Interrogation and output correction for capillary confined oxygen sensors

Abstract

A method of operating a capillary confinement type electrochemical gas detection device includes: applying an electrical signal to an electrochemical sensor of the gas detection device to generate a current flow between a working electrode and a counter electrode of the electrochemical gas sensor via an electrolyte of the electrochemical gas sensor; measuring a parameter of the response of the electrochemical sensor to the electrical signal; comparing the measured parameter with a predetermined characterization of the parameter, wherein the predetermined characterization of the parameter provides a relationship between the parameter and a response of the electrochemical sensor in a changing state of the electrochemical sensor; and determining an output value of the gas detection device as a function of an output signal of the electrochemical sensor when sensing oxygen in the ambient environment and a comparison of the measured parameter to a predetermined characterization.

Description

BACKGROUND OF THE INVENTION

[0001] The following information is provided to assist the reader in understanding the technologies disclosed hereinafter and the environments in which these technologies can generally be used. Unless otherwise expressly stated in this document, the terms used herein are not intended to be limited to any particular narrow interpretation. The references listed herein may assist in understanding the technologies or their background. The disclosures of all references cited herein are incorporated by reference.

[0002] Electrochemical sensors are effective in detecting various gases. The low cost, response speed, and selectivity of electrochemical sensors are just a few of the characteristics that make such sensors attractive for safety products. However, a necessary requirement for using an electrochemical sensor is frequent calibration using a test gas that includes an analyte gas of known concentration. In addition, gas detection instruments that include electrochemical gas sensors must be tested regularly for functionality. For example, it is common practice to perform a "bump test" or functionality check on a portable gas detection instrument every day. The purpose of this test is to ensure the functionality of the entire gas detection system (including the sensor(s) and delivery path), which is commonly referred to as the instrument. Periodic bump tests or functionality checks can also be performed on fixed gas detection instruments, for example, to extend the period between full calibrations. A gas detection system includes at least one gas sensor, electronic circuitry for driving the sensor, interpreting its response, and displaying its response to a user, and a power source. The system also includes a housing for enclosing and protecting these components. A bump test typically includes: a) applying a gas of interest (usually a gas that is an analyte gas of known concentration or an analog thereof); b) collecting and interpreting the sensor response; and c) indicating to the end user the functional status of the system (i.e., whether the instrument is operating properly).

[0003] Numerous systems and methods have been proposed to, for example, reduce the frequency of periodic testing using a test gas in a diffusion-limited electrochemical gas sensor while providing frequent measurements of the lifespan and health of the sensor. Such systems can, for example, include electronically interrogating the sensor in the absence of a test gas. In a diffusion-limited electrochemical sensor, sensitivity fluctuations due to moisture loss or gain occur gradually but predictably with slow changes in the average relative humidity in such sensors. Similarly, the response of the sensor to electronic interrogation (in the absence of or without applying a test gas that includes an analyte gas of known concentration or a surrogate thereof) also changes in a similar manner. Electronic interrogation can be used, for example, to measure sensitivity changes and correct the sensor output for such sensitivity changes.

[0004] For example, electronic interrogation techniques and resulting calibrations for diffusion-limited electrochemical gas sensors are disclosed 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 methods, an electrical signal (e.g., a potential pulse) is typically applied to the sensor, and the resulting response is measured and recorded. Electronic interrogation of capillary-limited gas sensors is described in U.S. Patent No. 11,112,378, the disclosure of which is incorporated herein by reference.

[0005] Although electronic interrogation of capillary-limited electrochemical gas sensors for oxygen is sensitive to failure modes, such interrogation does not deliver consistent data in the field for correcting for sensor behavior / sensitivity variations. Accordingly, improved electronic interrogation techniques for use in conjunction with capillary-limited electrochemical gas sensors for oxygen are desired. SUMMARY OF THE INVENTION

[0006] In one aspect, a method of operating a gas detection device (the gas detection device including a capillary-limited electrochemical sensor that has an analytical response to oxygen, wherein the electrochemical sensor includes: a housing that includes a capillary through which gas diffuses from the environment into the housing; a working electrode within the housing; a counter electrode within the housing; and an electrolyte within the housing that is in ionic contact with the working electrode and the counter electrode) includes: applying an electrical signal to the electrochemical sensor to generate a current flow between the working electrode and the counter electrode via the electrolyte; measuring a parameter of the response of the electrochemical sensor to the electrical signal; comparing the measured parameter to a predetermined characterization of the parameter, wherein the predetermined characterization of the parameter provides a relationship between the parameter and the response of the electrochemical sensor in a varying state of the electrochemical sensor; and determining an output value of the gas detection device based on an output signal of the electrochemical sensor when sensing oxygen in the surrounding environment and the comparison of the measured parameter to the predetermined characterization. In various embodiments, the method further includes: operating the electrochemical sensor in a sensing mode, wherein the output signal is generated, the output signal representing the oxygen concentration in the environment; and operating the electrochemical sensor in an interrogation mode, during which the electrochemical sensor is electronically interrogated by applying the electrical signal to the electrochemical sensor, and the measured parameter is measured in the interrogation mode.

[0007] The gas detection device may further include a control system, the control system including a processor system and a memory system, wherein the working electrode is operably connected to the control system, and the counter electrode is operably connected to the control system. The memory system includes one or more algorithms stored therein and executable by the processor system to perform one or more actions of the method. The predetermined characterization may be stored in the memory during manufacture.

[0008] In multiple embodiments, the parameter is an amperometric parameter. The parameter may be the maximum peak, area under the curve, minimum peak, peak-to-peak value, and area under the reverse curve of the response of the electrochemical sensor to the electrical signal applied in the interrogation mode, or may be a function of any of the foregoing.

[0009] The predetermined characterization may be determined in a changing state of the electrochemical sensor. The changing state of the electrochemical sensor may be caused by environmental conditions.

[0010] In multiple embodiments, the predetermined characterization is determined based on the baseline response of the sensor to changes in the absence of oxygen. The baseline response of the sensor in the absence of oxygen is determined in a nitrogen atmosphere.

[0011] In multiple embodiments, the ambient current output of the sensor is less than 300 μA, optionally less than 150 μA, or optionally less than 30 μA.

[0012] In another aspect, a gas detection device includes: a control system including a processor system and a memory system, and an electrochemical sensor having an analytical response to oxygen, including: a housing including a capillary through which gas diffuses from the environment into the housing; a working electrode within the housing and operably connected to the control system; a counter electrode within the housing and operably connected to the control system; and an electrolyte within the housing and in ionic contact with the working electrode and the counter electrode. The control system is configured, via software executed by the processor system and stored in the memory system, to: apply an electrical signal to the electrochemical sensor to generate a current flow between the working electrode and the counter electrode via the electrolyte; measure a parameter of the response of the electrochemical sensor to the electrical signal, compare the measured parameter with a predetermined characterization of the parameter, wherein the predetermined characterization of the parameter provides a relationship between the parameter and the response of the electrochemical sensor in a changing state of the electrochemical sensor; and determine an output value of the gas detection device based on the analytical response of the electrochemical sensor when sensing oxygen in the surrounding environment and the comparison of the measured parameter with the predetermined characterization.

[0013] The control system can also be configured to operate the electrochemical sensor in a sensing mode, where an output signal is generated that represents the oxygen concentration in the environment; and to operate the electrochemical sensor in an interrogation mode, during which the electrochemical sensor is electronically interrogated by applying the electrical signal to the electrochemical sensor, and the parameter being measured is measured in the interrogation mode. The predetermined characterization can be stored in the memory system at the time of manufacture.

[0014] In multiple embodiments, the parameter is a chronoamperometric parameter. The parameter can be, for example, the maximum peak, area under the curve, minimum peak, peak-to-peak value, and area under the reversed curve of the response of the electrochemical sensor to the electrical signal applied in the interrogation mode, or can be a function of any of the foregoing.

[0015] In multiple embodiments, the ambient current output of the sensor is less than 300 μA, optionally less than 150 μA, or optionally less than 30 μA.

[0016] In yet another aspect, a method of characterizing a change in the response of an electrochemical sensor (where the electrochemical sensor is capillary-restricted and has an analytical response to oxygen, and the electrochemical sensor includes: a housing that includes a capillary through which gas diffuses from the environment into the housing; a working electrode within the housing; a counter electrode within the housing; and an electrolyte within the housing that is in ionic contact with the working electrode and the counter electrode) in a changing state, the method including: determining a predetermined characterization that provides a relationship between a parameter measured when an electrical signal is applied to the electrochemical sensor to generate a current flow between the working electrode and the counter electrode via the electrolyte and the response of the electrochemical sensor in the changing state.

[0017] The devices, systems, and methods herein, as well as their characteristics and attendant advantages, will be best understood and appreciated by reading the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A A cross-sectional view of a capillary-restricted electrochemical gas sensor herein is schematically shown.

[0019] Figure 1B A perspective cross-sectional view of a capillary-restricted electrochemical gas sensor herein is schematically shown.

[0020] Figure 1C Schematically shown is Figure 1AMagnified view of the capillary inlet of a capillary-constrained electrochemical gas sensor.

[0021] Figure 2 Shows representative examples of the sensor's response to the pulse tests herein (for two different working electrode sizes), in which the energy applied to the working electrode is varied, causing a change in the current passing through it.

[0022] Figure 3 Shows a study of a representative capillary-constrained electrochemical gas sensor herein, which shows the changes in the AUC, DeltaPeak, and MaxPeak parameters due to the pulse tests herein, indicating that such parameters contain the same or very similar analytical information.

[0023] Figure 4A Shows the correlation of the nitrogen baseline (capacitive) current with the change in the parameter AUC.

[0024] Figure 4B Shows the measurement of the nitrogen baseline with respect to the baseline sensor current in the absence of oxygen.

[0025] Figure 5 Shows the environmental sensor output that is linearly correlated with the change in the nitrogen baseline, indicating that the oxygen effect is constant under the evaluated environmental changes.

[0026] Figure 6 Shows the correlation of the environmental output of the sensor with the change in the chronoamperometric pulse test parameters.

[0027] Figure 7 Shows that the chronoamperometric pulse test parameters allow prediction of the sensor output with relevant values. Detailed Description

[0028] It will be readily understood that the components of the embodiments generally described and illustrated herein in the figures can be arranged and designed in a variety of different configurations in addition to the representative embodiments described. Thus, as shown in the figures, the following more detailed description of the representative embodiments is not intended to limit the scope of the claimed embodiments, but is merely illustrative of the representative embodiments.

[0029] References throughout this specification to "one embodiment" or "an embodiment" (or similar expressions) mean that the particular features, structures, or characteristics described in connection with that embodiment are included in at least one embodiment. Thus, the phrases "in one embodiment" or "in an embodiment" and the like appearing in various places throughout this specification do not necessarily all refer to the same embodiment.

[0030] In addition, 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 to give a thorough understanding of the 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 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.

[0031] As described above, response measurements resulting from correlating lifetime and health status analysis data of a sensor via electronic interrogation with sensor sensitivity have not in the past been well correlated enough to permit sufficiently accurate correction of the output value or reading of a capillary-limited electrochemical oxygen sensor. As used herein, "sensor sensitivity" generally refers to the ratio of the change in an output signal (e.g., current or voltage) to the property being measured.

[0032] Without being limited to any underlying mechanism, studies of the devices, systems, and sensors herein have shown that electrochemical parameters measured in an electronic interrogation in which the energy to the working electrode of the sensor is altered are not correlated with changes in sensor sensitivity. Studies of the electrochemical capillary-limited oxygen sensors herein have shown that the sensor signal height or amplitude is determined solely by the capillary and diffusion characteristics of the gas inlet of the sensor. Primarily, these characteristics include the effective capillary diameter and length and the carrier gas background. Again, without being limited to any mechanism, this study has shown that the sensor nitrogen baseline (or oxygen-unaffected baseline) depends on changes in the sensor state, such as those caused by environmental conditions (such as humidity development) and the sensor usage history. The overall sensor signal or response is the sum of both the sensor baseline in the absence of oxygen (sometimes referred to herein as the nitrogen baseline) and the response to oxygen. This study further shows that the sensor state and a characterization of the corresponding response of the sensor can be determined based on one or more parameters determined in an electronic interrogation in which an electrical signal is applied to the electrochemical sensor to cause current to flow between the working electrode and the counter electrode via the electrolyte. Such a characterization or a predetermined characterization may provide, for example, the relationship between one or more parameters and the response of the electrochemical sensor in a varying state of the electrochemical sensor. The response of the electrochemical sensor measured in the predetermined characterization of the electrochemical sensor may include only the baseline output / response of the electrochemical sensor in the absence of oxygen, or may be the ambient output / response (including both the baseline response of the electrochemical sensor in the absence of oxygen and the response to oxygen).

[0033] During determination of the predetermined characterization, a change in the state of the electrochemical sensor (e.g., changes in electrolyte concentration and local water content at the working and reference electrodes of the electrochemical sensor system) or a change in the state of one or more representative similar electrochemical sensors can be caused, for example, by exposure over time to ambient conditions different from the "standard" ambient conditions during calibration. One or more parameters to be characterized and the sensor response can be measured at different times (e.g., periodically) during the time of exposure to non-standard ambient conditions. It is also possible to cause a change in state without long-term exposure to ambient conditions different from the calibration ambient conditions. For example, the electrolyte concentration / water content in the electrochemical sensor under study can be manually or automatically changed, and one or more parameters can be measured after each such change while, for example, keeping the ambient conditions the same or substantially the same as the ambient conditions during calibration.

[0034] The output value or sensor reading of an electrochemical capillary-limited oxygen sensor (e.g., provided as vol% O 2 ) can be determined based on two sensor parameters. In this regard, first, the sensor current (I 2 or the current output under ambient conditions) during operation in ambient air at 20.8 vol% O amb is determined. The output current during operation at a known calibration gas concentration also needs to be determined. As described above, the calibration gas can be, for example, pure nitrogen with a 0.0 vol% O 2 content. Also as described above, the current output during operation in a nitrogen atmosphere is referred to herein as the nitrogen baseline (I nitrogen ) of the sensor. The sensor sensitivity can be calculated from the above two values as follows:

[0035] Sensitivity [A / Vol%] = (I amb - I nitrogen ) [A] / 20.8 [Vol%]

[0036] For calculating the sensitivity, other pairs or multiple pairs of O 2 concentrations can be used. The choice of concentration can be determined by the desired measurement range and background of the technical application. According to the above equation for sensitivity, the sensor output reading of an electrochemical capillary-limited oxygen sensor can be calculated by the following equation:

[0037] Sensor reading [Vol%] = (Actual / Measured sensor current - I nitrogen ) [A] / Sensitivity

[0038] [A / Vol%]

[0039] Currently, the sensor nitrogen baseline is considered a constant value. However, this study shows that the sensor output reading or value can be affected by changes in both sensitivity and the nitrogen baseline. Regardless of the underlying mechanism, the devices, systems, and methods herein provide a predetermined characterization that provides a relationship between parameters determined in an electronic interrogation of the sensor and the response of an electrochemical sensor in varying sensor states. The response of the electrochemical sensor in the predetermined characterization can be determined as a change in the response of the electrochemical sensor compared to the response at a value determined in an initial or calibration state under defined conditions. Without being limited to any mechanism, the varying state / response of the electrochemical sensor may be associated with changes in electrolyte concentration and local water content at, for example, the working and reference electrodes of an electrochemical sensor system. The predetermined characterization can be used to determine a sensor output reading or value, which can be considered a corrected sensor output reading or value. In this regard, the output value of a gas detection device can be determined based on: (i) the measured output signal (e.g., a current signal) in response to exposure to a gas in the surrounding environment, and (ii) a comparison of the parameter measured in the electronic interrogation (simultaneous with the measured output signal) to the predetermined characterization of that parameter. The implementation of the correction method in the devices, systems, and methods herein provides improved accuracy of the sensor output reading or value and can be accomplished in various ways. In this regard, the variation in the sensor output reading (associated with the parameter measured in the electronic interrogation, with reference to the predetermined characterization of that parameter) can be implemented, for example, into algorithms that change the overall sensitivity of the sensor, change the nitrogen baseline, change a general correction factor, etc. The implementation of sensor output determination can be independent of the actual naming of the above variables.

[0040] Currently available methods for determining the lifetime and health of a capillary-limited electrochemical gas sensor for oxygen have attempted to determine signal height or overall signal. In multiple embodiments, the devices, systems, and methods herein provide for determining or characterizing a sensor state (and associated response) based on parameters determined in an electronic interrogation to predict the overall signal by adding a constant signal height provided by the presence of atmospheric oxygen. As described above, the characterization of the sensor state / associated response based on parameters determined in the electronic interrogation can be determined, for example, by the correlation of the parameters to the changing sensor state of the electrochemical sensor over time. In multiple studies herein, the change in sensor state was caused by exposure to predetermined environmental conditions over time. Such environmental conditions may be significantly different from the environmental conditions during calibration (e.g., in terms of temperature and / or relative humidity).

[0041] Prior to the present study, investigations of capillary-constrained oxygen sensors, which are typically operated at relatively high power, have shown that the ambient output signal height or amplitude is independent of ambient conditions such as humidity. Given the relatively small effect of variations in capacitive or non-Faradaic current associated with changes in the nitrogen baseline caused by a changing state of the electrochemical sensor, such as due to ambient conditions as described herein, the signal-to-noise ratio of the electronics of such sensors is generally insufficient to observe and characterize the phenomenon.

[0042] As used herein and in 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 multiple such parameters known to those skilled in the art and their equivalents, etc., and a reference to "the parameter" refers to one or more such parameters known to those skilled in the art and their equivalents, etc. The ranges of values recited herein are merely intended as a convenient method of individually referring to each individual value falling within the range. Unless otherwise indicated herein, each individual value and intermediate ranges are incorporated into this specification as if individually recited herein. Unless otherwise indicated herein or clearly prohibited by the text, all methods described herein may be performed in any suitable order.

[0043] As used herein, the terms "electronic circuitry", "circuitry", or "circuit" include, but are not limited to, hardware, firmware, software, or combinations thereof for performing one or more functions or actions. For example, depending on the desired features or requirements, a circuit may include a software-controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmable logic device. A circuit may also be embodied entirely as software. As used herein, "circuit" is considered synonymous with "logic". As used herein, the term "logic" includes, but is not limited to, hardware, firmware, software, or combinations thereof for performing one or more functions or actions, or causing a function or action from another component. For example, depending on the desired application or requirements, logic may include a software-controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmable logic device. Logic may also be embodied entirely as software.

[0044] As used herein, the term "processor" includes, but is not limited to, one or more of almost 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 a variety of other circuits that support the operation of the processor, such other circuits being, for example, random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), clocks, decoders, memory controllers, or interrupt controllers, among others. These support circuits may be internal or external to the processor or its associated electronic package. The support circuits communicate with the operation of the processor. In block diagrams or other figures, the support circuits are not necessarily shown separately from the processor.

[0045] As used herein, the term "controller" includes, but is not limited to, any circuit or device that coordinates and controls the operation of one or more input and / or output devices. For example, a controller may include a device having one or more processors, microprocessors, or central processing units that are programmable to perform functions.

[0046] 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, actions, or behaviors in a desired manner. These instructions may be embodied in various forms, such forms being, for example, routines, algorithms, modules, or programs, including stand-alone applications or code from dynamic link libraries. Software may also be implemented in various forms, such forms being, for example, stand-alone programs, function calls, server-side servlets, client-side applets, instructions stored in memory, a portion of an operating system, or other types of executable instructions. One of ordinary skill in the art will appreciate that the form of the software depends, for example, on the requirements of the desired application, the environment in which it runs, or the expectations of the designer / programmer, among other things.

[0047] In the case of applying an electrical signal to the working electrode of an electrochemical gas sensor during an electronic interrogation, the response can be measured, for example, in the form of (or according to) the following: (i) the maximum peak (MaxPeak), which is the maximum current observed when applying a potential pulse; (ii) the area under the curve (AUC), which is the integrated current response of the working electrode after applying the potential pulse (this corresponds to the charging response of the sensor); (iii) the minimum peak (minPeak), which is the minimum current obtained when removing or reversing the potential pulse, typically as the difference in current observed immediately after and before removing or reversing the potential pulse, but it can also be tabulated and used as the difference between the minimum current and the baseline; (iv) the peak-to-peak (PP), which is the algebraic difference between the maximum observed current and the minimum observed current; and (v) the reverse area under the curve (rAUC), or more precisely the area under the reverse curve, which is the charging current obtained by integrating the current response after removing or reversing the potential pulse. In several embodiments herein, one or more of these parameter values determined during a period of time when the sensor is used to monitor the analyte concentration can be compared, for example, with the parameter values in a predetermined characterization, in which the sensor response (e.g., as represented by a change in the nitrogen baseline) is related to the parameter in a varying sensor state. The predetermined characterization can be stored, for example, in the memory of a device including the sensor during manufacture. During a test or pulse cycle of the interrogation mode, the energy to the working electrode increases or decreases (e.g., via a change in current or voltage) over a period of time that is typically a short period of time, and the resulting response is measured.

[0048] The electronic interrogation can, for example, have a relatively short duration to minimize the amount of time the sensor is offline for sensor test diagnostics (i.e., during the sensor electronic interrogation cycle). In several embodiments, the electronic interrogation can allow the electrochemical sensors herein to return to normal (gas sensing) mode operation within 10 seconds, within 5 seconds, even within 1 second, or even within 0.5 seconds. Devices, systems, and methods for electronic interrogation of the sensor can allow an instrument including one or more sensors to remain "online". In addition, such devices, systems, and methods can also provide active automatic sensor condition monitoring as a background operation without requiring user initiation. The frequency of the electronic interrogation can vary. Providing sensor interrogation at a frequency of, for example, several times per hour can provide nearly constant monitoring of the sensor life and health status.

[0049] In the case of a gas sensor, detection is desired to occur in the gas phase or at the phase boundary. Typically, this observation indicates that the speed of the sensor will be limited only by the rate of diffusion of the target gas molecules into the gas phase of the sensor. For the purpose of limiting the sensor output, a gas sensor (e.g., an electrochemical gas sensor) can be, for example, permeation- or diffusion-controlled or -limited, where a permeable membrane is used to limit the diffusion of the target gas into the sensor; or capillary-controlled or -limited, where a capillary inlet is used to limit the diffusion of the target gas into the sensor.

[0050] In this regard, in an electrochemical gas sensor, the gas to be measured (sometimes referred to as the target gas or analyte gas) is typically transferred from the surrounding atmosphere or environment to the first electrode or working electrode (sometimes referred to as the sensing electrode) in the sensor housing through, for example, a gas-permeable or gas-pervious membrane, or through a capillary inlet, where a chemical reaction occurs at the first electrode or working electrode. A complementary chemical reaction occurs at a second electrode referred to as the counter electrode (or auxiliary electrode). The electrochemical sensor generates an analytical signal via current generation directly at the working electrode due to the oxidation or reduction of the analyte gas (i.e., the gas to be detected). Cao, Z. and Stetter, J.R. also provided a comprehensive discussion of electrochemical gas sensors in "The Properties and Applications of Amperometric Gas Sensors", Electroanalysis , 4(3), 253 (1992), the disclosure of which is incorporated herein by reference.

[0051] The working electrode and the counter electrode combination produce an electrical signal that (1) is related to the concentration of the analyte gas and (2) is strong enough to provide a signal-to-noise ratio suitable for distinguishing the concentration levels of the analyte gas over the entire range of interest. In other words, the current flow between the working electrode and the counter electrode must be measurably proportional to the concentration of the analyte gas over the concentration range of interest.

[0052] In addition to the working electrode and the counter electrode, an electrochemical sensor typically also includes a third electrode, commonly referred to as the reference electrode. The reference electrode is used to hold the working electrode at a known voltage or potential. The reference electrode should be physically and chemically stable in the electrolyte.

[0053] The electrical connection between the working electrode and the counter electrode is maintained through the electrolyte. The functions of the electrolyte include: (1) to effectively carry the ionic current; (2) to dissolve the analyte gas; (3) to support the counter electrode reaction and the working electrode reaction; and (4) to form a stable reference potential with the reference electrode. The criteria for the electrolyte can 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.

[0054] Generally, the electrodes of an electrochemical cell provide surfaces at which oxidation or reduction (redox) reactions occur to provide a mechanism whereby the ionic conduction of the electrolyte solution is coupled with the electronic conduction of the electrodes, thus providing a complete circuit for the current. The measurable current generated due to the cell reaction of the electrochemical cell is proportional to the extent of the reaction occurring at the electrodes. Preferably, therefore, a high reaction rate is maintained in the electrochemical cell. For this reason, the counter electrode and / or the working electrode of an electrochemical cell typically contain a suitable electrocatalyst on their surfaces to support the reaction rate.

[0055] Due to electrostatic forces, the volume of the solution very close to the working electrode surface is of a very highly ordered structure. This structure is important for understanding the electrode process. The volume of the solution very close to the electrode surface is variously referred to as the diffusion layer, the diffuse layer, and / or the Helmholtz layer or plane.

[0056] The magnitudes of the resistance and capacitance present in an electrochemical cell are determined by the nature and characteristics of the materials used in its manufacture. The resistance of the electrolyte is determined by the number and type of ions dissolved in the solvent. The capacitance of the electrode varies mainly according to the effective surface area of the electrocatalyst. In an ideal world, these quantities would be constant. However, the solution resistance in a galvanometer-type gas sensor using an aqueous (water-based) electrolyte can vary, for example, due to exposure to different ambient relative humidity levels. When water evaporates from the sensor, the chemical concentration of the ionic electrolyte increases. This concentration change can cause the resistivity of the electrolyte to increase or decrease, depending on the actual electrolyte used.

[0057] In addition, even for substances that are generally considered insoluble in a particular solvent, there is a low but finite concentration of the substance in the solvent. For example, there is a very low but finite concentration of metal from the electrodes dissolved in the electrolyte of an electrochemical sensor. This low concentration of dissolved metal is constantly changing. That is, metal atoms are constantly dissolving from the electrode and then re-plating elsewhere. The net effect of this process is to reduce the effective surface area of the electrode. This has the effect of reducing the capacitance of the sensor over time. Both of the above effects have the net effect of changing the output of the sensor over its useful life.

[0058] Figure 1A and 1B FIG. 6 shows a schematic diagram of a representative embodiment of a capillary-constrained electrochemical sensor 10 of the devices, systems, and methods of the present disclosure. The sensor 10 includes a housing 20 having a gas inlet 30 in the form of a capillary for one or more target gases or analyte gases to enter the sensor 10. As its name indicates, a capillary-constrained sensor such as sensor 10 uses a very small inlet hole 30 (i.e., a capillary) that has a common or typical aspect ratio (length: diameter or l:d) of approximately 100:1 (see, for example Figure 1C , which shows an axial and radial cross-sectional view of the inlet 30 and the cylindrical portion of the housing 20 surrounding it).

[0059] In Figure 1C , p 2 is the partial pressure of the target gas outside the inlet 30, p 1 is the partial pressure of the target gas at the inner opening of the inlet 30, c 2 is the concentration of the target gas outside the inlet 30, and c1 is the concentration of the target gas at the inner opening (or surface working electrode 50, which is essentially zero) of the inlet 30. The phenomenon commonly referred to as "normal capillary diffusion" is actually a special case of Graham's law of effusion. See, for example, Barrow, G.M.,: 《Physical Chemistry》 , 4th ed. New York, NY: McGraw-Hill (1979). Generally speaking, "diffusion" refers to the overall flow of a gas from a region of higher pressure (or partial pressure) or higher concentration through a porous wall or tube of very small diameter to a region of lower pressure or lower concentration. "Effusion" refers to the process of movement caused by the molecular flow through an orifice or membrane rather than the overall flow.

[0060] Capillary-constrained oxygen or O 2 sensors are the dominant O 2 sensors on the market. This dominance is most likely because many performance criteria are written in terms of volume-percentage (vol-%) O 2 concentration. Capillary-constrained O 2 sensors measure vol-% O2 , rather than relying on O 2 partial pressure (which varies with the total atmospheric pressure even at a constant vol-% O 2 concentration). In other words, regardless of the pressure, the capillary-restricted sensor responds only to the vol-% target gas in the sample. The output of the capillary sensor is provided by the following equation:

[0061]

[0062] This equation shows that the sensor output i lim depends directly on the dimensions d 2 / l of the capillary. D 0 is the diffusion coefficient of the target gas (e.g., O 2 ). In addition, the sensor output varies according to the square root of the temperature (T 1 / 2 , or approximately 0.17% per degree Celsius). In addition, v 1 / V (or the volume v 1 of the target gas divided by the volume V of the test environment sensed by the sensor) is the volume fraction of the target gas in the test environment (e.g., the volume of O 2 in the test atmosphere).

[0063] In various embodiments, the electrolyte-saturated core materials 40a, 40b, and 40c can separate the working electrode 50 within the sensor 10 from the reference electrode 70 and the counter electrode 80, and / or provide ionic conduction between them via the electrolyte 44 within the housing 20 and absorbed within the core materials 40a, 40b, and 40c. An electronic circuitry system 100 known in the art is provided, for example, to maintain the desired potential difference between the working electrode 50 and the reference electrode 70, change or pulsate the potential difference described herein, and process the output signal from the sensor 10. The sensor electrodes are placed to be connected to the electrical circuitry system 100 via a connector 90, which provides conductive electrical conductivity / connectivity through the housing 20.

[0064] In the illustrated embodiment, the working electrode 50 can be formed, for example, by depositing a first layer of electrocatalyst 54 on a gas diffusion membrane 52 (using catalyst deposition techniques known in the sensor art, for example). Although the sensor 10 can include a gas diffusion membrane 52 behind the capillary inlet 30, unlike the case of permeation or diffusion-limited sensors, 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 to support the electrocatalytic layer / surface 54 within the sensor 10. Gases are easily transferred or transported through the diffusion membrane 52 (e.g., via diffusion), but the electrolyte 44 cannot be easily transferred or transported through the diffusion membrane. The diffusion membrane 52 of the working electrode 50 can be attached (e.g., via heat sealing) to the inner surface of the top, cap, or lid 22 of the housing 20. A representative working electrode 50 can, for example, comprise platinum or platinum dispersed on carbon as the electrocatalyst layer 54. An acidic electrolyte such as H 2 SO 4 .

[0065] The electronic circuitry 100 includes, for example, a processor or controller system 102 that includes one or more processors or microprocessors to control various aspects of the operation of the sensor 10. A memory system 104 can be placed in operative or communicative connection with the processor system 102 and can store software for control, measurement, and / or analysis in the sensor 10. A user interface system 106 (including, for example, a display, speaker, etc.) can also be placed in operative or communicative connection with the processor system 102. A communication system 108 (such as a transceiver) can be placed in operative or communicative connection with the processor system 102 for wired and / or wireless communication. A power source 110 (e.g., a battery system and / or line power) can provide power to the electronic circuitry 100.

[0066] As Figure 1A and 1B shown, in multiple embodiments, an exhaust port 26 is formed in the sensor housing 20 that is in gas communication with the counter electrode 80. The exhaust port 26 allows O 2 generated at the counter electrode 80 to escape from the housing 20. The amount of O 2 generated is quite small (only a few nanoliters per second). However, over the lifespan of the sensor 10, the amount of O 2 generated can become quite substantial. Unless the sensor 10 is effectively vented, the pressure within the sensor housing 20 will increase and can disrupt the sensor signal or cause electrolyte leakage.

[0067] In several studies herein, using based on The sensors of an oxygen sensor (obtainable from MSA Safety Incorporated, Cranberry Township, Pennsylvania) were used to characterize the capillary-limited oxygen sensor. Oxygen sensors with a capillary diameter of 12 μm were tested for 6 months under different storage conditions. After calibration under ambient conditions, in one study group, the sensors were placed in a chamber at 25 °C and 10% relative humidity (r.h.). The ambient conditions used during calibration were approximately 22 °C and a relative humidity in the range of 40% to 50%. In another study group, after calibration under ambient conditions, the sensors were placed in a chamber at 25 °C and 85% r.h. All sensors were tested periodically for nitrogen baseline (i.e., the baseline in the absence of oxygen or 0 vol% oxygen output), 20.8 vol% oxygen output, and 10.4 vol% oxygen output. After storing in these chambers for approximately 2 months, the conditions were reversed, and the sensors that were previously kept under dry conditions were placed under humid conditions, and vice versa. Each sensor test was accompanied by a chronoamperometric pulse or interrogation test. Chronoamperometry refers to an electrochemical technique in which the potential of the working electrode is changed (e.g., stepped), and the resulting current is monitored over time. The electronic interrogation in this article occurs without applying a test gas with an analyte gas of known concentration or its analog from a container to the sensor. In multiple studies, the pulse or interrogation test included a 10 mV bias change for 1 second. The result of the voltage change is a current curve, from which representative parameters such as Baseline, MaxPeak, Area Under the Curve (AUC), and Signal Height (DeltaPeak) between the baseline and MaxPeak were determined. All values were corrected for their baseline values.

[0068] To study the effect of the working electrode size, the sensors tested included two different sizes of working electrodes with the same specific surface area. One group of sensors had working electrodes of standard size (diameter 0.19 inches or 4.83 mm), while the second group of sensors had larger working electrodes (diameter 0.312 inches or 7.92 mm). The results of the study on the working electrode size demonstrated two different groups in the pulse test response, as shown, for example, in Figure 2 As such, it was found that the working electrode size changes the absolute value of the current response during the pulse test but does not change the gas response. The gas response current is determined only by the capillary characteristics. The working electrode size affects the pulse pattern, but the conclusions drawn from the chronoamperometric data are independent of the working electrode size. Such studies indicate that the system response evaluation in this article is universal, and the devices, systems, and methods in this article allow for the prediction of the system behavior of multiple electrochemical O 2 sensing embodiments.

[0069] The predictive evaluation of pulse test or electronic interrogation data involves two steps and highlights new and revealing aspects of the system behavior of capillary-limited oxygen sensors. In general, all pulse parameters are strongly interconnected, and the prediction results are independent of the parameter selection, as shown, for example, in the matrix plot of Figure 3 As mentioned above, the evaluation of all environment-related data has not previously shown a detectable direct link between pulse data and the sensor environmental output in sensors that typically operate at relatively high power. However, in multiple embodiments of the devices, systems, and methods herein, the nitrogen baseline of the sensor (independent of the sensor state that varies with environmental conditions) is related to, for example, chronoamperometric pulse data and / or one or more parameters determined via other electrochemical characterization(s). The nitrogen baseline current in the absence of oxygen represents the background current of the electrochemical system of the sensor. This parameter depends on environmental conditions / usage history and varies predictably with the chronoamperometric response, as shown, for example, in Figure 4A .

[0070] Figure 4B shows the difference between the nitrogen baseline (i.e., the baseline in the absence of oxygen) and the environmental baseline (i.e., the baseline of 20.8 vol% oxygen or O 2 (which is the standard oxygen concentration in ambient air)). In the absence of oxygen (e.g., in an atmosphere of pure nitrogen or N 2 ), the current passing through the sensor is almost entirely a capacitive current driven by the double-layer process within the sensor. In the presence of oxygen, the sensor signal includes a combination of the capacitive "nitrogen baseline" signal and a signal due to the Faradaic reduction current. As shown in the studies herein, the capacitive nitrogen baseline current undergoes a detectable change with variations in environmental factors (such as humidity).

[0071] As mentioned above, the actual sensor reading or sensor output is a combination of its nitrogen baseline and an additional signal generated by the influence of incoming oxygen. The influence of oxygen entering the sensor is driven only by the capillary and is constant in the humidity variations that affect the nitrogen baseline (see, for example, Figure 5 ). Without being limited to any mechanism, the electrolyte concentration and local water content at the working and reference electrodes of the electrochemical sensor system are likely to affect the nitrogen baseline in terms of humidity and environmental conditions. This correlation is also visible in the environmental output of the sensors studied herein, which is a combination of the baseline and the oxygen influence (see, for example, Figure 6 ). Since the actual sensor reading is determined only by its actual current output, the correlations herein allow for the prediction of sensor reading variations based on chronoamperometry or other electrochemical evaluations (see, for example, Figure 7 , which shows the prediction of sensor readings based on the parameter AUC (mA 2) change in the sensor output change (vol%). The output change refers to the difference between the measured value of the parameter and the value determined during sensor calibration under the above environmental conditions. Thus, a reading change value of 0.0 vol% (no signal change) occurs at a parameter output change of 0.0.

[0072] Characterization of amperometric data (and / or other parameters measured after causing current flow) within a sensor state range (e.g., where changes in the sensor state are caused by environmental conditions such as relative humidity, temperature, etc.), as described in some embodiments herein, provides a predefined relationship between such parameters and changes in the state of the sensor. Such a change in state can be indicated, for example, by a change in the nitrogen baseline response (and thus the sensor output) of the sensor herein in response to a change in the sensor state caused by environmental conditions / usage history. The determined relationship between one or more measured electrochemical parameters and the sensor output / response at varying sensor states can be stored in the memory system of the sensor (e.g., as an equation or algorithm, or stored in a look-up table). Suitable measured parameters are not limited to amperometric parameters, but can be parameters measured in any type of electrochemical measurement in which an electrical signal is applied to an electrochemical sensor to generate a current flow between the working electrode and the counter electrode of the electrochemical sensor via an electrolyte (e.g., in electrochemical impedance spectroscopy EIS, cyclic voltammetry or CV, etc.). One or more algorithms can further be stored in the memory system for execution by a processor system to correct the sensor's analyte gas (oxygen) concentration output based on one or more electrochemical parameters measured near real-time or simultaneously with the sensor measuring the analyte gas concentration (e.g., within its day, within its hour, within its minutes, or within its seconds), thereby generating a sensor output. In this regard, during the period (after manufacture) in which the sensor is in operation to measure the target analyte (oxygen), one or more parameters, such as amperometric parameters, are measured. As described above, in multiple embodiments, the choice of parameter is not critical since various parameters provide similar or identical analytical data. For example, referring to Figure 7 , data on the output reading change according to amperometry or other parameters can be stored in the memory (e.g., at the time of manufacture - e.g., identified within the sensor state range), and applied to the sensor output based on simultaneous measurements of the amperometric parameter and / or another electrochemical parameter. In this regard, the sensor device displays a certain output value, which can be calculated using the sensitivity and nitrogen baseline stored as described above. The predefined characterization data determined in the methods herein can be used to calculate and / or adjust the output value determined in the calculation to provide a more accurate output value.

[0073] A predetermined characterization or relationship between a sensor state / output reading change and a (one or more) chronoamperometric current or other electrochemical parameter can be determined, for example, for an individual sensor or one or more sensors representative of a class of similar or like sensors. As used herein, the term "similar sensor" or "like sensor" refers to sensors having the same or similar design parameters (e.g., the same or similar electrodes, electrolytes, etc.). As described herein, the predetermined characterization can be determined based on changes in the nitrogen baseline response or environmental response under a change in the induced sensor state. Alternatively, one or more mathematical models can be used to determine the predetermined characterization, for example, based on the design parameters of the sensor or sensor class and the characterization of relationships developed from theoretical and / or experimental data.

[0074] Accordingly, the devices, systems, and methods herein provide prediction / correction of the readings of capillary-constrained oxygen sensors within relevant ranges and under practically available environmental conditions. In addition to improving the maintenance of sensor output accuracy, this functionality can be used for various improvements in oxygen sensing technology, including, for example, predictive maintenance, increased worker safety, reduced sensor downtime, and providing sensor operation under a wider range of environmental conditions.

[0075] A recent trend in the field of gas sensors is towards sensors that require less power. In sensors operating at relatively high power, the Faradaic current is relatively large compared to the environmentally driven changes in capacitive current. As described above, in sensors operating at relatively high power, it is more difficult to detect changes in capacitive current that represent a small fraction of the environmental output current. As the sensor current associated with the smaller capillaries in capillary-constrained gas sensors typically decreases, the relative influence of the capacitive nitrogen baseline increases. The change in the capacitive baseline becomes large enough such that the change in the sensor output due to environmental changes is significant. In the case of a standard relatively high-power capillary-constrained oxygen sensor, the environmental output can be, for example, in the range of about 300 μA to about 250 μA. In multiple embodiments of the sensors herein, the environmental current output is not greater than 300 μA, not greater than 250 μA, not greater than 150 μA, not greater than 100 μA, not greater than 80 μA, or not greater than 30 μA. Generally, the lower the environmental current output of the sensor, the greater the percentage of the capacitive current in that output due to environmental changes. Although, as Figure 6 shown, the effect of the capacitive current change with environmental conditions can be observed in the environmental output of the sensor, given the larger percentage of the total signal associated with the capacitive current change in the case of measuring the nitrogen baseline signal, studying the predetermined characterization of this change measured within the sensor state range may provide better characterization results.

[0076] The apparatus, system, and method of the present disclosure can be used in conjunction with relatively high-power capillary-constrained oxygen sensors. However, the electronics of such sensors (e.g., high-power, low-noise potentiostats) must provide an appropriate signal-to-noise ratio to accurately and reproducibly determine the effects of the capacitive current variations described herein.

[0077] In summary, in the apparatus, system, and method of the present disclosure, a characterization of the change in the response of a sensor (e.g., as represented by a change in a nitrogen baseline value) under a change in the sensor state (which can be caused, for example, by a change in the usage history or environmental conditions) is determined. In this regard, a characterization or a predetermined characterization of a parameter determined in an electronic interrogation provides a relationship between the parameter and the response of the electrochemical sensor in a changed state of the electrochemical sensor. Electrochemical parameters are measured, for example, in a pulse test / electronic interrogation where the energy to the working electrode of the electrochemical sensor is changed. The predetermined characterization is used to modify or correct a sensor output reading or value based on a relationship or comparison of the predetermined characterization with a simultaneous measurement of the electrochemical parameter. Thus, the sensor output reading or value can be adjusted or corrected for a change in the sensor state caused by, for example, the effects of a change in environmental conditions or usage history.

[0078] The foregoing description and drawings set forth several representative embodiments of the present disclosure. Of course, various modifications, additions, and alternative designs will become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope of the present disclosure as indicated by the appended claims rather than the foregoing description. All variations that fall within the meaning and scope of the claims are intended to be embraced within their scope.

Claims

1. A method of operating a gas detection device, the gas detection device comprising a capillary-constrained electrochemical sensor (10), the capillary-constrained electrochemical sensor having an analytical response to oxygen, the electrochemical sensor comprising: a housing (20), the housing including a capillary (30) through which gas diffuses from the environment into the housing (20); a working electrode (50) within the housing (20); a counter electrode (80) within the housing (20); and an electrolyte (44) within the housing (20) in ionic contact with the working electrode (50) and the counter electrode (80), the method comprising: applying an electrical signal to the electrochemical sensor (10) to generate a current flow between the working electrode (50) and the counter electrode (80) via the electrolyte (44); measuring a parameter of the response of the electrochemical sensor (10) to the electrical signal, comparing the measured parameter with a predetermined characterization of the parameter, wherein the predetermined characterization of the parameter provides a relationship between the parameter and the response of the electrochemical sensor (10) in a varying state of the electrochemical sensor (10); and determining an output value of the gas detection device based on the output signal of the electrochemical sensor when sensing oxygen in the surrounding environment and the comparison of the measured parameter with the predetermined characterization.

2. The method according to claim 1, further comprising: operating the electrochemical sensor (10) in a sensing mode, wherein optionally the output signal is generated, the output signal preferably representing the oxygen concentration in the environment; and / or operating the electrochemical sensor (10) in an interrogation mode, during which the electrochemical sensor (10) is optionally electronically interrogated by applying the electrical signal to the electrochemical sensor (10), and the measured parameter is measured in the interrogation mode.

3. The method according to claim 1 or 2, wherein the gas detection device further comprises a control system (100), the control system comprising a processor system (102) and a memory system (104), wherein optionally the working electrode (50) is operatively connected to the control system (100), and / or the counter electrode (80) is operatively connected to the control system (100), and / or the memory system (104) includes one or more algorithms stored therein and executable by the processor system (102) to perform one or more actions of the method.

4. The method according to one of the preceding claims, wherein the predetermined characterization is stored in a memory during manufacturing.

5. The method according to one of the preceding claims, wherein the parameter is a chronoamperometric parameter.

6. The method according to claims 3 to 5, wherein the parameter is the maximum peak, area under the curve, minimum peak, peak-to-peak value and / or area under the reverse curve of the response of the electrochemical sensor to the electrical signal applied in the interrogation mode, or a function of any of the foregoing.

7. The method according to any one of claims 1 to 6, wherein the predetermined characterization is determined in a changing state of the electrochemical sensor (10).

8. The method according to claim 7, wherein the changing state of the electrochemical sensor (10) is caused by environmental conditions.

9. The method according to one of the preceding claims, wherein the predetermined characterization is determined based on a baseline response of the electrochemical sensor (10) in the absence of oxygen.

10. The method according to claim 9, wherein the baseline response of the electrochemical sensor (10) in the absence of oxygen is determined in a nitrogen atmosphere.

11. The method according to any one of the preceding claims, wherein the ambient current output of the electrochemical sensor (10) is less than 300 μA, optionally less than 150 μA, or optionally less than 30 μA.

12. A gas detection device, comprising: a control system (100), the control system comprising a processor system (102) and a memory system (104), and an electrochemical sensor (10), the electrochemical sensor having an analytical response to oxygen, comprising: a housing (20), the housing comprising a capillary (30) through which gas diffuses from the environment into the housing (20); a working electrode (50) within the housing (20) and operably connected to the control system (100); a counter electrode (80) within the housing (20) and operably connected to the control system (100); and an electrolyte (44) within the housing (20) and in ionic contact with the working electrode (50) and the counter electrode (80), the control system (100) being configured by software executed by the processor system (102) stored in the memory system (104) to: apply an electrical signal to the electrochemical sensor (10) to generate a current flow between the working electrode (50) and the counter electrode (80) through the electrolyte (44); measure a parameter of the response of the electrochemical sensor (10) to the electrical signal; compare the measured parameter with a predetermined characterization of the parameter, wherein the predetermined characterization of the parameter provides a relationship between the parameter and the response of the electrochemical sensor (10) in a changing state of the electrochemical sensor (10); and determine an output value of the gas detection device based on the analytical response of the electrochemical sensor (10) when sensing oxygen in the surrounding environment and the comparison of the measured parameter with the predetermined characterization.

13. The device according to claim 12, wherein the control system (100) is further configured to operate the electrochemical sensor (10) in a sensing mode, wherein an output signal is optionally generated, which preferably represents the oxygen concentration in the environment; and / or to operate the electrochemical sensor (10) in an interrogation mode, during which the electrochemical sensor (10) is electronically interrogated, optionally by applying the electrical signal to the electrochemical sensor (10), and the parameter to be measured is measured in the interrogation mode.

14. The device according to claim 12 or 13, wherein the predetermined characterization is stored in the memory system during manufacturing.

15. The device according to any one of claims 12 to 14, wherein the parameter is a chronoamperometric parameter.

16. The device according to any one of claims 13 to 15, wherein the parameter is the maximum peak, area under the curve, minimum peak, peak-to-peak value, and / or area under the reverse curve of the response of the electrochemical sensor (10) to the electrical signal applied in the interrogation mode, or a function of any of the above.

17. The device according to any one of claims 12 to 16, wherein the ambient current output of the electrochemical sensor (10) is less than 300 μA, optionally less than 150 μA, or optionally less than 30 μA.

18. A method of characterizing the change in the response of an electrochemical sensor (10) in a changing state of the electrochemical sensor (10), the electrochemical sensor (10) being capillary-restricted and having an analytical response to oxygen, the electrochemical sensor (10) comprising: a housing (20) including a capillary (30) through which gas diffuses from the environment into the housing (20); a working electrode (50) within the housing (20); a counter electrode (80) within the housing (20); and an electrolyte (44) within the housing (20) in ionic contact with the working electrode (50) and the counter electrode (80), the method comprising: determining a predetermined characterization that provides a relationship between a parameter measured when an electrical signal is applied to the electrochemical sensor (10) to generate a current flow between the working electrode (50) and the counter electrode (80) via the electrolyte (44) and the response of the electrochemical sensor (10) in the changing state of the electrochemical sensor (10).

Images