Gas sensor based on thermal conductivity detector and related method

Abstract

To provide a sensing device.SOLUTION: For example, the sensing device may include a conductive element, a DC voltage source, a voltage measurement device, a first switching circuit for selectively connecting the DC voltage source to the conductive element, and a processor that controls the first switching circuit. The conductive element includes a first dissimilar material and a second dissimilar material, and the first and second dissimilar materials are arranged such that a first junction exists between the dissimilar materials and a second junction exists between the dissimilar materials. The processor controls the first switching circuit, connects the DC voltage source to the conductive element, applies a DC voltage for a first period, cuts off the DC voltage source, and measures a voltage over a second period.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to sensing devices, and more specifically, to thermal conductivity detector (TCD)-based sensing devices.

Background Art

[0002] Heated sensing devices, such as thermal conductivity gas sensing devices, raise a sensing element to a desired operating temperature. In many such devices, there is a heating element separate from the sensing element to raise the sensing element to the desired operating temperature.

[0003] Such heated sensing devices are plagued by technical problems and limitations. Through the efforts, ingenuity, and innovation applied, many of these identified problems are solved by developing the solutions included in the embodiments of the present disclosure, and many of those examples are described in detail herein.

Summary of the Invention

[0004] The various embodiments described herein relate to sensing devices and related methods for sensing a thermally conductive gas and / or an air flow.

[0005] Various embodiments of the present disclosure provide sensing devices. In some embodiments, the sensing device comprises a substrate; a conductive element positioned on the substrate, the conductive element comprising a first dissimilar material and a second dissimilar material, the first dissimilar material and the second dissimilar material being arranged such that there is a first junction between the first dissimilar material and the second dissimilar material and a second junction between the first dissimilar material and the second dissimilar material; a direct current (DC) voltage source; a voltage measuring device; a first switching circuit for selectively connecting the DC voltage source to a first and a second connection terminal of the conductive element; and a processor for controlling the first switching circuit. The conductive element further comprises a first and a second connection terminal. The processor controls a first switching circuit to selectively connect a DC voltage source to a first and second connection terminal of a conductive element, applying a DC voltage between the first and second connection terminals of the conductive element for a first period of time, and selectively disconnects the DC voltage source from the first and second connection terminals of the conductive element, measuring the voltage between the first and second connection terminals over a second period of time.

[0006] In some embodiments, the first dissimilar material and the second dissimilar material of the conductive element are arranged such that there are a plurality of first joints between the first dissimilar material and the second dissimilar material, and a plurality of second joints between the first dissimilar material and the second dissimilar material.

[0007] In some embodiments, the substrate comprises a first portion and a second portion that is thinner than the first portion, with a plurality of first bonding points positioned on the first portion of the substrate and a plurality of second bonding points positioned on the second portion of the substrate.

[0008] In some embodiments, the first period is long enough for the voltage between the first and second connection terminals to reach a steady-state voltage, and the second period is long enough for the temperatures of the first and second junctions to decrease by a measurable amount.

[0009] In some embodiments, the processor determines a steady-state voltage between a first connection terminal and a second connection terminal, and uses the determined steady-state voltage to determine (i) the presence and / or concentration of a thermally conductive gas adjacent to the conductive element, and / or (ii) the presence and / or amount of airflow across the conductive element.

[0010] In some embodiments, the processor determines a time constant of the voltage between a first terminal and a second terminal over a second period, and uses the determined time constant to determine (i) the presence and / or concentration of a thermally conductive gas adjacent to the conductive element, and / or (ii) the presence and / or amount of airflow across the conductive element.

[0011] In some embodiments, the first dissimilar material and the second dissimilar material include the first and second dissimilar conductive or semiconductive materials.

[0012] In some embodiments, the first dissimilar material and the second dissimilar material include Chromel and Alumel, respectively.

[0013] In some embodiments, the processor causes a DC voltage source to apply a plurality of different voltages between a first and second connection terminal of a conductive element, each different voltage being applied with a first polarity for a first time and a second opposite polarity for a second time; the processor causes a voltage measuring device to measure the voltage between the first and second connection terminals of the conductive element after each of the plurality of different voltages has been applied; the processor detects when there is a sudden change in the time constant of the voltage between the first and second connection terminals; and determines a temperature that is consistent with the sudden change in the time constant of the voltage between the first and second connection terminals, where the temperature is the dew point.

[0014] In some embodiments, the DC voltage source comprises one or more batteries.

[0015] Various embodiments of the present disclosure provide a method for sensing a thermally conductive gas and / or airflow. In some embodiments, the method includes: using a processor of a sensing device to cause a first switching circuit to selectively connect a direct current (DC) voltage source to first and second connection terminals of a conductive element; applying a DC voltage between the first and second connection terminals of the conductive element for a first period of time using the DC voltage source; using a processor of the sensing device to cause the first switching circuit to selectively disconnect the DC voltage source from the first and second connection terminals of the conductive element; and measuring the voltage between the first and second connection terminals over a second period of time using a voltage measuring device. The conductive element comprises a first dissimilar material and a second dissimilar material, which are arranged such that a first junction exists between the first and second dissimilar materials and a second junction exists between the first and second dissimilar materials.

[0016] The above-mentioned illustrative overview, as well as other exemplary purposes and / or advantages of the present disclosure, and the methods by which they are achieved, are further described in the following embodiments for carrying out the invention and the accompanying drawings. [Brief explanation of the drawing]

[0017] The description of the illustrated embodiments can be read in conjunction with the accompanying drawings. Unless otherwise noted, it should be understood that for the sake of simplification and clarity, the elements shown in the drawings are not necessarily drawn to scale. For example, unless otherwise noted, the dimensions of some elements may be exaggerated relative to others. Embodiments incorporating the teachings of this disclosure are shown and described in relation to the drawings presented herein. [Figure 1] This is a block diagram of an exemplary sensing device according to an exemplary embodiment of the present disclosure. [Figure 2] This is a model of an exemplary sensing device according to an exemplary embodiment of the present disclosure. [Figure 3]A model of an exemplary sense element of an exemplary sensing device according to an alternative exemplary embodiment of the present disclosure. [Figure 4] This graph illustrates the voltage response of the sensing element of an exemplary sensing device according to an exemplary embodiment of the present disclosure. [Figure 5] This flowchart illustrates an exemplary method for operating an exemplary sensing device according to an exemplary embodiment of the present disclosure. [Modes for carrying out the invention]

[0018] Next, several embodiments of this disclosure will be described in more detail below with reference to the accompanying drawings, but these are only some embodiments, not all of the disclosure. In fact, this disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments described herein, but rather these embodiments are provided to satisfy the legal requirements to which this disclosure is applicable. Similar figures refer to similar elements throughout.

[0019] Where used herein, terms such as “front,” “rear,” “top,” “bottom,” “left,” and “right” are used for illustrative purposes in the examples provided below to describe the relative position of a particular component or part of a component. Furthermore, as will be apparent to those skilled in the art from the viewpoint of this disclosure, the terms “substantially” and “approximately” indicate that the referenced element or related description is accurate within applicable engineering tolerances.

[0020] As used herein, the term “comprising” means, but not necessarily, to include, and should be interpreted in the manner typically used in patent contexts. It should be understood that the use of broader terms such as “comprises,” “includes,” and “having” supports narrower terms such as “consisting of,” “consisting essentially of,” and “comprised substantially of.”

[0021] The phrases "in one embodiment," "according to one embodiment," "in several embodiments," and similar phrases generally mean that a particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the Disclosure, and may be included in two or more embodiments of the Disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

[0022] The phrases "in one embodiment," "according to one embodiment," "in some embodiments," and similar phrases generally mean that a particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the Disclosure, and may be included in two or more embodiments of the Disclosure (such phrases do not necessarily refer to the same embodiment).

[0023] When this specification presents that a certain component or feature “may”, “can”, “could”, “should”, “would”, “preferably”, “optionally”, “typically”, “arbitrarily”, “for example”, “as an embodiment”, “in some embodiments”, “in many cases”, or “might” (or other such expressions) is included or has a characteristic, that particular component or feature is not required to be included or to have the characteristic. Such a component or feature may optionally be included in or excluded from some embodiments.

[0024] As used herein, the terms “example” or “exemplary” mean “serving as an example, instance, or illustration”. Any embodiment described herein as an “example” or “exemplary” should not necessarily be construed as being more preferable or advantageous than other embodiments.

[0025] In the present disclosure, the terms “electronically coupled”, “electronically coupling”, “couple electronically to”, “communicate with”, “electronically communicate with”, or “connected” refer to two or more elements or components that are connected via wired means and / or wireless means such that signals, electrical voltage / current, data, and / or information can be transmitted and / or received by these elements or components.

[0026] The term “component” may refer to an article, device, or apparatus that may comprise one or more surfaces, parts, layers, and / or elements. For example, an exemplary component may comprise one or more substrates that may provide a lower layer for the component, may form a part of the substrate, and / or may comprise one or more elements disposed on the substrate. In the present disclosure, the term “element” may refer to an article, device, or apparatus that may provide one or more functions.

[0027] The term "sensing device" can refer to an article, device, or apparatus that measures physical input from its environment and converts that input into data that can be interpreted by either a human or a machine. Sensing devices can be used in a variety of applications, including the detection of hazardous gases in the environment. Sensing devices may be mounted in a fixed location or may be portable so that they are carried by a user. Portable sensing devices are typically battery-powered. One common type of sensing device is a thermal conductivity gas sensing device, which can measure the concentration of a gas according to the difference in thermal conductivity between different gases and air.

[0028] Terms such as "sensor," "sensor circuit," "sensing circuit," "sensing element," and "sense element" can refer to one or more components, integrated circuits, etc., within a sensing device that interact with the environment, detect inputs to be detected (e.g., the presence of a hazardous gas), and provide outputs to be interpreted (e.g., voltage) to other components within the sensing device. In some conventional thermal conductivity gas sensing devices, the sensing circuit comprises a resistive heating element and one or more thermopiles. When power is applied to the resistive heating element, a temperature gradient is generated across the thermopile(s), producing an output voltage corresponding to the temperature difference. When exposed to a gas with a higher thermal conductivity than air (e.g., hydrogen), there is more heat loss from the resistive heating element, and therefore a lower temperature. This temperature difference changes with the gas concentration and can be detected, measured, and used to provide an alarm.

[0029] Various embodiments of this disclosure can be provided to address the challenges and limitations associated with conventional sensing devices. For example, various embodiments of this disclosure may provide exemplary sensing devices, apparatus, methods, and systems having a sense element without a separate heating element, compared to some conventional sensing devices. Exemplary sensing devices include sense elements that utilize the Peltier effect and the Seebeck effect, as described herein. The Peltier effect provides that a voltage applied across a thermocouple causes a temperature difference between the junctions of different materials within the thermocouple. The Seebeck effect provides that a temperature difference between two dissimilar conductors or semiconductors generates a voltage difference between the two materials.

[0030] Various embodiments of the present disclosure provide exemplary sensing devices having a sense element comprising first and second heterogeneous conductive or semiconductive materials, the first and second heterogeneous conductive or semiconductive materials arranged such that at least a first junction exists between the first heterogeneous material and the second heterogeneous material, and at least a second junction exists between the first heterogeneous material and the second heterogeneous material. In various embodiments, a direct current (DC) voltage is applied between the terminals of the sense element for a first predetermined period, which, according to the Peltier effect, causes one or more of the junctions to become hotter than ambient air and one or more of the junctions to become colder than ambient air. In various embodiments, when the DC voltage is removed from the terminals of the sense element, the junctions are at different temperatures, and according to the Seebeck effect, a voltage is generated between the terminals of the sense element due to the temperature difference. In various embodiments, the voltage between the terminals of the sense element is measured over a second predetermined period. In various embodiments, which of the junctions becomes hotter and which becomes colder can be changed by reversing the polarity of the applied DC voltage.

[0031] In various embodiments, after the DC voltage is removed from the terminals of the sense element, the temperature difference between the junctions decreases by a measurable amount. In various embodiments, after the DC voltage is removed from the terminals of the sense element, the temperature of each junction reaches the ambient air temperature.

[0032] In various embodiments, a DC voltage is applied between the terminals of the sense element by closing the first switch assembly, and the DC voltage is removed from the terminals of the sense element by opening the first switch assembly. In various embodiments, a processor controls the opening and closing of the first switch assembly.

[0033] In various embodiments, the rate at which heat dissipates from the junction into the surrounding air increases in the presence of a gas with a higher thermal conductivity than air (hydrogen or helium) and / or with increasing airflow across the sense element. Under such conditions, the time it takes for the junction temperature to reach equilibrium is shortened. Generally, the time to reach thermal equilibrium decreases by about 1 percent for every 1 percent increase in the hydrogen concentration in the air.

[0034] In various embodiments, the shape and characteristics of the measured voltage signal change as the temperature difference dissipates. In various embodiments, the shape and characteristics of the measured voltage signal may correlate with the presence and / or concentration of a gas having a higher thermal conductivity than air, and / or the presence and amount of airflow across the sense element.

[0035] In various embodiments, a voltage measuring device (e.g., a voltmeter) is selectively connected to a sense element to measure the voltage between the terminals of the sense element. In various embodiments, the voltage measuring device is connected to the sense element by closing a second switch assembly, and disconnected from the sense element by opening the second switch assembly. In various embodiments, a processor controls the opening and closing of the second switch assembly.

[0036] In various embodiments, the sense element is mounted on a substrate. In various embodiments, the sense element comprises a plurality of thermocouples forming a thermopile such that a plurality of first junctions exist between a first dissimilar material and a second dissimilar material, and a plurality of second junctions exist between the first dissimilar material and the second dissimilar material. In various embodiments, the substrate comprises thinner and thicker portions such that a plurality of first junctions are positioned on thinner portions of the substrate, and a plurality of second junctions are positioned on thicker portions of the substrate.

[0037] Embodiments of the present disclosure may be used with any suitable sensing device, including but not limited to gas detection sensors, airflow sensors, and dew point / humidity sensors.

[0038] Referring here to Figure 1, a block diagram of an exemplary sensing device 100 according to various embodiments of the present disclosure is provided. As depicted in Figure 1, in some embodiments the sensing device 100 comprises a processor or processing circuit 102, a memory circuit 104, an input / output circuit 106, a communication circuit 108, a sensing circuit 110, and a power supply 118. In some embodiments, the sensing device 100 is configured to perform and carry out the operations described herein.

[0039] While the components are described with respect to their functional limitations, it should be understood that at least some of the particular implementations will inevitably involve the use of certain computing hardware. It should also be understood that in some embodiments, some of the components described herein will involve similar or common hardware. For example, in some embodiments, two sets of circuitry both utilize the use of the same processor(s), memory(s), circuit(s), etc., to perform these related functions, thereby eliminating the need for redundant hardware for each set of circuitry.

[0040] The processing circuit 102 can be embodied in numerous different ways. In various embodiments, the use of the terms “processor” or “processing circuit” should be understood to include single-core processors, multi-core processors, multiple processors within the sensing device 100, and / or one or more remote or “cloud” processors outside the sensing device 100. In some exemplary embodiments, the processing circuit 102 may include one or more processing devices configured to function independently. Alternatively or additionally, the processing circuit 102 may include one or more processors configured in tandem via a bus to enable independent execution of operations, instructions, pipelines, and / or multithreads.

[0041] In one exemplary embodiment, the processing circuit 102 may be configured to execute instructions stored in the memory circuit 104 or instructions that are otherwise accessible to the processor. Alternatively, or additionally, the processing circuit 102 may be configured to perform hardcoded functions. In this way, whether configured by hardware or software methods or a combination thereof, the processing circuit 102 may represent entities (e.g., physically embodied in the circuit) that can perform the operations according to embodiments of the present disclosure while configured accordingly. Alternatively, or additionally, the processing circuit 102 may be embodied as an executor of software instructions, the instructions may specifically configure the processing circuit 102 to perform various algorithms embodied in one or more operations described herein when such instructions are executed. In some embodiments, the processing circuit 102 includes hardware, software, firmware, and / or a combination thereof to perform one or more operations described herein.

[0042] In some embodiments, the processing circuit 102 (and / or coprocessor, or any other processing circuit that assists or is otherwise associated with the processor) communicates with the memory 104 via a bus for passing information between components of the sensing device 100.

[0043] The memory or memory circuit 104 may be non-temporary and may include, for example, one or more volatile and / or non-volatile memories. In some embodiments, the memory circuit 104 includes or embodies an electronic storage device (e.g., a computer-readable storage medium). In some embodiments, the memory circuit 104 is configured to store information, data, content, applications, instructions, etc., to enable the sensing device 100 to perform various operations and / or functions according to exemplary embodiments of the disclosure.

[0044] An input / output circuit 106 may be included within the sensing device 100. In some embodiments, the input / output circuit 106 may provide an output to a user and / or receive an input from a user. The input / output circuit 106 may communicate with the processing circuit 102 to provide such functionality. The input / output circuit 106 may include one or more user interfaces. In some embodiments, the user interface may include a display with an interface that is rendered as a web user interface, application user interface, user device, backend system, etc. In some embodiments, the input / output circuit 106 may also include a keyboard, mouse, joystick, touchscreen, touch area, soft keys, microphone, speaker, or other input / output mechanism. The processing circuit 102 and / or the input / output circuit 106 may be configured to control one or more operations and / or functions of one or more user interface elements through computer program instructions (e.g., software and / or firmware) stored on memory accessible to the processor (e.g., memory circuit 104, etc.). In some embodiments, the input / output circuit 106 includes or utilizes a user-facing application to provide input / output functionality to a computing device and / or other display associated with the user.

[0045] A communication circuit 108 may be included within the sensing device 100. The communication circuit 108 may include any means, such as a device or circuit embodied in either hardware or a combination of hardware and software, configured to send and receive data to and from a network and / or any other device, circuit, or module communicating with the sensing device 100. In some embodiments, the communication circuit 108 includes, for example, a network interface to enable communication with a wired or wireless network. Additionally or alternatively, the communication circuit 108 may include one or more network interface cards, antennas, buses, switches, routers, modems, and support hardware, firmware, and / or software, or any other devices suitable for enabling communication over one or more communication networks. In some embodiments, the communication circuit 108 may include a circuit to interact with antennas and / or other hardware or software to cause the transmission of signals over the antennas and / or to handle the reception of signals received over the antennas. In some embodiments, the communication circuit 108 enables the transmission of data to and / or reception of data from a user device, one or more sensors, and / or other external computing devices that communicate with the sensing device 100.

[0046] The sensing circuit 110 may comprise any suitable circuit for providing the desired sensing function. In the case of a thermal conductivity gas sensing device, the sensing circuit 110 comprises a DC voltage source 112, a sense element 114 (comprising one or more thermopiles), and a voltage measuring device 116.

[0047] The power supply 118 provides power to the sensing device 100, including power to the sensing circuit 110. The power supply 118 may consist of any suitable power source, and in the case of a portable sensing device, it is likely to consist of one or more batteries.

[0048] In some embodiments, two or more sets of circuits 102-110 can be combined. Alternatively or additionally, one or more sets of circuits 102-110 perform some or all of the operations and / or functions described herein as being associated with another circuit. In some embodiments, two or more sets of circuits 102-110 are combined into a single module embodied in hardware, software, firmware, and / or a combination thereof.

[0049] The above description provides an exemplary sensing device 100, but it should be noted that the scope of this disclosure is not limited to the above description. In some embodiments, the exemplary sensing device 100 according to this disclosure may take other forms. In some embodiments, the exemplary sensing device 100 may comprise one or more additional and / or alternative elements and / or may be structured differently from that illustrated in Figure 1.

[0050] Herein, we refer to Figure 2, which is a model of an exemplary sensing device according to an exemplary embodiment of the present disclosure. The exemplary sensing device 200 in Figure 2 comprises a processing circuit 202, a DC voltage source 212, a sense element (e.g., a thermocouple) 214, a voltage measuring device 216, a first switch assembly S1, and a second switch assembly S2. As described above, the DC voltage source 212 is selectively connected to the sense element 214 via the first switch assembly S1, and the voltage measuring device 216 (e.g., a voltmeter) is selectively connected to the sense element 214 via the second switch assembly S2. In the simplified model of Figure 2, the sense element 214 comprises a single thermocouple having two dissimilar materials (one material indicated by hatching and the other material indicated by cross-hatching). The two dissimilar materials are arranged such that there are two junctions J1, J2 between the two dissimilar materials. In various embodiments, the thermocouple of the sense element 214 is exposed to ambient air so that the sensing device 200 can detect a gas having a higher thermal conductivity than air based on the rate at which heat is dissipated from the junctions J1, J2 into the ambient air. Since the rate at which heat is dissipated from the junctions J1, J2 also increases with increasing airflow across the sense element, in some embodiments, the sense element 214 in a device used as a gas sensor is positioned in a housing having a structure (e.g., a baffle) that allows ambient air to reach the sense element 214 but shields it from the air flowing over it. Conversely, in embodiments, the sense element 214 in a device used as a flow sensor is positioned in a housing having a structure (e.g., a tunnel) that allows flowing air to reach the sense element 214.

[0051] In the embodiment illustrated in Figure 2, the processing circuit 202 sends control signals to the first switch assembly S1 and the second switch assembly S2 to control the opening and closing of their switches. The processing circuit 202 closes the first switch assembly S1 and opens the second switch assembly S2, connecting the DC voltage source 212 to the sense element 214 and disconnecting the voltage measuring device 216 from the sense element 214. Due to the two dissimilar materials, the voltage applied across the sense element 214 causes the temperature of one junction (e.g., J1) to rise above the ambient temperature and the temperature of the other junction (e.g., J2) to fall below the ambient temperature, due to the Peltier effect. Which junction sees a temperature rise and which junction sees a temperature fall depends on the polarity of the applied DC voltage, which can be changed by changing the polarity of the applied DC voltage.

[0052] The processing circuit 202 closes the second switch assembly S2 and opens the first switch assembly S2, connecting the voltage measuring device 216 to the sense element 214 and disconnecting the DC voltage source 212 from the sense element 214. After the DC voltage is disconnected from the sense element 214, the temperatures of the two junctions begin to equilibrium and return to ambient temperature over time. Due to the two dissimilar materials, the temperature difference between the two dissimilar conductors or semiconductors generates a voltage difference between the two materials due to the Seebeck effect. This voltage decreases over time as the temperature difference decreases. The voltage measuring device 216 measures this voltage over the period during which the temperature difference decreases and the voltage decreases accordingly. Thus, in some embodiments, the same sense element (i.e., the same thermocouple(s)) is used both to generate the temperature difference and then to measure the voltage generated by the temperature difference as the temperature difference decreases. In this regard, a separate heating element is not required in various embodiments of the present invention.

[0053] In some embodiments, the first and second dissimilar materials of the sense element are conductive or semiconducting materials. For example, the first and second dissimilar materials may include Chromel and Alumel, respectively. Chromel is an alloy of nickel and chromium with nine other elements. Alumel is an alloy containing nickel-manganese, aluminum, silicon, and nine other elements. However, any suitable dissimilar conductive or semiconducting material may be used. For example, in various embodiments, any of the materials listed in Figure 11 of U.S. Patent No. 11,747,184, issued September 5, 2023, entitled "THERMOPILE-BASED FLOW SENSING DEVICE," may be used as the first and / or second dissimilar materials described herein. The contents of U.S. Patent No. 11,747,184 are incorporated herein by reference in their entirety.

[0054] In the embodiment illustrated in Figure 2, the processing circuit 202 is connected to the voltage measuring device 216 to receive the measured voltage. In some embodiments, the processing circuit 202 processes the measured voltage (as further described below) to determine the presence and / or concentration of a thermally conductive gas adjacent to the sense element 214, and / or the presence and / or amount of airflow across the sense element 214. In some embodiments, the processing circuit 202 generates an output signal to transmit the determined gas concentration and / or airflow to, for example, a display element and / or a central monitoring device for display to the user.

[0055] Refer here to Figure 3, which is a model of an exemplary sense element of an exemplary sensing device according to an exemplary embodiment of the present disclosure. The exemplary sensing device 300 in Figure 3 comprises a DC voltage source 312, a sense element 314, and a first switch assembly S1. For simplicity, Figure 3 omits the voltage measuring device, processing circuitry, and second switch assembly. In the embodiment illustrated in Figure 3, the sense element 314 comprises multiple thermocouples wired in series such that there are multiple segments of two dissimilar materials (one material indicated by hatching and the other material indicated by cross-hatching), having multiple first junctions J1 (five shown) and multiple second junctions J2 (four shown). Having multiple thermocouples wired in series causes a larger temperature difference when a voltage is applied by the DC voltage source 312, and the temperature difference between the dissimilar materials generates a larger voltage, thereby providing a voltage that is easier to measure.

[0056] In various embodiments, the sense element is mounted on a substrate (typically planar), such as a silicon substrate. In various embodiments, thinner substrates are preferred so that the substrate itself does not conduct too much heat from the sense element, and the main source of heat loss is heat conduction through the gas surrounding the sense element, rather than heat conduction through the substrate.

[0057] In some embodiments, the substrate has a thinner portion and a thicker portion. In the embodiment illustrated in Figure 3, the substrate includes a thinner portion 320 to which the second joint J2 is attached and a thicker portion 322 to which the first joint J1 is attached.

[0058] As described above, when a DC voltage is applied to the terminals of the sense element of a thermal conductivity gas sensing device as described herein, a temperature gradient is generated across the thermopile(s) that produce the temperature-corresponding output voltage. Herein, we refer to Figure 4, which is Graph 400 illustrating the voltage response of an exemplary thermal conductivity gas sensing device. Graph 400 in Figure 4 shows the voltage (V(sense), y-axis) across the terminals of the exemplary sense element of the exemplary sensing device against time (t, x-axis). In Graph 400, time t(s) is the time after the DC voltage has been applied and the temperature difference (and therefore the voltage) has reached its maximum value (this may be called the “steady-state time”), time t(1) is when the DC voltage has been removed from the terminals of the exemplary sense element and (after a short delay) the temperature and corresponding voltage first begin to change, time t(2) is the end of the measurement period, V(e) is the voltage across the sense element at time t(2), and V(s) is the initial or steady-state voltage (during time t(s)). The end of the measurement period t(2) may be, for example, when the steady-state voltage V(s) has decreased by 50 percent, when the voltage V(sense) has reached zero (indicating that the junction temperature has equalized), or any other suitable time.

[0059] As described above, for faster temperature dissipation, the presence of a gas with a higher thermal conductivity than air or the presence of an airflow lowers the steady-state voltage V(s) and causes the voltage V(sense) to decrease more rapidly after the voltage is removed from the sense element. In this way, the steady-state voltage V(s) is proportional to the concentration of the gas with a higher thermal conductivity than air and proportional to the airflow. Similarly, the time constant (τ) of the voltage V(sense) curve is also proportional to the concentration of the gas with a higher thermal conductivity than air and proportional to the airflow. Therefore, in various embodiments, the presence of a gas with a higher thermal conductivity than air and / or the presence of an airflow can be determined using the measured steady-state voltage V(s) and / or the time constant (τ) of the voltage V(sense) curve.

[0060] In some embodiments, the time constant (τ) of the voltage V (sense) curve can be determined using the following equation:

[0061]

number

[0062] Once the time constant (τ) is determined, V (sense) at any given time (t) can be calculated using the following equation.

[0063]

number

[0064] In some embodiments, the steady-state voltage (Vs) and / or time constant (τ) are determined when only air is present (i.e., when no gas with a higher thermal conductivity than ambient air is present) and / or when no airflow is present, and are stored for use in gas and / or airflow detection. Such prior determination of the steady-state voltage (Vs) and / or time constant (τ) when only air is present and / or when no airflow is present may be performed in any preferred manner and at any preferred time. For example, in some embodiments, the steady-state voltage (Vs) and / or time constant (τ) when only air is present and / or when no airflow is present are determined during device calibration. Such calibration may be performed, for example, during the manufacturing process. In some embodiments, the steady-state voltage (V(s)) and / or time constant (τ) are also determined for several different gas concentrations and / or airflows and are stored for use in gas and / or airflow detection. In this regard, in some embodiments, the measured steady-state voltage (V(s)) and / or time constant (τ) are compared with stored values ​​of the steady-state voltage (V(s)) and / or time constant (τ) to determine the gas concentration and / or airflow.

[0065] In some embodiments, the time constant can be determined by measuring the time it takes for the voltage to decrease by a predetermined amount.

[0066] In some embodiments, the voltage during power supply does not need to reach a steady state. Knowing how long the DC voltage is applied and how hot it gets still allows for the use of the device as described herein, although this involves more complex signal processing. Keeping the power supply portion of the process as short as possible has the advantage of minimizing power consumption.

[0067] In some embodiments, the substrate has a uniform thickness. For example, in some embodiments, the substrate may contain planar silicon about 10 to 15 thousandths of an inch thick. In some embodiments, all of the junctions of the sense element are thermally isolated from the substrate. In some embodiments, some of the junctions of the sense element (e.g., a first junction J1) are thermally isolated from the substrate, while others (e.g., a second junction J2) are not. Embodiments in which all of the junctions of the sense element are thermally isolated from the substrate are sometimes called "symmetrical," in which case, when a voltage is applied to the sense element, one set of junctions (e.g., the first junction J1) becomes hotter than the substrate, while the other set of junctions (e.g., the second junction J2) becomes colder. Embodiments in which some junctions of a sense element are thermally isolated from the substrate while others are not are sometimes referred to as "asymmetrical," in which case one set of junctions (e.g., the first junction J1) remains close to the substrate temperature, while the other (floating) set of junctions (e.g., the second junction J2) is heated or cooled relative to the substrate. In some embodiments, the thermally isolated junctions are thermally isolated because the junctions are positioned on a relatively thin substrate.

[0068] In some symmetrical embodiments, the polarity of the applied DC voltage is changed with each measurement cycle, thereby causing the hot and cold junctions of the device to switch places with each alternating measurement cycle, resulting in a temperature gradient, and therefore the thermopile output voltage, being reversed with each alternating measurement cycle. In such embodiments, offset voltage errors within the electronic device can cancel each other out.

[0069] For a device to be classified as "inherently safe," its maximum temperature must be kept below the temperature at which flammable gases can ignite. This maximum temperature can be lowered to around 100°C depending on the presence of flammable gases. By heating one end of the device and cooling the other end (symmetric sensor), a temperature difference of twice the same upper limit can be created. In the case of an asymmetric sensor, the floating end can be cooled rather than heated relative to the substrate, thereby keeping the maximum temperature of the device lower than the ambient temperature. In this regard, in some embodiments of the present invention, it is possible to avoid excessive temperature rises exceeding the gradient.

[0070] In some asymmetric embodiments, in dry air, the output signal due to the thermal conductivity of air should be the same regardless of whether the floating end is heated or cooled relative to the surroundings (apart from reverse polarity). Similarly, since the heat loss from the device is the same under all conditions, the output voltage signal should simply increase or decrease with the applied voltage, and the transient signal should remain constant with the applied voltage. However, when the floating end is cooled below the dew point of the air, there is a rapid change in heat loss due to condensation occurring on the floating end, and therefore the signal will be quite different from the signal measured at other voltages or when the floating end is heated. Thus, in practice, the devices of some embodiments of the present disclosure can function as both a thermal conductivity device and similar to a cooled mirror dew point meter by performing multiple measurements at different applied voltages and polarities and paying attention to when rapid changes in heat loss occur. In some embodiments, the measured dew point can be used to calculate absolute humidity, which can then be used to apply compensation to the gas thermal conductivity measurement.

[0071] Herein, we refer to Figure 5, which provides a flowchart illustrating exemplary steps, processes, procedures, and / or operations according to various embodiments of the present disclosure. Various methods described herein, including, for example, the method shown in Figure 5, can provide various technical benefits and improvements.

[0072] Referring here to Figure 5, an exemplary method 500 is illustrated. In some embodiments, the exemplary method includes a method for sensing a thermally conductive gas and / or airflow. In step / operation 501, a processor (such as, but not limited to, the processing circuit 102 of the exemplary sensing device 100 described above in relation to Figure 1) causes a first switch assembly to close and a second switch assembly to open. As described above, by closing such a first switch assembly, a DC voltage source (such as, but not limited to, the DC voltage source 112 of the exemplary sensing device 100 described above in relation to Figure 1) is connected to a sense element (such as, but not limited to, the sense element 114 of the exemplary sensing device 100 described above in relation to Figure 1).

[0073] In step / operation 503, a DC voltage source (such as, but not limited to, the DC voltage source 112 of the exemplary sensing device 100 described above in relation to Figure 1) applies a DC voltage to the sense element. The applied DC voltage can have any preferred magnitude and duration. In some exemplary embodiments, a DC voltage in the millivolt-volt range is applied for tens of milliseconds, depending on how physically large the sense element is (generally, the larger the sense element, the longer the DC voltage must be applied to reach a steady-state voltage). This voltage should typically be at a level that can cause a significant temperature difference across the junction (e.g., about 100 degrees Celsius).

[0074] In step / operation 505, a processor (such as, but not limited to, the processing circuit 102 of the exemplary sensing device 100 described above in relation to Figure 1) causes a first switch assembly to open and a second switch assembly to close. As described above, opening such a first switch assembly disconnects the DC voltage source, and closing such a second switch assembly connects a voltage measuring device (such as, but not limited to, the voltage measuring device 116 of the exemplary sensing device 100 described above in relation to Figure 1) to the sense element.

[0075] In step / operation 507, a voltage measuring device (such as, but not limited to, the voltage measuring device 116 of the exemplary sensing device 100 described above in relation to Figure 1) measures the voltage across the sense element. As described above, when the second switch assembly is first closed, the temperature difference between the junctions is at its maximum, there is a short delay, then the temperature difference between the junctions begins to equilibrium, and the measured voltage begins to decay toward zero.

[0076] Although not illustrated in Figure 5, as described above, the voltage measured immediately after the second switch assembly is first closed (i.e., the steady-state voltage) can be used to determine the presence and / or concentration of the thermally conductive gas, and / or the presence and / or amount of airflow.

[0077] In step / operation 509, the processor (such as, but not limited to, the processing circuit 102 of the exemplary sensing device 100 described above in relation to Figure 1) determines the time constant of the voltage curve as described above.

[0078] In step / operation 511, the processor (such as, but not limited to, the processing circuit 102 of the exemplary sensing device 100 described above in relation to Figure 1) uses the determined time constant of the voltage curve to determine the presence and / or concentration of the thermally conductive gas, and / or the presence and / or amount of the airflow, as described above.

[0079] In some embodiments, the method repeats steps / operations 501-511 continuously or periodically.

[0080] The operations and processes described herein support combinations of means for performing a specified function and combinations of operations for performing a specified function. It will be understood that one or more operations, and combinations of operations, may be implemented by a dedicated hardware-based computer system or a dedicated combination of hardware and computer instructions for performing the specified function.

[0081] In some exemplary embodiments, certain behaviors described herein may be modified or further extended as described below. Furthermore, in some embodiments, additional optional behaviors may also be included. It should be understood that each of the modifications, optional additions, or extensions described herein may be included in the behaviors described herein, either alone or in combination with any other feature among those described herein.

[0082] The descriptions of methods and processes described herein are provided merely as illustrative examples and are not intended to require or suggest that the steps of the various embodiments must be performed in the order presented. As those skilled in the art will understand, the order of the steps in the embodiments described herein may be performed in any order. Words such as "then," "next," and "then," and similar words, are not intended to limit the order of the steps. These words are simply used to guide the reader through the description of the method. Furthermore, any reference to a claim element in the singular form using, for example, the articles "a," "a," or "the," should not be interpreted as limiting the element to the singular form, and in some cases may be interpreted as plural.

[0083] Various embodiments of the principles disclosed herein have been shown and described above, and modifications thereof can be made by those skilled in the art without departing from the teachings of this disclosure. The embodiments described herein are merely representative and are not intended to limit. Many variations, combinations, and modifications are possible and within the scope of this disclosure. Alternative embodiments resulting from combining, integrating, and / or omitting features of the embodiments (may be multiple) are also within the scope of this disclosure. Accordingly, the scope of protection is not limited by the above description but is defined by the claims that follow, which include all equivalents of the subject matter of the claims. Each and all of the claims are incorporated herein as further disclosures, and the claims are embodiments of this disclosure. Furthermore, any advantages and features described above may relate to specific embodiments, but the application of such issued claims is not limited to processes and structures that achieve any or all of the advantages described above or have any or all of the features described above.

[0084] In addition, the section headings used herein are provided to be consistent with the proposals under 37, Section 1.77 of the Code of Federal Regulations, or to provide a structural implication. These headings are not intended to limit or characterize the disclosures described in any claims that may be issued from this disclosure. For example, the description of the technology in “Background Art” is not to be construed as acknowledging that a particular technology is prior art to any disclosure in this disclosure. Similarly, the “Abstract” is not to be considered a limiting feature of the disclosures described in any claims that may be issued. Furthermore, no reference in this disclosure to the singular “Disclosure” or “Embodiment” should be used to assert that there is only one point of novelty in this disclosure. Multiple embodiments of this disclosure may be described in accordance with the limitations of multiple claims issued from this disclosure, and such claims, therefore, define this disclosure and their equivalents protected thereby. In all cases, the claims should be considered on their own merit in light of this disclosure, but not constrained by the headings described herein.

[0085] Furthermore, the systems, subsystems, apparatus, techniques, and methods described and illustrated individually or separately in various embodiments may be combined with or integrated with other systems, modules, techniques, or methods without departing from the scope of this disclosure. Other devices or components shown or described as being coupled to or communicating with one another may be indirectly coupled, whether electrically, mechanically, or otherwise, through several intermediate devices or components. Other embodiments of modifications, substitutions, and alterations are readily apparent to those skilled in the art and may be made without departing from the scope disclosed herein.

[0086] Many modifications and other embodiments of the disclosure described herein will be conceived by those skilled in the art who are interested in these embodiments and who benefit from the teachings presented in the foregoing description and the accompanying drawings. The drawings show only certain components of the apparatus and systems described herein, but various other components may be used in conjunction with the components and structures disclosed herein. It should be understood that this disclosure is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, various elements or components may be combined, rearranged, or integrated in another system, or certain features may be omitted or not implemented. Furthermore, the steps in any of the methods described above do not necessarily have to be performed in the order depicted in the appended drawings, and in some cases one or more of the depicted steps may be performed substantially simultaneously, or additional steps may be included. Certain terms are used herein, but they are used in a general and descriptive sense only and not for limiting purposes.

Claims

1. A sensing device, circuit board and A conductive element positioned on the substrate, wherein the conductive element comprises a first dissimilar material and a second dissimilar material, the first dissimilar material and the second dissimilar material are arranged such that a first joint exists between the first dissimilar material and the second dissimilar material and a second joint exists between the first dissimilar material and the second dissimilar material, and the conductive element further comprises a first connection terminal and a second connection terminal, A direct current (DC) voltage source, Voltage measuring device, A first switching circuit for selectively connecting the DC voltage source to the first and second connection terminals of the conductive element, A processor coupled to the first switching circuit, The first switching circuit is controlled to selectively connect the DC voltage source to the first and second connection terminals of the conductive element, thereby applying a DC voltage between the first and second connection terminals of the conductive element for a first period of time, and the DC voltage source is selectively disconnected from the first and second connection terminals of the conductive element, thereby measuring the voltage between the first and second connection terminals over a second period of time. The time constant of the voltage between the first and second connection terminals over the second period is determined, wherein the time constant is proportional to (i) the concentration of a gas having a higher thermal conductivity than air at the first and second joints, and (ii) the airflow at the first and second joints. A sensing device comprising: a processor that uses the determined time constant to determine at least one of (i) the presence and / or concentration of a thermally conductive gas adjacent to the conductive element, and (ii) the presence and / or amount of airflow across the conductive element.

2. The first dissimilar material and the second dissimilar material of the conductive element are arranged such that there are a plurality of first joints between the first dissimilar material and the second dissimilar material, and a plurality of second joints between the first dissimilar material and the second dissimilar material. The substrate includes a first portion and a second portion that is thinner than the first portion. The plurality of first joints are positioned on the first portion of the substrate, The sensing device according to claim 1, wherein the plurality of second bonding portions are positioned on the second portion of the substrate.

3. The first period is a period long enough for the voltage between the first connection terminal and the second connection terminal to reach a steady state voltage. The second period is long enough for the temperature of the first joint and the temperature of the second joint to decrease by a measurable amount. The processor determines the steady-state voltage between the first connection terminal and the second connection terminal. The sensing device according to claim 1, wherein the processor uses the determined steady-state voltage to determine (i) the presence and / or concentration of a thermally conductive gas adjacent to the conductive element, and / or (ii) the presence and / or amount of airflow across the conductive element.

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