Operating a combustible gas sensor in a dynamic mode with a constant resistance set point

Abstract

A method of operating a sensing element, the sensing element including a heating element operably connected to an electronic circuitry, wherein the sensing element forms a resistive element in the circuitry of the electronic circuitry, the method comprising: in at least a first stage, activating the electronic circuitry to heat the sensing element to a temperature at which the sensing element responds to an analyte gas via an energy input to the heating element in a pulsed manner. A constant resistance set point is set for the sensing element and is variably controlled via the energy of the circuitry via a pulsed energy input to achieve the constant resistance set point. The method further includes measuring the response of the sensing element over time to the pulsed energy input.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 711,413, filed on December 11, 2019, the disclosure of which is incorporated herein by reference. Background of the Invention

[0003] The following information is provided to assist the reader in understanding the technology disclosed below and the environments in which such technology can generally be used. Unless explicitly stated otherwise in this document, the terms used herein are not limited to any specific narrow interpretation. The references set forth herein can facilitate an understanding of the technology or its background. The disclosures of all references cited herein are incorporated by reference.

[0004] Catalytic or combustible (flammable) gas sensors have been used for many years, for example, to prevent accidents caused by the explosion of combustible or flammable gases. Generally, combustible gas sensors operate by the catalytic oxidation of combustible gases.

[0005] The operation of a catalytic combustible gas sensor is carried out by the electrical detection of the heat of reaction of the combustible gas on an oxidation catalyst, typically by a change in resistance. The oxidation catalyst generally operates at a temperature above 100 °C (and more typically above 300 °C) to catalyze the combustion of the analyte (e.g., methane detection is carried out in the temperature range of 350 to 600 °C). Therefore, the sensor must sufficiently heat the sensing element by resistive heating. In many combustible gas sensors, the heating and detection elements are one and the same and are composed of a platinum alloy because of its large resistance temperature coefficient and the associated large signal in the target / analyte gas. The heating element can be a helical coil of fine wire or a planar meander formed as a hot plate or other similar physical form. The heated catalyst is typically an active metal catalyst dispersed on a refractory catalyst substrate or support structure. Generally, the active metal is one or more noble metals, such as palladium, platinum, rhodium, silver, etc., and the support structure is a refractory metal oxide, including one or more oxides of, for example, aluminum, zirconium, titanium, silicon, cerium, tin, lanthanum, etc. The support structure may or may not have a high surface area (i.e., greater than 75 m 2 / g). The precursors of the support structure and the catalytic metal can be adhered to the heating element, for example, using thick - film or ceramic slurry techniques, in one step or multiple separate steps. The catalytic metal salt precursor can be heated, for example, to decompose it into the desired dispersed active metal, metal alloy, and / or metal oxide.

[0006] As shown in FIGS. 1A and 1B, many conventional combustible gas sensors, such as the sensor 10 shown, typically include an element, such as a platinum heating element wire or coil 20, encapsulated in a refractory material (e.g., alumina) bead 30, which bead 30 is impregnated with a catalyst (e.g., palladium or platinum) to form an active or sensing element, sometimes referred to as a p-element 40, a pellistor, a detector, or a sensing element. A detailed discussion of p-elements and catalytic combustible gas sensors including such p-elements can be found in Mosely, P.T. and Tofield, B.C., editors, Solid State Gas Sensors ( Solid State Gas Sensors) , Adams Hilger press, Bristol, England (1987). Combustible gas sensors are also reviewed in Firth, J.G. et al., Combustion and Flame ( Combustion and Flame) 21, 303 (1973) and Cullis, C.F., and Firth, J.G., editors, Detection and Measurement of Hazardous Gases ( Detection and Measurement of Hazardous Gases) , Heinemann, Exeter, 29 (1981).

[0007] The bead 30 will respond to phenomena other than catalytic oxidation that can alter its output (i.e., anything that changes the energy balance on the bead), thus introducing errors in the measurement of combustible gas concentration. Some of these phenomena are changes in ambient temperature, humidity, and pressure.

[0008] To minimize the effects of secondary effects on the sensor output, the oxidation rate of combustible gas can be measured, for example, based on the change in the resistance of the sensing element or p-element 40 relative to a reference resistance implemented in an inactive compensating element or p-element 50. These two resistances can be, for example, part of a measurement circuit, such as the Wheatstone bridge circuit shown in FIG. 1C. The output or voltage generated across the bridge circuit in the presence of combustible gas provides a measure of the combustible gas concentration. The characteristics of the compensating p-element 50 are typically matched as closely as possible to those of the active or sensing p-element 40. However, in many systems, the compensating p-element 50 may not carry a catalyst or may carry a deactivated or poisoned catalyst. Typically, changes in the characteristics of the compensating element caused by ambient conditions are used to adjust or compensate for similar changes in the sensing element.

[0009] The active or sensing p-element 40 and the compensating p-element 50 can be arranged, for example, within the bores 60a and 60b of the explosion-proof housing 70 and can be separated from the surrounding environment by a flame arrester (such as a porous metal frit 80). The porous metal frit 80 allows ambient gas to enter the housing 70 but prevents flammable gas in the surrounding environment from being ignited by the hot element. Such catalytic gas sensors are typically installed in instruments which, in some cases, must be portable or wireless and thus self-powered. Therefore, it is desirable to minimize the power consumption of the catalytic gas sensor.

[0010] The oxidation catalyst formed on the helical heater is commonly referred to as the p-element, while those formed on a hot plate (whether a microelectromechanical systems (MEMS) hot plate or a traditional larger hot plate) are sometimes referred to as the substrate. The oxidation catalyst formed on the MEMS heating element is sometimes referred to herein as the MEMS supported catalytic element. As described above, the sensing p-element or catalytically active hot plate can be paired with a heater of similar size that is coated with a material having a similar thermal conductivity to the active catalyst but no active sites. The inactive p-element or hot plate can be used to compensate for changes in ambient temperature, relative humidity, or background thermal conductivity not associated with combustible gas and is thus commonly referred to as a compensator. The matched pair of sensing and compensating elements can be assembled in a Wheatstone bridge configuration for operation and combustible gas detection, which requires both the detector and the compensator to operate at the same elevated temperature. The elevated temperature operation of the catalytic sensing element requires a large amount of power consumption. In the case of detecting combustible gas, power consumption is particularly a problem because the detection should be performed very frequently or continuously to ensure a safe environment. Portable instruments and wireless devices rely on battery systems for power.

[0011] In many currently available combustible gas sensors that include sensing and compensating beads, a third bead that requires very little power is included, sometimes referred to as a trigger or "sniffer bead". In many such sensors, the trigger bead does not need to provide a linear response and does not need to be resistant to positive offset temperature / humidity fluctuations. Due to the elimination of the limitations on linearity and resistance to positive temperature and humidity fluctuations, the size and power limitations of the "trigger" bead may be reduced compared to the detector bead.

[0012] Existing embodiments of combustible sensors have used steady-state constant voltage Wheatstone bridges or analog Wheatstone bridges to achieve combustible gas detection. Additionally, trigger elements have employed a constant voltage set point control method to operate in a pulsed mode to reduce the overall power consumption of the sensor. The pulsed method can use, for example, an analog Wheatstone bridge with elements having a small thermal time constant, and thus can respond to analyte gas within a short time period (e.g., less than 500 ms). Such methods allow duty cycle operation (e.g., a sensor on-time of less than 10%), thereby reducing power consumption. Information from these elements is analyzed by a support circuitry. If the presence of a combustible analyte is determined via the trigger element, a more accurate and higher power sensing element is enabled or activated. Such methods provide a combination of low power trigger operation with an accurate and linear signal from the main combustible sensing element. Summary of the Invention

[0013] In one aspect, a method of operating a sensing element that includes a heating element operably connected to an electronic circuitry, where the sensing element forms a resistive element in the circuitry of the electronic circuitry, the method includes: activating, at least in a first stage, the electronic circuitry to heat the sensing element to a temperature at which the sensing element responds to an analyte gas via an energy input to the heating element in a pulsed manner. A constant resistance set point is set for the sensing element, and is variably controlled via an energy (e.g., voltage, current, or a combination thereof) of the circuit via the pulsed energy input to achieve the constant resistance set point. The method further includes measuring the response of the sensing element over time to the pulsed energy input.

[0014] In multiple embodiments, the sensing element operates in at least one of the following modes: a mode of detecting an analyte gas via a change in thermal conductivity resulting from the response of the sensing element over time to the pulsed energy input; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas resulting from the response of the sensing element over time to the pulsed energy input. The sensing element can include, for example, a catalyst loaded thereon for catalyzing the combustion of the analyte gas. In multiple embodiments, the sensing element operates in the following modes: a mode of detecting an analyte gas via a change in thermal conductivity resulting from the response of the sensing element over time to the pulsed energy input in a lower temperature range; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas resulting from the response of the sensing element over time to the pulsed energy input in a higher temperature range.

[0015] In multiple embodiments, the circuitry of the electronic circuitry including the heating element is controlled as a Wheatstone bridge circuit or an analog Wheatstone bridge circuit to achieve the constant resistance set point. The method can include, for example, applying energy to the circuit for a period of time prior to at least the first stage to unbalance the circuit. Energy can be applied to the circuit for a predetermined time at a predetermined constant voltage prior to at least the first stage to unbalance the circuit.

[0016] In multiple embodiments, the method further includes restricting a voltage, a current, or a combination thereof applied to the sensing element or the support circuitry during at least a first phase if a voltage, a current, or a combination thereof measured on the electronic circuitry is equal to or greater than a predetermined threshold. For example, a voltage across the sensing element can be measured and compared to a reference voltage.

[0017] In multiple embodiments, the method further includes beginning a second phase when it is determined by the electronic circuitry that: if a current through the electronic circuitry is to be variably controlled via a pulsed energy input to achieve a constant resistance setpoint, a measured voltage, current, or combination thereof will be less than a predetermined threshold; during this second phase, energy is input to the heating element in a pulsed manner, and the current through the electronic circuitry is variably controlled via the pulsed energy input to achieve the constant resistance setpoint, and the response of the sensor element to the pulsed energy input over time is measured.

[0018] In multiple embodiments, the method can further include measuring an amount of time during which a voltage, a current, or a combination thereof is restricted. The amount of time can be related to or used to determine a concentration of an analyte gas in the environment.

[0019] The sensing element can be, for example, a low thermal mass element that operates in a trigger mode of operation as a trigger element of a trigger sensor for a primary combustible gas sensor via a pulsed energy input to the heating element at a first duty cycle. In multiple embodiments, the sensing element includes a catalyst and, when a response value at or above a threshold is measured, the sensing element operates as a primary combustible gas sensor element at a second duty cycle higher than the first duty cycle.

[0020] On the other hand, a gas sensor includes a sensing element that includes a heating element and an electronic circuitry operably connected to the heating element, wherein the sensing element forms a resistive element in the electronic circuitry. The electronic circuitry is configured to operate the sensing element in at least a first stage, in which the sensing element is heated to a certain temperature at which the sensing element responds to an analyte gas via an energy input to the heating element in a pulsed manner. A constant resistance set point is set for the sensing element, and is variably controlled via an energy (e.g., voltage, current, or a combination thereof) of the electronic circuitry via the pulsed energy input to achieve the constant resistance set point. The electronic circuitry is further configured to measure the response of the sensor element over time to the pulsed energy input. The electronic circuitry can be configured to operate the sensing element, for example, in at least one of the following modes: a mode of detecting an analyte gas via a change in thermal conductivity caused by the response of the sensing element over time to the pulsed energy input; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas caused by the response of the sensing element over time to the pulsed energy input. The sensing element can include, for example, a catalyst loaded thereon for catalyzing the combustion of the analyte gas. The characteristics of the gas sensor can be additionally as described herein.

[0021] On the other hand, a sensor system includes an electronic circuitry that includes a control system and a main combustible gas sensor that includes a first main element operably connected to the electronic circuitry. The main combustible gas sensor includes a first main support structure, a first main catalyst supported on the first main support structure, and a first main heating element operably connected to the first main support structure. The main combustible gas sensor further includes a second main element that is operably connected to the electronic circuitry and includes a second main support structure, a second main catalyst supported on the second main support structure, and a second main heating element operably connected to the second main support structure. The sensor system further includes a trigger sensor that includes a first trigger element of low thermal mass that includes a first trigger heating element. The first trigger element is operably connected to the electronic circuitry and forms a resistive element in the electronic circuitry. The electronic circuitry is configured to operate the trigger sensor to detect a response value at or above a threshold. When the threshold is detected by the trigger sensor, the main combustible gas sensor is activated from a low power state. The electronic circuitry is further configured to heat the first trigger element to a certain temperature at which the first trigger element responds to an analyte gas via an energy input to the first trigger heating element in a pulsed manner. A constant resistance set point is set for the first trigger heating element, and is variably controlled via an energy (e.g., voltage, current, or a combination thereof) of the electronic circuitry via the pulsed energy input to achieve the constant resistance set point. The electronic circuitry is further configured to measure the response of the first trigger element over time to the pulsed energy input.

[0022] In multiple embodiments, the electronic circuit system is configured to operate a first trigger element in at least one of the following modes: a mode of detecting an analyte gas via a change in thermal conductivity caused by a response of the first trigger element over time to a pulsed energy input; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas caused by a response of the first trigger element over time to a pulsed energy input. In multiple embodiments, the first trigger element includes a catalyst loaded thereon for catalyzing the combustion of the analyte gas. The characteristics of the main combustible gas sensor and the trigger sensor may be further as described herein.

[0023] On the other hand, a gas sensor includes a sensing element that includes a heating element and an electronic circuit system operably connected to the heating element, wherein the sensing element forms a resistive element in the electronic circuit system. The electronic circuit system is configured to operate the sensing element in a trigger operation mode by inputting energy to the heating element in a pulsed manner at a first duty cycle, and to operate the sensing element in a main operation mode by inputting energy to the heating element in a pulsed manner at a second duty cycle. The second duty cycle is greater than the first duty cycle. The electronic circuit system is further configured to measure the response of the sensing element over time to the pulsed energy input. When a response value at or above a threshold is measured in the trigger operation mode, it enters the main operation mode. In multiple embodiments, a constant resistance set point is set for the sensing element, and the energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system is variably controlled via the pulsed energy input to achieve the constant resistance set point at least in the trigger operation mode. Alternatively, a constant voltage set point may be set, and the energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system is variably controlled via the pulsed energy input to achieve the constant voltage set point.

[0024] On the other hand, a method of operating a sensing element that includes a heating element and an electronic circuit operably connected to the heating element, where the sensing element forms a resistive element in the electronic circuit system, the method includes operating the sensing element in a trigger operation mode by triggering, at a first duty cycle, an energy input to the heating element in a pulsed manner; measuring a response of the sensing element over time to the pulsed energy input in the trigger operation mode; and entering a main operation mode, at a second duty cycle greater than the first duty cycle, by triggering, in a pulsed manner, an energy input to the heating element when a response value at or above a threshold is measured in the trigger operation mode. In various embodiments, a constant resistance set point is set for the sensing element and variably controlled via pulsed energy input of energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant resistance set point in at least the trigger operation mode. Alternatively, a constant voltage set point can be set and variably controlled via pulsed energy input of energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant voltage set point.

[0025] In a further aspect, a gas sensor includes a sensing element that includes a heating element operably connected to an electronic circuit system, where the sensing element forms a resistive element in the electronic circuit system. The electronic circuit system is configured to operate the sensing element by activating the electronic circuit system to heat the sensing element to a temperature at which the sensing element responds to an analyte gas via a pulsed energy input to the heating element in at least a first stage; and measuring a response of the sensing element over time to the pulsed energy input. The electronic circuit system is configured to operate the sensing element in the following modes: a mode of detecting an analyte gas via a change in thermal conductivity caused by a response of the sensing element over time to a pulsed energy input in a lower temperature range; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas caused by a response of the sensing element over time to a pulsed energy input in a higher temperature range. In various embodiments, a constant resistance set point is set for the sensing element and variably controlled via pulsed energy input of energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant resistance set point in at least the trigger operation mode. Alternatively, a constant voltage set point can be set and variably controlled via pulsed energy input of energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant voltage set point. In fact, such operation modes can be effective in any heating / cooling cycle of the sensing element.

[0026] In yet another aspect, a method of operating a sensing element that includes a heating element operably connected to an electronic circuit system, where the sensing element forms a resistive element in the electronic circuit system, the method includes, in at least a first stage, activating the electronic circuit system to heat the sensing element to a temperature at which the sensing element responds to an analyte gas via pulsed energy input to the heating element; and measuring the response of the sensing element over time to the pulsed energy input. The sensing element operates in the following modes: a mode of detecting an analyte gas via a change in thermal conductivity resulting from the response of the sensing element over time to pulsed energy input in a lower temperature range; and a mode of detecting an analyte gas via a combustion reaction of the analyte gas resulting from the response of the sensing element over time to pulsed energy input in a higher temperature range. In various embodiments, a constant resistance set point is set for the sensing element and is variably controlled via pulsed energy input by the energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant resistance set point in at least a trigger operation mode. Alternatively, a constant voltage set point can be set and is variably controlled via pulsed energy input by the energy (e.g., voltage, current, or a combination thereof) of the electronic circuit system to achieve the constant voltage set point. Again, such operating modes can be effective in any heating / cooling cycle of the sensing element.

[0027] The devices, systems, and methods herein, together with their attributes and their attendant advantages, will be best appreciated and understood by the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1A schematically illustrates one embodiment of a conventional combustible gas sensor.

[0029] FIG. 1B schematically shows an enlarged view of the sensing element of the combustible gas sensor of FIG. 1A.

[0030] FIG. 1C shows a schematic diagram of a Wheatstone bridge circuit incorporating the sensing element and a compensating element of the combustible gas sensor of FIG. 1A.

[0031] Figure 2 Shows one embodiment of a circuit system for a sensor of the present invention, the circuit system including an analog Wheatstone bridge circuit system.

[0032] Figure 3A Shows a comparison of operating a thermal conductivity sensor in a constant resistance mode and in a constant voltage mode.

[0033] Figure 3B Shows a comparison of operating a catalytic combustible gas sensor in a constant resistance mode and in a constant voltage mode.

[0034] Figure 4Shows an embodiment of a part of the electronic circuit system of the present invention for control with a constant resistance set point.

[0035] Figure 5 Shows the relationship between the output of the sensor of the present invention and a dynamic / pulse input with a constant resistance set point, where the vertical dashed line indicates the start of the dynamic / pulse input, and where the voltage applied to the element at the resistance set point is applied within 2.5 seconds as the element is heated towards the operating resistance set point.

[0036] Figure 6 Shows the response of the low thermal mass combustible gas p-element of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations.

[0037] Figure 7 Shows the response of the standard combustible gas p-element of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations (expressed as a percentage of the lower explosive limit or LEL).

[0038] Figure 8 Shows the response of the thermal conductivity p-element of the present invention without a catalyst to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations.

[0039] Figure 9 Shows an embodiment of the circuit of the present invention for implementing a preliminary stage, which can be considered a preheating or bridge imbalance stage.

[0040] Figure 10 Shows the relationship between the sensor output of the present invention and a dynamic / pulse input with a constant resistance set point (which includes a bridge imbalance stage), where the first vertical dashed line indicates the start of a preliminary constant voltage heating stage for unbalancing the circuit, and the second vertical dashed line indicates the start of the dynamic / pulse input.

[0041] Figure 11 Shows the response of the low thermal mass combustible gas p-element of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations, where the dynamic / pulse input follows a preliminary bridge imbalance stage.

[0042] Figure 12 Shows the response of the standard combustible gas p-element of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations, where the dynamic / pulse input follows a preliminary bridge imbalance stage.

[0043] Figure 13Shows the response of the thermal conductivity p-element of the present invention, without a catalyst, to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations, where the dynamic / pulse input follows a preliminary bridge imbalance phase.

[0044] Figure 14A Shows an embodiment of the electronic circuit system topology of the present invention including an active clamping circuit that monitors the voltage across the element during the application of a dynamic / pulse input with a constant resistance set point and clamps the voltage to a predetermined threshold level based on the D / A reference voltage.

[0045] Figure 14B Shows another embodiment of the electronic circuit system topology of the present invention including an active clamping circuit.

[0046] Figure 15 Shows the relationship between the output of the sensor of the present invention and a dynamic / pulse input with a constant resistance set point (including a bridge imbalance phase), where the first vertical dashed line represents the start of a preliminary constant voltage heating phase to unbalance the circuit, the second vertical dashed line represents the start of the dynamic / pulse input, the third vertical dashed line represents the start of the clamping / constant voltage phase, and the fourth vertical line represents the end of the clamping / constant voltage phase and the resumption of the dynamic / pulse input with a constant resistance set point.

[0047] Figure 16 Shows the response of the combustible gas p-element of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations, where the dynamic / pulse input follows a preliminary bridge imbalance phase and resumes after the clamping voltage phase.

[0048] Figure 17 Shows the response of the thermal conductivity p-element (without a catalyst) of the present invention to a dynamic / pulse input with a constant resistance set point in the presence of methane at different concentrations, where the dynamic / pulse input follows a preliminary bridge imbalance phase and resumes after the clamping voltage phase.

[0049] Figure 18A Shows a comparison between the response of a thermal conductivity sensor to a dynamic / pulse input with a constant voltage set point and the response of a thermal conductivity sensor to a dynamic / pulse input with a constant resistance set point.

[0050] Figure 18B Shows, on an enlarged scale, Figure 18A the response of the thermal conductivity sensor to a dynamic / pulse input with a constant voltage set point.

[0051] Figure 18CShows a comparison of the response of a catalytic combustible gas sensor to a dynamic / pulsed input with a constant voltage setpoint and the response of a catalytic combustible gas sensor to a dynamic / pulsed input with a constant resistance setpoint.

[0052] Figure 18D Is shown in an enlarged scale Figure 18C Of the response of the catalytic combustible gas sensor to a dynamic / pulsed input with a constant voltage setpoint.

[0053] Figure 19 Shows Figure 16 A portion of, which includes the response of the catalytic p-element to a dynamic / pulsed input up to the point of a clamped voltage phase with an enlarged scale that confirms the thermal conductivity response of the catalytic p-element (in the absence of catalytic combustion) before reaching the temperature of the p-element at which the catalyst of the p-element catalyzes the combustion of methane.

[0054] Figure 20 Shows Figure 17 A portion of, which includes the response of the thermal conductivity p-element (excluding the catalyst) to a dynamic / pulsed input up to the point of a clamped voltage phase with an enlarged scale that confirms the thermal conductivity response.

[0055] Figure 21 Shows a comparative study of the clamp time versus the analyte concentration for each of the thermal conductivity sensor and the catalytic combustible gas sensor.

[0056] Figure 22 Schematically shows a cross-sectional view of the device or system of the present invention, the device or system including a main combustible gas sensor comprising a sensing element and a compensating element and a MEMS-triggered combustible gas sensor, wherein the electronic circuit system of the present invention is configured to operate at least the triggered combustible gas sensor via a dynamic / pulsed input with a constant resistance setpoint.

[0057] Figure 23 Schematically shows a cross-sectional view of the device or system of the present invention, the device or system including a main combustible gas sensor comprising a sensing element and a compensating element, and a low thermal mass sensor operating as a trigger sensor, wherein the electronic circuit system of the present invention is configured to operate at least the trigger sensor via a dynamic / pulsed input with a constant resistance setpoint.

[0058] Figure 24 Shows a cross-sectional view of the device or system of the present invention, the device or system including a low thermal mass sensor that operates as a trigger sensor at a first duty cycle via a dynamic / pulsed input (e.g., with a constant resistance setpoint), and operates as a main sensor at a higher second duty cycle when a threshold response when operating as a trigger sensor is measured. Detailed Description

[0059] It will be readily understood that, in addition to the representative embodiments described, the components of the embodiments, as generally described and illustrated in the accompanying drawings herein, may be arranged and designed in a variety of different configurations. Accordingly, the following more detailed description of the representative embodiments as shown in the drawings is not intended to limit the scope of the claimed embodiments, but is merely illustrative of the representative embodiments.

[0060] References throughout this specification to "one embodiment" or "an embodiment" (or the like) mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" or the like throughout this specification are not necessarily all referring to the same embodiment.

[0061] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of the embodiments. However, those skilled in the relevant art will recognize that various embodiments may be practiced without one or more of the specific details, or using 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.

[0062] 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, reference to "a processor" includes multiple such processors known to those skilled in the art and their equivalents, and so forth, and reference to "the processor" is a reference to one or more such processors known to those skilled in the art and their equivalents, and so forth. The recitation of numerical ranges herein is merely intended to be a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each separate value, as well as intermediate ranges, is incorporated into the specification as if individually recited herein. Unless otherwise indicated herein or clearly prohibited by context, all methods described herein may be performed in any suitable order.

[0063] In various embodiments of the present invention, the combustible gas sensor operates in a dynamic mode for gas detection, wherein a constant resistance set point is established.

[0064] In many currently available sensors, a combustible gas sensing element is placed in or forms part of a Wheatstone bridge or an analog Wheatstone bridge, and a predetermined constant voltage is applied, which heats the element to a sufficiently high operating temperature via Joule heating for the catalyst on the element to catalyze the reaction of combustible analytes. For many representative sensing elements, the approximately required temperature can be 450 °C. The Callendar-Van Dusen equation describing the temperature-based resistance of the element is as follows:

[0065] R = R 0 [1 + α(T - T 0 )] Eq, 1

[0066] After rearrangement, the equation can be expressed as:

[0067] R - R 0 = αR 0 (T - T 0 ) Eq, 2

[0068] Or

[0069] ΔR = αR 0 ΔT Eq. 3

[0070] In Equation 3 or Eq. 3, R 0 is the resistance of the element without voltage applied at a certain ambient temperature T 0 , and α is the temperature coefficient of resistance. Eq. 3 shows that the change in resistance is proportional to the change in temperature. If the starting temperature and resistance are known, (1) the operating temperature can be obtained via measuring the operating resistance, or (2) the operating resistance can be obtained via measuring the operating temperature. Measuring the resistance of a combustible gas sensing element to determine its temperature is a commonly used method.

[0071] One or more sensors or sensor assemblies, which include, for example, a p-element as shown in Figure 1A, or include one or more low thermal mass p-elements, or include, for example, one or more MEMS sensor assemblies discussed in U.S. Patent Application Serial No. 16 / 037,882, U.S. Patent No. 8,826,721, and U.S. Patent No. 9,228,967 (the disclosures of which are incorporated herein by reference), can be placed in relation to such as Figure 2The electronic circuit system 300 of the present invention shown is connected. The low thermal time constant associated with the low thermal mass element / sensor helps to provide a fast response time, thereby reducing the time during which the element may be unavailable in the detection mode and reducing the power requirements. In multiple embodiments, the low thermal mass element of the present invention has a thermal time constant of 8 seconds or less, 6 seconds or less, 1 second or less, 0.5 seconds or less, or 0.250 seconds or less. The low thermal mass / low thermal time constant sensor may include, for example, the MEMS carrier catalytic element or the low thermal mass p element as described above to provide the thermal time constant. As used herein, the thermal time constant of an element is defined as the time required to change 63.2% of the total difference between its initial temperature and final temperature when subjected to a step function change in drive power under zero power initial conditions. The MEMS carrier catalytic element typically has a lower thermal time constant than the low thermal mass p element. The MEMS carrier catalytic element may have, for example, a thermal time constant of 1 second or less, 0.5 seconds or less, or 0.250 seconds or less.

[0072] The electronic circuit system 300 may be placed, for example, in electrical connection with the conductive contact elements of the sensor element of the present invention (see, for example, contact posts 62a and 62b in FIG. 1A). In the case where the sensor is fixed in a certain position within the facility, power may be provided from a remote source. As described above, in the case of a portable sensor, the power supply 304 may include one or more batteries. The electronic circuit system 300 of the sensor system of the present invention may further include a control system 306, which may include, for example, one or more processors 310 (e.g., microprocessors) and an associated memory system 320 communicatively connected to the one or more processors 310. Control and / or measurement algorithms may be stored, for example, in the memory system 320 for execution by the one or more processors 310. A user interface system 330 (including, for example, a data input system, such as a touch screen display, keyboard, mouse, microphone, etc.; and / or a data output system, such as a display, speaker, etc., to provide information to the user, such as concentration, morphological analysis, alerts, etc.) and a wired and / or wireless communication system 340 for sending and / or receiving data / information may also be provided in the circuit system 300.

[0073] As used herein, the terms "electronic circuitry", "circuitry", or "circuit" include, but are not limited to, hardware, firmware, software, or combinations of each to perform one (or more) functions or one (or more) 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 devices. 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 of each to perform one (or more) functions or one (or more) actions, or to cause the function or action of 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 devices. Logic may also be embodied entirely as software.

[0074] As used herein, the term "processor" includes, but is not limited to, one or more of any combination of virtually any number of processor systems or stand-alone processors [such as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors (DSPs)]. A processor may be associated with various other circuits that support the operation of the processor, such as random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), 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 operably with the processor. The support circuits are not necessarily shown separately from the processor in a block diagram or other drawing.

[0075] 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. A controller may include, for example, a device having one or more processors, microprocessors, or central processing units that can be programmed to perform functions.

[0076] As used herein, the term "logic" includes, but is not limited to, hardware, firmware, software, or combinations thereof to perform one (or more) functions or one (or more) actions, or to cause the function or action of another element or component. Depending on the particular application or requirements, logic may include, for example, a software-controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmable logic devices. Logic may also be embodied entirely as software. As used herein, the term "logic" is considered synonymous with the term "circuit".

[0077] 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 behave in a desired manner. The instructions can be embodied in various forms, such as routines, algorithms, modules, or programs, including separate applications or code from dynamic link libraries. Software can also be implemented in various forms such as stand-alone programs, function calls, servlets, applets, instructions stored in memory, a part of an operating system, or other types of executable instructions. Those of ordinary skill in the art will understand 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, etc.

[0078] In the case of constant voltage operation, as Figure 2 shown by a Wheatstone bridge or an analog Wheatstone bridge circuit, etc., allows the combustible gas sensor element to reach thermal equilibrium with its environment. Under specific environmental conditions without combustible gas, such equilibrium will result in a specific element resistance R p1 . In the presence of combustible gas under similar environmental conditions, the sensor element will react to the combustible analyte, resulting in a temperature increase and thus a change in resistance to a new resistance R p2 . Such a change in resistance can be measured or determined via the circuit system 300 and the change in voltage across the sensor element or the change in current through the sensor element can be detected and analyzed.

[0079] The system changes at equilibrium can be further described via the law of conservation of energy as follows:

[0080] ΔE E +ΔE C -ΔE T =0 Eq.4

[0081] In Eq.4, ΔE E represents the change in electrical energy provided via the control circuit system, ΔE C represents the change in chemical potential energy presented to the system, and ΔE T represents the change in the element heat loss to the surrounding environment.

[0082] For the above constant voltage example, it can be assumed that ΔE E is close to 0 because the voltage presented to the Wheatstone bridge or analog Wheatstone bridge does not change and only a small change in current is observed when the element is in the analyte gas. Eq.4 can thus be simplified as follows:

[0083] ΔE C =ΔE T Eq,5

[0084] In this regard, the change in chemical potential energy in the system is proportional to the change in temperature in the constant voltage operation mode. Eq. 5 can be extended as follows:

[0085]

[0086] In Eq. 6, h is the heat transfer coefficient and A is the area. Eq. 6 shows that the change in chemical potential energy is proportional to the change in resistance in the system. In Eq. 6, R and R 0 R is described here S +R P is the full bridge resistance. However, R s must be constant, so ΔR = ΔR p . Considering ΔR P , the measured voltage change can be described as follows:

[0087]

[0088] Eq. 7 can be solved for ΔR as follows:

[0089]

[0090] When Eq. 8 is substituted into Eq. 6 to replace ΔR and ΔV is solved, the result is:

[0091]

[0092] The amplitude of the voltage signal is asymptotically positively correlated with the change in chemical potential energy. Then the maximum possible signal in the constant voltage mode is described as the ratio of the applied voltage, the series resistance R s and the operating resistance R of the p-element p as follows:

[0093]

[0094] Alternatively, the steady-state constant resistance operation mode keeps the temperature of the sensing element constant under specific environmental conditions by controlling R (see Eq. 3 for example). Assuming that the combustible gas sensing element consumes chemical potential energy proportional to the concentration via a combustion reaction and is limited by mass transfer towards the element, and the change in thermal conductivity is relatively small and can be ignored, Eq. 4 can be rewritten as:

[0095] ΔE C =-ΔE E Eq. 11

[0096] In this regard, the change in the effective or mass transfer-limited chemical potential energy in the system is proportional to the change in the electrical energy provided for the constant resistance operation mode. This equation can be further written as follows at a specific point in time:

[0097]

[0098] In Eq. 12, V A is the voltage applied by the control circuitry to heat the element to a constant resistance setpoint R CR . To maintain the resistance R CR constant, the control circuitry must vary the applied voltage V CR in response to changes in the effective or mass-transfer limited chemical potential energy (i.e., in the presence of the analyte gas). When expanded, the equation can be expressed as:

[0099]

[0100] In Eq. 13, V Ai is the initial voltage applied under ambient conditions and ΔV is the voltage change provided in response to the change in chemical potential energy. Eq. 13 shows that the voltage change ΔV is related to the square root of the change in chemical potential energy ΔE C . When compared to Eq. 9, which shows an asymptotic positive correlation between ΔV and the change in chemical potential energy in the constant voltage mode, Eq. 13 further confirms that for the same change in chemical potential energy, the constant resistance operating mode results in a greater change in the measured voltage.

[0101] The greater signal amplitude provides an important motivation for considering the constant resistance operating mode for analyte detection. It has been observed that in practice, for the same concentration of analyte gas, the signal amplitude difference in the constant resistance mode can be up to 50 times that observed in the constant voltage mode. Thus, constant resistance operation can provide significant advantages. Figure 3A and Figure 3B respectively show graphical comparisons of a thermal conductivity sensor and a catalytic combustible gas sensor operating in a steady-state, constant resistance control mode with such sensors operating in a constant voltage control mode.

[0102] The constant resistance operation or control mode can be implemented, for example, via a control circuit / system as shown in Figure 4 . In the Figure 4 system, an error amplifier allows current to flow through, for example, an analog Wheatstone bridge that includes R S , R P , R T and R D , where R D may or may not have an adjustable resistance. The error amplifier can, for example, adjust the current through the bridge to ensure that V D and V P match, which heats the combustible element R P to its predetermined resistance setpoint. In this configuration, R D , R T and R SRelative value setting R P resistance. This relationship (for non-zero bridge voltages) is described as:

[0103]

[0104] Given the advantage of a significant increase in signal in the constant resistance mode, the operation of a combustible gas sensor in a "pseudo-constant" resistance / dynamic response mode was explored, with the goal of having a larger voltage signal in an analyte gas with similar power requirements when compared to a dynamic response mode in which a constant voltage is set. As described above, the operating mode described herein can be described, for example, as a dynamic or pulsed mode with a constant resistance set point.

[0105] The dynamic or pulsed mode can be used with any sensor element and is particularly suitable for (but not limited to) low thermal mass elements such as low thermal mass p-elements and MEMS hotplate / carrier catalytic elements. In the dynamic or pulsed mode, one or more sensor elements are rapidly heated and cooled in a pulsed power mode. One advantage of operating in a pulsed mode compared to a continuous mode is a significant reduction in power consumption. Another advantage is an improved span response compared to continuously powering the catalyst at operating temperatures between 100 and 700 °C, which is due to the adsorption of excess combustible gas on the catalyst at lower temperatures during periods of no power or lower power operation (i.e., during the off-time).

[0106] Pulse width modulation can be used, for example, to control the energy delivered to one (or more) heating elements of the trigger sensor and the main sensor of the present invention. Pulse width modulation is a well-known control technique for controlling the average power and / or energy delivered to a load. In embodiments of the present invention, a voltage is supplied to the heating element to heat the oxide layer and the catalyst / structure of the load (when present) in a controlled manner. In the case of an element with a relatively low thermal mass, the cycle time can be relatively short.

[0107] In the pulsed operation mode, heating energy [i.e., one (or more) heating voltages or one (or more) heating currents] can be periodically supplied to one (or more) heating elements during the "on-time" in "pulse mode". Rest energy [i.e., one (or more) rest voltages or one (or more) rest currents] less than the heating energy can be supplied during the "off-time". The sum of the higher energy or on-time plus the lower energy or off-time corresponds to a cycle time or a cycle duration. The gas concentration of the analyte is measured during the on-time. The heating energy (voltage / current) supplied during the on-time can be constant or can vary during the on-time (e.g., supplied as a heating voltage / current plateau or as a heating voltage / current ramp). The rest energy (voltage / current) can be equal to zero or low enough below the heating energy such that the trigger gas sensor does not interact with the gas to be detected in a significant manner (or consume any or substantially any of the gas to be detected). Similar to the on-time, the rest energy supplied during the off-time can remain constant or can vary during all off-times (e.g., supplied as a rest voltage / current plateau or as a rest voltage / current ramp). The cycle can be repeated.

[0108] The on-duration can depend, for example, on the thermal mass of the element. In various embodiments of the present invention, the on-duration can be, for example, in the range of 100 milliseconds to 1 second or in the range of 300 milliseconds to 500 milliseconds. In various embodiments, the on-duration can be kept as short as possible to improve the response time. In various embodiments, the duty cycle can be, for example, in the range of 5% to 12% [the ratio of on-time / (on-time + off-time)]. In an illustrative or representative embodiment, the on-time is approximately 350 milliseconds (i.e., equal to or less than 10% of this value), and the duty cycle is approximately 10% (i.e., equal to or less than 20% of this value). In a representative example, the cycle time or cycle duration is 4000 milliseconds, during which the on-time is 350 milliseconds and the off-time is 3650 milliseconds. Thus, the duty cycle is 8.75%.

[0109] In representative embodiments of many studies, a dynamic or pulsed operating mode with a constant resistance setpoint is applied by setting the circuitry 300 to a constant resistance topology, where the duty cycle of the p-element is 2.5 seconds on for every 7.5 seconds (33% duty cycle, 7.5 second period). When the constant resistance setpoint control is not enabled, the voltage across the p-element is set to 0V. In many such embodiments, the method has at least two phases, including: (1) a first heating phase, where the energy passing through the element (e.g., voltage, current, or a combination thereof) is variably controlled to heat the element towards a predetermined setpoint resistance over a predetermined amount of time, where thermal equilibrium may or may not be reached, and (2) a second phase, where energy is removed from the element over a predetermined amount of time to cool it. This procedure is sometimes referred to herein as Procedure No. 1.

[0110] The resulting response waveform is shown in Figure 5 which. Figure 5 shows the voltage applied to the p-element at a specific resistance setpoint R over 2.5 seconds as the element is heated towards the operating resistance setpoint. In this example of Procedure No. 1, the p-element does not reach thermal equilibrium because the resistance never becomes constant (refer to Eq. 3). The method is applicable to standard p-elements, such as those used in an MSA CR combustible gas sensor (available from MSA Safety Incorporated, Cranberry Township, PA). The method is also applicable to low thermal mass combustible p-elements and "thermal conductivity p-elements" at various methane concentrations. In the studies of the present invention, the thermal conductivity p-elements are manufactured in the same manner as combustible gas p-elements (whether low thermal mass p-elements or conventional p-elements), but without a catalyst. Variations in the dynamic, constant resistance setpoint voltage response at different methane concentrations are shown in Figures 6 to 8 which. As will be clear to those skilled in the art, the current passing through the p-element could alternatively be measured. The "standard" MSA XCELL combustible gas sensor p-element is a sphere approximately 430 microns in diameter that includes a ceramic catalyst carrier and a noble metal oxidation catalyst. The "low thermal mass" p-element is a sphere approximately 260 microns in diameter that includes a ceramic catalyst carrier and a noble metal oxidation catalyst. The low thermal mass p-elements are discussed, for example, in U.S. Patent No. 8,826,721, the disclosure of which is incorporated herein by reference. The thermal conductivity p-element is a sphere approximately 260 microns in diameter that includes a ceramic catalyst carrier without a catalyst.

[0111] Figure 6 , Figure 7 and Figure 8It has been confirmed that the dynamic, pulsed, or duty - cycle operation of all three types of test elements with a constant resistance set - point produces an available dynamic signal that is sufficient to distinguish the concentration of the analyte gas, whether or not the element reaches thermal equilibrium. However, for some operating embodiments, it would be desirable to reduce the response time. Figure 6 , Figure 7 and Figure 8 the response time of the elements in, for example, is slower than the response time when operating in a dynamic or pulsed operating mode with a constant voltage set - point (which can, for example, perhaps use an 8.75% duty - cycle and a 4 - second period).

[0112] To achieve a faster response time, the dynamic program applied to the combustible element was modified to add a preliminary stage that can be considered a pre - heating or bridge - imbalance stage. The energy applied to the combustible element during such a preliminary stage can be, for example, constant (e.g., constant voltage or constant current) or varying (e.g., ramping). In the control of the circuit in Figure 4 , V D and V P are set equal in the constant - resistance set - point operating mode. When the voltage is 0 and Eq.14 is true, V D and V P are equal. In Figures 5 to 8 , the zero response lasts approximately 1000 milliseconds. In these embodiments, one relies on the noise in the system to unbalance the zero set - point. Figure 9 An embodiment of a partial circuit system for implementing the "unbalance" method by placing a non - zero voltage on the bridge circuit is shown. In a plurality of embodiments of this operating mode, the combustible gas sensing element (e.g., a p - element) is initially set to 0V by setting the D / A reference voltage to 0V. Subsequently, for a short period (e.g., 10 ms), a non - zero voltage (e.g., 2V) is applied to the p - element by changing the D / A reference voltage. This operating stage initializes the heating of the p - element and creates an imbalance in the bridge circuit system. Alternatively, a heating pulse can be applied to the entire analog bridge V A . After the initial heating period has passed, S 1Switch the position to enable the above-mentioned constant resistance setpoint topology for the remainder of the pulse period (e.g., 2490 milliseconds). In such embodiments, the method includes the following three stages: (1) an initial heating stage for a predetermined time, where the voltage across the element is increased (e.g., to a constant predetermined setpoint) to initialize the heating of the element (during which thermal equilibrium is not reached); (2) a second heating stage, where the energy passing through the element (e.g., voltage, current, or a combination thereof) is variably controlled to heat the element towards the constant resistance setpoint within a predetermined amount of time (during which thermal equilibrium may or may not be reached); and (3) a third stage, where energy is removed from the element within a predetermined amount of time to cool the element. This procedure is sometimes referred to herein as Program No. 2.

[0113] During the course of Program No. 2, the voltage V across the p-element P can be monitored by the electronic circuit system 300 of the present invention. A representative example of the resulting dynamic response is as Figure 10 shown. In the Figure 10 study, energy pulses are applied using a duty cycle of 2.5 seconds on time per 7.5 seconds (33% duty cycle, 7.5-second period).

[0114] Compared with the Figure 5 results, it is clear that compared with Figure 5 the 1500 milliseconds in Figure 10 , the voltage applied to the p-element reaches its maximum value significantly faster (at approximately 250 milliseconds) in

[0115] . The faster response enables the voltage signal to be determined from the dynamic response at an earlier time in the response waveform and thus using lower operating power. In addition, the element can reach thermal equilibrium near the end of the applied pulse (>1000 milliseconds), but does not reach thermal equilibrium at the start of the pulse (<1000 milliseconds) because the resistance varies with time (refer to Eq. 3).

[0115] The dynamic or pulsed operation method of Program No. 2 is applicable to the p-elements of standard MSA XCELL combustible gas sensors, low thermal mass combustible gas sensors, and thermal conductivity combustible gas sensors (as described above) at various methane concentrations. The variations in the dynamic voltage response (under constant resistance setpoint control) of such p-elements at different methane concentrations are shown in Figure 11 , Figure 12 and Figure 13 . Similarly, for equivalent effects, the current passing through the p-element can alternatively be measured.

[0116] Figure 11 , Figure 12 and Figure 13It is confirmed that a significant signal can be obtained earlier in the dynamic response (under constant resistance setpoint control) by using an initial heating or bridge imbalance step / phases (during which the element may or may not reach thermal equilibrium), for example, at a constant voltage. Additionally, Figure 11 and Figure 12 show that while larger elements or detectors can generate larger signals, smaller elements or detectors can achieve faster response times.

[0117] Although the circuit of the present invention (such as the representative embodiment shown in Figure 4 ) is sometimes referred to herein as a bridge circuit or an analog bridge circuit, such a circuit operates in a bridge manner by balancing or maintaining equal V D and V P to control the circuit only to a constant resistance setpoint. During the response measurement, the circuit is not used in a bridge manner. In fact, since V D and V P are controlled to be equal, one cannot use a "bridge" circuit system to measure changes. In this regard, Figure 4 there is no left side of the "bridge" for response measurement. In other words, the left side of the circuit does not need to be used as a reference for response measurement. The response can be referenced to ground, for example. To measure the response, one can simply measure the current through R P . Any circuit system suitable for measuring the current through or the voltage across, for example, the following items can be used to measure the response in the circuit of the present invention: R P , R S , R T , R D , or R P and R S in combination, or R D and R T in combination.

[0118] Important issues to be addressed in many embodiments of the dynamic, constant resistance setpoint, analyte gas response include: (1) providing a duty cycle low enough compared to existing methods; and (2) controlling the voltage on the sensing element during the initial heating phase, which is limited only by the power supply voltage V SUPPLY . The current during heating of the element under constant resistance setpoint control can reach a theoretical maximum value, which is higher than the current that, for example, an integrated device might be able to provide from a specific battery, resulting in a power-down event. In many embodiments, pulse programs and control methods are further adapted to address such issues. To address the power-down problem in multiple embodiments of the present invention, one or more additional circuits are integrated into the electronic circuit system of the present invention to ensure that the voltage on the element does not increase above a predetermined threshold voltage. Representative embodiments of such circuit system topologies are shown in Figure 14Ashown in

[0119] Figure 14A Embodiments of the circuit system topology shown include adding an active clamp circuit that can monitor, for example, the voltage V on the p-element based on a D / A reference voltage. P . If the error amplifier attempts to raise the voltage of the p-element above a predetermined threshold when the clamp circuit is enabled, the clamp circuit system will override the error amplifier and hold the voltage on the p-element. For the same or similar effect, the clamp circuit system can be monitored passively (e.g., monitored by a Zener diode) and other voltages can be monitored (e.g., the voltage V applied to an analog Wheatstone bridge). A ). One can, for example, monitor or measure V A , V P , V D or current and clamp V P , or monitor or measure V A , V P , V D or current and clamp V A . Similarly, one can monitor current or voltage and / or some combination (or function) of current to determine if a threshold is met.

[0120] In multiple embodiments, the p-element is initially set to 0V by setting the D / A reference voltage to 0V. Then, by changing the D / A reference voltage, a non-zero voltage (e.g., 2V) is applied to the p-element for a short period of time (e.g., 10 ms). As described above, this initializes the heating of the p-element and unbalances the bridge. Again, such heating pulses can be applied to the entire analog bridge V A . After the initial heating period has passed, S 1 switches position to enable the above-described constant resistance setpoint topology for the remainder of the pulse period (e.g., 500 milliseconds). Throughout the procedure, the clamp circuit system is enabled to ensure that the monitored voltage does not rise above a predetermined threshold. If the voltage rises above the predetermined threshold, the clamp circuit system overrides the error amplifier until the p-element is sufficiently heated, at which point the error amplifier regains control and holds the p-element resistance R CR . The method is thus as Figure 15The research has confirmed that it includes five stages: (1) an initial heating stage at a predetermined time, where the voltage across the element can be increased to, for example, a constant predetermined set point to initiate heating of the element (during which thermal equilibrium is not reached); (2) a second heating stage, where the energy passing through the element (e.g., voltage, current, or a combination thereof) is variably controlled to heat the element towards a constant resistance set point over a variable amount of time (during which thermal equilibrium is not reached); (3) a third stage, where the voltage across the element is held constant over a variable amount of time while the element heats towards its set point temperature / resistance (during which thermal equilibrium is not reached); (4) a fourth stage, where the energy passing through the element (e.g., voltage, current, or a combination thereof) is variably controlled to heat the element towards a constant resistance set point over a variable amount of time (during which thermal equilibrium may or may not be reached); and (5) a fifth stage, where energy is removed from the element over a predetermined amount of time to cool it. In summary, stages 2, 3, and 4 occur over a predetermined amount of time in the Figure 14A and Figure 15 embodiments. However, the time for each of these stages can vary individually based on the heating characteristics and environmental conditions around the element. This procedure is sometimes referred to as Program No. 3 in this document.

[0121] During the process of Program No. 3, the voltage V across the p-element can be monitored through the circuitry 300 P . Representative examples of the resulting dynamic responses are shown in Figure 15 . Energy is applied to the sensing element using a duty cycle of 0.5 seconds every 5 seconds (10% duty cycle, 5-second period). For the same effect, the voltage V of the entire analog bridge can be monitored A or the current passing through the p-element. In Figure 15 , at time T = 0, the voltage across the p-element increases from 0 V to 2 V in a constant voltage mode, and then the circuitry switches to a constant resistance topology at T = 10 milliseconds. From T = 10 milliseconds to approximately T = 40 milliseconds, the error amplifier is increasing the voltage across the p-element to heat it to the resistance set point R CR . At approximately T = 40 milliseconds, the voltage across the p-element reaches 2.75 V, which is the maximum / threshold reference voltage on the clamp monitoring circuitry in the representative embodiment. Therefore, at approximately T = 40 milliseconds, the clamp circuitry overrides the error amplifier and holds the voltage constant until approximately T = 175 milliseconds. At this time, the p-element is sufficiently heated, and the error amplifier regains control and adjusts the resistance of the p-element to the set point R CR . In the illustrated study, the element did not reach thermal equilibrium at the end of the predetermined pulse time because the resistance changes over time (refer to Eq. 3).

[0122] Refer to Figure 14Aand Figure 14B In a representative embodiment, to deliver power to the bridge circuit system in this embodiment, the error amplifier drives the voltage at the output of the amplifier lower. In fact, this turns on the PMOS transistor and allows current to flow. In the configuration of the illustrated embodiment, the lower the voltage at the gate of the transistor (i.e., at the output of the amplifier), the greater the current allowed to flow from the power supply to the bridge. In this regard, if 0V is applied to the gate of the transistor, it is 100% on, and the full supply voltage will be applied to the bridge. If the supply voltage is applied to the gate of the transistor, it is 100% off, and the voltage across the bridge will be 0V. In other words, the voltage at the gate of the PMOS transistor is inversely proportional to the voltage across the bridge.

[0123] When enabled, the clamp amplifier can be configured to perform constant voltage operation at a specified voltage. It also attempts to turn on the PMOS transistor by driving the voltage at its output lower. In this way, the error amplifier and the clamp amplifier compete for control of the gate of the PMOS transistor in the illustrated embodiment.

[0124] In the illustrated embodiment, the circuit system is configured such that the amplifier with the higher output voltage (i.e., the amplifier that attempts to control the bridge to a lower voltage) is the amplifier that controls the PMOS gate. Table 1 below describes the process discussed above in the context of Program No. 3. There are various ways to implement the control scheme of Table 1. In the representative embodiment as Figure 14B shown, a "diode Or" configuration is used. In other embodiments, the functions of the clamp amplifier and the error amplifier can be integrated into a single amplifier.

[0125] Table 1

[0126]

[0127]

[0128] The dynamic or pulsed operation method of Program No. 3 as described above is applicable to the standard MSAXCELL combustible gas sensor p-element and the thermal conductivity combustible gas sensor p-element (as described above) at various methane concentrations. Figure 16 and Figure 17 shows the variation of the voltage response at different methane concentrations under dynamic, constant resistance set points.

[0129] Figure 16 and Figure 17Both confirm that significant signals are possible from approximately T = 175 ms to T = 500 ms at a duty cycle comparable to pulsed operation at a constant voltage set point on the MEMS device. However, the voltage signals provided herein are approximately ten times the voltage signals observed in similar constant voltage set point applications. These results confirm the advantages of constant resistance set point, dynamic response at non-optimized power consumption, which is approximately 15% higher than the power consumption of existing constant voltage set point procedures using MEMS devices. Figure 18A Shows a comparison of the dynamic responses to various concentration analytes of the thermal conductivity sensor of the present invention measured in a constant resistance set point operation method and a constant voltage set point operation method. Figure 18A The ratio makes it difficult to view the response in the constant voltage set point operation method. Figure 18B Is set at an enlarged scale Figure 18A Of the thermal conductivity sensor in the constant voltage set point operation method. Figure 18C Shows a comparison of the dynamic responses to various concentration analytes of the catalytic combustible gas sensor of the present invention measured in a constant resistance set point operation method and a constant voltage set point operation method. Similar to Figure 18A Similar, Figure 18C The ratio makes it difficult to view the response in the constant voltage set point operation method. Figure 18D Is set at an enlarged scale Figure 18C Of the catalytic combustible gas sensor in the constant voltage set point operation method.

[0130] All signals visible respectively in Figure 16 And Figure 17 Occur at times when the element has not yet reached thermal equilibrium (refer to Figure 15 ). In addition, Figure 16 And Figure 17 Both show significant differential signals at T < 50 ms. Figure 19 And Figure 20 Expand Figure 16 And Figure 17 To view this time range at an enlarged scale. Figure 19 And Figure 20 Confirm that for both the standard p-element and the thermal conductivity p-element, there are significant differential voltage signals at T < 50 ms for different concentrations of methane. The signal directions of both the standard p-element and the thermal conductivity p-element are the same, indicating that at this time scale, the standard detector is operating in the thermal conductivity mode. Since T < 50 ms is when the p-element is fully heated to the set point resistance R CRPreviously, the temperature of the p-element was thus lower than the temperature required to combust the analyte gas. In other words, in this state (i.e., below the temperature at which one or more analyte gases combust), the detector is operating in a thermal conductivity mode. Additionally, these figures confirm that even lower duty cycles can accurately detect and / or distinguish methane concentrations by using a dynamic, constant resistance setpoint response.

[0131] An initial heating (T < 50 ms) response and a post-clamp (T > 175 ms) response have been established as possible methods for detecting and / or distinguishing methane concentrations in a dynamic, constant resistance setpoint response. A third metric that can be considered is the length of time the clamping circuitry is enabled. In higher concentrations of analyte gas, the p-element heats up at a faster rate. As a result, the length of time the clamping circuitry overrides the error amplifier decreases, and the time measurement may be sufficient to approximate the concentration of the analyte gas. Figure 21 A comparative study of the clamp time versus methane concentration for the thermal conductivity sensor of the present invention and the catalytic combustible gas sensor of the present invention is shown, confirming the dependence of the clamp time on the analyte concentration for each mode of operation.

[0132] The dynamic, constant resistance setpoint devices, systems, and methods of the present invention can be used in combination with a combustible gas detection trigger element and / or a "main" combustible gas sensing element for concentration discrimination to increase the signal-to-noise ratio compared to existing available devices, systems, and methods. In multiple embodiments of the combustible gas sensor of the present invention, the sensor can include, for example, a sensing element and a compensating element and at least one other element (as is known in the art and sometimes referred to as a trigger or "sniffing element"). Generally, the trigger element does not need to provide a linear response and does not need to be resistant to positive offset temperature / humidity fluctuations. Due to the elimination of the limitations of linearity and resistance to positive temperature and humidity fluctuations, the size and power limitations of the trigger element may be reduced compared to the "detection" element used for concentration discrimination.

[0133] Figure 22For example, a schematic diagram showing an embodiment of the MEMS or micro-hotplate trigger sensor 100 of the present invention is presented, which includes a housing 102 having a gas inlet 110. A screen or cap 120, which may include or serve as a filter 130, may be placed, for example, in connection with the inlet 110. The energy (current and voltage) used in the MEMS micro-hotplate trigger sensor 100 may be, for example, low enough to provide intrinsic safety, such that a flashback preventer, as known in the field of combustible gas detectors, may not be necessary. As described above, a flashback preventer (e.g., a porous frit) allows ambient gas to enter the housing but prevents combustible / flammable gas in the surroundings from being ignited by the heating element within the housing. One or more heating elements or hot plates 140 and 146 may be used, for example, to heat the oxidation layer 152 (which may be, for example, an oxidation catalyst layer) of the first MEMS element or carrier catalytic element 144 to a first operating temperature. In a plurality of embodiments, a second MEMS element or second carrier catalytic element 150 may be included within the MEMS hotplate trigger sensor 100 to be heated to a second operating temperature.

[0134] In a plurality of embodiments, the first MEMS element 150 may operate as a sensing or detecting element, while the second MEMS element 150 may operate as a compensating element, as known in the field of combustible gas sensors. In other embodiments, the operation of the MEMS elements 144 and 150 may be switched by changing their operating modes. In a plurality of embodiments, the operation of a particular element as a sensing element or a compensating element may be controlled by controlling its operating temperature, for example, as described in U.S. Patent No. 8,826,721. In this regard, if the operating temperature of the element remains at or above the temperature at which the gas will burn on its surface, it may operate as a sensing element. If the operating temperature of the element remains below the temperature at which the gas will burn on its surface, it may operate as a compensating element. The temperature at which the gas will burn on the surface of the element depends on the composition of this surface. A surface including a catalytic material will generally cause combustion at a lower temperature (catalytic ignition temperature) than a surface not including a catalytic material.

[0135] If only operating as the MEMS compensating element 150, it may, for example, include an inactive layer that can be heated by one or more heating elements or hot plates 146. In this case, the second operating temperature may be maintained at a temperature lower than the temperature required to cause combustion on its surface in the absence of a catalyst. Alternatively, an active catalyst may be included on the compensating element 150 and the compensating element 150 may operate at a low enough temperature to prevent catalytic oxidation of combustible gas on its surface.

[0136] The MEMS hotplate sensor 100 can be mounted, for example, on a printed circuit board or PCB 400. The two resistances of the sensing element 144 and the compensating element 150 can be, for example, part of the measurement circuit of the circuit 300 (schematically shown in Figure 22 ; see Figure 2 ), which measurement circuit includes the Wheatstone bridge circuit or an analog Wheatstone bridge as discussed above. Representative examples of MEMS hotplate sensors suitable for the present disclosure are the SGX MP7217 hotplate sensor or the pellistor available from SGX Sensortech, SA, Corcelles-Coromondreche, Switzerland. Such MEMS hotplate sensors are disclosed, for example, in U.S. Patent No. 9,228,967.

[0137] The trigger sensor can be arranged, for example, together with the main combustible gas sensor as a dual-sensor system, or the trigger sensor can be embedded into a single combustible gas sensor system, which single combustible gas sensor system includes, for example, a main combustible gas sensor that provides a calibrated response depending on the analyte gas concentration. The main combustible gas sensor 200 as Figure 22 shown can be, for example, a conventional or regular catalytic bead system, a low thermal mass p-element system, or a low thermal mass MEMS system. Figure 22 An embodiment of the sensor system or device 10a of the present invention is schematically shown, which includes a MEMS hotplate combustible gas sensor 100 as a trigger combustible gas sensor and a conventional or low thermal mass p-element combustible gas sensor 200 as the main combustible gas sensor. As Figure 22 shown, the MEMS hotplate combustible gas sensor 100 and the combustible gas sensor 200 can be placed, for example, to be operably connected to the circuitry 300 via the PCB 400.

[0138] The electronic circuitry 300 of the sensor system or device 10a can be operatively connected, for example, to each of the MEMS microhotplate, the triggering combustible gas sensor 100, and the primary combustible gas sensor 200 to, for example, control the power of the sensors (as described above) and process the output signals from the sensors (as described above). One or more algorithms for controlling the sensors 100 and 200 and / or for processing data can be stored, for example, in the memory system 320 and executed by the processor system 310. The output of the sensor 100 and / or 200 can be provided, for example, to one or more users via a user interface 330 (e.g., including one or more devices for input / output information, including a touchscreen display, a speaker, etc.) that is operatively connected to the processor system 310. The user interface 330 can be provided, for example, as a component of the combustible gas sensor system or device 10a and / or remotely from the combustible gas sensor. An alarm signal can be generated, for example, via the electronic circuitry and provided to the user via one or more components of the user interface 330 (e.g., in a visual, audible manner, etc.).

[0139] The primary combustible gas sensor 200 includes a first element or p-element 240 and a second element or p-element 250. As described above, one of the first element 240 and the second element 250 serves as a sensing element, while the other of the first element 240 and the second element 250 serves as a compensating element. Again, the function of the element can be controlled, for example, by its operating mode / operating temperature. The temperature can be controlled by controlling the power supplied to the element. The two resistances can be, for example, part of a measurement circuit, which is, for example, a Wheatstone bridge circuit or an analog Wheatstone bridge circuit as shown in Figure 2 The characteristics of the second p-element 250 can be matched as closely as possible to those of the active or sensing p-element. In a number of embodiments where the second element 250 operates alone as a compensating p-element, the second element 250 can, for example, not carry a catalyst or carry an inactivated or poisoned catalyst.

[0140] In the illustrated embodiment, the first element or p-element 240 and the second element or p-element 250 are positioned within the holes 260a and 260b of the explosion-proof housing 270 and can be separated from the surrounding environment by a flame arrester (e.g., a porous metal frit 280). A filter element 282 can also be present.

[0141] When the system or device 10a operates in a first mode, the MEMS hotplate trigger sensor 100 operates to detect changes in one or more analyte gases entering the system or device 10a, while the main combustible gas sensor 200 remains in a low-power, inactive, or off state. If the response signal from the MEMS hotplate trigger sensor 100 is determined by the circuitry 300 to indicate that the concentration of one or more analyte gases has changed or has changed by an amount greater than a predetermined threshold, a second operating mode is initiated and activation of the main combustible gas sensor 200 occurs (i.e., activation of the powered-on, active, or on state of the main combustible gas sensor 200). Once the main combustible gas sensor 200 determines that the analyte gas is absent or present at a concentration below the predetermined threshold, the device 10a can return to the first operating mode.

[0142] As described above, the trigger sensor of the present invention need not be but can be a "diagnostic" sensor that has characteristics sufficient to provide an accurate indication of the concentration of the combustible gas analyte being sensed. Such characteristics would include, for example, a sufficient response range to provide an accurate indication of the gas content within the desired concentration range, long-term baseline stability, significant resistance to changes caused by environmental conditions, etc. The trigger sensor of the present invention can be "non-diagnostic" or "pseudo-diagnostic". In this regard, the trigger sensor can have a sufficient range and accuracy to be useful for implementing the trigger function described herein. Stability and accuracy are not important in this function since non-conservative false-negative biases can be avoided. In multiple embodiments, in the case of the non-diagnostic trigger sensor of the present invention, it is not necessary to reference an earlier established calibration event. In the case of a non-diagnostic trigger sensor, a compensating element may not be required.

[0143] Providing both a first MEMS or other low thermal mass element and a second MEMS or other low thermal mass element in the trigger sensor of the present invention requires very little operating energy. The trigger sensor of the present invention can provide a relatively accurate gas concentration output. In this regard, the MEMS or other low thermal mass combustible gas trigger sensor of the present invention provides a compensated gas concentration output or reading when the main combustible gas sensor (e.g., the p-element based sensor 200) is inactive and / or when activated and fully preheated to take a reading. Additionally, if desired, the readings or measurements from the micro-hotplate or other low thermal mass trigger sensor of the present invention can be used to activate an alarm level.

[0144] Even in the case where the trigger sensor of the present invention includes only a single element, the use of a MEMS element provides a significant reduction in power requirements compared to currently available trigger beads. Additionally, regardless of whether the trigger sensor of the present invention includes one or two elements, a significant reduction in power requirements can be achieved by operating in a pulsed mode.

[0145] As described above, providing a low power trigger sensor can reduce the demand power by allowing a very low power (including zero power) operation of a higher power main analysis sensor until the secondary trigger sensor detects a change in the combustible gas concentration or a threshold change. As described herein, operating the trigger sensor in a dynamic or pulsed mode at a constant resistance set point provides intermediate monitoring of the gas mixture in the environment fluidly connected to the sensor device, system, or instrument, while providing an increased signal compared to a constant voltage set point control mode.

[0146] Also as described above, the first main element 240 and the second main element 250 can be operated in a cyclic mode (e.g., the cyclic mode disclosed in U.S. Patent Nos. 8,826,721 and 9,625,406). In this regard, the sensor can cycle between a first mode and a second mode, in which the first main element 240 operates in a higher power mode and the second main element 250 operates in a lower power mode, while in the second mode, the second or compensating element operates in a higher power mode and the first or sensing element operates in a lower power mode. In this regard, the electronic circuitry of the system of the present invention can be adapted or configured, for example, to cycle between a first mode and a second mode, in which the first main element operates in a higher power (higher temperature) mode and the second sensing element operates in a lower power (lower temperature) mode, while in the second mode, the second sensing element operates in a higher power (higher temperature) mode and the first sensing element operates in a lower power (lower temperature) mode. In the first mode, the second sensing element can be used, for example, to compensate for ambient temperature changes. In the second mode, the first sensing element can be used, for example, to compensate for ambient temperature changes. The electronic circuitry can be adapted, for example, to periodically switch between the first mode and the second mode. The electronic circuitry can be adapted, for example, to switch between the first mode and the second mode upon a manual control event. The manually controlled event can include, for example, a power-on event.

[0147] Figure 23 Another embodiment of a system 10B that is operationally similar to system 10A is shown. However, in Figure 23 this embodiment, the trigger sensor 100' includes a first low thermal mass p-element 144' and a second low thermal mass p-element 150'.

[0148] In Figure 22 and Figure 23 this embodiment, the elements of the trigger sensor may, for example, not include a catalyst and operate in a thermal conductivity mode as described herein. In cases where such elements include a catalyst, one can operate the trigger sensor in a thermal conductivity mode and / or a combustible gas sensor mode.

[0149] Figure 24Another embodiment of the system 10c of the present invention is shown, which includes a sensor 200", the sensor 200" includes a first low thermal mass element (e.g., a low thermal mass p element or a MEMS element) 260a" and a second low thermal mass element (e.g., a lower thermal mass p element or a MEMS element) 260b", which can operate as a compensation element as described herein. The first low thermal mass element 260a" may include a catalyst. In a first operating mode, the sensor 200" operates in a pulsed or dynamic trigger mode (with a constant voltage set point or a constant resistance set point) at a first duty cycle. In various embodiments, the sensor 200" operates in a dynamic or pulsed mode with a constant resistance set point. When a threshold response is measured in the trigger mode, the sensor 200" switches to a main mode at a second duty cycle greater than the first duty cycle. The second duty cycle can be, for example, 100%. In various embodiments, the first low thermal mass element 260a" and the second low thermal mass element 260b" are low thermal mass p elements.

[0150] The dynamic, constant resistance set point method described herein is feasible to use with different types of p elements and MEMS devices. Including a heating phase (e.g., at a constant voltage) before enabling constant resistance set point control significantly improves the response time of the sensors of the present invention, but the natural response of the constant resistance set point topology significantly increases the voltage across the element while attempting to heat the element to the desired set point resistance. This voltage can reach levels that are incompatible with some integrated devices on, for example, battery-powered gas detection instruments. Therefore, a voltage monitoring circuit is included to reduce the risk of power-off conditions. The response with both an initial constant voltage heating phase and a phase with a clamping circuit system enabled exhibits a signal that is, for example, sufficient to trigger detection and / or concentration discrimination of a combustible gas analyte (e.g., methane) at a certain duty cycle, which is feasible for low-power operation when the element may or may not have been turned on (energized) long enough to reach thermal equilibrium. The results also show that there are further opportunities to reduce the duty cycle of these elements and thus further reduce power consumption.

[0151] The foregoing description and drawings set forth various representative embodiments of the present. 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 invention, which is indicated by the claims rather than by the foregoing description. All changes and alterations that fall within the equivalent meaning and scope of the claims should be embraced within their scope.

Claims

1. A method of operating a sensing element, the sensing element comprising a heating element operably connected to an electronic circuit system, the sensing element forming a resistive element in the circuit of the electronic circuit system, the method comprising: activating the electronic circuit system to heat the sensing element to a certain temperature, the sensing element responding to an analyte gas at the temperature via an energy pulse input to the heating element, wherein a constant resistance set point is set for the sensing element, variably controlling the energy passing through the circuit during at least a first stage of the energy pulse to achieve the constant resistance set point, and measuring the dynamic response of the sensing element over time during the at least first stage of the energy pulse to detect the analyte gas.

2. The method according to claim 1, wherein the sensing element operates in at least one of the following modes: a mode of detecting the analyte gas via a change in thermal conductivity caused by the response of the sensing element over time during the energy pulse; and a mode of detecting the analyte gas via a combustion reaction of the analyte gas caused by the response of the sensing element over time during the energy pulse.

3. The method according to claim 2, wherein the sensing element comprises a catalyst loaded thereon for catalyzing the combustion of the analyte gas.

4. The method according to claim 3, wherein the sensing element operates in the following modes: a mode of detecting the analyte gas via a change in thermal conductivity caused by the response of the sensing element over time during the energy pulse in a lower temperature range; and a mode of detecting the analyte gas via a combustion reaction of the analyte gas caused by the response of the sensing element over time during the energy pulse in a higher temperature range.

5. The method according to claim 2, wherein the circuit of the electronic circuit system including the heating element is controlled as a Wheatstone bridge circuit or an analog Wheatstone bridge circuit to achieve the constant resistance set point.

6. The method according to claim 5, further comprising applying energy to the circuit for a period of time before the at least first stage to unbalance the circuit.

7. The method according to claim 6, wherein energy is applied to the circuit at a predetermined constant voltage for a predetermined time before the at least first stage to unbalance the circuit.

8. The method according to claim 2, further comprising restricting the voltage, current, or a combination thereof applied to the sensing element or the support circuit system during the at least first stage if the voltage, current, or a combination thereof measured on the electronic circuit system is equal to or greater than a predetermined threshold.

9. The method according to claim 8, wherein the voltage across the sensing element is measured and compared with a reference voltage.

10. The method according to claim 8, comprising starting a second stage during the energy pulse when it is determined by the electronic circuit system that: if the current through the electronic circuit system is to be variably controlled via the energy input to achieve the constant resistance setpoint, the measured voltage, current, or a combination thereof will be less than the predetermined threshold; during the second stage, energy is input to the heating element, and the current through the electronic circuit system is variably controlled via the energy input to achieve the constant resistance setpoint, and the response of the sensing element is measured as the response of the sensing element changes over time.

11. The method according to claim 6, further comprising restricting the voltage, current, or a combination thereof applied to the sensing element during at least the first stage if the voltage, current, or a combination thereof measured on the electronic circuit system is equal to or greater than a predetermined threshold.

12. The method according to claim 11, wherein the measured voltage is the voltage across the sensing element compared to a reference voltage.

13. The method according to claim 11, comprising starting a second stage during the energy pulse when it is determined by the electronic circuit system that: if the current through the electronic circuit system is to be variably controlled via the energy pulse to achieve the constant resistance setpoint, the measured voltage, current, or combination will be less than the predetermined threshold; during the second stage, energy is input to the heating element, and the current through the electronic circuit system is variably controlled via the energy pulse to achieve the constant resistance setpoint, and the response of the sensing element is measured as the response of the sensing element changes over time.

14. The method according to claim 2, wherein the sensing element is a low thermal mass element that operates in a trigger mode of operation by inputting energy pulses to the heating element in a pulsed manner at a first duty cycle.

15. The method according to claim 14, wherein the sensing element comprises a catalyst, and when a response value at or above a threshold is measured, the sensing element operates in a main mode of operation at a second duty cycle higher than the first duty cycle.

16. The method according to claim 10, further comprising measuring the amount of time for which the voltage, current, or a combination thereof is restricted and using the measured amount of time to determine the concentration of the analyte gas.

17. A gas sensor comprising a sensing element, the sensing element comprising a heating element and an electronic circuitry operably connected to the heating element, the sensing element forming a resistive element in the electronic circuitry, the electronic circuitry being configured to heat the sensing element to a certain temperature, the sensing element responding to an analyte gas at the temperature via an energy pulse input to the heating element, wherein a constant resistance set point is set for the sensing element, and during at least a first stage of the energy pulse, the energy through the electronic circuitry is variably controlled to achieve the constant resistance set point, and the electronic circuitry is further configured to measure the dynamic response of the sensing element over time during the at least first stage of the energy pulse.

18. The gas sensor according to claim 17, wherein the electronic circuitry is configured to operate the sensing element in at least one of the following modes: a mode of detecting the analyte gas via a change in thermal conductivity caused by the response of the sensing element over time during the energy pulse; and a mode of detecting the analyte gas via a combustion reaction of the analyte gas caused by the response of the sensing element during the energy pulse.

19. The gas sensor according to claim 18, wherein the sensing element comprises a catalyst loaded thereon for catalyzing the combustion of the analyte gas.

20. A sensor system comprising: an electronic circuitry comprising a control system; a main combustible gas sensor comprising a first main element, the first main element being operably connected to the electronic circuitry and comprising a first main support structure, a first main catalyst supported on the first main support structure, and a first main heating element operably connected to the first main support structure ； a second main element, the second main element being operably connected to the electronic circuitry and comprising a second main support structure, a second main catalyst supported on the second main support structure, and a second main heating element operably connected to the second main support structure; and a trigger sensor including a first trigger element of low thermal mass comprising a first trigger heating element, the first trigger element being operably connected to the electronic circuitry, the first trigger element forming a resistive element in the electronic circuitry, The electronic circuit system is configured to operate the trigger sensor to detect a response value at or above a threshold; when the threshold is detected by the trigger sensor, the main combustible gas sensor is activated from a low power state; the electronic circuit system is further configured to: heat the first trigger element to a certain temperature, the first trigger element responding to an analyte gas at the temperature via an energy pulse input to the first trigger heating element, wherein a constant resistance set point is set for the first trigger heating element, and the energy of the electronic circuit system is variably controlled during the energy pulse to achieve the constant resistance set point, and the electronic circuit system is further configured to measure the dynamic response of the first trigger element over time during the energy pulse.

21. The sensor system according to claim 20, wherein the electronic circuit system is configured to operate the first trigger element in at least one of the following modes: a mode of detecting the analyte gas via a change in thermal conductivity caused by the response of the first trigger element over time during the energy pulse; and a mode of detecting the analyte gas via a combustion reaction of the analyte gas caused by the response of the first trigger element over time during the energy pulse.

22. The sensor system according to claim 21, wherein the first trigger element comprises a catalyst loaded thereon for catalyzing the combustion of the analyte gas.

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