Abstract:
A method of manufacturing an electrochemical sensing system is provided. The method includes forming a sensor with a first sensing element disposed on a sensor, the first sensing element configured to detect a target gas, disposing a second sensing element on the sensor, the second sensing element configured to detect the target gas, and coupling a protective feature to the second sensing element, the protective feature configured to prevent non-target gases from contacting the second sensing element. The sensor is configured such that if the first sensing element generates a current exceeding a first threshold current value and the second sensing element does not exceed a second threshold current value it is determined that the first sensing element is contaminated and a restoration protocol is performed on the first sensing element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from U.S. Provisional Patent Application No. 62/204,618 filed Aug. 13, 2015. The contents of the priority application are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The subject matter disclosed herein generally relates to electrochemical sensors and, more particularly, to state of health monitoring and restoration of electrochemical sensors. 
         [0003]    Electrochemical gas sensors are gas detectors that measure a concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the current that is generated. Electrochemical gas sensors are normally designed to operate in a diffusion limited mode. This is normally achieved by using a capillary or membrane, which limits gas access in a well-defined and repeatable way. The sensor is designed such that the capillary or membrane provides the limiting factor. For example, the gas sensing electrode is designed to have sufficient activity reserve that the actual activity of the electrode can generally be ignored (since it is much greater than required to consume the available gas). Under certain conditions, however, sensors can deviate from the ideal diffusion limited behavior: for example, if the catalytic activity of the electrode degrades significantly, or if blocking or flooding occurs, then the sensor response may deviate from the predetermined relationship between concentrations of species to be detected and an analog output. 
         [0004]    In addition to such faults which can result in a change in the level of gas response, certain faults can result in a reduction in the speed of response, even though the steady state response remains unchanged: for example, if the membrane electrode assembly becomes partially flooded or poisoned this may result in a slow response, and in some cases a reduction in steady state response. The same is true if the catalytic activity of the electrode is reduced, which can be a particular problem for sensors with low activity reserve. 
         [0005]    An example of a gas that may be monitored, and related sensors which may be subject to faults, is low global warming potential (LGWP) refrigerants that may be used in HVAC systems. Various LGWP refrigerants are mildly flammable, and thus leak detection is desired. Electrochemical sensors have been successfully applied for toxic gas sensing. Passive fault mitigation methods such as adsorption by activated carbon have been used successfully to protect CO sensors from poisoning, i.e., electrode poisoning or saturation or coverage by an undesirable chemical. Such a method can be ineffective when the targeted species adsorbs on the adsorbent, resulting in substantial interference of the sensing process or completely defeat the detectability of the sensor. The electrochemical sensor failure mechanisms resulting from catalyst deactivation due to ambient volatile species can be extremely difficult to detect by the sensors, particularly when the sensors are deployed for leak detection expected to occur rarely. This is because during catalyst deactivation a sensor can generate a similar response as if a leak is detected and low cost electrochemical sensors may lack the ability to determine the identification of the species detected. However, it would be necessary to deploy a fail-safe operation of the sensors for safety monitoring, e.g., for leak detection of flammable refrigerants. Therefore, it is may be desirable to enable an electrochemical sensor to examine the state of health of the sensor pertaining to catalyst activity and restore the sensor&#39;s activity when the state of health is compromised due to exposure to active species. 
       SUMMARY 
       [0006]    According to one embodiment, a method of manufacturing an electrochemical sensing system is provided. The method includes forming a sensor with a first sensing element disposed on a sensor, the first sensing element configured to detect a target gas, disposing a second sensing element on the sensor, the second sensing element configured to detect the target gas, and coupling a protective feature to the second sensing element, the protective feature configured to prevent non-target gases from contacting the second sensing element. The sensor is configured such that if the first sensing element generates a current exceeding a first threshold current value and the second sensing element does not exceed a second threshold current value it is determined that the first sensing element is contaminated and a restoration protocol is performed on the first sensing element. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the target gas is a low global warming potential gas. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments may include configuring at least one of the first sensing element and the second sensing element to be biased with a voltage. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that both the first sensing element and the second sensing element are configured to be biased with a respective first voltage and a respective second voltage. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments may include configuring the sensor to signal the presence of the target gas. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the target gas is a first target gas, the method further comprising forming a third sensing element on the sensor, the third sensing element configured to detect a second target gas. 
         [0012]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first target gas is a low global warming potential gas and the second target gas is carbon monoxide. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments may include configuring the sensor to record a state of health after determining the first sensing element has been contaminated. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the restoration protocol comprises applying a predetermined biasing voltage to the first sensing element. 
         [0015]    According to another embodiment, an electrochemical sensing system is provided. The system includes a first sensing element disposed on a sensor and configured to detect a target gas, a second sensing element disposed on the sensor and configured to detect the target gas, and a protective feature coupled to the second sensing element and configured to prevent non-target gases from contacting the second sensing element. If the first sensing element generates a current exceeding a first threshold value and the second sensing element does not exceed a second threshold value it is determined that the first sensing element is contaminated and a restoration protocol is performed on the first sensing element. 
         [0016]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the target gas is a low global warming potential gas. 
         [0017]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that at least one of the first sensing element and the second sensing element is biased with a voltage. 
         [0018]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that both the first sensing element and the second sensing element are biased with a respective first voltage and a respective second voltage. 
         [0019]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the target gas is a first target gas, the sensor further comprising a third sensing element configured to detect a second target gas. 
         [0020]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first target gas is a low global warming potential gas and the second target gas is carbon monoxide. 
         [0021]    According to another embodiment, an electrochemical sensing system is provided. The system includes a first sensing element disposed on a sensor and configured to detect a first group of target gases and a group of contaminants, a second sensing element disposed on the sensor and configured to be active to the first group of target gases, a third sensing element disposed on the sensor and configured to be active to at least the first group of target gases, the group of contaminants, a second group of target gases, and a third group of target gases, and a fourth sensing element disposed on the sensor and configured to detect the first of target gases and the third group of target gas. The system further includes a first protective feature coupled to the second sensing element and configured to prevent non-target gases from contacting the second sensing element and a second protective feature coupled to the fourth sensing element and configured to prevent the group of contaminants and the second group of target gases from contacting the fourth sensing element. If the second sensing element and the fourth sensing element each do not generate a current exceeding a respective second threshold value and fourth threshold value and the first sensing element and the third sensing element each generate a current exceeding a respective first threshold value and a third threshold value, it is determined that the third sensing element is contaminated. 
         [0022]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the third sensing element is configured to have a restoration protocol performed thereon 
         [0023]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that the restoration protocol comprises applying a predetermined voltage to the third sensing element. 
         [0024]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that at least one of the third sensing element and the fourth sensing element is biased with a voltage. 
         [0025]    In addition to one or more of the features described above, or as an alternative, further embodiments may include that both the third sensing element and the fourth sensing element are biased with a respective first voltage and a respective second voltage. 
         [0026]    Technical effects of embodiments of the present disclosure include providing an electrochemical sensor that has efficient state of health monitoring and restoration properties. Further technical effects include applying a predetermined pulse voltage to restore the sensing capability of the electrochemical sensor. Further technical effects include electrochemical gas sensors that are configured to determine when catalyst deactivation has occurred and perform a restoration protocol as needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0028]      FIG. 1  is a schematic illustration of a sensor in accordance with a non-limiting embodiment of the present disclosure; 
           [0029]      FIG. 2  is a flow chart of a process in accordance with a non-limiting embodiment of the present disclosure; 
           [0030]      FIG. 3  is a flow chart of a process in accordance with an alternative non-limiting embodiment of the present disclosure; and 
           [0031]      FIG. 4  is a chart of logic for determining the state of health of a sensor configured in one or more non-limiting embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    As shown and described herein, various features of the disclosure will be presented. Various embodiments may have the same or similar features and thus the same or similar features may be labeled with the same reference numeral, but preceded by a different first number indicating the figure to which the feature is shown. Thus, for example, element “a” that is shown in FIG. X may be labeled “Xa” and a similar feature in FIG. Z may be labeled “Za.” Although similar reference numbers may be used in a generic sense, various embodiments will be described and various features may include changes, alterations, modifications, etc. as will be appreciated by those of skill in the art, whether explicitly described or otherwise would be appreciated by those of skill in the art. 
         [0033]    Electrochemical (“EC”) gas sensors are gas detectors that measure a concentration or determine the presence of a target gas by oxidizing or reducing the target gas at an electrode (e.g., a sensing element) and measuring or detecting a resulting current. The magnitude of the current is governed by how much of the target gas is oxidized at the working electrode portion of the sensor. Electrochemical sensors are usually designed so that the gas supply is limited by diffusion and thus the output from the sensor is linearly proportional to the gas concentration. The linear output of an electrochemical sensor is one of the advantages over other sensor technologies. A linear output allows for precise measurement of low concentrations of a target gas and also allows for simple calibration. Further, electrochemical sensors enable changing of a diffusion barrier or filter to tailor the sensor to be selective to a particular target gas concentration range. 
         [0034]    Although not limiting herein, low global warming potential (“LGWP”) refrigerants may be one category of gases that are desired to be monitored by electrochemical sensors. LGWP refrigerants may be mildly flammable and thus leak detection may be highly desirable. It may be desirable to employ the same or similar electrochemical sensors that are currently used to sense toxic household gases, such as carbon monoxide, as LGWP refrigerants become more ubiquitous. One challenge of making such a combination EC sensor is that traditional EC sensors are unable to selectively identify gas species, and false alarms may result. Detecting sensor malfunctioning due to reactions of gaseous species is also impossible for traditional EC sensors due to the lack of identification ability. It is known that catalyst (i.e., sensing element) contamination or poisoning by volatile organic compounds (“VOC”) in the ambient atmosphere that is around the sensor is a dominant mechanism that may cause failure or faults in the electrochemical sensors. When an EC sensor is deactivated, it may go undetected, leading to failure of the system and the risk of undetected toxic gas or flammable refrigerant leak. A failsafe EC sensor would thus require prevention, detection, and mitigation of catalyst deactivation. 
         [0035]    Preventative measures or passive mitigation methods have been used to prevent contamination of a sensing element. For example, activated carbon may be used to target contaminants. This method can be very successful when the sensor is detecting only one gas species, and that species has no adsorption on the adsorbent. However, the use of an adsorbent may interfere with the detection of LGWP refrigerant, due to entrapment of some LGWP refrigerants, resulting in a delayed and/or weaker response of the sensor. Therefore, it may be necessary to have the ability to detect sensor deactivation and, to restore a deactivated sensor when EC sensing is used for refrigerant detection. 
         [0036]    Further, LGWP sensors may operate at higher voltages than other types of sensors, i.e., continuously biased, which may cause the LGWP sensors to be more susceptible to a large variety of contaminants that may result in sensor contamination. Sensor state of health determination pertaining to EC sensing is an important aspect of the present disclosure. Although described herein with respect to an LGWP sensor, it will be appreciated by those of skill in the art that the embodiments disclosed herein may be used for any types of sensors, including, but not limited to refrigerant sensors, carbon monoxide sensors, hydrogen sulfide sensors, and/or any other type of electrochemical sensor. 
         [0037]    Embodiments described herein enable an electrochemical sensor that has been deactivated by a contaminant, e.g., a VOC, to be recovered by applying a pulse voltage at a sufficiently high level to refresh or restore the sensing element, e.g., restore the catalyst of the sensor. That is, a pulse voltage may be used to convert and remove a contaminant on the surface of the sensing element and to restore the sensor to a fully operational state to detect a target gas. 
         [0038]      FIG. 1  shows a non-limiting embodiment of an electrochemical sensor that may employ embodiments disclosed herein. Sensing system  100  may include two sensing elements: a first sensing element  102  and a second sensing element  104  configured on a sensor  106 . In one non-limiting embodiment, the first sensing element  102  and the second sensing element  104  may be identical with respect to composition and may be placed by printing or laminating onto an ion transport medium (separator) such as an ion conduction polymer or liquid electrolyte flooded porous substrate or other sensor structure. A counter electrode (not shown) may be placed on the opposite side of the separator. The first sensing element  102  may be a state of health sensing element and the second sensing element  104  may be configured to detect and/or sense a target gas, i.e., a primary sensing element. The first and second sensing elements  102 ,  104  may be electrochemical sensing elements as known in the art. For example, the first and second sensing elements  102 ,  104  may be configured as electrodes and associated electrolytes configured to generate a current when an electrochemically active gas is present. 
         [0039]    The first sensing element  102  includes a first aperture  108  configured to allow gases to pass through and interact with the first sensing element  102 . The second sensing element  104  includes a second aperture  110  configured to allow only selected or predetermined gases to pass through and interact with the second sensing element  104 , such as a target gas. As shown, a protective feature  112  is coupled to the second aperture  110  to filter or absorb gases such that only predetermined or selected gases interact with the second sensing element  104 . The protective feature  112  may be configured as an adsorbent, a barrier, a filter, or other device or structure configured to allow some gases to pass therethrough and to prevent other gases from passing therethrough. 
         [0040]    In some embodiments, the protective feature  112  may be configured to allow only a target gas to pass therethrough and interact with the second sensing element  104 . That is, in some embodiments, the protective feature  112  may be configured or selected to absorb or prevent all other gases from interacting with the second sensing element  104 . In some embodiments, the protective feature  112  may adsorb sensor contamination gases, such as VOCs, and prevent the contamination gases from interacting with the second sensing element  104 . 
         [0041]    The first sensing element  102  is configured with a first sensing circuit  114 . The first sensing circuit  114  includes first processing circuitry  116  and a first load  118 . When a gas such as the target gas contacts and/or reacts with the first sensing element  102  a current may be generated in the sensing circuit  114  and detected by the processing circuitry  116 . The current generated may be proportional to the amount of gas present in the atmosphere. Thus, the first sensing circuit  114  may be used to detect the presence of a target gas. In some embodiments a threshold value may be set such that false alarms or natural concentrations may be avoided. As used herein, a threshold value may be zero or any predetermined value. Depending on the composition of the first sensing element  102 , other gases, such as sensor contamination gases, may also interact with the first sensing element  102  and generate current in the first sensing circuit  114 . 
         [0042]    The second sensing element  104  is similarly configured with a second sensing circuit  120 . The second sensing circuit  120  includes second processing circuitry  122  and a second load  124 . When a gas such as the target gas is present, it may pass through the protective feature  112  of the second sensing element  104  and interact with the second sensing element  104  to generate a current at the same level as generated in the first sensing element  102 . However, as noted, the protective feature  112  may be configured to prevent other gases from interacting with the second sensing element  104 . That is, the second sensing element  104  will only have a generated current when the target gas is present, and other gases will not reach and/or react with the second sensing element  104  to generate a current. Again, in some embodiments a threshold value may be set such that false alarms or natural concentrations may be avoided. 
         [0043]    Each of the first sensing circuit  114  and the second sensing circuit  120  may be connected to a controller, processor, or other device, e.g., controller  126 . The controller  126  may be a processing device having a processor, memory, and other elements and/or components and may be connected to other devices such as alarms, displays, etc. In some non-limiting embodiments, the controller  126  may be configured within the sensor  106  and may be electrically connected to the first sensing circuit  114  and the second sensing circuit  120 . 
         [0044]    A comparison between response of the first sensing circuit  114  and response of the second sensing circuit  120  may be made, e.g., at the controller  126 . If both the first sensing circuit  114  and the second sensing circuit  120  detect a current above the threshold, it may be determined that the target gas is present and appropriate action may be taken, e.g., sound an alarm, activate an emergency system, etc. However, if the first sensing circuit  114  detects a current above the threshold but the second sensing circuit  120  does not, then it may be determined that a contamination gas is present and it may be determined that the first sensing element may be potentially contaminated if extended exposure to that species occurs without reversing the effects. Appropriate action may then be taken. For example, a restoration process or protocol may be initiated to restore the first sensing element  102  after being contaminated. In some embodiments, the controller  126  may be in wireless communication with one or more components of the sensing system  100  and may be physically separate therefrom. 
         [0045]    As will be appreciated by those of skill in the art, variations on the sensing system  100  may be made without departing from the scope of the present disclosure. For example, in other embodiments, one or both of the loads  118 ,  124  may be replaced by biasing voltages that are configured to bias the respective sensing element. Further, in some embodiments, a counter-electrode may be electrically coupled to the sensor and/or one or both of the sensing elements. Further, in some embodiments, the sensing element with the protective feature  112  may be the state of health sensing element and the sensing element without the protective feature may be the primary sensing element, i.e., the reverse of the above described configuration. Furthermore, in some embodiments, the protective feature may be omitted. In some embodiments, one of the sensing elements may be biased and the other sensing element may be unbiased. 
         [0046]    Turning now to  FIG. 2 , a non-limiting embodiment of a process in accordance with the present disclosure is shown. Process  201  is a state of health (“SOH”) monitoring and regeneration process for an electrochemical sensor and may be used by a sensor such as sensing system  100  of  FIG. 1 , where a combination of sensing elements described as sensing elements  1  and  2  in  FIG. 4  is included. Process  201  may be performed by appropriate circuitry, components, etc. that are configured to monitor the presence of a target gas in an atmosphere. For example, the process may be performed using one or more sensing systems similar to that shown in  FIG. 1  along with appropriate processors, memory, controllers, software, applications, and/or other hardware, components, and/or elements as known in the art. 
         [0047]    A sensor health state check may be initiated (step  203 ). The initiation may be automatic, prompted by software, manually initiated, or otherwise initiated. The health state check may involve comparing responses of sensing elements of the sensing system. As such, it may be determined if a first sensing element, e.g., an unprotected sensing element, generated a current that was greater than a first threshold value (step  205 ). If the first sensing element did not exceed the first threshold, it may be determined that there has been no change in the state of health of the sensor (step  207 ). Appropriate circuitry and/or processing equipment may record that no change in health has occurred (step  209 ), and the process may restart or perform a loop beginning with step  203 . Such recording may be made in a memory that may provide for logging or data collection/retention of the state of health of the sensor that is monitored. 
         [0048]    If it is determined that the first sensing element has generated a current that exceeded the first threshold (step  205 ), the logic process may continue to analyze the response characteristics of the second sensing element. It is next determined whether the second sensing element has generated a current that exceeded a second threshold value (step  211 ). If it is determined that the second threshold is exceeded, it may be determined that a target gas is present (step  213 ). That is, because the first sensing element and the second sensing element are the same and the second sensing element includes a protective feature that only permits the target gas to interact with the second sensing element, it may be positively determined that the target gas is present. Accordingly, an appropriate action, such as signaling the presence of the target gas (step  215 ), may be performed. The signal may include visual alerts, audible alerts, digital notifications, activation of emergency systems, etc., as known in the art. Additionally, when the target gas is detected the event may be logged or recorded (step  217 ) 
         [0049]    However, if it determined that the second sensing element has not exceeded the second threshold (step  211 ) but the first sensing element has exceeded the first threshold, it may be determined that a contamination gas is present (step  219 ). Contaminants may include gases that may poison or damage the ability of the sensing system to detect the target gas. When it is determined that a contamination gas is present, the state of the health of the sensing system may be recorded or logged, i.e., it may be recorded that a contaminant was present (step  221 ). If a contaminant is determined to be present (step  219 ) and the first sensing element is thus contaminated, the first sensing element may be required to be regenerated or restored such that it may return to a healthy state. Thus, a restoration protocol or process may be performed (step  223 ). The restoration protocol may involve subjecting the first sensing element to a biasing voltage sufficient to burn off or otherwise remove the contaminant from the first sensing element. Subsequently, the restoration may be recorded (step  225 ). 
         [0050]    In some non-limiting embodiments, steps  203 ,  207 , and  209  may be omitted, and the process may begin at step  205  when the first sensing element exceeds the first threshold. That is, when the first sensing element exceeds the first threshold, the process  201  is initiated such that a comparison between the first sensing element and the second sensing element is made. 
         [0051]    Turning now to  FIG. 3 , an alternative, non-limiting embodiment of a process in accordance with the present disclosure is shown. The process  301  shown in  FIG. 3  is substantially similar to that shown in  FIG. 2 , but a third sensing element is configured as part of the sensing system. Such configuration may enable the detection of more than one target gas, while allowing for determining when a restoration or regeneration of one or more sensing elements may be required. 
         [0052]    A non-limiting example of a sensing system that may be used to perform the process  301  may be one configured with an open, unbiased first sensing element (i.e., no protective feature (non-filtration, non-adsorption) and no biasing voltage), a protected, unbiased second sensing element (i.e., protective feature and unbiased electrode), and a biased, open third sensing element (i.e., no protective feature and biasing voltage). Each of the sensing elements may have identical or different catalyst composition, but configured differently with respect to the presence of a protective feature and/or biasing of the sensing element, i.e., the application of a voltage to the sensing element. 
         [0053]    In process  301 , a sensor health state check may be initiated (step  303 ) similar to that described above. The health state check may involve comparing responses of the sensing elements of the sensing system. As such, it may be determined if the first sensing element generated a current that was greater than a first threshold value (step  305 ). 
         [0054]    If it is determined that the first sensing element has generated a current that exceeded the first threshold (step  305 ), the process may continue to the second sensing element. It then is determined whether the second sensing element has generated a current that exceeded a second threshold value (step  311 ). If it is determined that the second threshold is exceeded, it may be determined that a first target gas is present (step  313 ). That is, because the first sensing element and the second sensing element are the same and the second sensing element includes a protective feature that only permits the first target gas to interact with the second sensing element, it may be positively determined that the first target gas is present. Accordingly, an appropriate action, such as signaling the presence of the first target gas (step  315 ), may be performed. The signal may include visual alerts, audible alerts, digital notifications, emergency actions, etc., as known in the art. Additionally, when the first target gas is detected the event may be logged or recorded (step  317 ). 
         [0055]    However, if it determined that the second sensing element has not exceeded the second threshold (step  311 ), and the first sensing element has exceeded the first threshold, it may be determined that a contamination gas is present (step  319 ). Contaminants may include gases that may poison or damage the ability of the sensing system to detect the target gases. The state of the health of the sensing system may be recorded or logged, i.e., it may be recorded that a contaminant is present (step  321 ). If a contaminant is determined to be present (step  319 ) the first sensing element may be required to be regenerated or restored such that it may maintain a healthy state. Thus, a restoration protocol or process may be performed (step  323 ). The restoration process may involve subjecting the first sensing element to a biasing voltage sufficient to convert or otherwise remove the contaminant from the first sensing element. 
         [0056]    Still referring to process  301 , if the first sensing element did not exceed the first threshold (step  305 ), the process  301  may continue to the third sensing element. A determination is made whether the third sensing element has generated a current that is greater than a third threshold (step  327 ). If the third sensing element is determined to have exceeded the third threshold, it may be determined that a second target gas is present (step  329 ). Accordingly, an appropriate action, such as signaling the presence of the second target gas (step  331 ), may be performed. The signal may include visual alerts, audible alerts, digital notifications, emergency actions, etc., as known in the art. When the second target gas is detected the event may be logged or recorded (step  333 ). 
         [0057]    If there is no response in the first sensing element and no response in the third sensing element, i.e., no induced currents, it may be determined that there has been no change in the state of health of the sensing system (step  307 ). Appropriate circuitry and/or processing equipment may record that no change in health has occurred (step  309 ). Such recording may be made in a memory that may provide for logging of the state of health of the sensing system that is monitored. 
         [0058]    Turning now to  FIG. 4 , a table providing one non-limiting example of a four-sensing-element sensing system is shown. The first column provides the sensing element number, the second column provides the sensing element configuration (e.g., biased, protective feature, etc.), and columns three through six provide the gas and response of the associated sensing element where “Y” represents positive response and “N” represents no response from the respective sensing/SOH elements. The above described processes, and/or variations thereon, may be performed with a sensing system or configured with the elements shown in  FIG. 4 . Further, those of skill in the art will appreciate that more or fewer sensing elements and sensing element configurations may be employed without departing from the scope of the present disclosure. Moreover, it will be appreciated by those of skill in the art that the unprotected or “open” sensing elements may require restoration as described above. 
         [0059]    The first sensing element may be an unbiased sensing element with no protection, i.e., no protective feature. The second sensing element may be an unbiased sensing element with a protective feature. The third sensing element may be a biased sensing element with no protection, i.e., no protective feature. The fourth sensing element may be a biased sensing element with a protective feature. Thus, a sensing system configured with the four above sensing elements may be able to detect the presence of multiple target gases and/or determine when various sensing elements of the sensor may require to be regenerated, i.e., when contamination gases are present. 
         [0060]    For example, when all four sensing elements generate a current above a threshold set for each sensing element, a first target gas may be determined to be present and appropriate action may be taken (e.g., perform a signal or other alert regarding the first target gas). If, however, only the first and the third sensing elements generate a current above the respective thresholds and the second and fourth sensing elements do not exceed the respective thresholds, then it may be determined that a contamination gas is present and appropriate action may be taken, e.g., a restoration protocol may be carried out. Similar sensing element current generations or lack thereof may be appreciated from  FIG. 4 . Throughout any and all iterations, the system may be configured to log which gases are present and/or what action is taken and when. Thus, a historical log or record may be maintained by or for the sensing system. 
         [0061]    As will be appreciated by those of skill in the art, various combinations or changes, substitutions, and/or additions may be made with respect to the sensing element configurations or numbers thereof without departing from the scope of the present disclosure. For example, the chart shown in  FIG. 4  may be employed to configure a sensing system having any desired combination of sensing elements. 
         [0062]    Advantageously, embodiments described herein provide an electrochemical gas sensor or sensing system configured to monitor the state of health of the sensor or sensing system and determine when a restoration process should be performed on one or more sensing elements of the sensor or sensing system. Further, advantageously, embodiments described herein enable multiple-sensing-element sensors that may be configured to detect multiple types of gases, ranging from multiple target gases to contaminating gases, and further enable determination of poisoning of one or more of the sensing elements. Additionally, restorative processes may be performed based on the various sensing elements in view of the processes disclosed herein. 
         [0063]    Further, advantageously, false alarms regarding a target gas may be eliminated. For example, if both a first and second sensing element are configured to detect a target gas, but the second sensing element has a protective feature as described herein, it may be possible to determine when the first sensing element has been contaminated with a gas or substance that may induce a current in the sensing element and thus potentially trigger a signal or alarm. However, because the second sensing element includes the protective feature, and thus not have an induced current, it may be deduced that the activation of the first sensing element was due to a contaminant that is not the target gas, and thus a false alarm may be avoided. 
         [0064]    Moreover, advantageously, embodiments disclosed herein enable a sensor to be configured to monitor for target gases for substantially the entire life of the sensor. That is, a regeneration protocol, which may prevent detection of a target gas, may only be performed when needed, and thus at all other times, the sensor may be able to detect a target gas. In other words, embodiments disclosed herein reduce the amount of downtime of a sensor due to restoration protocols performed on the sensor. 
         [0065]    While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. 
         [0066]    For example, although described and shown herein with respect to a single sensor configuration, those of skill in the art will appreciate that various other configurations of sensor(s) and/or sensing systems may be employed without departing from the scope of the present disclosure. For example, sensors having two or more sensing elements, however configured, may employ embodiments disclosed herein. Further, sensors may have sensing elements with or without protective features, and may be biased or unbiased, and still employ embodiments disclosed herein. Moreover, although described with respect to LGWP gases, those of skill in the art will appreciate that any target gas may be configured to be sensed and/or any contaminating gas may be configured to be monitored for by systems and processes disclosed herein. 
         [0067]    Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.