In various embodiments, detection of amplitude and / or phase changes associated with the porous member resonant frequency and / or detection of changes in the porous member resonant frequency can be enhanced by designing the geometry of the volume(s) or chamber(s) that couple the first sensor and the second reference sensor to the speaker and / or the porous member. The resonant frequency of such a system can be determined, for example, by the combined acoustic impedance of the porous member and the acoustic properties of the connecting chamber.

[0116] Retroreflective systems as described herein provide advantages by allowing the pressure wave source / speaker and sensor to reside within the device housing rather than in the surrounding environment outside the porous member. This arrangement is particularly beneficial when the porous member is used to separate a hazardous or explosive environment on one side (outside) from components on the other side (inside) that may be damaged or compromised by the hazardous environment or represent a potential ignition source for the external environment.

[0117] In addition to the sensor output correction associated with the electronic interrogation of the sensor as described above, the apparatus and system of the present invention can also be used for or suitable for applying one or more corrections to the sensor output determined as a result of the flow path / blockage test. In this regard, for example, the sensor can be considered as a "molecular counter". Therefore, the calibration mode of the analytical sensor is that when a certain amount of analyte molecules diffuse through the instrument, they react on the analytical working or sensing electrode (multiple), and the measured value is converted to, for example, parts per million (ppm) or equivalent readings based on percentages based on previous calibration. When the porous member or barrier associated with the sensor entrance is open and unobstructed, the diffusion rate is very repeatable under the same conditions. When the porous member is blocked or the flow path is otherwise blocked, the speed at which the molecule diffuses from the outside of the instrument housing to the sensor slows down, thereby reducing the speed at which the molecule encounters the active part of the sensor, and thereby reducing the output in some embodiments. By measuring the partial blockage as a result of one or more tests of the present invention, people can adjust the sensitivity of the sensor to maintain accurate readings regardless of such partial blockage.

[0118] For example, the blockage percentage can be easily experimentally correlated to the correction factor. An associated lookup table or an associated algorithm / formula can be stored, for example, in a memory of the device and system, and the correction factor for the sensor sensitivity can be determined therefrom.

[0119] The foregoing description and the accompanying drawings illustrate several representative embodiments of the present invention. Various modifications, additions and alternative designs will certainly be apparent to those skilled in the art based on the foregoing teachings without departing from the scope of the invention as indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the equivalent meaning and range of the claims are included within their scope.

Claims

1. A method for detecting at least a blockage state in a porous member, the porous member separating a surrounding environment from a measurement chamber of a device, the device comprising a gas sensor located in the measurement chamber, the gas sensor being responsive to an analyte in the surrounding environment to be sampled, the method comprising: emitting a pressure wave from a pressure wave source, the pressure wave propagating in the measurement chamber, measuring a first response by a first sensor responding to the pressure wave, the first sensor being located at a first position in the measurement chamber, measuring a second response by a second sensor at a second position, the second position being different from the first position, and the second sensor being in fluid communication with the pressure wave source, and determining a blockage state of the porous member based on a functional relationship between the first response and the second response, The second position of the second sensor is within the measurement chamber or within a reference chamber separate from the measurement chamber. The method according to claim 1 , wherein the second sensor is used as a reference sensor.

3. A method according to claim 2, wherein the pressure wave source includes a speaker, and emitting pressure waves that propagate in the measurement chamber includes activating the speaker to emit sound waves in the measurement chamber; the first sensor includes a first microphone, and the second sensor includes a second microphone. The method of claim 3 , wherein the reference chamber is fluidly connected to the speaker. The method of claim 4 , wherein the reference chamber is separated from the measurement chamber by the speaker.

6. The method according to any one of claims 1 to 5, wherein the first response and the second response are measured in the time domain over a time period, and the measured time domain responses are transformed into the frequency domain. 7 . The method of claim 6 , wherein at least one of an amplitude and a phase is determined at a frequency for each of the first sensor and the second sensor.

8. The method according to claim 7, further comprising: A ratio of at least one of the amplitude and the phase measured by the first sensor and the second sensor is determined.

9. The method according to claim 8, further comprising: A ratio of each of the amplitude and phase measured by the first sensor and the second sensor is determined.

10. The method according to claim 9, further comprising: The two-dimensional map of the determined ratio of the amplitude and the phase is compared to a previously determined reference map to determine a blockage state of the porous member.

11. The method of claim 10, wherein determining the clogging state of the porous member comprises: At least one of a degree of blockage or a type of blockage in the porous member is determined.

12. The method according to claim 1, further comprising: The pressure level of the pressure wave source is driven to a determined level in a closed loop control method using a feedback signal from the second sensor.

13. A gas sensor device for detecting an analyte gas in an ambient environment, comprising: a housing including a measurement chamber and ports; a porous member operatively connected to the port to separate the measurement chamber from the surrounding environment; a sensor responsive to an analyte gas within the measurement chamber; a pressure wave source located within the measurement chamber; a first sensor at a first position within the measurement chamber, responsive to the pressure wave; a second sensor at a second location different from the first location, responsive to the pressure wave, the second sensor being fluidly connected to the source of the pressure wave, and circuitry operably connected to the first sensor and the second sensor to determine a blockage state of the porous member based on a functional relationship between a response of the first sensor and a response of the second sensor, The second position of the second sensor is within the measurement chamber or within a reference chamber separate from the measurement chamber. The device according to claim 13 , wherein the second sensor is used as a reference sensor.

15. The apparatus of claim 14, wherein the pressure wave source comprises a speaker that emits sound waves when activated, the first sensor comprises a first microphone, and the second sensor comprises a second microphone.

16. The apparatus of claim 15, wherein the reference chamber is fluidly connected to the speaker.

17. The apparatus of claim 16, wherein the reference chamber is separated from the measurement chamber by the speaker.

18. The apparatus of any one of claims 13 to 17, wherein the response of the first sensor and the response of the second sensor are measured by the circuit in the time domain over a period of time, and the measured time domain responses are transformed into the frequency domain.

19. The apparatus of claim 18, wherein at least one of an amplitude and a phase is determined for each of the first sensor and the second sensor at a frequency.

20. The apparatus of claim 17, wherein a ratio of the responses of the first sensor and the second sensor is determined by the circuit.

21. The apparatus of claim 19, wherein the circuit determines a ratio of at least one of the measured amplitude and the measured phase of the first sensor and the second sensor.

22. The apparatus of claim 19, wherein the circuit determines a ratio of each of the measured amplitude and the measured phase of the first sensor and the second sensor.

23. The apparatus of claim 20, wherein the circuit compares the determined ratio of the measured amplitude and the measured phase to a previously determined reference map to determine a blockage state of the porous member.

24. The apparatus of claim 23, wherein determining the clogging state of the porous member comprises: At least one of a degree of blockage or a type of blockage in the porous member is determined.

25. An apparatus according to any one of claims 13 to 17, wherein the circuit comprises a processor system operatively connected to a memory system.

26. The apparatus of claim 13, wherein the circuit is further configured to drive the pressure level of the pressure wave source to a determined level in a closed-loop control method using a feedback signal from the second sensor.

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