Method and controller for controlling a fluid flow sensor

Abstract

A method for controlling a fluid flow sensor in the presence of a flowing fluid, the method comprising determining an initial estimate of a parameter corresponding to the flow rate of the flowing fluid, comparing the initial estimate to a threshold parameter, and based on the comparison, determining the parameter corresponding to the flow rate of the flowing fluid based on a combination of signals from a heater and a temperature sensor of the fluid flow sensor. A controller for a fluid flow sensor is also described.

Description

Technical Field

[0001] This disclosure relates to a method and controller for controlling a fluid flow sensor. In particular, this disclosure relates to a sensor (e.g., a micromechanical sensor) capable of measuring the flow rate of liquids and gases. Specifically, but not exclusively, this disclosure relates to a fluid flow sensor having a heater formed within a discontinuous dielectric film for sensing fluid flow rate or fluid composition characteristics based on thermal conductivity properties. Background Technology

[0002] Thermal fluid flow sensors utilize the thermal interaction between the sensor itself and the fluid. Based on the physical phenomena governing this interaction, flow sensors can be classified into the following three categories:

[0003] (i) An anemometer sensor that measures convective heat transfer caused by fluid flow through a heated element;

[0004] (ii) A heat measurement sensor that detects the asymmetry in temperature distribution generated by the heated element and caused by forced convection of the fluid flow; and

[0005] (iii) Time-of-flight (ToF) sensor, which measures the time elapsed between the application of a thermal pulse and its sensing.

[0006] A review of thermal fluid flow sensors has been published in (B. Van Oudheusden, “Silicon Flow Sensors,” *Control Theory & Applications*, IEEE Transactions on Electrical Engineering, D, 1988, pp. 373-380; B. Van Oudheusden, “Silicon Thermal Flow Sensors,” *Sensors & Actuators A: Physics*, Vol. 30, pp. 5-26, 1992; N. Nguyen, “Micromechanical Flow Sensors—A Review A,” *Flow Measurement & Instrumentation*, Vol. 8, pp. 7-16, 1997; Y.-H. Wang et al., “MEMS-Based Gas Flow Sensors,” *Microfluidics & Nanofluidics*, Vol. 6, pp. 333-346, 2009; J.T. Kuo et al., “Micromechanical Thermal Flow Sensors—A Review A,” *Micromechanics*, Vol. 3, pp. 550-573, 2012). Further background information can also be found in US6460411 by Kersjes et al.

[0007] Typically, a thermal flow sensor comprises a heating element and a temperature sensing element thermally isolated from the substrate (e.g., embedded in a thin film, bridge, cantilever, etc.). Both the heating element and the temperature sensing element are usually located in the most thermally insulated areas (e.g., at the center of the thin film, at the center of the bridge, and at the end of the cantilever, etc.). Flow sensors based on other principles, such as those based on ultrasound or pressure, are also possible.

[0008] Typically, sensor chips are packaged on a substrate and covered with a cap that has inlets and outlets for fluid flow. Examples are given in US8418549B2 and US20180172493. However, such packages tend to be bulky, making them unsuitable for space-constrained applications, such as handheld devices.

[0009] US2014 / 0311912 discloses an apparatus in which a sensor chip / substrate is covered by a cap having channels. Bonding pads are not covered and are used to provide electrical connections. US7905140B2 discloses an apparatus in which a substrate with flow channels is attached to the top of a flow sensor chip, with electrical connections made via wire bonding or vias. US2004 / 0118218 also shows a similar apparatus in which a flow channel substrate is attached to the chip and wires are used to form electrical connections. US10139256 describes an apparatus made of two semiconductor substrates bonded together, one having an inlet to a flow channel and the other having an outlet. One of the substrates contains a flow sensor. Electrical connections are achieved through conductive vias and conductive flow paths on the substrate surfaces. US4548078A describes a flow channel through the back side of a flow sensor chip. US6763710B2 discusses a sensor with two sensing modes. Summary of the Invention

[0010] According to the present invention, there is a flow sensor comprising a heater, a first temperature sensor and a controller, which has three different measurement modes in three different measurement zones: (1) at low flow rate, the flow rate is reported using a signal from the first temperature sensor (using heat measurement method); (2) at high flow rate, the flow rate is reported using a signal from the heater (using wind speed measurement method); and (3) at medium flow rate, the flow rate is reported using a weighted average of signals from the heater and the temperature sensor (using wind speed measurement method and heat measurement method).

[0011] A second temperature sensor may also be used. The first and second temperature sensors can be located on opposite sides of the heater. The signals from these two temperature sensors can be the difference in temperature, voltage, current, or power between them.

[0012] This disclosure relates to a flow sensor and a connected controller. The controller may be integrated with the sensor on the same substrate. Alternatively, the controller may be integrated with the sensor within the same component package. Alternatively, the controller may be separate from the sensor component but connected to the sensor component via wires, traces, or other electrical connections.

[0013] This document describes a method for controlling a fluid flow sensor in the presence of flowing fluid. The method may include: determining an initial estimate of a parameter corresponding to the flow rate of the flowing fluid, and comparing the initial estimate with a threshold parameter. The method may further include, based on the comparison, determining the parameter corresponding to the flow rate of the flowing fluid based on:

[0014] Signal from the temperature sensor of the fluid flow sensor;

[0015] Signal from the heater of the fluid flow sensor; or

[0016] A combination of signals from the heater and temperature sensor from the fluid flow sensor.

[0017] The parameter corresponding to the flow rate of a flowing fluid can correspond to a value determined based on measurement results and / or signals, which is similar to the flow rate.

[0018] The initial estimate of the parameters can be determined directly, or it can be determined based on values ​​similar to or corresponding to the flow rate (e.g., determined from measurements and / or signals).

[0019] An initial estimate can be determined based on signals from the temperature sensor of the fluid flow sensor, signals from the heater of the fluid flow sensor, or a combination of both.

[0020] The threshold parameter can be a first (e.g., lower) threshold parameter. The threshold parameter can also be a second (e.g., upper) threshold parameter.

[0021] The method may include comparing an initial estimate with a first threshold parameter, and when the initial estimate is lower than the first threshold parameter: determining a parameter corresponding to the flow rate based on a signal from a temperature sensor of the fluid flow sensor.

[0022] When the initial estimate is below a first threshold parameter, the method may include determining a parameter corresponding to the flow rate by normalizing (e.g., dividing) the signal from the heater based on the signal from the temperature sensor of the fluid flow sensor.

[0023] The method may include comparing an initial estimate with a second threshold parameter, and when the initial estimate is higher than the second threshold parameter: determining a parameter corresponding to the flow rate based on a signal from the heater of the fluid flow sensor.

[0024] The method may include determining the parameters corresponding to the flow rate based on a combination of signals from the heater and temperature sensor when the initial estimate is between a first threshold parameter and a second threshold parameter.

[0025] The combination of signals from the heater and temperature sensor from the fluid flow sensor can include a weighted average of the signals.

[0026] The contribution rates of the signals from the heater and temperature sensor from the fluid flow sensor can depend on the difference between the initial estimate and the first threshold parameter and the difference with the second threshold parameter.

[0027] The signal from the temperature sensor may include signals from two temperature sensors, and / or may include the difference between the signals from the two temperature sensors.

[0028] It should be noted that it is not necessary to use the actual flow rate value for the initial estimate. Instead, another value or parameter corresponding to the flow rate can be used. This could be a heat transfer coefficient, voltage, current, or power, or any other value that can be derived from signals received from the heater and / or temperature sensor. Similarly, the values ​​of the first threshold parameter and the second threshold parameter can be values ​​corresponding to the flow rate. The method can also determine the value or parameter corresponding to the flow rate, rather than the flow rate itself, as the output.

[0029] Flow can be expressed as mass flow, volumetric flow, pressure difference, or velocity.

[0030] Each signal can include, for example, voltage, current, power, and / or temperature.

[0031] This method is advantageous because it utilizes the optimal sensitivity of both the wind speed measurement mode and the heat measurement mode. The wind speed measurement mode is more sensitive at higher flow rates, while the heat measurement method is more sensitive at lower flow rates. A third mode of the medium flow (e.g., between the first and second thresholds) allows for a smooth transition between the two modes, which might otherwise be impossible.

[0032] This paper also describes a controller for controlling a fluid flow sensor in the presence of flowing fluid. The controller can be configured to, when flowing fluid is present at the fluid flow sensor,: determine an initial estimate of a parameter corresponding to the flow rate of the flowing fluid, and compare the initial estimate with a threshold parameter. The controller can be further configured to: based on the comparison, determine the parameter corresponding to the flow rate of the flowing fluid based on:

[0033] Signal from the temperature sensor of the fluid flow sensor;

[0034] Signal from the heater of the fluid flow sensor; or

[0035] A combination of signals from the heater and temperature sensor from the fluid flow sensor.

[0036] The parameter corresponding to the flow rate of a flowing fluid can correspond to a value determined based on measurement results and / or signals, which is similar to the flow rate.

[0037] The controller can be configured to determine an initial estimate of the parameters corresponding to the flow rate, either directly or based on values ​​similar to the flow rate (e.g., determined from measurements and / or signals).

[0038] An initial estimate can be determined based on signals from the temperature sensor of the fluid flow sensor, the heater of the fluid flow sensor, or a combination of both.

[0039] The threshold parameter can be a first (e.g., lower) threshold parameter. The threshold parameter can also be a second (e.g., upper) threshold parameter.

[0040] The controller can be configured to: compare an initial estimate with a first threshold parameter, and when the initial estimate is lower than the first threshold parameter: determine a parameter corresponding to the flow rate based on a signal from a temperature sensor of the fluid flow sensor.

[0041] The controller can be configured to: compare an initial estimate with a first threshold parameter, and when the initial estimate is lower than the first threshold parameter: determine the parameter corresponding to the flow rate based on the signal from the temperature sensor from the fluid flow sensor, by normalizing (e.g., dividing) the signal from the heater.

[0042] The controller can be configured to compare an initial estimate with a second threshold parameter, and when the initial estimate is higher than the second threshold parameter, to determine the parameter based on the signal from the heater of the fluid flow sensor.

[0043] The controller can be configured to determine the parameters corresponding to the flow rate based on a combination of signals from the heater and temperature sensors when the initial estimate is between a first threshold parameter and a second threshold parameter.

[0044] The combination of signals from the heater and temperature sensor from the fluid flow sensor includes a weighted average of the signals.

[0045] Each signal can include, for example, voltage, current, power, and / or temperature.

[0046] Advantageously, the fluid flow sensor controlled by the controller according to this disclosure is advantageous because it utilizes the optimal sensitivity of both the wind speed measurement mode and the heat measurement mode. The wind speed measurement mode is more sensitive at higher flow rates, while the heat measurement mode is more sensitive at lower flow rates. A third mode of the medium flow (e.g., between the first and second thresholds) allows for a smooth transition between the two modes, which might otherwise be impossible.

[0047] The controller determines the flow rate (or a corresponding value or parameter) using wind speed measurement (using only heater signals) and / or heat measurement (using signals from one or more temperature sensors). Signals from one or both methods can be used to initially determine the flow rate (or its corresponding value or parameter) to ascertain whether it falls within a low, medium, or high flow range. Based on this, the controller determines whether the flow rate is low, medium, or high and uses appropriate methods to report a more accurate flow rate value and / or the corresponding parameter.

[0048] The value or flow rate used to determine whether the flow rate is in the low, medium, or high flow range can be compensated for with respect to temperature or pressure, or it can be left uncompensated.

[0049] Initial estimates of parameters or flow rates can be provided by sources outside the sensor.

[0050] The heater can operate in constant current, constant power, constant voltage, or constant temperature modes. It can operate under constant bias, pulsed bias, or pulse width modulation (PWM) bias. Signals from the heater can be voltage, current, power, temperature, or even the PWM duty cycle. Signals from the temperature sensor can be voltage, current, power, or temperature.

[0051] Preferably, there are two temperature sensors, one located upstream of the heater and the other downstream. The temperature sensors can be at the same distance from the heater, or at different distances. Alternatively, the temperature sensors can be located on the same side of the heater, but at different distances.

[0052] At low flow rates, heat measurement is used to determine and report the flow rate. In this case, a signal from a temperature sensor is used. This can be a signal from one temperature sensor or from two temperature sensors.

[0053] At high flow rates, wind speed measurement is used to determine and report the flow rate. In this case, a signal from the heater is used.

[0054] Under medium flow conditions, the flow rate (or the value or parameter corresponding to the flow rate) is determined independently by both the wind speed measurement method (signal from the heater) and the heat measurement method (signal from the temperature sensor), and the flow rate is determined and reported using a weighted average of the two methods based on the initial estimated flow rate or the corresponding parameter.

[0055] For example, the controller can be designed to treat flow rates below "X" as low flow rates and flow rates below "Y" as high flow rates. If the initially determined flow rate is found to be exactly between "X" and "Y", the reported flow rate will be the average of the flow rates determined by wind speed and heat measurement methods.

[0056] However, if the initial estimated flow rate is closer to "Y", a larger proportion of the wind speed measurements will be used to determine and report the final flow rate value.

[0057] As an equation, this can be written as:

[0058]

[0059] in:

[0060] FF is the final determined flow rate.

[0061] IF is the initial flow estimate

[0062] FA is the flow rate determined by wind speed measurement.

[0063] FC is the flow rate determined by calorimetry.

[0064] Alternatively, instead of the actual flow rate, another value corresponding to the flow rate can be used, which is then converted to the actual flow rate. This value can be compensated for at any stage of the calculation (e.g., for temperature or pressure). The compensation can also be applied to the final flow rate value before reporting. Averaging or other signal processing techniques can also be applied at any stage.

[0065] This example uses a linearly weighted average. However, other calculations can be used based on other function types, such as quadratic or exponential functions.

[0066] The flow sensor may include: a semiconductor substrate including an etched portion; a dielectric region on the substrate, wherein the dielectric region includes at least one dielectric film located above the etched portion of the semiconductor substrate; a heating element located within the dielectric film; a first temperature sensing element and a second temperature sensing element located within the dielectric film; and a controller.

[0067] This article also describes an apparatus that includes a fluid flow sensor and controller as described herein.

[0068] Additionally, this document describes a controller for controlling a fluid flow sensor in which a fluid is flowing, the fluid flow sensor including a heater and one or more temperature sensors.

[0069] The controller can be configured in a first mode to determine parameters corresponding to the flow rate of the flowing fluid based on signals from one or more temperature sensors and from the heater.

[0070] The controller can be configured in a second mode to determine parameters based solely on signals from the heater.

[0071] The controller can be further configured to determine an initial estimate of the parameters.

[0072] When the initial estimate is below a first threshold parameter, the controller can be configured to operate in the first mode.

[0073] When the initial estimate is higher than the second threshold parameter, the controller can be configured to operate in the second mode.

[0074] When the initial estimate is between the first threshold parameter and the second threshold parameter, the controller can be configured to operate in a combination of the first mode and the second mode.

[0075] Operating under a combination of the first and second modes may include determining a weighted average of parameters determined according to the first mode and parameters determined according to the second mode.

[0076] The fluid flow sensor may include two temperature sensors. The controller can be configured to determine parameters based on signals from both temperature sensors and from the heater in a first mode.

[0077] The controller can be configured to determine parameters based on the signal difference between the two temperature sensors in a first mode, and further normalize them using the signal from the heater.

[0078] In some non-limiting examples, the method and / or controller according to this disclosure may be adapted for use with a fluid flow sensor according to one or more of the following examples:

[0079] A flow and thermal conductivity sensor may include: a semiconductor substrate including an etched portion; a dielectric region on the substrate, wherein the dielectric region includes at least one dielectric film located above the etched portion of the semiconductor substrate; a heating element located on or within the dielectric film; and a first temperature sensor located on or within the dielectric film.

[0080] A second temperature sensor may be located on or within the dielectric film. The first and second temperature sensors may be located on opposite sides of the heater, at the same distance from the heater. Alternatively, they may be located at different distances from the heater.

[0081] The first and second temperature sensors can be located on the same side of the heater, but at different distances.

[0082] The dielectric film may include one or more recessed regions. These recessed regions help reduce device power consumption and also help equalize the pressure on both sides of the dielectric film.

[0083] The dielectric region may include a dielectric layer or multiple layers including at least one dielectric layer. The heating element may be fully or partially embedded within the dielectric film.

[0084] Generally, dielectric film regions can be located immediately adjacent to the etched portion of the substrate. A dielectric film region corresponds to a region of dielectric area above an etched cavity portion of the substrate. Each dielectric film region can be located above a single etched portion of the semiconductor substrate.

[0085] The sensor can be designed to function as both a flow sensor and a thermal conductivity sensor.

[0086] The heater temperature can be adjusted by applying different power levels to increase sensitivity and selectivity to different flow rates and fluid types.

[0087] The heater can operate in pulse mode (e.g., driven by square wave, sine wave, pulse width modulation wave, pulse density modulation, etc.) or continuous mode. Pulse mode has advantages such as reduced power consumption, reduced electromigration to enhance device reliability / lifespan, and improved fluid characteristic sensing capabilities.

[0088] In anemometer measurement, a heating element can be configured to operate as a sensing element by, for example, sensing changes in resistance due to temperature variations. The heating element can operate simultaneously as both a heating element and a sensing element. Electrically, a heating element is equivalent to a resistor. The thermal conductivity of most heater materials (tungsten, titanium, platinum, aluminum, polycrystalline silicon, monocrystalline silicon) changes with temperature. This change is primarily linear, characterized by the TCR (temperature coefficient of resistance). TCR can be positive or negative, but most metals have a positive and stable TCR, meaning their resistance increases as temperature rises. When current flows through the heating element, the element heats up, heating the surrounding film. If the heater operates at the same power, when fluid flows over the heater, it cools the heater due to convection, thus changing its resistance (lower resistance for a positive TCR). The heater can also be driven in constant resistance or constant temperature modes, and the power change required to maintain the heater resistance or temperature can be correlated with the flow rate change. Sensors are capable of measuring flow characteristics such as flow rate, velocity, mass or volumetric flow rate, and the composition of the fluid. The device can be configured to measure flow characteristics, such as flow rate, velocity, mass flow rate, or volumetric flow rate, by sensing changes in temperature, voltage, current, resistance, or power that depend on the bias applied to the heater.

[0089] Alternatively, flow rate can be measured using one or more sensing elements. Preferably, two temperature-sensitive elements are placed on either side of the heater within the same dielectric film and optionally used as a differential pair. The differential pair can be formed by an upstream sensing element and a downstream sensing element.

[0090] A recessed area may exist between the heater and the temperature sensor.

[0091] Temperature sensing elements can include resistive temperature detectors, diodes, or thermopile. Thermopiles can be used to measure the temperature difference between a dielectric film and a dielectric region above a substrate, or to measure the temperature difference across a heating element. Compared to thermopile, diodes and detectors reduce heat loss from the semiconductor substrate because they are entirely located on or within the dielectric film. One type of sensing element can be used, or a combination of different types of sensing elements can be used.

[0092] The sensing element can be temperature sensitive and can be any one of a resistive temperature detector, a calorimeter, a diode, a transistor, or a thermopile, or an array in series or in parallel, or a combination thereof.

[0093] The sensing element can also be made of a thermopile. A thermopile comprises one or more thermocouples connected in series. Each thermocouple may comprise two different materials that form a junction at a first region of the film, while the other end of the materials forms a junction at a second region of the film or in a heat dissipation region (on the substrate outside the film region), where they are electrically connected to adjacent thermocouples or to pads for external readout. Thermocouple materials may include metals such as aluminum, tungsten, titanium, or combinations of these metals or any other metal available in the process. Alternatively, thermocouple materials may include thermocouples based on n-type and p-type silicon or polycrystalline silicon or a combination of metals and semiconductors. The location of each junction of the thermocouples, as well as the number and shape of the thermocouples, can be any location, number, and shape required to fully map the temperature distribution curve on the film to achieve specific performance.

[0094] Heat measurement can be performed by a single temperature sensor or two temperature sensors. Preferably, there are two temperature sensors on either side of the heater. The temperature sensors can be resistors, thermopile, and / or diodes. Preferably, if they are resistors or diodes, the same bias is applied to both temperature sensors. The thermopile does not necessarily need to be biased. The controller can directly read signals (voltage, current, resistance, or power) from both and subtract them. The controller can also apply different calculations or functions to the signals from the two temperature sensors. Alternatively, there can be a circuit that uses the voltages from the two sensors as inputs to a differential amplifier and uses the output as the signal from the temperature sensors.

[0095] The sensing element formed within the dielectric film can be configured as a temperature resistive detector (TRD) or a calorimeter, a diode, a transistor, or an array of transistors or diodes to enhance sensitivity and selectivity.

[0096] In use, the heating element can extend in a direction perpendicular to the direction of flow through the sensor. The heating element may not be at a precise right angle to the flow direction, and can extend diagonally or at an acute angle to the flow direction; however, a component of the extension of the heating element may be perpendicular to the flow. Optionally, the heating element may be substantially perpendicular to the direction of flow through the sensor, or may be arranged at an angle of less than 10° to the direction perpendicular to the flow through the sensor.

[0097] The dielectric film can be circular. Heating and sensing elements can also have circular shapes. This improves the utilization of the film area and enhances thermal performance.

[0098] The sensor may further include an application-specific integrated circuit (ASIC) coupled to the sensor. The ASIC can be located beneath the sensor, for example, using die stacking technology. Alternatively, the ASIC can be located elsewhere. The ASIC can be connected to the sensor using wire bonding and pads or using through-silicon vias (TSVs) extending through the semiconductor substrate. The controller can be located within the ASIC.

[0099] An ASIC can be housed within the same system or package, or on a chip, to provide electronic circuitry for driving, reading out, and processing signals from a sensor. The ASIC can be placed in a stacked die configuration below the sensor, and the sensor and ASIC can be housed within a manifold.

[0100] Analog / digital circuitry can be integrated on-chip. The circuitry may include IPTAT, VPTAT, amplifiers, analog-to-digital converters, memory, RF communication circuitry, timing blocks, filters, or any other components used to drive heating elements, read out temperature sensing elements, or electronically manipulate sensor signals. For example, it has been demonstrated that driving heating elements in a constant temperature mode results in enhanced performance, and having on-chip devices for implementing such driving methods leads to significant advancements in state-of-the-art flow sensors. In the absence of on-chip circuitry, this disclosure also covers off-chip implementations of such circuit blocks when applied to flow sensors having one or more features described in any of the preceding embodiments. Such off-chip implementations can be accomplished in an ASIC or by discrete components or a combination of both.

[0101] The device can be packaged in a metal TO package, ceramic, metal, or plastic SMD (surface mount device) package. It can also be packaged directly on a PCB or using a flip-chip approach. Alternatively, the device can be embedded in a substrate (e.g., a custom version of one of the aforementioned packages, rigid PCBs, semi-rigid PCBs, flexible PCBs, or any other substrate) so that the device surface is flush with the substrate surface. The package can also be a chip or wafer-level package, for example, formed through wafer bonding.

[0102] The device can also be assembled within a manifold that provides inlet, outlet, and predefined channels through which fluid flow occurs. The manifold provides protection for the device and allows for easier and more controlled measurement of flow rate or fluid composition. ASICs or external readout circuitry can also be placed in the same manifold in a lateral or die-stack configuration.

[0103] Flow sensors can have through-silicon vias (TSVs) to avoid the presence of bonding leads near the sensitive area of ​​the device that could affect flow sensor readings. Advantageously, flow sensors with TSVs can implement 3D stacking techniques. For example, the flow sensor chip can be located on top of an ASIC, thereby reducing the size of the sensor system.

[0104] The semiconductor substrate may be silicon, and the dielectric film may be formed primarily of oxide and nitride materials, wherein the heater is made of metals such as tungsten, titanium, copper, aluminum, gold, platinum or combinations thereof, or of semiconductors such as highly doped n-type or p-type silicon or polycrystalline silicon, and wherein the heater has a tortuous, spiral or hot wire shape.

[0105] The starting substrate can be any semiconductor, such as silicon, silicon-on-insulator (SOI), silicon carbide, sapphire, or diamond. The use of silicon is particularly advantageous because it ensures the manufacturability of sensors with high volume, low cost, and high reproducibility. The use of silicon substrates also enables on-chip circuitry for sensor performance enhancement and system integration facilitators. This on-chip circuitry can be implemented using analog, digital, or mixed-signal blocks placed outside the dielectric film.

[0106] Dielectric films or multiple films can be formed by back etching using depth reactive ion etching (DRIE) of the substrate, which produces vertical sidewalls, enabling a reduction in sensor size and cost. However, back etching can also be performed using anisotropic etching, such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide), which produces sloping sidewalls. The dielectric layer within the film, which can be formed by oxidation or oxide deposition, can be used as an etch stop layer during DRIE or wet etching processes. Films can also be formed by front etching or a combination of front and back etching to produce a suspended film structure supported by only two or more beams. The film can be circular, rectangular, or rectangular with rounded corners to reduce stress in the corners, but other shapes are also possible. Additionally, holes can be formed within the film to reduce heat dissipation through thermal conduction via the dielectric film and to enhance heat loss through heat exchange and conduction in the regions below and above the film, and optionally in the fluid path (above the film). Optionally, holes or discontinuities can be formed by front etching after film formation.

[0107] The dielectric film may include silicon dioxide and / or silicon nitride. The film may also include one or more spin-on glass layers, and a passivation layer on one or more dielectric layers. Using materials with low thermal conductivity (e.g., dielectrics) can significantly reduce power consumption and increase the temperature gradient within the film, which has direct benefits in terms of sensor performance (e.g., sensitivity, frequency response, range, etc.). Temperature sensing elements or heaters made of materials such as single-crystal or polycrystalline semiconductors or metals can be suspended or embedded in the dielectric film.

[0108] The membrane may also have other structures made of metals or other conductive materials or other materials with high mechanical strength. These structures may be embedded within the membrane, or embedded above or below the membrane, to design the membrane's thermomechanical properties (e.g., stiffness, temperature distribution profile, etc.) and / or the fluid-membrane hydrodynamic interaction. More generally, these structures may also be located outside the membrane and / or bridged between the inside and outside of the membrane.

[0109] The sensed fluid can be a gas, and the gas can consist of air and / or other components (such as CO2, methane, or hydrogen, or other gases with a different thermal conductivity than air). The sensed fluid can also be a liquid.

[0110] The substrate may include: more than one etched portion; a dielectric region located on the substrate, wherein the dielectric region comprises a dielectric film on each region of the etched portion of the substrate. At least one film may contain any combination of the above features.

[0111] In some examples, the methods and / or controllers disclosed herein may be suitable for use with sensors of the type described in US 2021 / 0116281, the contents of which are incorporated herein by reference in their entirety. Attached Figure Description

[0112] Some embodiments of this disclosure will now be described by way of example and with reference to the accompanying drawings, in which:

[0113] Figure 1 A flowchart of an example algorithm used by the controller of a flow sensor is shown;

[0114] Figure 2 An example method according to this disclosure is shown; and

[0115] Figure 3 A system including a fluid flow sensor and a controller is schematically shown. Detailed Implementation

[0116] Figure 1 A flowchart (e.g., its algorithm) for a flow sensor used to determine the actual flow rate is shown.

[0117] The controller initially receives signals from the heater and / or temperature sensor.

[0118] Then use (one or more) of these signals to make an initial estimate of the flow.

[0119] • If the flow rate is below the lower threshold, the flow rate is determined based on the signal from the temperature sensor (thermal measurement method); otherwise, proceed to the next step.

[0120] • If the flow rate is higher than the upper threshold, the flow rate is determined based on the signal from the heater (wind speed measurement method); otherwise, proceed to the next step.

[0121] • If none of the above conditions are met, the flow rate is determined based on the weighted average of the heater signal (wind speed measurement method) and the temperature sensor signal (heat measurement method) based on the initial estimated flow rate, as well as the difference between the estimated flow rate and the upper and lower thresholds.

[0122] In the last case, if the estimated flow rate is closer to the upper threshold, a higher proportion of wind speed measurement is used to determine the final flow rate. If the estimated flow rate is closer to the lower threshold, a lower proportion of heat measurement is used to determine the final flow rate.

[0123] It should be understood that the diagram presents a possible sequence of events. It's also possible that the controller first checks against the upper threshold and then against the lower threshold. Alternatively, it might first check if the estimated traffic falls between the upper and lower thresholds.

[0124] In addition, although Figure 1 The actual flow rate value being used is shown, but signals or values ​​that are not actual flow rate values ​​can also be used, instead of values ​​corresponding to the flow rate. These signals or values ​​may have already been compensated for environmental factors such as temperature or pressure, or they may need to be compensated for environmental factors.

[0125] Such a value or signal can be the heat loss factor from the heater, the temperature difference between two temperature sensors, the temperature value from the heater and / or temperature sensors, voltage, current, or power. It can also be a value derived from any of these values.

[0126] Depending on the controller implementation, the upper and lower thresholds can be fixed. They can also vary based on calibration and / or environmental changes, such as variations in temperature or pressure.

[0127] The signal from the temperature sensor can be two separate signals or just one signal—for example, the difference between the signals from two temperature sensors.

[0128] Figure 2 An example of method 200 according to this disclosure is shown. Method 200 can be executed by a controller according to this disclosure. For example, one or more steps of method 200 can be provided to the controller as instructions, such as in the form of computer code. In some examples, method 200 of this disclosure can be executed by executing computer code stored on or accessible by the controller.

[0129] In step S202 of method 200, an initial estimate of the parameters corresponding to the flow rate of the flowing fluid is determined.

[0130] In step S204 of method 200, the initial estimate is compared with the threshold parameter.

[0131] In step S206 of method 200, based on this comparison, the parameters corresponding to the flow rate of the flowing fluid are determined based on the following:

[0132] Signal from the temperature sensor of the fluid flow sensor

[0133] Signal from the heater of the fluid flow sensor; or

[0134] A combination of signals from the fluid flow sensor, temperature sensor, and heater.

[0135] Figure 3 The apparatus 300 is shown, which includes a controller 302 according to the present disclosure and a fluid flow sensor 304.

[0136] The fluid flow sensor 304 includes a temperature sensor 306 and a heater 308. A controller 302 is connected to the temperature sensor 306 and the heater 308 of the fluid flow sensor 304 (i.e., communicates with the temperature sensor 306 and the heater 308 of the fluid flow sensor 304). That is, the controller 302 is capable of receiving signals from the temperature sensor 306 and the heater 308. Preferably, the controller 302 is also capable of sending signals to the temperature sensor and / or the heater 308.

[0137] The controller 302 is configured to determine an initial estimate of a parameter corresponding to the flow rate of the flowing fluid when the fluid flow sensor 304 is present in the flowing fluid. For example, the initial estimate may be determined based on signals from the temperature sensor 304 and / or the heater 306. For example, the controller 302 may be configured to determine the initial estimate based on wind speed measurement and / or heat measurement.

[0138] The controller 302 is also configured to compare the initial estimate with a threshold parameter. The threshold parameter may be stored in memory or may otherwise be provided to the controller 302.

[0139] The controller 302 is also configured to determine parameters corresponding to the flow rate of the flowing fluid based on this comparison. The parameters corresponding to the flow rate can be determined based, for example, signals (e.g., voltage) received by the controller 302 from the temperature sensor 306 and / or from the heater 308.

[0140] It's possible that at lower flow rates (lower air velocities), thermal measurement provides a stronger signal than wind speed measurement, while at higher flow rates (higher air velocities), wind speed measurement provides a stronger signal than thermal measurement. Therefore, using thermal measurement at low flow rates and wind speed measurement at high flow rates may be advantageous.

[0141] The fluid flow sensor 304 may further include a second temperature sensor (not shown), for example, the first temperature sensor may be located upstream of the heater 308 (depending on the path of the flowing fluid), and the second temperature sensor may be located downstream of the heater 308. The controller 302 may be configured to receive signals from (or send signals to) the first and second temperature sensors. The first and second temperature sensors may be used in a heat measurement method for measuring flow rate.

[0142] The method and controller 302 according to this disclosure advantageously enable “alternating weakening” or switching between two measurement methods based on flow rate to benefit from the best possible signal-to-noise ratio for a given measurement.

[0143] Thus, two operating modes can be defined for the controller 302: a first mode in which signals from the heater and the temperature sensor(s) are used to determine the flow rate (parameter corresponding to the flow rate) (i.e., calorimetry); and a second mode in which only the signal from the heater is used to determine the flow rate (parameter corresponding to the flow rate) (i.e., anemometry).

[0144] The controller 302 can be configured to operate the fluid flow sensor 302 according to the first mode when an initial estimate of the flow rate (parameter corresponding to the flow rate) is below a first threshold (threshold parameter), and to operate the fluid flow sensor 302 according to the second mode when the initial estimate is above a second threshold (threshold parameter).

[0145] There can be a transition region in which the initial estimate is between the first threshold (first threshold parameter) and the second threshold (second threshold parameter). In the transition region, both measurement methods (calorimetry and anemometry) can provide relatively similar strength signals (i.e., similar signal-to-noise ratios).

[0146] In the transition region, the controller 302 can be configured to operate according to a combination of the first mode and the second mode based on the initial estimate. For example, the controller 302 can be configured to determine a weighted average of the flow rate (parameter corresponding to the flow rate) determined according to the first mode and the second mode.

[0147] In one example, the bottom of the transition region is defined as (t_min) and the top of the transition region is defined as (t_max). Then a first polynomial mapping f is determined that maps h_c to h_a flowing from 0 to the top of the transition region (t_max). This ensures that a second polynomial mapping g from h_a to flow rate / velocity / DP etc. can be used over the entire flow rate range.

[0148] From 0 to the bottom of the transition region (t_min), h_c is mapped to h_a using the first polynomial mapping f, and then f(h_c) is mapped to the flow rate using the second polynomial mapping g.

[0149] Thus: for h_a < t_min, flow rate = g(f(h_c))

[0150] Within the transition region, a weighted average between f(h_c) and h_a is used to determine the heat transfer coefficient, which is converted to flow rate / DP / velocity using the second polynomial mapping. The weighting linearly varies from 100% f(h_c) at t_min to 100% h_a at t_max.

[0151] Therefore: for t_min < h_a < t_max, flow rate = g[h_a*(h_a – t_min) / (t_max – t_min)+f(h_c)*(t_max – h_a) / (t_max – t_min)]

[0152] Above the transition region, the second polynomial mapping is used to convert h_a to the flow rate.

[0153] Therefore: for h_a > t_max, flow rate = g(h_a)

[0154] The above example calculations can be performed by the controller 302.

[0155] As described herein, the controller 302 can be configured to perform the methods described herein (e.g., Figure 2 method 200 as shown). For example, the controller 300 can be configured to execute instructions as described herein (e.g., in the form of computer program code). The instructions can be provided on one or more carriers. For example, there can be one or more non-transitory memories, such as EEPROM (e.g., flash memory), magnetic disk, CD or DVD-ROM, programmable memory, such as read-only memory (e.g., for firmware), one or more transitory memories (e.g., RAM) and / or (one or more) data carriers, such as optical or electrical signal carriers. The (one or more) memories can be integrated into the corresponding processing chip and / or separated from the chip. The code (and / or data) for implementing the embodiments of the present disclosure can include source code, object code or executable code in a conventional programming language such as C (interpreted or compiled), or assembly code, code for setting or controlling an ASIC (application specific integrated circuit) or FPGA (field programmable gate array), or code for a hardware description language.

[0156] The present disclosure can be further defined in accordance with one or more of the following non-limiting clauses:

[0157] 1. A fluid flow sensor, comprising a heater, a first temperature sensor, a controller, wherein the controller is configured to:

[0158] make an initial estimate of the flow rate or a value corresponding to the flow rate;

[0159] if the initial estimate of the flow rate or the value corresponding to the flow rate is below a lower threshold, use the signal from the temperature sensor to determine the final flow rate or the value corresponding to the flow rate;

[0160] if the initial estimate of the flow rate or the value corresponding to the flow rate is above an upper threshold, use the signal from the heater to determine the final flow rate or the value corresponding to the flow rate;

[0161] If the initial estimate of the flow rate or the value corresponding to the flow rate is between the upper and lower thresholds, the final flow rate or the value corresponding to that flow rate is determined using signals from the heater and from the temperature sensor.

[0162] 2. The fluid flow sensor according to Clause 1, wherein a second temperature sensor is present.

[0163] 3. The fluid flow sensor according to Clause 2, wherein the first temperature sensor and the second temperature sensor are located on opposite sides of the heater.

[0164] 4. The fluid flow sensor as described in Clause 1, wherein the upper threshold and the lower threshold are always fixed.

[0165] 5. The fluid flow sensor as described in Clause 1, wherein the upper threshold and lower threshold may be changed based on calibration or environmental changes.

[0166] 6. The fluid flow sensor according to Clause 1, wherein the initial estimate of the flow rate is based on a signal from the heater.

[0167] 7. The fluid flow sensor as described in Clause 1, wherein the initial estimate of the flow rate is based on a signal from a temperature sensor.

[0168] 8. The fluid flow sensor as described in Clause 1, wherein the initial estimate is based on a signal from the heater and a signal from the temperature sensor.

[0169] 9. The fluid flow sensor as described in Clause 1, wherein the initial estimate is based on a signal external to the sensor.

[0170] 10. The fluid flow sensor according to Clause 1, wherein if an initial estimate of the flow rate or a value corresponding to the flow rate is between an upper threshold and a lower threshold, the controller uses a weighted average of the signal from the heater and the signal from the temperature sensor to determine the final flow rate, or the value corresponding to the flow rate.

[0171] 11. The fluid flow sensor according to Clause 10, wherein if an initial estimate of the flow rate or a value corresponding to the flow rate is between an upper threshold and a lower threshold, then if the initial estimate is closer to the upper threshold, the portion of the heater signal used is larger, and if the initial estimate is closer to the lower threshold, the portion of the temperature sensor signal used is larger.

[0172] Typically, any of the functions described herein can be implemented using software, firmware, hardware (e.g., fixed logic circuitry), or a combination of these implementations.

[0173] Although this disclosure has been described with reference to preferred embodiments as described above, it should be understood that these embodiments are merely illustrative and the claims are not limited to those embodiments. In view of the content of this disclosure, those skilled in the art will be able to make modifications and substitutions, which are considered to fall within the scope of the appended claims. Each feature disclosed or illustrated in this specification may be combined in this disclosure individually or in any suitable combination with any other feature disclosed or illustrated herein.

[0174] Those skilled in the art will conceive of many other effective alternatives. It should be understood that this disclosure is not limited to the described embodiments, but includes all modifications falling within the spirit and scope of this disclosure.

Claims

1. A method for controlling a fluid flow sensor (304) in which a fluid is flowing, the method comprising: Receives a signal from the heater (308) of the fluid flow sensor (304); Receive a signal from the temperature sensor (306) of the fluid flow sensor (304); determine an initial estimate of the parameters corresponding to the flow rate of the fluid; The initial estimate is compared with the threshold parameter; and Based on the comparison, the parameter corresponding to the flow rate of the flowing fluid is determined based on a combination of signals from the heater (308) of the fluid flow sensor (304) and signals from the temperature sensor (306).

2. The method of claim 1, further comprising determining the parameter corresponding to the flow rate based on a combination of the signals from the heater (308) and the temperature sensor (306) of the fluid flow sensor (304) when the initial estimate is between the first threshold parameter and the second threshold parameter.

3. The method according to any one of the preceding claims, wherein, The combination of the signals from the heater (308) and the temperature sensor (306) of the fluid flow sensor (304) includes a weighted average of the signals.

4. The method according to claim 3, wherein, The weighted average depends on the difference between the initial estimate and the first threshold parameter and the second threshold parameter.

5. The method according to claim 1 or 2, wherein, The signal from the fluid flow sensor (304) and the temperature sensor (306) includes signals from both temperature sensors.

6. The method according to claim 1 or 2, wherein, The signal from the fluid flow sensor (304) and the temperature sensor (306) includes the difference between the signals from the two temperature sensors.

7. A controller (302) for a fluid flow sensor (304), the controller (302) being configured to, when a flowing fluid is present in the fluid flow sensor (304): Receives a signal from the heater (308) of the fluid flow sensor (304); Receive a signal from the temperature sensor (306) of the fluid flow sensor (304); determine an initial estimate of the parameters corresponding to the flow rate of the fluid; The initial estimate is compared with the threshold parameter; and Based on the comparison, a parameter corresponding to the flow rate of the flowing fluid is determined based on a combination of signals from the heater (308) of the fluid flow sensor (304) and signals from the temperature sensor (306).

8. The controller (302) according to claim 7, further configured to, when the initial estimate is between a first threshold parameter and a second threshold parameter: The parameter corresponding to the flow rate is determined based on a combination of signals from the heater (308) and the temperature sensor (306) from the fluid flow sensor (304).

9. The controller (302) according to claim 7 or 8, wherein, The combination of the signals from the heater (308) and the temperature sensor (306) of the fluid flow sensor (304) includes a weighted average of the signals.

10. The controller (302) according to claim 9, wherein, The weighted average depends on the difference between the initial estimate and the first threshold parameter and the second threshold parameter.

11. An apparatus (300), comprising: Fluid flow sensor (304); and The controller (302) according to any one of claims 7 to 10.

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