Thermal conductivity detector based gas sensor 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] TECHNICAL FIELD Embodiments of the present disclosure relate generally to sensing devices, and more specifically to thermal conductivity detector (TCD) based sensing devices. [Background technology]

[0002] Heated sensing devices, such as thermal conductivity gas sensing devices, raise the 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 suffer from technical challenges and limitations. Through exerted effort, ingenuity, and innovation, many of these identified problems have been resolved by developing solutions contained in embodiments of the present disclosure, many examples of which are described in detail herein. Summary of the Invention

[0004] Various embodiments described herein relate to sensing devices and associated methods for sensing thermally conductive gas and / or air flows.

[0005] According to various embodiments of the present disclosure, a sensing device is provided. In some embodiments, the sensing device includes a substrate, a conductive element positioned on the substrate, the conductive element including 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 connection terminal and a second connection terminal of the conductive element, and a processor for controlling the first switching circuit. The conductive element further includes a first connection terminal and a second connection terminal. The processor controls a first switching circuit to selectively connect a DC voltage source to the first and second connection terminals of the conductive element to apply a DC voltage between the first and second connection terminals of the conductive element for a first period of time, and to selectively disconnect the DC voltage source from the first and second connection terminals of the conductive element to measure a voltage between the first and second connection terminals for 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 a plurality of first junctions exist between the first dissimilar material and the second dissimilar material and a plurality of second junctions exist 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, and a plurality of first junctions are positioned on the first portion of the substrate and a plurality of second junctions are positioned on the second portion of the substrate.

[0008] In some embodiments, the first period of time is long enough for the voltage between the first connection terminal and the second connection terminal to reach a steady state voltage, and the second period of time is long enough for the temperature of the first junction and the temperature of the second junction to decrease by a measurable amount.

[0009] In some embodiments, the processor determines a steady-state voltage between the first connection terminal and the 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 air flow across the conductive element.

[0010] In some embodiments, the processor determines a time constant of the voltage between the first connecting terminal and the second connecting terminal over a second period of time 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 air flow across the conductive element.

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

[0012] In some embodiments, the first dissimilar material and the second dissimilar material comprise chromel and alumel, respectively.

[0013] In some embodiments, the processor causes a DC voltage source to apply a plurality of different voltages between the first and second connection terminals of the conductive element, each different voltage being applied with a first polarity for a first time and with a second opposite polarity for a second time, the processor causes a voltage measurement device to measure a voltage between the first and second connection terminals of the conductive element after each of the plurality of different voltages is applied, the processor detects when an abrupt change occurs in a time constant of the voltage between the first and second connection terminals, and determines a temperature coinciding with the abrupt change in the time constant of the voltage between the first and second connection terminals, the temperature being the dew point.

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

[0015] According to various embodiments of the present disclosure, a method for sensing a thermally conductive gas and / or air flow is provided. In some embodiments, the method includes: causing a processor of the sensing device to cause a first switching circuit to selectively connect a direct current (DC) voltage source to a first connection terminal and a second connection terminal of the conductive element; applying a DC voltage between the first connection terminal and the second connection terminal of the conductive element for a first period of time by the DC voltage source; causing a processor of the sensing device to cause the first switching circuit to selectively disconnect the DC voltage source from the first connection terminal and the second connection terminal of the conductive element; and measuring a voltage between the first connection terminal and the second connection terminal for a second period of time by the voltage measuring device. The conductive element includes a first dissimilar material and a second dissimilar material, the first dissimilar material and the second dissimilar material being arranged such that a first junction exists between the first dissimilar material and the second dissimilar material and a second junction exists between the first dissimilar material and the second dissimilar material.

[0016] The foregoing illustrative summary, as well as other exemplary objects and / or advantages of the present disclosure, and the manner in which the same are accomplished, are further described in the following detailed description and its accompanying drawings. [Brief description of the drawings]

[0017] The description of the illustrated embodiments may be read in conjunction with the accompanying drawings. It will be understood that, unless otherwise noted, for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn to scale. For example, unless otherwise noted, dimensions of some of the elements may be exaggerated relative to other elements. Embodiments incorporating the teachings of the present disclosure are illustrated and described in conjunction with the figures presented herein. [Figure 1] FIG. 2 is a block diagram of an exemplary sensing device, according to an exemplary embodiment of the present disclosure. [Diagram 2] 1 is a model of an exemplary sensing device, according to an exemplary embodiment of the present disclosure. [Diagram 3]1 is a model of an exemplary sense element of an exemplary sensing device according to an alternative exemplary embodiment of the present disclosure. [Figure 4] 1 is a graph illustrating a voltage response of a sensing element of an exemplary sensing device, according to an exemplary embodiment of the present disclosure. [Diagram 5] 1 is a flow diagram illustrating an example method of operating an example sensing device according to an example embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Certain embodiments of the present disclosure will now be described in more detail below with reference to the accompanying drawings, which illustrate some, but not all, embodiments of the present disclosure. Indeed, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0019] As used herein, terms such as "front," "rear," "top," "bottom," "left," "right," and the like are used for explanatory purposes to describe the relative positions of particular components or portions of components in the examples provided below. Additionally, as will be apparent to one of ordinary skill in the art in view of this disclosure, the terms "substantially" and "approximately" indicate that the referenced element or associated description is accurate to within applicable engineering tolerances.

[0020] As used herein, the term "comprising" means including, but not limited to, and should be interpreted in the manner typically used in patent context. The use of broader terms such as "comprises," "includes," and "having" should be understood to provide support for narrower terms such as "consisting of," "consisting essentially of," and "comprised substantially of."

[0021] The phrases "in one embodiment," "according to one embodiment," "in some embodiments," and similar phrases generally mean that the particular feature, structure, or characteristic that follows the phrase may be included in at least one embodiment of the present disclosure, and may be included in more than one embodiment of the present 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 the particular feature, structure, or characteristic that follows the phrase may be included in at least one embodiment of the present disclosure, and may be included in more than one embodiment of the present disclosure (although such phrases do not necessarily refer to the same embodiment).

[0023] When the specification states that a certain component or feature is included or has a characteristic, using the term "may," "can," "could," "should," "would," "preferably," "possibly," "typically," "optionally," "for example," "in one embodiment," "in some embodiments," "in many cases," or "might" (or other such phrases), it does not require that the particular component or feature be included or have the characteristic. Such component or feature may be optionally included or excluded in some embodiments.

[0024] As used herein, the word "example" or "exemplary" means "serving as an example, instance, or illustration." Any embodiment described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0025] In this disclosure, the terms "electronically coupled," "electronically coupled," "electronically coupled," "communicating with," "in electronic communication with," or "connected" refer to two or more elements or components that are connected via wired and / or wireless means such that signals, electrical voltage / current, data, and / or information can be transmitted to and / or received from those elements or components.

[0026] The term "component" may refer to an article, device, or apparatus that may comprise one or more surfaces, portions, layers, and / or elements. For example, an example component may comprise one or more substrates that may provide an underlying layer for the component, may form part of the substrate, and / or may comprise one or more elements disposed on the substrate. In this disclosure, the term "element" may refer to an article, device, or apparatus that may provide one or more functions.

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

[0028] Terms such as "sensor," "sensor circuit," "sensing circuit," "sensing element," "sense element," and the like, may refer to one or more components, integrated circuits, and the like in a sensing device that interacts with the environment, detects an input to be detected (e.g., the presence of a hazardous gas), and provides an output to be interpreted (e.g., a voltage) to another component in 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 created across the thermopile(s), generating an output voltage corresponding to the temperature difference. When exposed to a gas that has 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 concentration of the gas and can be detected, measured, and used to provide an alarm.

[0029] Various embodiments of the present disclosure may be provided to address the challenges and limitations associated with conventional sensing devices. For example, various embodiments of the present disclosure may provide exemplary sensing devices, apparatus, methods, and systems having a sense element without a separate heating element, as compared to some conventional sensing devices. The exemplary sensing device includes a sense element that utilizes 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 in the thermocouple. The Seebeck effect provides that a temperature difference between two dissimilar conductors or semiconductors creates a voltage difference between the two materials.

[0030] Various embodiments of the present disclosure provide an exemplary sensing device, the sensing device having a sense element including first and second dissimilar conductive or semiconductive materials arranged such that there is at least a first junction between the first dissimilar material and the second dissimilar material and there is at least a second junction between the first dissimilar material and the second dissimilar material. In various embodiments, a direct current (DC) voltage is applied between the terminals of the sense element for a first predetermined period of time, which causes one or more of the junctions to be hotter than the ambient air and one or more of the junctions to be cooler than the ambient air according to the Peltier effect. 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 for a second predetermined period of time. 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 of the junctions reaches the ambient air temperature.

[0032] In various embodiments, a DC voltage is applied across the terminals of the sense element by closing the first switch assembly, and a 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 is dissipated from the junction to the surrounding air increases in the presence of a gas with a higher thermal conductivity than air (hydrogen or helium) and / or with increased air flow across the sense element. Under such conditions, the time for the junction temperature to reach equilibrium is reduced. Generally, the time to reach thermal equilibrium decreases by about 1 percent for every 1 percent increase in hydrogen concentration in the air.

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

[0035] In various embodiments, a voltage measurement device (e.g., a voltmeter) is selectively connected to the sense element to measure a voltage across the terminals of the sense element. In various embodiments, the voltage measurement device is connected to the sense element by closing the second switch assembly, and the voltage measurement device is 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 the first dissimilar material and the 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 a thinner portion and a thicker portion such that the plurality of first junctions are positioned on the thinner portion of the substrate and the plurality of second junctions are positioned on the thicker portion 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] 1, a block diagram of an exemplary sensing device 100 is provided, in accordance with various embodiments of the present disclosure. As depicted in FIG. 1, in some embodiments, sensing device 100 comprises a processor or processing circuitry 102, a memory circuitry 104, an input / output circuitry 106, a communication circuitry 108, a sensing circuitry 110, and a power source 118. In some embodiments, sensing device 100 is configured to execute and perform the operations described herein.

[0039] Although the components are described in terms of functional limitations, it should be understood that at least some of the specific implementations necessarily involve the use of specific computing hardware. It should also be understood that in some embodiments, some of the components described herein include similar or common hardware. For example, in some embodiments, two sets of circuits both leverage the use of the same processor(s), memory(s), circuit(s), etc. to perform their related functions, such that duplicate hardware is not required for each set of circuits.

[0040] The processing circuit 102 may be embodied in a number of different ways. In various embodiments, use of the term "processor" or "processing circuit" should be understood to include a single-core processor, a multi-core processor, multiple processors internal to the sensing device 100, and / or one or more remote or "cloud" processor(s) external to 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 in addition, the processing circuit 102 may include one or more processor(s) configured in tandem via a bus to enable independent execution of operations, instructions, pipelines, and / or multi-threads.

[0041] In an exemplary embodiment, the processing circuit 102 may be configured to execute instructions stored in the memory circuit 104 or otherwise accessible to the processor. Alternatively, or in addition, the processing circuit 102 may be configured to execute hard-coded functions. As such, whether configured by hardware or software methods, or a combination thereof, the processing circuit 102 may represent an entity (e.g., physically embodied in a circuit) capable of performing operations according to embodiments of the present disclosure while configured accordingly. Alternatively, or in addition, the processing circuit 102 may be embodied as an executor of software instructions, which, when executed, may specifically configure the processing circuit 102 to perform various algorithms embodied in one or more operations described herein. 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 a coprocessor, or any other processing circuitry 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 circuitry 104 may be non-transitory, e.g., include one or more volatile and / or non-volatile memories. In some embodiments, the memory circuitry 104 includes or embodies an electronic storage device (e.g., a computer-readable storage medium). In some embodiments, the memory circuitry 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 present 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 output to a user and / or receive 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 interface(s). In some embodiments, the user interface may include a display with the interface(s) rendered as a web user interface, an application user interface, a user device, a back-end system, or the like. In some embodiments, the input / output circuit 106 also includes a keyboard, a mouse, a joystick, a touch screen, a touch area, soft keys, a microphone, a 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 a memory (e.g., memory circuit 104, etc.) accessible to a processor. In some embodiments, the input / output circuitry 106 includes or utilizes user-facing applications to provide input / output functionality to a computing device and / or other display associated with a user.

[0045] A communication circuit 108 may be included within the sensing device 100. The communication circuit 108 may include any means, such as devices or circuits embodied in either hardware or a combination of hardware and software, configured to transmit and receive data to and from a network and / or any other devices, circuits, or modules in communication with the sensing device 100. In some embodiments, the communication circuit 108 includes a network interface, for example, to enable communication with a wired or wireless communication network. Additionally or alternatively, the communication circuit 108 may include one or more network interface card(s), antenna(s), bus(es), switch(es), router(s), modem(s), and supporting hardware, firmware, and / or software, or any other devices suitable for enabling communication over one or more communication network(s). In some embodiments, the communication circuit 108 may include circuitry for interacting with the antenna(s) and / or other hardware or software to cause transmission of signals via the antenna(s) and / or handle reception of signals received via the antenna(s). In some embodiments, the communications circuitry 108 enables transmission of data to and / or reception of data from a user device, one or more sensors, and / or other external computing device(s) in communication with the sensing device 100.

[0046] The sensing circuit 110 may comprise any suitable circuitry to provide a 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 measurement device 116.

[0047] The power source 118 provides power to the sensing device 100, including power to the sensing circuitry 110. The power source 118 may comprise any suitable power source and, in the case of a portable sensing device, will likely comprise one or more batteries.

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

[0049] Although the above description provides an example sensing device 100, it should be noted that the scope of the present disclosure is not limited to the above description. In some embodiments, the example sensing device 100 according to the present disclosure may be in other forms. In some embodiments, the example sensing device 100 may include one or more additional and / or alternative elements and / or may be structured differently than illustrated in FIG.

[0050] Reference is now made to FIG. 2, which is a model of an exemplary sensing device, according to an exemplary embodiment of the present disclosure. The exemplary sensing device 200 of FIG. 2 includes a processing circuit 202, a DC voltage source 212, a sense element (e.g., a thermocouple) 214, a voltage measurement 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 measurement 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 FIG. 2, the sense element 214 includes a single thermocouple having two dissimilar materials (one material is indicated by hatching and the other material is 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 such that the sensing device 200 can detect gases having a higher thermal conductivity than air based on the rate at which heat is dissipated from the junctions J1, J2 to the ambient air. Because the rate at which heat is dissipated from the junctions J1, J2 also increases with increasing air flow across the sense element, in some embodiments, the sense element 214 in devices used as gas sensors is positioned within a housing having a structure (e.g., a baffle) that allows ambient air to reach the sense element 214 but shields the sense element 214 from the flowing air. Conversely, in embodiments, the sense element 214 in devices used as flow sensors is positioned within a housing having a structure (e.g., a tunnel) that allows flowing air to reach the sense element 214.

[0051] In the illustrated embodiment of FIG. 2, the processing circuit 202 sends control signals to the first switch assembly S1 and the second switch assembly S2 to control their opening and closing. The processing circuit 202 causes the first switch assembly S1 to close and the second switch assembly S2 to open, connecting the DC voltage source 212 to the sense element 214 and disconnecting the voltage measurement device 216 from the sense element 214. Due to the two dissimilar materials, a voltage applied across the sense element 214 causes one junction (e.g., J1) to increase in temperature above the ambient temperature and the other junction (e.g., J2) to decrease in temperature below the ambient temperature due to the Peltier effect. Which junctions see an increase in temperature and which junctions see a decrease in temperature depend on the polarity of the applied DC voltage and can be changed by changing the polarity of the applied DC voltage.

[0052] The processing circuit 202 causes the second switch assembly S2 to close and the first switch assembly S2 to open, 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 temperature of the two junctions begins to equilibrate and return to the ambient temperature over time. For two dissimilar materials, the temperature difference between the two dissimilar conductors or semiconductors creates 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 a period of time during which the temperature difference decreases and the voltage correspondingly decreases. 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 dissimilar material and the second dissimilar material of the sense element are conductive or semiconductive materials. For example, the first dissimilar material and the second dissimilar material may include chromel and alumel, respectively. Chromel is an alloy of nickel and chromium plus nine other elements. Alumel is an alloy containing nickel manganese, aluminum, silicon, and nine other elements. However, any suitable dissimilar conductive or semiconductive material may be used. For example, in various embodiments, any of the materials listed in FIG. 11 of U.S. Patent No. 11,747,184, entitled "THERMOPILE-BASED FLOW SENSING DEVICE," issued on September 5, 2023, may be used as the first dissimilar material and / or the second dissimilar material described herein. The contents of U.S. Patent No. 11,747,184 are incorporated herein in their entirety.

[0054] 2, processing circuit 202 is connected to voltage measurement device 216 to receive the measured voltage. In some embodiments, processing circuit 202 processes the measured voltage (as described further below) to determine the presence and / or concentration of thermally conductive gas adjacent to sense element 214 and / or the presence and / or amount of air flow across sense element 214. In some embodiments, processing circuit 202 generates output signals for transmitting the determined gas concentration and / or air flow, for example, to a display element for display to a user and / or a central monitoring device.

[0055] Reference is now made to FIG. 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 of FIG. 3 includes a DC voltage source 312, a sense element 314, and a first switch assembly S1. For simplicity, FIG. 3 omits the voltage measurement device, processing circuitry, and second switch assembly. In the embodiment illustrated in FIG. 3, the sense element 314 includes multiple thermocouples wired in series such that there are multiple segments of two dissimilar materials (one material shown by hatching and the other material shown 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 a larger voltage is generated by the temperature difference between the dissimilar materials, thereby providing a voltage that is easier to measure.

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

[0057] In some embodiments, the substrate has thinner and thicker portions. In the illustrated embodiment of 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 mentioned 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 generates an output voltage corresponding to temperature. Reference is now made to FIG. 4, which is a graph 400 illustrating the voltage response of an exemplary thermal conductivity gas sensing device. The graph 400 of FIG. 4 shows the voltage (V(sense), y-axis) across the terminals of the exemplary sense element of the exemplary sensing device versus time (t, x-axis). In the graph 400, time t(s) is the time after the DC voltage is applied and the temperature difference (and thus the voltage) reaches its maximum value (which may be referred to as the "steady state time"), time t(1) is when the DC voltage is 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 (for 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) reaches zero (indicating that the temperature of the junction has equilibrated), or any other suitable time.

[0059] Due to faster temperature dissipation as described above, the presence of a gas having a higher thermal conductivity than air or the presence of an air flow causes the steady-state voltage V(s) to be lower and the voltage V(sense) to decrease faster after the voltage is removed from the sense element. As such, the steady-state voltage V(s) is proportional to the concentration of the gas having a higher thermal conductivity than air and is proportional to the air flow. Similarly, the time constant (τ) of the voltage V(sense) curve is also proportional to the concentration of the gas having a higher thermal conductivity than air and is proportional to the air flow. Thus, in various embodiments, the presence of a gas having a higher thermal conductivity than air and / or the presence of an air flow 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 time (t) can be calculated using the following equation:

[0063]

number

[0064] In some embodiments, the steady state voltage (V(s)) and / or time constant (τ) when only air is present (i.e., no gas having a higher thermal conductivity than ambient air is present) and / or when no airflow is present is determined and stored for use in gas and / or airflow detection. Such pre-determination of the steady state voltage (V(s)) and / or time constant (τ) when only air is present and / or when no airflow is present may be performed in any suitable manner and at any suitable time. For example, in some embodiments, the steady state voltage (V(s)) and / or time constant (τ) when only air is present and / or when no airflow is present is determined during calibration of the device. 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 at a number of different gas concentrations and / or airflows and 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 to stored values ​​of steady state voltage (V(s)) and / or time constant (τ) to determine 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, it is not necessary for the voltage during powering to reach a steady state. If it is known how long the DC voltage has been applied and how hot it has become, it is still possible to use the device as described herein, albeit with more complex signal processing. Keeping the powering part 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 comprise planar silicon approximately 10-15 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 junctions of the sense element (e.g., the first junction J1) are thermally isolated from the substrate while other junctions (e.g., the second junction J2) are not. An embodiment in which all of the junctions of the sense element are thermally isolated from the substrate may be referred to as "symmetrical," in that application of a voltage to the sense element causes one set of junctions (e.g., the first junction J1) to become hotter than the substrate and the other set of junctions (e.g., the second junction J2) to become cooler. Embodiments in which some junctions of the sense element are thermally isolated from the substrate while other junctions are not may be referred to as "asymmetric," where one set of junctions (such as the first junction J1) remains near the substrate temperature while the other (floating) set of junctions (such as 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, so that the hot and cold junctions of the device switch with each alternating measurement cycle, and the resulting temperature gradient, and therefore the thermopile output voltage, reverses with each alternating measurement cycle. In such embodiments, offset voltage errors in the electronics may cancel each other out.

[0069] For a device to be classified as "intrinsically safe", the maximum temperature of the device must be kept below the temperature at which flammable gases can be ignited. This maximum temperature can be as low as 100°C depending on the flammable gases present. By heating one end of the device and cooling the other (symmetric sensor), a two-fold temperature difference can be created for the same upper limit temperature. For asymmetric sensors, the floating end can be cooled rather than heated relative to the substrate, thereby keeping the maximum temperature of the device below the ambient temperature. In this regard, some embodiments of the present invention can avoid excessive temperature rise above the gradient.

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

[0071] Reference is now made to Figure 5, which provides a flow diagram illustrating exemplary steps, processes, procedures, and / or operations according to various embodiments of the present disclosure. The various methods described herein, including, for example, the method as shown in Figure 5, can provide various technical advantages and improvements.

[0072] 5, an exemplary method 500 is illustrated. In some embodiments, the exemplary method includes a method for sensing a thermally conductive gas and / or air flow. 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 connection with FIG. 1) causes a first switch assembly to close and a second switch assembly to open. As described above, closing such a first switch assembly connects a DC voltage source (such as, but not limited to, the DC voltage source 112 of the exemplary sensing device 100 described above in connection with FIG. 1) to a sense element (such as, but not limited to, the sense element 114 of the exemplary sensing device 100 described above in connection with FIG. 1).

[0073] In step / operation 503, a DC voltage source (such as, but not limited to, DC voltage source 112 of the exemplary sensing device 100 described above in connection with FIG. 1) applies a DC voltage to the sense element. The applied DC voltage can have any suitable magnitude and duration. In some exemplary embodiments, a DC voltage in the millivolts to volts range is applied for tens of milliseconds, depending on how large the sense element is physically (generally speaking, 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 induce 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, processing circuit 102 of the exemplary sensing device 100 described above in connection with FIG. 1 ) causes a first switch assembly to be opened and a second switch assembly to be closed. As described above, opening such a first switch assembly disconnects the DC voltage source and closing such a second switch assembly connects a voltage measurement device (such as, but not limited to, voltage measurement device 116 of the exemplary sensing device 100 described above in connection with FIG. 1 ) to the sense element.

[0075] In step / operation 507, a voltage measurement device (such as, but not limited to, voltage measurement device 116 of the example sensing device 100 described above in connection with FIG. 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, and then the temperature difference between the junctions begins to equilibrate and the measured voltage begins to decay toward zero.

[0076] Although not illustrated in FIG. 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 thermally conductive gas and / or the presence and / or amount of air flow.

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

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

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

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

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

[0082] The foregoing method and process descriptions are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of ordinary skill in the art, the order of steps in the foregoing embodiments may be performed in any order. Words such as "then," "then," "following," and similar words are not intended to limit the order of the steps. These words are merely used to guide the reader through the method description. Furthermore, any reference to claim elements in the singular, for example using the articles "a," "a," or "the," should not be construed as limiting the element to the singular, but may be construed in the plural, as the case may be.

[0083] Although various embodiments according to the principles disclosed herein have been shown and described above, modifications thereof may be made by those skilled in the art without departing from the teachings of the present disclosure. The embodiments described herein are merely representative and are not intended to be limiting. Many variations, combinations and modifications are possible and are within the scope of the present disclosure. Alternative embodiments resulting from combining, integrating and / or omitting features of the embodiment(s) are also within the scope of the present disclosure. Thus, the scope of protection is not limited by the above description, but is defined by the claims that follow, the scope of which includes all equivalents of the subject matter of the claims. Each and every claim is incorporated herein as a further disclosure, and the claims are embodiments of the present disclosure. Furthermore, any advantages and features described above may be related to a particular embodiment, but the application of such issued claims is not limited to processes and structures that achieve any or all of the above advantages or have any or all of the above features.

[0084] In addition, the section headings used herein are provided to be consistent with the suggestions under Title 37, Code of Federal Regulations, Section 1.77 or to otherwise provide organizational implications. These headings are not intended to limit or characterize the disclosure set forth in any claims that may be issued from this disclosure. For example, the description of a technology in the "Background" section should not be construed as an admission that a particular technology is prior art to any disclosure in this disclosure. The "Abstract" section should also not be considered a limiting feature of the disclosure set forth in the claims to be issued. Furthermore, any reference in this disclosure to the singular "disclosure" or "embodiments" should not be used to assert that there is only a single point of novelty in this disclosure. Multiple embodiments of the disclosure may be described according to the limitations of multiple claims that may be issued from this disclosure, and such claims thus define the disclosure and their equivalents protected thereby. In all cases, the claims should be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

[0085] Additionally, the systems, subsystems, devices, techniques, and methods described and illustrated in various embodiments, individually or separately, may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other devices or components shown or described as being coupled or in communication with each other may be indirectly coupled through some intermediate device or component, whether electrical, mechanical, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one of ordinary skill 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 come to mind to one skilled in the art to which these embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Although the drawings show only certain components of the devices and systems described herein, various other components may be used in conjunction with the components and structures disclosed herein. It should be understood, therefore, that the 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 method described above need not necessarily be performed in the order depicted in the accompanying drawings, and in some cases, one or more of the depicted steps may be performed substantially simultaneously, or additional steps may be included. Although certain terms have been employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A sensing device, comprising: 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 a first junction exists between the first dissimilar material and the second dissimilar material and a second junction exists between the first dissimilar material and the second dissimilar material, the conductive element further comprising a first connection terminal and a second connection terminal; A direct current (DC) voltage source; A voltage measuring device; a first switching circuit for selectively connecting the DC voltage source to the first connection terminal and the second connection terminal of the conductive element; and a processor that controls the first switching circuit to selectively connect the DC voltage source to the first and second connection terminals of the conductive element to apply a DC voltage between the first and second connection terminals of the conductive element for a first period of time and to selectively disconnect the DC voltage source from the first and second connection terminals of the conductive element to measure a voltage between the first and second connection terminals for a second period of time.

2. the first dissimilar material and the second dissimilar material of the conductive element are arranged such that there are a plurality of first junctions between the first dissimilar material and the second dissimilar material and there are a plurality of second junctions 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 bonds are positioned on the first portion of the substrate; The sensing device of claim 1 , wherein the plurality of second junctions are positioned on the second portion of the substrate.

3. the first period of time being long enough for the voltage between the first connection terminal and the second connection terminal to reach a steady-state voltage; the second period of time being long enough for the temperature of the first junction and the temperature of the second junction to decrease by a measurable amount; the processor determines the steady state voltage between the first connection terminal and the second connection terminal; the processor using the determined steady state voltage to determine (i) a presence and / or concentration of a thermally conductive gas adjacent to a conductive element, and / or (ii) a presence and / or amount of air flow across the conductive element; the processor determines a time constant of the voltage between the first and second connection terminals over the second time period; 2. The sensing device of claim 1, wherein the processor uses the determined time constant to determine (i) the presence and / or concentration of thermally conductive gas adjacent the conductive element and / or (ii) the presence and / or amount of air flow across the conductive element.

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