Method for operating a gas detection device and an electrochemical gas sensor

Abstract

A method of operating a gas detection device having a capillary-limited electrochemical gas sensor comprises operating the gas sensor in a detection mode, in which a signal from the gas sensor indicates the concentration of an analyte gas measured by the gas sensor, and an interrogation mode, in which the gas sensor is electronically interrogated by applying an electrical signal to the gas sensor to generate a non-Faradaic current between a working electrode and a counter electrode without delivering a test gas; periodically transitioning to the interrogation mode; measuring a parameter of the gas sensor output during the interrogation mode; comparing the measured parameter with one or more previously measured parameters; determining an operating condition from the comparison; and returning the gas sensor to the detection mode if the operating condition is determined to be within a predetermined range.

Description

Background Art

[0001] The following information is provided to assist the reader in understanding the technologies disclosed below and the environments in which such technologies are commonly used. The terms used in this specification are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this specification. The references described in this specification assist in the understanding of the technology or the background of the technology. The disclosure of all references cited in this specification is incorporated by reference.

[0002] Electrochemical sensors have been proven over the decades to be effective in detecting toxic gases in workplace environments. The low cost, response speed, and selectivity of electrochemical sensors are only some of the characteristics that have made such sensors attractive as safety products. However, one of the requirements for using these sensors is frequent calibration. For example, the sensitivity of an electrochemical sensor is affected by the amount of moisture contained in the electrolyte, and as a result of fluctuations in the ambient relative humidity, the amount of moisture changes seasonally throughout the year. Due to such fluctuations in relative humidity, the sensitivity is low in dry seasons and high in rainy seasons.

[0003] The functionality of gas detectors is periodically tested with due care. For example, it is common practice to perform a "bump check" or functionality check on portable gas detectors every day. The purpose of this test is generally to ensure the functionality of the entire gas detection system, which is generally referred to as equipment. Also, periodic bump checks and functionality checks may be performed on permanent gas detectors, for example, to extend the period until a full calibration is done. A gas detection system includes at least one gas sensor, an electronic circuit, and a power source for driving the sensor, interpreting its response, and displaying the response to the user. The system further includes a housing for surrounding and protecting such components. A bump check typically includes a) applying the target gas (usually a gas containing the gas that the device is intended to detect at a known concentration or an analogue thereof), b) collecting and interpreting the response of the sensor, and c) indicating to the end user the functional status of the system (i.e., whether the device is functioning properly).

[0004] Such bump tests are performed regularly, typically every day. The bump check provides the user with a relatively high level of assurance that the gas detection device is functioning properly. The bump check makes all the necessary functionality of all parts of the gas detection device work in the same way as the method required for detecting the alarm level of harmful gases. In this regard, the bump check ensures that there is efficient gas transfer through several transport paths (including, for example, a protective film and / or a diffusion film) from the outside of the device to contact the active sensor components. Also, the bump check ensures that the detection function of the sensor itself is operating properly and that the sensor is providing a normal response function or signal. Furthermore, the bump check ensures that the sensor is correctly connected to the relevant power source and electronic circuit and that the sensor signal is correctly interpreted. Additionally, the bump check ensures that the indicator or user interface (such as a display and / or notification function) of the gas detector is functioning as intended.

[0005] However, there are many significant drawbacks to regular / daily bump check requirements. For example, such bump checks are time-consuming, especially in facilities such as industrial facilities equipped with many gas detection systems or devices. Also, bump checks require the use of expensive and dangerous calibration gases. Furthermore, bump checks typically require a dedicated gas transfer system having, for example, a pressurized gas bottle, a pressure reducing regulator, tubes, and adapters to correctly transfer the calibration gas to the device. Due to the need for a dedicated gas transfer system, the opportunity to perform a bump check on a personal gas detector is often restricted in terms of location and time depending on the availability of the gas transfer device.

[0006] In recent years, many systems and methods have been proposed to reduce the number of bump tests in electrochemically based gas sensors with diffusion limitations. Such systems can include, for example, an electronic interrogation of the sensor in the absence of a test gas. Sensitivity variations resulting from moisture loss or gain occur gradually as expected as the average relative humidity changes slowly. Similarly, the response of the sensor to an electronic interrogation changes as well (when there is no test gas containing an analyte gas of known concentration or its substitute, or when not applicable). The electronic interrogation can be used, for example, to measure changes in sensitivity and correct the sensor output in accordance with such changes in sensitivity. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0007] In one aspect, a method of operating a gas detection device includes a capillary-restricted amperometric electrochemical gas sensor that reacts to an analyte gas, A step of operating a gas sensor, including: a detection mode in which a signal from the gas sensor indicates the concentration of an analysis target gas measured by the gas sensor; and an inquiry mode in which an electronic inquiry is made to the gas sensor to test the function of the gas sensor by applying an electrical signal to the gas sensor. In the inquiry mode, a non-Faradaic current is generated between the working electrode and the counter electrode of the gas sensor through an electrolytic solution that makes ionic contact with the working electrode and the counter electrode, without sending an analysis target gas with a known concentration or its simulated gas from a container to the sensor. A step of periodically transitioning to the inquiry mode; A step of measuring the output parameters of the gas sensor during the inquiry mode; A step of comparing the measured parameters with one or more parameters previously measured in a previous inquiry mode; A step of determining the operating state from the comparison between the measured parameters and one or more parameters previously measured; A step of returning the gas sensor to the detection mode when it is determined that the operating state is within a predetermined range. In some embodiments, the gas sensor is an oxygen sensor.

[0008] Unless clearly indicated otherwise from the context, the term "periodically" as used in this specification means an operation that occurs frequently or occasionally (e.g., the start of the inquiry mode). The inquiry mode of this specification can start, for example, with a regular occurrence interval, but it is not necessary to start with a regular occurrence interval.

[0009] The measured parameter may be, for example, the maximum peak value (MPV), the area under the curve (AUC), the minimum peak value (mPV), the peak-to-peak value (PP), the area under the reversed curve (rAUC), or the baseline value. A plurality of parameters may be measured. In some embodiments, the measured parameter is the baseline output of the gas sensor. The baseline output or baseline output value of the sensor may be measured, for example, before applying an electrical signal to the gas sensor. The change in the baseline output (when compared to one or more previously measured baseline output values) may be used, for example, to adjust the sensitivity of the gas sensor. The measured value may be directly compared to one or more previously measured values, for example, to determine whether the change in the value (change over time) exceeds a predetermined threshold. Additionally or alternatively, the rate of change of the parameter may be determined from the measured parameter and the previous value of the measured parameter and compared to the rate of change of a predetermined threshold.

[0010] In some embodiments, when it is determined that the measured parameter is outside a predetermined range, the gas sensor is determined to be in a failure state. The method may further include providing a warning (notification), for example, when it is determined that the gas sensor is in a failure state.

[0011] In some embodiments in which the baseline output is measured, at least one other parameter is measured during the interrogation mode. The at least one other parameter may be selected, for example, from the group consisting of the maximum peak value, the area under the curve, the minimum peak value, the peak-to-peak value, and the area under the reversed curve.

[0012] In some embodiments, the method further includes performing a fresh air setup that compares the output of the gas sensor to a reference value. In some such embodiments, when the output of the gas sensor is within a predetermined range of the reference value, the output of the gas sensor is adjusted to correspond to 20.8 volume % oxygen.

[0013] In another aspect, an electro-chemical gas sensor that responds to a gas to be analyzed includes a housing that includes a capillary inlet, an electrolytic solution within the housing, a working electrode that is ionically in contact with the electrolytic solution, a counter electrode that is ionically in contact with the electrolytic solution, and an electronic circuit that is operably connected to the working electrode and the counter electrode. The electronic circuit is configured to operate the gas sensor in a detection mode in which a signal from the gas sensor indicates the concentration of the gas to be analyzed measured by the gas sensor, and in an interrogation mode in which, without sending an analyte gas of a known concentration or a simulated gas thereof from a container to the sensor, an electrical signal is applied to the gas sensor to generate a non-Faradaic current between the working electrode and the counter electrode through the electrolytic solution to electronically interrogate the gas sensor to test the functionality of the gas sensor. The electronic circuit is configured to periodically transition to the interrogation mode, measure parameters of the gas sensor output during the interrogation mode, compare the measured parameters with one or more parameters previously measured in a previous interrogation mode, determine an operating state from the comparison of the measured parameters with the one or more previously measured parameters, and further configured to return the gas sensor to the detection mode if the operating state is determined to be within a predetermined range. In some embodiments, the gas sensor is an oxygen sensor.

[0014] As described above, the measured parameter may be, for example, a maximum peak value, an area under the curve, a minimum peak value, a peak-to-peak value, an area under the inversion curve, or a baseline value. A plurality of parameters may be measured. In some embodiments, the measured parameter is the baseline output of the gas sensor. The baseline output or baseline output value of the sensor may be measured, for example, before applying an electrical signal to the gas sensor. A change in the baseline output (when compared to one or more previously measured baseline output values) may be used, for example, to adjust the sensitivity of the gas sensor. The measured value may be directly compared to one or more previously determined values, for example, to determine whether a change in the value (over time) exceeds a predetermined threshold. Additionally or alternatively, a rate of change of the parameter may be determined from the measured parameter and one or more previous values of the measured parameter and compared to a rate of change of a predetermined threshold.

[0015] In some embodiments, the gas sensor is determined to be in a fault state when the measured parameter is determined to be outside a predetermined range. The electronic circuit may be further configured to provide a warning via the user interface system of the gas sensor, for example, when the gas sensor is determined to be in a fault state.

[0016] To repeat, in some embodiments where the baseline output is measured, at least one other parameter may be measured during the interrogation mode. The at least one other parameter may be selected, for example, from the group consisting of a maximum peak value, an area under the curve, a minimum peak value, a peak-to-peak value, and an area under the inversion curve.

[0017] In some embodiments, the electronic circuit is further configured to effect, achieve, or perform a fresh air setup that compares the output of the gas sensor to a reference value. In some such embodiments, if the output of the gas sensor is within a predetermined range of the reference value, the output of the gas sensor is adjusted to correspond to 20.8 volume percent oxygen.

[0018] In a further aspect, a method of operating a gas detection device having a capillary-limited amperometric electrochemical gas sensor that responds to a gas to be analyzed includes periodically measuring a baseline output of the gas sensor, comparing the measured baseline output to one or more previous baseline output values, and determining an operating state from the comparison of the measured baseline output to the one or more previously measured baseline output values. A change in the measured baseline output as compared to the one or more previously measured baseline output values may be used, for example, to adjust sensitivity. In some embodiments, the gas sensor may be determined to be in a fault state if, for example, the measured baseline output is determined to be outside a predetermined range. An interrogation mode that electronically interrogates the gas sensor to test its functionality by applying an electrical signal to the gas sensor to generate a non-Faradaic current between the working electrode and the counter electrode through the electrolyte may or may not be associated with the baseline measurement.

[0019] In yet another aspect, an electrochemical gas sensor that reacts to a gas to be analyzed includes a housing (casing) including a capillary inlet, an electrolytic solution within the housing, a working electrode that ionically contacts the electrolytic solution, a counter electrode that ionically contacts the electrolytic solution, and an electronic circuit operably connected to the working electrode and the counter electrode. The electronic circuit is configured to periodically measure a baseline output of the gas sensor, compare the measured baseline output with one or more previous baseline output values, and determine an operating state from a comparison of the measured baseline output with the one or more previously measured baseline output values. Although repetitive, a change in the measured baseline output compared with the one or more previously measured baseline output values may be used, for example, to adjust sensitivity via the electronic circuit. In some embodiments, the gas sensor may be determined to be in a fault state via the electronic circuit if, for example, the measured baseline output is determined to be outside a predetermined range. An interrogation mode is provided in which an electronic interrogation is performed on the gas sensor to test the functionality of the gas sensor by applying an electrical signal to the gas sensor to generate a non-Faradaic current between the working electrode and the counter electrode via the electrolytic solution, and the baseline measurement may or may not be relevant.

[0020] The fault states determined in the devices, systems, and methods of the present invention are due to, for example, a significant change in relative humidity, a leak of the electrolytic solution, and / or a change in the functionality of the working electrode.

[0021] The devices, systems, and methods of the present invention, together with their attributes and attendant advantages, will be best understood and appreciated in the following detailed description taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0032] It will be readily understood that the components of the embodiments generally described and illustrated in the figures of this specification can be arranged and designed in a wide variety of different configurations in addition to the described representative embodiments. Accordingly, the following more detailed description of the representative embodiments as shown in the figures is not intended to limit the scope of the embodiments as recited in the claims, but merely to illustrate representative embodiments.

[0033] References to "one embodiment" or "an embodiment" (or the like) throughout this specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

[0034] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided for a thorough understanding of the embodiments. However, one of ordinary skill in the art will recognize that the embodiments can be practiced without one or more of the specific details, or that the embodiments can be practiced with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the description.

[0035] As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, a reference to "a parameter" includes a plurality of such parameters and equivalents known to those of ordinary skill in the art, and a reference to "the parameter" is a reference to one or more such parameters and equivalents known to those of ordinary skill in the art. The description of ranges of values herein is merely intended to serve as a shorthand method for referring individually to each value within the range. Each individual value and intermediate range is hereby incorporated into the specification as if it were individually recited herein, unless otherwise indicated. All methods described herein can be performed in any suitable order, unless otherwise indicated herein or clearly prohibited by context.

[0036] As used herein, the terms "electronic circuit", "circuit mechanism", or "circuit" include, but are not limited to, hardware, firmware, software, or any combination thereof for performing functions or operations. For example, depending on the desired function or requirement, a circuit may include a microprocessor controlled by software, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic devices. Also, a circuit may be fully embodied as software. When used herein, the term "circuit" is considered synonymous with "logic". As used herein, "logic" includes, but is not limited to, hardware, firmware, software, or any combination thereof that performs a function or operation, or causes a function or operation to occur from other components. For example, depending on the desired application or requirement, a circuit may include a software controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic devices. Also, logic may be fully embodied as software.

[0037] As used herein, the term "processor" includes, but is not limited to, any number of processor systems or stand-alone processors, such as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors (DSPs), in any combination. A processor may be associated with various other circuits that support the operation of the processor, such as random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), clock, decoder, memory controller, or interrupt controller. These support circuits may be internal or external to the processor or the electronic package associated therewith. The support circuits communicate operably with the processor. The support circuits are not necessarily shown separately from the processor in a block diagram or other drawing.

[0038] As used herein, the term "controller" includes, but is not limited to, any circuit or device that adjusts and controls the operation of one or more input devices and / or output devices. The controller may include, for example, a device having one or more processors, microprocessors, or central processing units that can be programmed to perform functions.

[0039] As used herein, the term "logic" includes, but is not limited to, hardware, firmware, software, or combinations thereof that perform a function or operation or cause a function or operation to occur from other elements or components. Also, depending on the application and needs, logic may include a microprocess controlled by software, discrete logic such as an ASIC (Application Specific Integrated Circuit), or other programmed logic devices. Also, the logic may be fully embodied as software. In this specification, the term "logic" is considered synonymous with the term "circuit".

[0040] As used herein, the term "software" includes, but is not limited to, one or more computer-readable or executable instructions that cause a computer or other electronic device to perform functions, operations, or function in a desired manner. The instructions may be embodied in various forms such as a program including routines, algorithms, modules, or code from individual applications or dynamic link libraries. Also, the software may be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, instructions stored in memory, a part of an operating system, or other types of executable instructions. For example, those skilled in the art will understand that the form of the software depends on requirements of a desired application, the environment in which it is executed, or desires of a designer / programmer.

[0041] Electronic interrogation techniques and resulting corrections for diffusion-limited electrochemical gas sensors are disclosed, for example, in U.S. Patent Nos. 7,413,645, 7,959,777, 9,784,755, and 9,528,957, and U.S. Patent Application Publication Nos. 2013 / 0186777 and 2017 / 0219515, the disclosures of which are incorporated herein by reference. In such electronic interrogation approaches, typically an electrical signal such as a potential pulse is applied to the sensor and the resulting response is measured and recorded.

[0042] When applying an electrical signal to the working electrode of a diffusion-limited electrochemical sensor, the response may be measured, for example, in the following manners. (i) The maximum peak value (MPV), which is the maximum current observed during the application of the potential pulse, (ii) the area under the curve (AUC) (corresponding to the charging response of the sensor), which is the integrated current response of the working electrode after the application of the potential pulse, (iii) the minimum peak value (mPV) (the minimum current obtained upon removal or inversion of the potential pulse, which is usually the difference in current observed immediately before and after the removal or inversion of the potential pulse, but can also be aggregated and used as the difference between the minimum current and the baseline), (iv) the peak-to-peak value (PP), which is the algebraic difference between the maximum current and the minimum current, and (v) the area under the reverse curve (rAUC) (more precisely, the area under the curve after removal, which is the charging current obtained by integrating the current response after the removal or inversion of the potential pulse). These responses are compared to values obtained during one or more previous gas tests / pulse cycles. In the case of permeation or diffusion-limited electrochemical gas sensors, changes from calibration values may, for example, correlate with changes in sensor sensitivity.

[0043] As described above, due to recent developments in the electronic interrogation of electrochemical gas sensors, the need for frequent calibration with test gases has been reduced in the case of diffusion-limited electrochemical gas sensors. For example, in order to minimize the time that the sensor is offline (i.e., during the sensor electronic interrogation cycle) to perform sensor test diagnostics, the electronic interrogation can be performed over a fairly short period of time. In some embodiments, the return of the electrochemical sensor of the present invention to normal (gas sensing) mode operation by electronic interrogation can be less than 10 seconds, less than 5 seconds, or less than 1 second. Devices, systems, and methods for electronic interrogation of sensors can make it possible to keep a device including one or more sensors in an "online" state. Further, such devices, systems, and methods can also provide active and automatic monitoring of the sensor state as background operation without the need for initiation by the user. The frequency of electronic interrogation can vary. For example, by providing sensor interrogation at a frequency of several times per hour, substantially constant monitoring of sensor life and health can be provided.

[0044] Many electronic interrogation techniques have been well demonstrated in permeation-limited or diffusion-limited electrochemical gas sensors. In the case of gas sensors, detection should be performed in the gas phase or at the phase boundary. This generally indicates that the rate of the sensor is limited only by the rate of gas-phase diffusion of the target gas molecules to the sensor. For the purpose of limiting the sensor output, a gas sensor such as an electrochemical gas sensor may be, for example, permeation control / diffusion control type or permeation limitation / diffusion limitation type, in which case a permeation membrane is used to limit the diffusion of the target gas to the sensor, or a capillary inlet is used to limit the diffusion of the target gas to the sensor.

[0045] Regarding this point, in an electrochemical gas sensor, the gas to be measured (which may also be referred to as the target gas or the gas to be analyzed) usually enters the sensor housing from the surrounding atmosphere or environment, for example, through a gas porous membrane or a gas permeable membrane, or through a capillary inlet, and reaches the first electrode or working electrode (which may also be called the detection electrode) where a chemical reaction occurs. In the second electrode known as the counter electrode (or auxiliary electrode), a complementary chemical reaction occurs. The electrochemical sensor generates an analysis signal by the generation of a current directly resulting from the oxidation or reduction of the gas to be analyzed (i.e., the gas to be detected) at the working electrode. A comprehensive discussion of electrochemical gas sensors is also described in Cao, Z. and Stetter, J.R., "The Properties and Applications of Amperometric Gas Sensors," Electroanalysis, 4(3), 253 (1992), the disclosure of which is incorporated herein by reference.

[0046] An electrical signal is generated by the combination of the working electrode and the counter electrode, and the electrical signal is (1) related to the concentration of the gas to be analyzed and (2) strong enough to provide a signal-to-noise ratio suitable for distinguishing the concentration levels of the gas to be analyzed over the entire range to be analyzed. In other words, the flow of current between the working electrode and the counter electrode must be proportional to the concentration of the gas to be analyzed in the target concentration range so as to be measurable.

[0047] In addition to the working electrode and the counter electrode, an electrochemical sensor often includes a third electrode generally referred to as a reference electrode. The reference electrode is used to maintain the working electrode at a known voltage or potential. It is desirable for the reference electrode to be physically and chemically stable in the electrolyte.

[0048] The electrical connection between the working electrode and the counter electrode is maintained through the electrolyte. The functions of the electrolyte are as follows: (1) efficiently carry ionic current, (2) solubilize the gas to be analyzed, (3) support the reactions of both the counter electrode and the working electrode, and (4) form a stable reference potential with the reference electrode. The criteria for the electrolyte include, for example, the following: (1) electrochemical inertness, (2) ionic conductivity, (3) chemical inertness, (4) temperature stability, (5) low cost, (6) low toxicity, (7) low flammability, and (8) appropriate viscosity.

[0049] Generally, the electrodes of an electrochemical cell provide a surface where oxidation or reduction (redox) reactions occur to provide a mechanism in which the ionic conduction of the electrolyte solution and the electronic conduction of the electrodes are combined to provide a complete circuit for current. The measurable current resulting from the cell reaction of the electrochemical cell is directly proportional to the extent of the reaction occurring at the electrodes. Therefore, it is preferred that a high reaction rate be maintained in the electrochemical cell. For this reason, the counter electrode and / or the working electrode of the electrochemical cell generally contain an appropriate electrode catalyst on their surfaces to support the reaction rate.

[0050] As a result of the electrostatic force, the volume portion of the solution very close to the working electrode surface has a highly ordered structure. This structure is important for understanding the electrode process. The volume portion of the solution very close to the electrode surface is variously referred to as the diffusion layer, the scattering layer, or the Helmholtz layer or plane.

[0051] The magnitudes of the resistance and capacitance present in an electrochemical cell are a result of the properties and uniqueness of the materials used in its manufacture. The resistance of the electrolyte solution is due to the number and type of ions dissolved in the solvent. The capacitance of the electrode is mainly a function of the effective surface area of the electrode catalyst. In an ideal environment, these quantities are invariant. However, in a current-measuring gas sensor using an aqueous electrolyte solution, the solution resistance may change as a result of being exposed to various ambient relative humidity changes. When moisture evaporates from the sensor, the chemical concentration of the ionic electrolyte increases. This concentration change can cause an increase or decrease in the resistivity of the electrolyte solution, depending on the electrolyte solution actually used.

[0052] Furthermore, even substances that are normally considered insoluble in a particular solvent have a low concentration in the solvent with an upper limit. For example, in the electrolyte solution of an electrochemical sensor, the metal of the electrode is dissolved, but its concentration is very low and has an upper limit value. This small concentration of dissolved metal is constantly in flux. That is, metal atoms are constantly dissolving from the electrode and reattaching elsewhere. The net effect of this process is to reduce the effective surface area of the electrode. This results in an effect of reducing the capacitance of the sensor over time. Both of the above effects have a net effect of changing the sensitivity of the sensor during the lifetime of the sensor.

[0053] Figures 1A and 1B show schematic views of exemplary embodiments of a capillary-restricted electrochemical sensor 10 that can be used in the apparatus, system, and method of the present invention. Sensor 10 includes a housing 20 having a capillary-shaped gas inlet 30 for introducing one or more target gases or analyte gases into sensor 10. As the name implies, a capillary-restricted sensor such as sensor 10 uses a very small inlet hole 30 (i.e., a capillary) having a typical or typical aspect ratio (length: diameter or l:d) of about 100:1 (see, for example, FIG. 1C showing an axial and radial cross-section of inlet 30 and the cylindrical portion of the surrounding housing 20).

[0054] In FIG. 1C, p2 is the partial pressure of the target gas outside the inlet 30, p1 is the partial pressure of the target gas at the inner opening of the inlet 30, c2 is the concentration of the target gas outside the inlet 30, and c1 is the concentration of the target gas at the inner opening of the inlet 30 (or at the surface working electrode 50, which is essentially zero). What is often called "ordinary capillary diffusion" is actually a special case of Graham's law of effusion. See, for example, Barrow, GM: Physical Chemistry, 4th edition. New York NY: McGraw Hill (1979). In general, "diffusion" refers to the bulk flow of gas from a region of high pressure (or partial pressure) or high concentration through a porous wall or tube with a very small diameter to a region of low pressure or low concentration, respectively. Also, "effusion" refers to the process of transfer due to molecular flow, rather than bulk flow through an orifice or membrane.

[0055] On the market, there are many capillary-restricted oxygen sensors (O 2 Sensor) is dominant 2 This advantage is due to the fact that many performance criteria are based on volume percent (vol%)O 2 This is mostly due to the fact that the concentration is shown in capillary type O 2 The sensor is 2 Partial pressure (vol% O 2 The volume percent O is not affected by the total atmospheric pressure (which varies even if the concentration is constant). 2 In other words, a capillary sensor simply responds to the volume percent target gas in a sample, regardless of pressure. The output of a capillary sensor is given by:

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[0056] In some embodiments, the core materials 40a, 40b, and 40c saturated with the electrolyte may separate the working electrode 50 from the reference electrode 70 and the counter electrode 80 within the sensor 10, and / or may provide ionic conduction therebetween through the electrolyte 44 absorbed in the core materials 40a, 40b, and 40c within the housing 20. An electronic circuit 100 known in the art provides, for example, maintaining a desired potential difference between the working electrode 50 and the reference electrode 70, varying or pulsing the potential difference as described herein, and processing the output signal from the sensor 10. The sensor electrodes are arranged to be connected to the electrical circuit 100 via a connector 90 that provides conductive electrical conductivity / connectivity through the housing 20.

[0057] In the illustrated embodiment, the working electrode 50 may be formed, for example, by depositing a first electrode catalyst layer 54 on the gas diffusion membrane 52 (e.g., using a catalyst deposition technique known in sensor technology). The sensor 10 may include the gas diffusion membrane 52 at the back portion of the capillary inlet 30, but unlike in the case of a permeation-type or diffusion-limited sensor, the diffusion through the gas diffusion membrane 52 is not rate-limiting. The membrane 52 serves to hold the electrolyte 44 within the housing 20 and support the electrode catalyst layer / surface 54 within the sensor 10. The gas moves or is transferred easily through the diffusion membrane 52 (e.g., via diffusion), but the electrolyte 44 does not move or transport easily through the diffusion membrane 52. The diffusion membrane 54 of the working electrode 50 may be attached (e.g., via heat sealing) to the upper portion of the housing 20, the inner surface of the cap or lid 22.

[0058] The electronic circuit 100 may include a processor or controller system 102 that includes, for example, one or more processors or microprocessors for controlling various aspects of the operation of the sensor 10. The memory system 104 may be operatively or communicatively connected to the processor system 102 and may store software for control, measurement, and / or analysis in the sensor 10. The user interface system 106 (including, for example, a display, a speaker, etc.) may also be operatively or communicatively connected to the processor system 102. A communication system 108, such as a transceiver, may be operatively or communicatively connected to the processor system 102 for wired and / or wireless communication. A power source 110 (such as a battery system) may supply power to the electronic circuit 100.

[0059] In a number of representative embodiments of the sensors considered herein, the electrochemical sensor 10 is an oxygen pump sensor. A representative working electrode 50 may include, for example, platinum or platinum dispersed on carbon as an electrode catalyst layer 54. Also, for example, an acidic electrolyte such as H 2 SO 4 may be used. The working electrode half-reaction, the corresponding counter electrode half-reaction, and the overall reaction of such an O 2 sensor are shown below. The term "oxygen pump" is derived from the observation that nothing is consumed in the overall reaction of the sensor. That is, every time an O 2 molecule is reduced at the working electrode, water in the electrolyte solution is oxidized at the counter electrode to generate another O 2 molecule.

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[0060] As shown in FIGS. 1A and 1B, a vent 90 that is spatially in communication with the counter electrode 70 is formed in the sensor housing 20. The vent 90 allows the O 2 generated at the counter electrode 70 to escape from the housing 20. The generated O 2The amount is extremely small (about several nanoliters per second). However, when it exceeds the lifespan of the sensor 10, the generated O 2 becomes quite a lot. If the sensor 10 is not efficiently ventilated, the pressure rises inside the sensor housing 20, disturbing the sensor signal or causing leakage of the electrolytic solution.

[0061] FIG. 1D schematically shows an embodiment of a part of an electronic circuit or a control circuit 100 suitable for use in some embodiments of the sensor of the present invention. A part of the electronic circuit 100 illustrated in FIG. 1B is sometimes referred to as a potential difference circuit. In a three-electrode sensor as shown in FIG. 1A, a specific potential difference or voltage is maintained between the reference electrode 70 and the detection electrode or the working electrode 50, the electrochemical reaction is controlled, and an output signal proportional to the current generated by the sensor is transferred. As described above, the working electrode 50 reacts with the analytical gas or the target gas to oxidize or reduce the gas. This oxidation-reduction reaction generates a current proportional to the concentration of the gas. The current is supplied to the sensor 10 via the counter electrode 80. At the counter electrode 80, an oxidation-reduction reaction opposite to the reaction at the working electrode 50 occurs, completing the circuit with the working electrode 50. The potential of the counter electrode 80 may be left to vary as it is. When the gas is detected, the cell current rises and the counter electrode 80 polarizes with respect to the reference electrode 70. As long as the circuit supplies sufficient voltage and current to maintain the normal potential of the working electrode 50, the potential at the counter electrode 80 is not important.

[0062] For example, as described in U.S. Patent Application Publication No. 2017 / 0219515, the measurement circuit of the electric circuit 100 includes a single-stage operational amplifier or an operational amplifier IC1. The sensor current is reflected across a gain resistor 120 (having a resistance of 5 kΩ in the illustrated embodiment) to generate an output voltage. The load resistor 122 (having a resistance of 56 Ω in the illustrated embodiment) may be selected, for example, by a balance between the fastest response time and the best signal-to-noise ratio.

[0063] The control operational amplifier IC2 provides potentiostatic control and supplies current to the counter electrode 80 to balance the current required by the working electrode 50. The inverting input to IC2 is connected to the reference electrode, but no significant current is drawn from the reference electrode.

[0064] During the electronic interrogation of a sensor of the present invention such as sensor 10, a non-Faradaic current may be induced (e.g., via the application of energy in the form of an electrical signal to the working electrode 50). For example, a stepwise potential change can be caused to generate a non-Faradaic current. The generated non-Faradaic current can be used to monitor the function or health of the sensor as a result of the charging of the electrodes. However, as described above, the sensor is then returned to its normal bias potential or potential range for normal operation to sense the target gas or the gas to be analyzed. In the process of returning the sensor to its operating bias or operating potential difference (which may be zero), a current peak (charge accumulation) occurs in the reverse direction. The current peak that occurs upon return to the operating potential difference may take several seconds to decay.

[0065] Information regarding the soundness or state of the sensor may be obtained from MPV, AUC, mPV, or rAUC analysis. The interrogation of the sensor may include, for example, measuring / analyzing a single data point or multiple data points over a short time span in the resulting response / current curve. When inducing a non-Faradaic current in sensor 10 (or another sensor of the present invention) and / or when returning sensor 10 (or another sensor of the present invention) to its operating potential difference, it can be achieved by active control of the sensor electronics 100 (e.g., by reducing the load resistance of the electronic circuit 100 between the working electrode 50 and the point in time when the output / response is measured after the test potential difference is applied). In some embodiments, the load resistance between the working electrode 50 and the output of the operational amplifier IC1 is reduced to a low value. Thereafter, after the charge has substantially dissipated or completely dissipated, the load resistance between the working electrode 50 and the output of the operational amplifier IC1 is restored to the normal or operating load resistance (or within the operating range of the load resistance).

[0066] In some embodiments, the load resistor 122 (see FIG. 1D) may be bypassed to reduce the load resistance between the working electrode 50 and the inverting terminal of the operational amplifier IC1. The bypass circuit 124 may be provided, for example, to bypass the load resistor 92. In some embodiments, a field effect transistor (FET) 126 is used as the switch of the bypass circuit 124 to controllably effect a bypass or short circuit around the load resistor 122. In some embodiments, a metal-oxide-semiconductor FET or MOSFET may be used.

[0067] Unlike the diffusion-limited current measurement (amperometric) electrochemical gas sensor, the capillary-limited sensor of the present invention is not sensitive to medium- and long-term humidity changes. Medium-term humidity changes are, for example, the relative humidity changes during the day, which can be, for example, ±30. Long-term humidity changes accumulate over a long period such as a period of two to three months. For example, FIG. 2 shows the response of the capillary-limited oxygen pump type sensor of the present invention to humidity in a normal environment and extreme atmospheres. The experiment shown in FIG. 2 was conducted by correlating the gas test results (◆) with the weight change (●) when a representative group of oxygen sensors was exposed to various humidities of the atmosphere. In these experiments, an oxygen sensor named "XCELL" (registered trademark) manufactured by MSA Safety Incorporated in Cranberry Township, Pennsylvania was used. As dramatically shown in FIG. 2, the electrolyte of the oxygen sensor increases or decreases moisture in response to the humidity in the atmosphere due to the hygroscopicity of the aqueous electrolyte commonly used in this type of sensor. The increase or decrease of moisture in the electrolyte occurs substantially through the vent 26 (see, for example, FIG. 1A). Unlike permeation-type or diffusion-limited sensors such as sensors designed to detect carbon monoxide (CO) and hydrogen sulfide (H 2 S), the output of the capillary-limited oxygen sensor does not respond to the humidity changes in the study of FIG. 2. Since it is relatively insensitive to these medium- and long-term humidity changes, it is suggested that a different approach is required to apply an inquiry about the operating state to capillary-limited electrochemical gas sensors such as oxygen pump type electrochemical gas sensors.

[0068] Figure 3 shows a typical response obtained when an electrical signal such as a potential pulse is applied to the working electrode of a typical oxygen pump type sensor with capillary restriction. The parameters of the pulse (magnitude and duration) are not important. However, by using short pulses, the time during which the electrochemical gas sensor of the present invention is in the interrogation mode can be minimized (thereby maximizing the time during which the sensor is in the sensor mode for detecting the analyte). A current pulse may be applied to the working electrode to observe the potential response and obtain similar data. The numerical parameters obtained from such experiments include at least six parameters, such as the baseline, i.e., the normal response of the sensor to the surrounding atmosphere (e.g., immediately before applying the potential pulse), the maximum peak value (MPV), the area under the curve (AUC), the minimum peak value (mPV), the peak-to-peak value (PP), and the area under the reversed curve (rAUC).

[0069] Parameters such as MPV, PP, AUC, mPV, and rAUC can be used both to detect the failure state of a diffusion-limited amperometric electrochemical gas sensor and to correct its output in real time. However, in contrast to a diffusion-limited electrochemical gas sensor, due to the differences in the design of a capillary-restricted electrochemical gas sensor, these parameters have been found to be less useful in managing and maintaining the signal of a capillary-restricted electrochemical gas sensor (e.g., an oxygen pump type sensor).

[0070] For example, Figure 4 shows the same MPV response as the sensor examined in Figure 2, along with the output of its surrounding environment. The data shown in Figure 4 were obtained simultaneously with the data shown in Figure 2. In Figure 4, the average ambient output of the oxygen sensor group is again represented by diamonds (◆), while the maximum peak value (MPV) is represented by squares (■). It can be seen that the change in MPV due to humidity is not a predictor of the average ambient output of this oxygen sensor group. Comparing Figure 2 and Figure 4, it can be seen that the change in MPV is caused by the change in the weight of the sensor, which is due to the increase and decrease of moisture occurring in a storage environment with high humidity.

[0071] The output and performance of a capillary-limited oxygen sensor change as a result of the loss of the electrolyte due to evaporation or other causes. To detect these other fault conditions, the interrogation techniques of the above-described lifetime and healthy (operating condition) sensors can be used. These fault conditions typically appear as a sudden change in output, or a gradual change in output over time that is not correlated with changes in the ambient humidity conditions.

[0072] For example, FIGS. 5 and 6 show the behavior of a capillary-limited oxygen pump type sensor when exposed to conditions that occur in the case of a sensor that has leaked under very dry conditions or more moderate humidity conditions. For example, such conditions can include exposure to a relative humidity of less than 20%, less than 15%, or less than 10%. A very dry state may be experienced, for example, during cold months or winters, especially within structures heated by forced air through a combustion furnace. As described above, unlike diffusion-limited amperometric electrochemical gas sensors, capillary-limited sensors do not show a change in output due to normal humidity changes. However, under the conditions of FIG. 5, as the studied sensor loses the moisture of the aqueous electrolyte and becomes very dry (as shown by the weight change data represented by the circles (●) in FIG. 5), when the sensor enters a fault state, the indicated volume % O 2 The output rises dramatically. The data in FIG. 6 shows the response of the baseline parameters of the pulse test that was observed simultaneously with the data in FIG. 5.

[0073] In FIG. 6, the indicated volume % O of the sensor 2 The output is again represented by diamonds (◆), while the response of the electronic interrogation or the baseline parameters of the pulse test is represented by circles (●). As is apparent, the baseline parameters of the pulse test are substantially a mirror image of the indicated output of these sensors.

[0074] Unlike a diffusion-limited current-measuring electrochemical sensor in which the output changes moderately when the humidity changes and can be corrected numerically easily and safely, in the capillary-limited oxygen sensor of the present invention, even when the humidity changes moderately, the change in the indicated output is relatively small, but when the humidity changes greatly, the indicated output changes very greatly. Such a large change is considered to be a failure or inoperable state in which the sensor output cannot be corrected safely. However, an electronic inquiry or a pulse test functions as a unique and clear test for this type of failure.

[0075] Among the measurable parameters related to an electronic inquiry, the baseline parameter represents the sensor output almost exactly. In certain situations, the baseline response may be used to correct the sensor output when the sensor is considered to be operable.

[0076] In the case of a capillary-limited oxygen sensor, a second failure state that can be diagnosed by an electronic inquiry or a pulse test (i.e., a failure state caused by something other than a significant change in humidity) is that the sensor output drifts slowly as a result of an external physical or chemical change. Such a slow drift occurs, for example, when the sensor is exposed to an interfering gas, a poison, an inhibitor, etc. In the case of a capillary-limited oxygen sensor, such a change in chemical conditions can cause drift, for example, by interfering with the electrochemical reduction of oxygen at the working electrode or due to drift at the internal reference electrode. Also, the cause of physical drift may include, for example, the slow blockage of the capillary by dust or moisture. In any case, an electronic inquiry or a pulse test can be advantageously applied to diagnose these states.

[0077] Many gas detection devices use the output of a capillary-limited oxygen sensor in clean ambient air as an indicator of normal operation. Such a methodology typically involves performing what is commonly referred to as a "fresh air setup" or FAS. During FAS, the instantaneous output of the sensor is compared to a reference value that is usually electronically stored in modern equipment. If the instantaneous output of the sensor is within a preset range of the reference value, the display output of the instrument is adjusted to indicate 20.8 volume % oxygen.

[0078] Figure 7 shows the behavior of a group of sensors that are undergoing slow, monotonic drift. The magnitude of the drift is such that the limits of a successful FAS are not exceeded during any setup. These are indicated by Run # on the lower side or x-axis of Figure 7. The x-axis of Figure 7 does not indicate elapsed time but only the sequential count of consecutive FAS operations. The actual or indicated volume % O of the sensors investigated 2 The data points corresponding to the output are represented by diamonds (◆) and plotted against the left axis. As shown in Figure 7, the actual or indicated output of the sensors under investigation decreased with each consecutive FAS operation. The indicated results of consecutive FAS operations are represented by squares (■) in Figure 7 and plotted against the left axis. Also, the baseline parameter data of the pulse test measured immediately before or after FAS operation are represented by triangles (▲) plotted against the right axis. As is clear from Figure 7, the baseline parameters calculated from the pulse test reflect the actual drift of the sensors under investigation, even for small drifts that are not detected by FAS operation.

[0079] Accordingly, electronic interrogation or pulse testing (applying an electrical signal for a short time or “pulse” to pass a current between the working electrode and the counter electrode) is clearly very effectively applicable to capillary-limited sensors such as oxygen sensors, even though this type of sensor exhibits behavior quite different from that of diffusion-limited sensors. Representative embodiments of electronic interrogation or pulse testing of capillary-limited oxygen sensors may include, for example, the following. (i) Ensuring that the sensor is in clean ambient air (i.e., air having 20.8% by volume of oxygen) (ii) Initiating an interrogation mode while the electronic interrogation is being performed, where the actual parameters of the test (magnitude, duration, etc.) are determined for a particular application (iii) Collecting the response of the sensor during the electronic interrogation at an appropriate sample rate determined by the application (iv) Calculating appropriate parameters, particularly the baseline response (v) Comparing the result of any electronic interrogation with a predetermined limit value and / or the history of previous electronic interrogations performed on a particular sensor (vi) Determining the operating state or soundness of the sensor, and (vii) Warning the user of a fault state, or, if it is determined that there is no fault state, saving the result of the electronic interrogation of the current and returning the device to its operating mode or target gas detection mode.

[0080] In some embodiments of the present invention, a baseline output is measured (e.g., before applying the current pulse or after returning to the baseline or zero analyte output after such a pulse), and compared to a previously measured (e.g., calibrated) value. The calibrated value may be determined, for example, at the last gas calibration (i.e., at the time of manufacture of the device and subsequent gas calibrations). In some embodiments, the comparison of the calibration value (and / or other previously determined values) to the measured value not only provides a determination of the sensor state, but also provides a means for adjusting the sensor output (e.g., correcting the sensor sensitivity). In some representative embodiments of the systems, devices, and / or methods of the present invention, as described herein (without applying the gas or surrogate therefor to be analyzed), internal electronic checks or interrogations of the sensor's functionality, connections may be performed, and for example, as described in U.S. Patent No. 7,413,645, the disclosure of which is incorporated herein by reference, the sensor output may be corrected. The correction factor applied to the sensor output may, for example, have a mathematical form.

Number

[0081] In the above equation, Sc is the corrected sensitivity of the sensor, and R 0 and S 0 are the initial values of the response function and sensitivity, respectively, and R i and S i are the response function and sensitivity at any point during the experiment, respectively, and a is an adjustable parameter. Note that the form of this equation is not unique, and other correction functions may be used. By applying this correction factor to the experimental data, the indicated response of the device throughout the experiment returns to the specified range, thereby eliminating the need to recalibrate the sensor against a known standard calibration gas.

[0082] The foregoing description and the accompanying drawings illustrate numerous representative embodiments at the present time. Of course, various changes, additions, and alternative designs will be apparent to those skilled in the art in light of the foregoing teachings without departing from the scope of the invention as set forth in the following claims rather than the foregoing description. All changes and modifications that fall within the meaning and scope of equivalence of the claims are intended to be embraced within their scope.

Claims

1. A method of operating a gas detection device including a capillary-restricted current-measuring electrochemical gas sensor that reacts with a gas to be analyzed, comprising: operating the gas sensor in a detection mode in which a signal from the gas sensor indicates the concentration of the gas to be analyzed measured by the gas sensor; a query mode of electronically querying the gas sensor to test the function of the gas sensor, applying an electrical signal to the gas sensor at a time during each query mode to generate a non-Faradaic current between the working electrode and the counter electrode of the gas sensor through an electrolyte in ionic contact with the working electrode and the counter electrode without applying the gas to be analyzed or its simulated gas of known concentration from a container to the sensor, and periodically transitioning to the query mode; measuring a response of the gas sensor to the non-Faradaic current in the query mode and monitoring the function of the gas sensor based on the response; measuring a baseline output of the gas sensor before applying the electrical signal to the gas sensor during each query mode; comparing the baseline output measured during each query mode with one or more baseline outputs previously measured in one or more previous query modes; determining an operating state from a comparison of the baseline output measured during each query mode with one or more previously measured baseline outputs; and returning the gas sensor to the detection mode if the operating state is determined to be within a predetermined range.

2. The method according to claim 1, wherein the gas sensor is an oxygen sensor.

3. The method according to claim 2, wherein if it is determined from a comparison of the measured baseline output with one or more previously measured baseline outputs that the measured baseline output is outside a predetermined range, the operating state of the gas sensor is determined to be a fault state.

4. The method of claim 3, further comprising providing a warning if the gas sensor is determined to be in a fault state.

5. The method according to claim 1, using a change in the baseline output to adjust sensitivity.

6. The method of claim 5, further comprising providing a warning when it is determined that the gas sensor is in a fault state.

7. The method of claim 2, wherein at least one parameter other than the baseline is measured during the interrogation mode in response to the electrical signal.

8. The method according to claim 7, wherein at least one parameter other than the baseline is selected from the group consisting of a maximum peak value, an area under the curve, a minimum peak value, a peak-to-peak value, and an area under the inverted curve.

9. The method according to claim 2, further comprising comparing the output of the gas sensor in the detection mode with a stored reference value and adjusting the output of the gas sensor to correspond to 20.8% by volume of oxygen when the output of the gas sensor is within a predetermined range of the stored reference value, thereby performing a setup of fresh air.

10. A capillary-restricted electrochemical gas sensor that reacts to a gas to be analyzed, a housing having a capillary inlet, an electrolyte within the housing, a working electrode in ionic contact with the electrolyte, a counter electrode in ionic contact with the electrolyte, and an electronic circuit operably connected to the working electrode and the counter electrode, wherein the electronic circuit is configured to operate the gas sensor in a detection mode in which a signal from the gas sensor indicates the concentration of the gas to be analyzed measured by the gas sensor, and is configured to periodically shift to an interrogation mode in which an electronic interrogation is performed on the gas sensor to test the function of the gas sensor, and is configured to generate a non-Faradaic current between the working electrode and the counter electrode through the electrolyte without sending the gas to be analyzed having a known concentration or a simulated gas thereof from a container to the sensor, and to apply an electrical signal to the gas sensor at a time during each interrogation mode, wherein the electronic circuit is configured to measure the response of the gas sensor to the non-Faradaic current in the interrogation mode and to monitor the function of the gas sensor based on the response. The electronic circuit is configured to measure the baseline output of the gas sensor before applying the electrical signal to the gas sensor during each interrogation mode, compare the baseline output measured in each interrogation mode with one or more baseline outputs previously measured in one or more previous interrogation modes, determine an operating state from a comparison between the baseline output measured during each interrogation mode and one or more of the previously measured baseline outputs, and further configured to return the gas sensor to the detection mode when the operating state is determined to be within a predetermined range. An electrochemical gas sensor.

11. The gas sensor according to claim 10, wherein the gas sensor is an oxygen sensor.

12. The gas sensor according to claim 10, wherein when it is determined that the measured baseline output is outside a predetermined range, a failure state is determined by the electronic circuit.

13. The gas sensor according to claim 12, further comprising an interface system that provides a warning when it is determined that the gas sensor is in a failure state.

14. The gas sensor according to claim 10, wherein when it is determined that the measured baseline output is outside a predetermined range, the electronic circuit determines that the gas sensor is in a failure state.

15. The gas sensor according to claim 10, wherein at least one parameter other than the baseline is measured during the interrogation mode.

16. The gas sensor according to claim 15, wherein at least one parameter other than the baseline is selected from the group consisting of a maximum peak value, an area under the curve, a minimum peak value, a peak-to-peak value, and an area under the inverted curve.

17. The electronic circuit compares the output of the gas sensor in the detection mode with a stored reference value, and when the output of the gas sensor is within a predetermined range of the stored reference value, further configured to perform a fresh air setup of adjusting the output of the gas sensor to correspond to 20.8% by volume of oxygen. The gas sensor according to claim 10.

18. The gas sensor according to claim 10, wherein the electronic circuit is further configured to adjust sensitivity in response to a change in the baseline output by comparing the measured baseline output with one or more of the previously measured baseline outputs.

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