Fluid flow sensing apparatus and related methods

Abstract

The present disclosure relates to an improved fluid flow sensing device and a method of operating the device. In particular, the present disclosure relates to a fluid flow sensing device having a compact design, the fluid flow sensing device having a microcalorimetric sensor disposed in a fluid flow channel of the device, and a control device configured to provide a sensor input to the microcalorimetric sensor, the sensitivity of the microcalorimetric sensor is set based on a control input corresponding to a characteristic of the fluid.

Description

Technical Field

[0001] The present disclosure relates to an improved fluid flow sensing device and a method of operating the device. In particular, the present disclosure relates to a fluid flow sensing device with a compact design and flexible control means. Background Art

[0002] Fluid flow sensing devices are typically used in fluid flow controllers, such as mass flow controllers.

[0003] A fluid flow sensing device used in a pressure-based fluid flow controller is configured to generate a sensor signal based on a pressure difference between two points in a fluid flow channel. This pressure difference in turn indicates the flow rate of the fluid flowing along the fluid flow channel.

[0004] EP 3 734 233 A1 discloses a fluid flow sensing device with an improved laminar flow generator. EP 3 734 234 B1 discloses a pressure-based fluid flow sensing device with a pressure compensation chamber.

[0005] The present invention provides a fluid flow sensing apparatus which provides an improvement over known arrangements. Summary of the invention

[0006] As discussed above, there is a need for improved configurations of fluid flow sensing devices. The fluid flow sensing device of the present invention provides several advantages over prior art configurations. In particular, when compared to prior art configurations, the present invention provides a simpler, more compact and flexible design of a fluid flow sensing device.

[0007] According to a first aspect of the present invention, a fluid flow sensing device is provided, which includes any one or all of the following features: a first fluid flow channel, the first fluid flow channel having an inlet and an outlet; a microcalorimetric sensor, the microcalorimetric sensor being arranged in the fluid flow channel; and a control device for the microcalorimetric sensor, wherein the control device is configured to provide input to the microcalorimetric sensor to set the sensitivity of the microcalorimetric sensor based on the characteristics of the fluid.

[0008] An advantage of the above configuration of a fluid flow sensing device is that the sensitivity of the sensor in the present invention is directly controlled by the control device and no longer depends on the physical size of the components (such as the laminar flow generator) in the fluid flow sensing device. In this way, the accuracy of the sensor can be improved for a wider range of different applications because its sensitivity is no longer dependent on mechanical changes in the size of the laminar flow elements. This configuration also allows for a more compact device with an improved flow range. In addition, when used to sense gas flows, the inventors have recognized that different gases require different sensitivity settings. By providing a control device to directly set the sensitivity of the sensor, the present invention provides a simple configuration that can be easily adapted to different types of gases.

[0009] According to a second aspect of the present invention, a fluid flow control device is provided, which includes any one or all of the following features: a fluid flow sensing device according to the first aspect as described above, wherein the fluid flow control device further includes a second fluid flow channel having an inlet and an outlet, and the fluid flow control device is configured to split the fluid flow between the second fluid flow channel and the first fluid flow channel, so that the first fluid flow channel is configured to receive a predetermined proportion of the fluid flowing through the second fluid flow channel.

[0010] According to a third aspect of the present invention, there is provided a method for operating a fluid flow sensing device, wherein the fluid flow sensing device comprises a microcalorimetric sensor, which is disposed in a first fluid flow channel of the fluid flow sensing device, and wherein the method comprises: receiving, by a control device, a fluid characteristic input corresponding to the characteristic of a fluid flowing through the first fluid flow channel; and providing, by the control device, an input to the microcalorimetric sensor to set the sensitivity of the microcalorimetric sensor based on the characteristic of the fluid.

[0011] Further embodiments of the present description are described in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings, which are not necessarily drawn to scale, the same reference numerals may describe similar components in different views. The same reference numerals with different letter suffixes may represent different instances of similar components. The drawings generally show the different embodiments discussed in this document by way of example and not limitation.

[0013] Figure 1 is an example of a prior art pressure-based fluid flow sensing device used in a mass flow controller.

[0014] Figure 2 is an example of a thermal-based fluid flow sensing device 200 for use in a mass flow controller.

[0015] Figure 3 A block diagram of a fluid flow sensing device 300 is shown, in accordance with an embodiment of the present disclosure.

[0016] Figure 4a A circuit diagram of a sensor in a fluid flow sensing device according to an embodiment of the present disclosure is shown.

[0017] Figure 4b A schematic layout of elements of a fluid flow sensing device according to an embodiment of the present disclosure is shown.

[0018] Figure 4c A circuit diagram of a sensor in a fluid flow sensing device according to another embodiment of the present disclosure is shown.

[0019] Figure 4d A schematic layout of elements of a fluid flow sensing device according to another embodiment of the present disclosure is shown.

[0020] Figure 5 shows the effect of different supply voltages applied to the sensor based on Figure 4a Examples of empirical results of the sensor measurements in .

[0021] Figure 6 A flow chart of a method for operating a fluid flow sensing device having a microcalorimetric sensor according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0022] The present disclosure relates to a fluid flow sensing device, which includes any or all of the following: a first fluid flow channel, the first fluid flow channel having an inlet and an outlet; a microcalorimetric sensor, the microcalorimetric sensor disposed in the fluid flow channel; and a control device for the microcalorimetric sensor, wherein the control device is configured to provide input to the microcalorimetric sensor to set the sensitivity of the microcalorimetric sensor based on the characteristics of the fluid.

[0023] As used herein, the term "fluid flow sensing device" refers to any device that may include at least one fluid flow channel having an inlet and an outlet to enable fluid to flow within the channel, wherein the device is configured to determine the fluid flow rate based on one or more characteristics of the fluid flowing through the channel. The fluid flow sensing device may include at least one sensor to measure one or more characteristics of the fluid flowing through the channel. The fluid may be a gas or a liquid or a mixture thereof, such as a vapor, a suspension, or a mixture of gas droplets and fluid droplets, or a gas with suspended particles or an aerosol, or any generally flowable medium.

[0024] As used herein, the term "microcalorimetric sensor" refers to any sensor configured to operate using the microcalorimetric principle. When used in a fluid flow sensing device such as in the present disclosure, a microcalorimetric sensor refers to any sensor that includes at least a heating element for introducing and / or maintaining a known amount of heat, a first sensing element disposed upstream of the heating element in the direction of fluid flow, and a second sensing element disposed downstream of the heating element in the direction of fluid flow. In some embodiments, the first sensing element and the second sensing element may each include a resistance temperature detector RTD or a thermopile.

[0025] As used herein, the phrase "disposed in a fluid flow channel" means that the sensor is at least partially disposed in the fluid flow channel. In one embodiment, the heating element, the first sensing element, and the second sensing element may be positioned within the fluid flow channel such that the sensor is completely disposed in the fluid flow channel. In some other embodiments, the heating element may be disposed on an outer surface of the fluid flow channel such that the fluid flowing through the channel is heated by conducting heat from the outer surface of the fluid flow channel.

[0026] As used herein, the term "sensitivity of a microcalorimeter" refers to the ratio of the change in the output signal based on the change in flow through the sensing device. It can be based on the measurement of the heat transfer of the fluid flowing through the fluid channel compared to the unit flow rate of the fluid in the fluid flow channel. The measurement of flow and / or heat transfer can be based on the difference between the measured characteristics of the downstream sensor and / or the upstream sensor of the microcalorimeter. These measured characteristics can be measured based on the electrical characteristics of the upstream resistor and the downstream resistor (such as their resistance), which can be measured by measuring or comparing the voltage drop across one or more of the upstream resistor and the downstream resistor.

[0027] The sensor input provided by the control device to the microcalorimetric sensor can be defined as any input that is configured to change the output of the sensor for a given flow input of a given fluid type. An example of a sensor input can be to set the power consumed by the sensor (and therefore the sensitivity of the sensor), for example by adjusting the power of one or more components of the sensor.

[0028] In some embodiments, the sensor input provided by the control device to the microcalorimeter sensor can be an electrical signal. For example, the sensor input can be a voltage, such as the power supply voltage of the microcalorimeter sensor, in the case where the power supply voltage range can be predefined for a specific configuration of the microcalorimeter sensor. The input can also be a current applied to the microcalorimeter sensor. The control device can be configured to provide a controlled sensor input, that is, the controller can be configured to provide an input to the microcalorimeter sensor when the input has a substantially constant value. This may be particularly useful when the fluid flow sensing device is used in a fluid flow controller (such as a mass flow controller).

[0029] As used herein, the term "property of a fluid" refers to any kinetic, thermodynamic, and / or physical property of a fluid. In some embodiments, the property of a fluid may be the type of the fluid. For example, when the fluid is a gas, the property of the fluid may be the type or class or kind of the gas. Other relevant properties may include density of the fluid, specific heat capacity of the fluid, viscosity of the fluid, or other physical or chemical properties of the fluid.

[0030] The sensor input provided by the control device may be selected by the control device based on the characteristics of the fluid. In one example, the control device may select a predetermined value of a supply voltage or current to be applied to the sensor based on the characteristics of the fluid passing through the fluid flow channel.

[0031] With respect to the control function of generating input to the microcalorimetric sensor, the control device is a non-feedback system because the control function of the control device is independent of the output of the control device (i.e., the input to the microcalorimetric sensor). In one example, information about the characteristics of the fluid can be provided to the control device by an operator using a fluid flow sensing device. In another example, the control device itself can be configured to determine the characteristics of the fluid flowing through the fluid flow channel.

[0032] The fluid flow sensing device of the present invention provides several advantages over prior art configurations. In particular, the present invention provides a simpler, more compact and flexible design of a fluid flow sensing device when compared to prior art configurations. In order to fully appreciate these advantages of the present invention, prior art configurations of fluid flow sensing devices will first be briefly discussed.

[0033] A mass flow controller (MFC) is a typical example of a fluid flow control device having a fluid flow sensing device. The fluid flow sensing device can be pressure based or thermal based.

[0034] Figure 1A prior art pressure-based fluid flow sensing device that can be used as an MFC is shown. The fluid flow sensing device 100 includes a pressure sensor 102 that is in fluid communication with a first location 104 of a fluid flow channel 106 that is upstream of a restriction 108 via a first fluid conduit 110, and is in fluid communication with a second location 112 of the fluid flow channel 106 that is downstream of the restriction 108 via a second fluid conduit 114. The pressure sensor 102 compares a first fluid pressure P1 at the first location 104 with a second fluid pressure P2 at the second location 112. The fluid sensor 102 is configured to generate a sensor signal based on a difference between P2 and P1, which in turn indicates a flow rate of a fluid flowing along the fluid flow channel 106. The control electronics of the MFC then use this information to control a desired flow rate through the MFC via a fluid control valve (not shown), which can be located upstream or downstream of the sensing device 100.

[0035] Figure 1 The prior art fluid flow sensing device is also shown to include a laminar flow element 120 extending along the fluid flow channel 106 to promote laminar flow and suppress turbulence, thereby improving flow sensing accuracy. In this configuration, the radius R of the laminar flow element 120 is L The sensitivity of the pressure flow sensor 102 (in this case, the sensitivity is the ratio of the pressure in the fluid flowing through the channel to the unit flow rate of the fluid flow) also depends on the radius R of the laminar flow element 120. L , because the sensitivity of the flow sensor 102 increases with the radius R of the laminar flow element L increases with the increase of .

[0036] Although laminar flow element 120 helps promote laminar flow and suppress turbulent flow, Figure 1A disadvantage of the pressure-based fluid flow sensing device in is that the sensitivity of the sensor 102 is set by the physical size of the laminar flow element 120. The physical size of the laminar flow element 120 also limits the flow range of the MFC and the overall size of the MFC. Adjusting the device to a different flow range requires physical replacement of the laminar flow generator. With respect to the present disclosure, the MFC may include a heat-based fluid flow sensing device as disclosed herein. The fluid flow sensing device used in a heat-based fluid flow controller typically includes a bypass path (the bypass path is configured to bypass the main fluid flow channel in the fluid flow controller) and a heating element, which is used to introduce a known amount of heat into the fluid flowing into the bypass path. The fluid flow sensing device is also configured to have a sensor arrangement that is used to sense the temperature of the fluid between two points in the fluid flow channel, which are positioned on both sides of the heating element. The temperature measurement results measured by the sensor arrangement can be used to determine the heat capacity of the fluid in the bypass path, and the measurement results can then be used to determine the fluid flow rate.

[0037] Figure 2 An example of a thermal-based fluid flow sensing device 200 for use in a mass flow controller is shown. Figure 2As seen in FIG. 1 , the MFC includes a main flow path 202 for a fluid flowing through the MFC and a bypass path 204 adjacent to the main flow path. (Multiple) flow paths may be formed in a manifold block 210. The fluid flow may or may not be divided between the main flow path 202 and the bypass path 204. In one operating mode, a single flow path may be provided. A single flow path may be arranged in a single path passing through the manifold block 210. A single flow path may be a bypass channel 204. A means for producing a single flow channel arrangement is to block the main channel 202 between the inlet and outlet of the bypass channel 204 (e.g., around a position indicated by line 212). This may be suitable for the first (generally lower) flow range of the device. In other embodiments, it may be desirable to handle higher flow rates. For embodiments of higher flow rates, it may be desirable to divert the fluid flow so that only a certain proportion of the fluid flow flows along the bypass path 204 to perform flow measurement. The fluid flow splitter can be arranged in the main flow path, and in some embodiments can be implemented by means of a laminar flow element 206 as shown in the figure. This can guide a small part of the fluid flowing through the main flow path into an adjacent bypass path. The heat-based fluid flow sensing device uses a microcalorimetric sensor arrangement 208 in the fluid flow path to measure the heat transfer achieved by the fluid in the bypass path. The microcalorimetric sensor 208 typically includes a heating element (not shown) that is configured to introduce heat into the fluid flowing through the fluid flow path. The microcalorimetric sensor also includes a first upstream sensor (not shown) located on a first side of the heating element and a downstream sensor (not shown) located on a second side opposite to the first side of the heating element. Since the fluid can take heat away from the upstream sensor and bring it to the downstream sensor, the mass flow rate can be measured. This effect will cause a temperature difference between the upstream sensor and the downstream sensor, which can then be used to determine the mass flow rate through the fluid flow channel. The device can be calibrated for different fluids and different fluid flows based on whether it is configured to have a split configuration with a main flow path and a bypass flow path or a single fluid flow path. The control electronics of the MFC then uses this information as a feedback signal to control valves in the flow path to set the desired flow through the MFC.

[0038] Since the thermal characteristics of a fluid depend on the type of fluid, thermal-based fluid flow sensing devices need to be calibrated for each type of fluid. The inventors have recognized that it would be advantageous to provide a device that enables the device to be adapted for a wide range of fluids and an improved fluid flow range without requiring complex, expensive circuitry for implementing a fluid flow sensing device based on a thermal sensor.

[0039] The inventors have achieved a configuration of a fluid flow sensing device that is adaptable to a wide range of fluids and fluid flow conditions. The fluid flow sensing device of the present invention is configured to provide an input to a microcalorimetric sensor to set the sensitivity of the sensor based on the characteristics of the fluid. In this way, the sensitivity of the sensor in the present invention is directly controlled by a control device and no longer depends on the physical dimensions of components (such as a laminar flow generator) in the fluid flow sensing device. In this way, the accuracy of the sensor is improved because its sensitivity is no longer dependent on mechanical changes in the dimensions of the laminar flow elements. This configuration also allows for a more compact device with an improved flow range. In addition, when used to sense gas flows, the inventors have recognized that different gases can be measured more accurately by using different sensitivity settings. By providing a control device to directly set the sensitivity of the sensor, the present invention provides a simple configuration that can be easily adapted to different types of gases.

[0040] Figure 3 3 shows a block diagram of a fluid flow sensing device 300. The fluid flow sensing device includes a fluid flow channel having an inlet and an outlet, which can form a fluid flow controller (e.g., Figure 2 For simplicity, in Figure 3 These details are omitted in the figure so that the figure only schematically illustrates the components of the fluid flow sensing device according to the present disclosure. Figure 3 As shown in FIG. 1 , the fluid flow sensing device includes a sensor 302, which may be a microcalorimetric sensor, and a control device 304. The microcalorimetric sensor 302 includes a first sensing element 302a, a heating element 302b, and a second sensing element 302c. The first sensing element 302a is disposed upstream of the heating element 302b along the fluid flow direction, and the second sensing element 302c is disposed downstream of the heating element 302b along the fluid flow direction.

[0041] Figure 3 Also shown is a control valve 308, which may be part of a fluid flow control device that includes the fluid flow sensing device 300. Figure 2 As described, control valve 308 is configured to control the flow of fluid through the main passage of the fluid flow control device, and thereby also control the flow of fluid through the fluid flow passage of the fluid flow sensing device. Figure 3 The control valve 308 is shown positioned upstream of the sensor 302, but in another embodiment, the control valve 308 may be positioned downstream of the sensor 302 to control the fluid flow of the fluid through the fluid flow control device.

[0042] The control device 304 is configured to receive an input 304a indicative of a property of the fluid flowing through the fluid flow channel and generate an output 304b based on the input 304a as an input to the sensor 302. With respect to the control function of generating the output 304b, the control device can be a non-feedback system because the control function of the control device is independent of the output 304b of the control device.

[0043] Where the fluid flow sensing apparatus 300 is used in a fluid flow control system, the control device may be configured to provide a controlled input 304b, ie the control device may be configured to provide an input 304b to the microcalorimeter, wherein the input has a substantially constant value.

[0044] Input 304a indicative of, related to, or based on a property of the fluid may be provided by an external source (e.g., an operator operating, calibrating, or configuring the fluid flow sensing device). The property of the fluid may be the fluid type. For example, when the fluid is a gas, the property of the fluid may be the gas type. Other relevant properties may include the density of the fluid, the specific heat capacity of the fluid, the viscosity of the fluid, or other physical or chemical properties of the fluid.

[0045] The control device 304 may optionally be further configured to receive an output 306 generated by the microcalorimeter, the output 306 being indicative of fluid flow in the fluid flow channel based on measurements taken by the first sensing element 302a and the second sensing element 302c.

[0046] The control device 304 may optionally be further configured to provide a control input to the control valve 308 to control the desired flow of the fluid. Alternatively, a separate control device may be used within a fluid flow control device having the fluid flow sensing device 300 to control the control valve 308 .

[0047] Figure 4a The control elements of a fluid flow sensing device 400 according to the present disclosure are shown, and the fluid flow sensing device 400 can be understood as a specific embodiment of the fluid flow sensing device 300, wherein the input 304b to the microcalorimeter is an electrical signal, in this case a supply voltage. The fluid flow sensing device 400 can be used in a MFC to sense gas flow. Figure 4b Shows Figure 4a 1 is a circuit diagram of a microcalorimetric sensor 402 in FIG. 1 , which illustrates the positioning of various elements of the sensor 402 relative to the direction of fluid flow in a fluid flow channel of a fluid flow sensing device. Figure 4b An additional sensor 402e is shown upstream of the other illustrated resistive elements, which may be used in a microcalorimetric sensor to measure ambient temperature.

[0048] like Figure 4a As seen in FIG. 4 , the fluid flow sensing device 400 includes a microcalorimetric sensor 402 and a control device 404. The microcalorimetric sensor 402 includes a first sensing element 402a, a heating element 402b, and a second sensing element 402c.

[0049] The first sensing element is implemented as a first resistance temperature detector (RTD) 402a. The second sensing element is implemented as a second resistance temperature detector (RTD) 402c, wherein the second RTD 402c is connected in series with the first RTD 402a. Figure 4b As seen in the figure, Figure 4a , the first RTD 402a is disposed downstream of the heating element 402b in the direction of fluid flow, and the second RTD 402c is disposed upstream of the heating element 402b in the direction of fluid flow.

[0050] The heating element 402b includes a fourth RTD 402b(i) and a fifth RTD 402b(ii), wherein the fourth RTD 402b(i) is connected in series with the fifth RTD 402b(ii). The sensor circuit is configured such that the first RTD 402a and the second RTD 402c are connected in parallel with the fourth RTD 402b(i) and the fifth RTD 402b(ii).

[0051] Figure 4a Also shown is a control device implemented as a microcontroller 404. The microcontroller 404 is configured to receive an input 404a indicative of a characteristic of the fluid flowing through the fluid flow channel. The input 404a may be provided by an operator operating, configuring, or calibrating the fluid flow sensing device. The input 404a indicative of a characteristic of the fluid may be provided by an external source. If the fluid flow sensing device is used in an MFC, the input 404a may be, for example, the type of gas flowing in the MFC and, therefore, in the fluid flow sensing device.

[0052] exist Figure 4a In FIG. 4 , microcontroller 404 generates controlled supply voltage signal 404b based on input 404a. As previously described with reference to FIG. Figure 3 As described above, microcontroller 404 is a non-feedback system with respect to the control function of generating output 404b because the control function of microcontroller 404 is independent of output 404b. Voltage buffer 408 is coupled to the output of microcontroller 404 so that a buffered supply voltage signal 404b is provided to microcalorimetric sensor 402.

[0053] Thus, the example microcontroller 404 shown sets the supply voltage of the microcalorimetric sensor 402 based on the input 404a, and this in turn can set the power consumed by the sensing element of the microcalorimetric sensor 402. Other inputs can also be used, such as by setting a current input or other electrical input to the sensor 402. In this way, the microcontroller 404 sets the sensitivity of the microcalorimetric sensor 402 based on the input 404a.

[0054] Figure 4a An alternative configuration is also shown in which the microcontroller 404 is configured to receive an input 406 generated by the microcalorimetric sensor 402, the input 406 indicating the fluid flow rate in the fluid flow channel based on the measurements taken by the first RTD 402a and the second RTD 402c. Figure 4a As seen in FIG. 4 , the instrumentation amplifier 402d is configured to receive a first input signal 402d(i) at a first node between the first RTD 402a and the second RTD 402c. The instrumentation amplifier 402d is further configured to receive a second input signal 402d(ii) at a second node between the third RTD 402b(i) and the fourth RTD 402b(ii). The amplified differential output (UDiff) 402d(iii) of the instrumentation amplifier 402 is digitized by the ADC 410 to generate an input 406 to the microcontroller 404. Figure 4a Also shown is a gain block 402d(iv) of the instrumentation amplifier 402d. The microcontroller 404 may also be configured to provide another controlled electrical signal 404c to the gain block 402d(iv) to adjust the gain G of the instrumentation amplifier 402d. This adjustment may be made so that the output 402(iv) of the amplifier 402d is amplified based on the full scale range of the ADC 410. This may help improve the signal-to-noise ratio of the input 406 provided to the microcontroller 404. Figure 4a In an embodiment, if no fluid is flowing through the fluid flow channel, UDiff (402d(iii)) will be zero, and if fluid is flowing through the fluid flow channel of the fluid flow sensing device, UDiff will have a value greater than zero.

[0055] Figure 4c FIG. 4 shows a control element of a fluid flow sensing device 400 according to another embodiment of the present disclosure. Figure 4a and Figure 4b The illustrated embodiments share some common features. Figure 4c In the embodiment, the control device 404 can be used with respect to Figure 4a The same method as described is implemented. Figure 4c The microcalorimeter in Figure 4aThe microcalorimeter of can differ in that the sensing elements 402a and 402c are thermopiles, and preferably further in that the heating element 402b comprises any suitable resistive element(s) configured to dissipate power, such as aluminum. Figure 4c As seen in FIG. 4 , the thermopile sensor 402a is coupled between a first input 402d(i) of a differential amplifier 402d and a reference potential. Another thermopile sensor 402c may be coupled between a second input 402d(ii) of the differential amplifier 402d and a reference potential (typically ground). Figure 4c The heating element 402b in is coupled between a controlled supply voltage 404b and a reference potential (typically ground). Figure 4c The operation of the remaining circuitry in the embodiment (including the control device 404 and the instrumentation amplifier 402d) can be performed in accordance with Figure 4a The corresponding elements in the embodiment are implemented in the same manner as described above.

[0056] Figure 4d Shows Figure 4c A circuit diagram of a microcalorimetric sensor 402 is provided which illustrates the manner in which various elements of the sensor 402 may be positioned relative to the direction of fluid flow in a fluid flow channel of a fluid flow sensing device. Figure 4d In some embodiments, the heating element 402b includes one or more resistive elements 402b(i) and 402b(ii) that may be arranged in parallel. In some embodiments, the resistive elements 402b(i) and 402b(ii) may be arranged in series. In some embodiments, the heating element 402b may be implemented using a single resistive element (e.g., Figure 4c shown). Figure 4d Also shown is an additional sensor 402e which may be used in the microcalorimetric sensor 402 to measure the ambient temperature, which additional sensor may, for example, be located upstream of the other illustrated resistive elements.

[0057] Figure 5 Shown in use Figure 4a Empirical results of UDiff versus flow rate (in this case, the set point flow rate of the fluid flowing through the channel) for different supply voltages applied to the microcalorimeter. Figure 5 As can be seen in Figure 1, the sensitivity of the microcalorimeter sensor depends on the supply voltage applied to the sensor by the microcontroller. The inventors have recognized that different gases require different sensitivity settings. By providing a control device to directly set the sensitivity of the microcalorimeter sensor, the present invention provides a simple configuration that can be easily adapted to different types of gases. The present invention also provides a more compact circuit when compared to prior art configurations because the sensitivity of the sensor is no longer dependent on the physical size of components (such as a laminar flow generator) in the fluid flow sensing device.

[0058] although Figure 4a The embodiments described herein are described with respect to using a microcontroller 404 to generate an input 404b to a microcalorimetric sensor 402, but are not limited to this type of controller, and the skilled person will appreciate that any other suitable control device may be used to generate the control signal.

[0059] Figure 6 A flow chart of a method for operating a fluid flow sensing device having a microcalorimetric sensor as in the above examples is shown. Figure 6 As seen in the method, the method includes receiving, by a control device, a characteristic of a fluid flowing through a fluid flow channel of a fluid flow sensing device (step 601). The control device then processes the received input (step 602) and provides an input to a microcalorimeter to set the sensitivity of the microcalorimeter based on the characteristic of the fluid (step 603). The characteristic of the fluid flowing through the channel can be provided to the control device by an operator using the fluid flow sensing device. In another example, the control device itself can be configured to determine the characteristic of the fluid flowing through the fluid flow channel.

[0060] Consistent with the above example, the method may optionally include another step (not shown) associated with receiving an input generated by the microcalorimeter, the input indicating the fluid flow rate in the fluid flow channel based on the measurements measured by the first sensing element and the second sensing element. In one example, where the input generated by the microcalorimeter is an electrical signal, the control device may be configured to further process the input generated by the microcalorimeter to improve its signal-to-noise ratio.

[0061] The method examples described herein may be implemented at least in part by a machine or computer. Some examples may include a computer-readable medium or machine-readable medium encoded with instructions, which may be operable to configure an electronic device for performing the method described in the above example. The implementation of such a method may include code, such as microcode, assembly language code, higher-level language code, etc. Such code may include computer-readable instructions for performing various methods. The code may form the parts of a computer program product. In addition, in an example, the code may be tangibly stored on one or more volatile, non-temporary, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media may include, but are not limited to, hard disks, removable disks, removable optical disks (such as compact disks and digital video disks), tapes, memory cards or memory sticks, random access memory (RAM), read-only memory (ROM), etc.

[0062] Although the invention has been described in terms of certain embodiments, these embodiments may be combined to provide further embodiments. In addition, certain features shown in the context of one embodiment may also be combined in other embodiments.

[0063] In this document, as is common in patent documents, the term "a or an" includes one or more than one, independent of any other examples or usages of "at least one" or "one or more". In this document, unless otherwise stated, the term "or" is used to indicate non-exclusivity, or so that "A or B" includes "A but not B", "B but not A", and "A and B". In this document, the terms "including" and "in which" are used as the plain English equivalents of the respective terms "comprising" and "wherein". Moreover, in the following claims, the terms "including" and "comprising" are open-ended, i.e., systems, devices, or processes that include elements other than those listed after such terms in the claims are still deemed to fall within the scope of the claims. Furthermore, in the following claims, the terms "first", "second", and "third", etc., are used only as labels and are not intended to impose numerical requirements on their objects.

[0064] Example

[0065] Example 1 is a fluid flow sensing device, which includes one or more or any combination of the following: a first fluid flow channel, the first fluid flow channel having an inlet and an outlet; a microcalorimetric sensor, the microcalorimetric sensor being arranged in the fluid flow channel; a control device for the microcalorimetric sensor, wherein the control device is configured to provide a sensor input to the microcalorimetric sensor to set the sensitivity of the microcalorimetric sensor based on a control input corresponding to a characteristic of the fluid.

[0066] Example 2 is the fluid flow sensing apparatus of any preceding example, wherein the control device is operable as a non-feedback control device for providing the input to the microcalorimetric sensor.

[0067] Example 3 is a fluid flow sensing apparatus according to any preceding example, wherein the sensor input to the microcalorimetric sensor is selectable from a plurality of constant values.

[0068] Example 4 is a fluid flow sensing device according to any of the preceding examples, wherein the sensor input is an electrical signal.

[0069] Example 5 is a fluid flow sensing apparatus according to Example 4, wherein the control device is configured to set the sensitivity of the microcalorimetric sensor, preferably by providing the sensor input to set the power consumption of the microcalorimetric sensor.

[0070] Example 6 is a fluid flow sensing device according to example 4 or 5, wherein the sensor input is a voltage or a current.

[0071] Example 7 is the fluid flow sensing device of Example 6, wherein the electrical signal is a supply voltage for the microcalorimeter.

[0072] Example 8 is a fluid flow sensing device according to any preceding example, wherein the characteristic of the fluid is a type of the fluid.

[0073] Example 9 is a fluid flow sensing device according to any of the preceding examples, wherein the microcalorimetric sensor comprises one or more or any combination of the following: a heating element; a first sensing element configured to measure a first temperature and disposed upstream of the heating element in the direction of fluid flow; and a second sensing element configured to measure a second temperature and disposed downstream of the heating element in the direction of fluid flow.

[0074] Example 10 is a fluid flow sensing device according to Example 9, wherein one or more or each of the first sensing element and the second sensing element comprises a resistance temperature detector (RTD) or a thermopile, optionally in any combination.

[0075] Example 11 is a fluid flow sensing device according to any of the preceding examples, wherein the control device is further configured to receive a first output from the microcalorimeter, the first output preferably indicating a flow rate of the fluid flowing in the fluid flow channel.

[0076] Example 12 is a fluid flow control device, which includes a fluid flow sensing device according to any of the preceding examples, wherein the fluid flow control device further includes a second fluid flow channel having an inlet and an outlet, and the fluid flow control device is preferably configured to split the fluid flow between the second fluid flow channel and the first fluid flow channel, so that the first fluid flow channel is preferably configured to receive a predetermined proportion of the fluid flowing through the second fluid flow channel.

[0077] Example 13 is a fluid flow control device according to Example 12, wherein the fluid flow control device is a mass flow controller.

[0078] Example 14 is a method for operating a fluid flow sensing device having a microcalorimetric sensor, which is disposed in a first fluid flow channel of the fluid flow sensing device, the method comprising one or more or any combination of the following: receiving a control input corresponding to a characteristic of a fluid flowing through the first fluid flow channel by a control device; processing the fluid characteristic input by the control device to generate a sensor input for the microcalorimetric sensor; and providing the input to the microcalorimetric sensor through the control device to set the sensitivity of the microcalorimetric sensor based on the characteristic of the fluid.

[0079] Example 15 is a fluid flow sensing device or method according to Example 14, wherein the input is an electrical signal.

Claims

1. A fluid flow sensing device, comprising: a first fluid flow channel having an inlet and an outlet; a microcalorimeter disposed in the fluid flow channel; A control device for the microcalorimeter, wherein the control device is configured to provide a sensor input to the microcalorimeter to set the sensitivity of the microcalorimeter based on a control input corresponding to a characteristic of the fluid.

2. A fluid flow sensing device according to any preceding claim, wherein: The control device is operable as a non-feedback control device for providing the input to the microcalorimetric sensor.

3. A fluid flow sensing device according to any preceding claim, wherein: The sensor input to the microcalorimetric sensor can be selected from a plurality of constant values.

4. A fluid flow sensing device according to any preceding claim, wherein: The sensor input is an electrical signal.

5. The fluid flow sensing device according to claim 4, wherein: The control device is configured to set the sensitivity of the microcalorimetric sensor by providing the sensor input to set the power consumption of the microcalorimetric sensor.

6. The fluid flow sensing device according to claim 4 or 5, wherein: The sensor input is either voltage or current.

7. The fluid flow sensing device according to claim 6, wherein: The electrical signal is the supply voltage for the microcalorimeter.

8. A fluid flow sensing apparatus according to any preceding claim, wherein: The characteristic of the fluid is the type of fluid.

9. A fluid flow sensing apparatus according to any preceding claim, wherein: The microcalorimeter includes: Heating elements; a first sensing element configured to measure a first temperature and disposed upstream of the heating element in the direction of fluid flow; and A second sensing element is configured to measure a second temperature and is disposed downstream of the heating element in the direction of fluid flow.

10. The fluid flow sensing device according to claim 9, wherein: Each of the first sensing element and the second sensing element includes a resistance temperature detector (RTD) or a thermopile.

11. A fluid flow sensing apparatus according to any preceding claim, wherein: The control device is further configured to receive a first output from the microcalorimeter, the first output indicating a flow rate of the fluid flowing in the fluid flow channel.

12. A fluid flow control device comprising a fluid flow sensing device according to any preceding claim, wherein: The fluid flow control device further includes a second fluid flow channel having an inlet and an outlet, and the fluid flow control device is configured to split the fluid flow between the second fluid flow channel and the first fluid flow channel, so that the first fluid flow channel is configured to receive a predetermined proportion of the fluid flowing through the second fluid flow channel.

13. The fluid flow control device according to claim 12, wherein: The fluid flow control device is a mass flow controller.

14. A method for operating a fluid flow sensing device having a microcalorimetric sensor disposed in a first fluid flow channel of the fluid flow sensing device, the method comprising: receiving, by a control device, a control input corresponding to a characteristic of the fluid flowing through the first fluid flow channel; processing, by the control device, the fluid property input to generate a sensor input for the microcalorimetric sensor; as well as The input is provided by the control device to the microcalorimeter to set the sensitivity of the microcalorimeter based on the characteristics of the fluid.

15. The method according to claim 14, wherein: The input is an electrical signal.

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