Fluid sensing device

Abstract

A fluid sensing device (120) is provided, the fluid sensing device comprising: a fluid flow channel (121); at least one fluid conduit (132, 134) in fluid communication with the fluid flow channel (121); and a fluid sensor (130) having a housing (131) and at least one sensor port (135, 136) in fluid communication with the at least one fluid conduit (132, 134) and providing access to the housing (137). The fluid sensing device (120) further comprises a pressure compensation chamber (142), the housing (137) of the fluid sensor (130) being enclosed within the pressure compensation chamber. The device further comprises at least one pressure compensation conduit (144) in fluid communication with the pressure compensation chamber (142) and the fluid flow channel (121). A mass flow controller (100) comprising such a fluid sensing device is also provided.

Description

Technical Field

[0001] The present invention relates to a fluid sensing device, and more particularly to a fluid sensing device for use with a fluid control valve, such as in a mass flow controller or a mass flow meter. Background Art

[0002] Fluid control valves are used in a wide variety of applications for controlling the flow rate of fluids. The fluids being controlled can include gases, liquids, or combinations thereof. In some cases, the fluid can also include suspended particles. Although fluid control valves vary widely in their particular configurations for opening and closing the fluid communication path through the valve, one particular type of valve actuation is performed using a solenoid. In a solenoid-actuated valve, an electric current passes through an electromagnetic coil, where the coil typically forms around a magnetic core. The coil generally includes a wire that is wound around a bobbin multiple times, thereby creating a plurality of so-called turns. The energized solenoid generates a magnetic field. The strength of the magnetic field is proportional to the number of turns and the current supplied to the wire. As is well known in the art, to enhance the magnetic field provided by the solenoid, the number of turns can be increased and / or the current supplied to the wire can be increased. The magnetic field typically acts on a movable armature connected to a plunger to change the flow restrictor created by the valve seat and the sealing portion of the plunger, which is configured to engage the valve seat surrounding an inlet and / or an outlet through which the fluid can pass. Other types of actuation can be used, such as piezoelectric actuation.

[0003] Mass flow controllers (“MFCs”) are widely used for measuring and controlling the flow rate of fluids. A typical MFC includes a fluid sensing device, a fluid control valve, and a controller for controlling the fluid control valve. The fluid sensing device typically includes a flow channel extending between an inlet and an outlet, and a fluid sensor in communication with the flow channel. During MFC operation, the controller determines the flow rate through the flow channel based on the sensor signal of the fluid sensor and correspondingly operates the control valve to maintain a desired flow rate. There are two main types of MFCs: thermal-based and pressure-based.

[0004] Pressure-based MFCs typically use flow restrictors, such as nozzles or orifices, along the flow channels to create a pressure drop based on which the flow rate can be determined. In such MFCs, the flow rate can be determined by physically measuring the bypass flow generated by the pressure difference, or it can be determined by mathematically calculating the flow rate based on the principle that the flow rate of the fluid through the flow restrictor is a function of the pressure drop across the flow restrictor. The pressure drop can be calculated and the flow rate determined by sensing the fluid pressure p1 upstream of the flow restricting device and the fluid pressure p2 downstream of the flow restricting device. In this or other applications, the fluid sensor can be a simple package having a housing and two or more ports through which the fluid can enter and leave the housing, whereby the flow rate along the flow channel can be determined by measuring the flow rate through the sensor housing. Alternatively, the fluid sensing device can have a single fluid conduit through which the fluid enters the housing of the fluid sensor through a single sensor port, whereby the flow rate along the flow channel can be determined by measuring the pressure of the fluid entering the housing of the fluid sensor.

[0005] In each of the above types of fluid sensing devices, the fluid passes from the flow channel through at least one fluid conduit and into the housing of the fluid sensor. This means that once the fluid has entered the sensor housing, the sensor housing must be able to resist the pressure of the fluid. However, the ability of the fluid sensor housing to resist internal pressure is limited. For example, the housing of a typical fluid sensor can have a maximum pressure rating of about 3 bar. This means that any pressure peak exceeding 3 bar can cause the sensor to malfunction and ultimately result in fluid leakage. To address this problem, it is known to reinforce the sensor housing to ensure that it can withstand the internal pressure experienced during use. However, such fluid sensors tend to be larger, heavier and more expensive and are therefore not suitable for all applications, such as micro MFCs. The increased robustness of the fluid sensor may also lead to increased manufacturing complexity and cost.

[0006] The present invention seeks to provide an improved flow sensing device that overcomes or mitigates one or more of these problems associated with the prior art. Summary of the Invention

[0007] According to a first aspect of the present invention, there is provided a fluid sensing device comprising: a fluid flow channel having an inlet and an outlet; at least one fluid conduit in fluid communication with the fluid flow channel; a fluid sensor having a housing and at least one sensor port in fluid communication with the at least one fluid conduit and providing access to the housing; a pressure compensation chamber in which the housing of the fluid sensor is enclosed; and at least one pressure compensation conduit in fluid communication with the pressure compensation chamber and the fluid flow channel, wherein the at least one pressure compensation conduit extends between the pressure compensation chamber and a location along the fluid flow channel such that fluid flowing along the fluid flow channel enters the pressure compensation chamber via the at least one pressure compensation conduit at the location of the at least one pressure compensation conduit during use, and wherein the at least one fluid conduit extends between the at least one sensor port and a location along the fluid flow channel such that fluid flowing along the fluid flow channel enters the housing of the fluid sensor via the at least one fluid conduit at the location of the at least one fluid conduit during use.

[0008] Optionally, the fluid sensor is mounted on a printed circuit board which forms part of the pressure compensation chamber.

[0009] Optionally, the pressure compensation chamber further comprises a reservoir, the printed circuit board being sealed against the reservoir to enclose the reservoir and thereby define the pressure compensation chamber. The fluid sensing device further comprises an elastic seal between the printed circuit board and the reservoir, wherein the printed circuit board is removably sealed against the reservoir by the elastic seal.

[0010] Optionally, the fluid sensing device further comprises a housing including a solid body in which the at least one fluid conduit and the at least one pressure compensation conduit are formed, wherein the reservoir is defined by a cavity in the solid body.

[0011] Optionally, the printed circuit board is a main printed circuit board on which control electronics and the fluid sensor are mounted.

[0012] Optionally, the printed circuit board is an auxiliary printed circuit board, and the fluid sensing device further comprises a main printed circuit board on which control electronics are mounted, the main printed circuit board being electrically connected to the auxiliary printed circuit board by one or more electrical connectors.

[0013] The fluid sensing device may further comprise a sensor seal between the at least one sensor port and the at least one fluid conduit, wherein the at least one fluid conduit is isolated from the pressure compensation chamber by the sensor seal.

[0014] The at least one fluid conduit includes a first fluid conduit extending from a first position along the fluid flow channel and a second fluid conduit extending from a second position along the fluid flow channel, and the at least one sensor port includes a first sensor port in fluid communication with the first fluid conduit and a second sensor port in fluid communication with the second fluid conduit.

[0015] The fluid flow channel includes a restrictor disposed between the first position and the second position, and wherein the fluid sensor is configured to measure a first pressure in the first fluid conduit and to measure a second pressure in the second fluid conduit.

[0016] The first fluid conduit, the sensor housing, and the second fluid conduit together form a bypass channel, a portion of the fluid flow of the fluid flow channel is diverted along the bypass channel during use, and the fluid sensor is configured to measure the bypass flow through the bypass channel.

[0017] The fluid flow channel is enclosed and defined by an outer wall of the fluid flow channel, and wherein the at least one pressure compensation conduit and the at least one fluid conduit extend through the outer wall of the fluid flow channel.

[0018] The at least one pressure compensation conduit extends between the pressure compensation chamber and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel enters the pressure compensation chamber via the at least one pressure compensation conduit at the location of the at least one pressure compensation conduit during use.

[0019] The at least one fluid conduit extends between the at least one sensor port and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel enters the housing of the fluid sensor via the at least one fluid conduit at the location of the at least one fluid conduit during use.

[0020] The pressure compensation chamber is remote from the fluid flow channel.

[0021] A portion of the fluid flowing along the fluid flow channel is diverted from the fluid flow channel at the location of the at least one pressure compensation conduit during use to enter the pressure compensation chamber via the at least one pressure compensation conduit.

[0022] A portion of the fluid flowing along the fluid flow channel is diverted from the fluid flow channel at the location of the at least one fluid conduit during use to enter the housing of the fluid sensor via the at least one fluid conduit.

[0023] The at least one pressure compensation conduit extends between the pressure compensation chamber and at least one location along the length of the fluid flow channel between the inlet and the outlet.

[0024] The at least one fluid conduit extends between the at least one sensor port and at least one location along the length of the fluid flow channel between the inlet and the outlet.

[0025] According to a second aspect of the present invention, there is provided a mass flow controller, comprising: a fluid control valve; control electronics; and the fluid sensing means as described above, wherein the control electronics is configured to control the fluid control valve based on a sensor signal provided by the fluid sensing means.

[0026] The fluid sensing means further comprises: a main printed circuit board on which the control electronics is mounted; and an auxiliary printed circuit board on which the fluid sensor is mounted and which forms part of the pressure compensation chamber, wherein the main printed circuit board is spaced apart from the auxiliary printed circuit board in a direction perpendicular to the plane of the auxiliary printed circuit board and is electrically connected to the auxiliary printed circuit board by one or more electrical connectors.

[0027] The mass flow controller is a micro mass flow controller.

[0028] According to a third aspect of the present invention, there is provided a fluid sensing means, comprising: a fluid flow channel having an inlet and an outlet; at least one fluid conduit in fluid communication with the fluid flow channel; a fluid sensor having a housing and at least one sensor port in fluid communication with the at least one fluid conduit and providing access to the housing; a pressure compensation chamber in which the housing of the fluid sensor is enclosed; and at least one pressure compensation conduit in fluid communication with the pressure compensation chamber.

[0029] With this arrangement, fluid can be supplied to the pressure compensation chamber via at least one pressure compensation conduit such that the fluid pressure outside the housing can be balanced with the fluid pressure inside the housing. Thus, the pressure compensation chamber compensates for the internal pressure within the housing, and thus the housing only has to resist the relatively small difference between the fluid pressure in the pressure compensation chamber and the fluid pressure in at least one fluid conduit. This reduces the risk of leakage or sensor failure compared to a sensor housing that has to withstand the full difference between the internal fluid pressure and the atmospheric pressure. The reduced burden on the housing also allows for simplification of the structure and manufacture of the fluid sensor and can facilitate the use of lighter, smaller, and less complex components. This can be particularly beneficial when the fluid sensing device is intended for use in a compact device such as a micro MFC.

[0030] One or more locations along the fluid flow channel to which at least one pressure compensation conduit extends can be regarded as pressure compensation locations. One or more locations along the fluid flow channel to which at least one fluid conduit extends can be regarded as fluid sensing locations.

[0031] The fluid sensing device of the present invention can be readily used in many different applications, for example, for controlling industrial processes, performing laboratory experiments, or for safety reasons. The fluid sensing device can be used only for flow rate information or can be used as a device for flow rate regulation, such as in a device for mass flow control or volume flow control. The fluid sensing device of the present invention is found to be particularly useful for accurate fluid sensing for flow control, for example, in a mass flow controller. The fluid sensing device of the present invention can be configured for use with gases or liquids.

[0032] Preferably, at least one pressure compensation conduit is in fluid communication with the fluid flow channel and extends between the pressure compensation chamber and the fluid flow channel.

[0033] With this arrangement, fluid in the fluid flow channel enters the pressure compensation chamber via at least one pressure compensation conduit and enters the housing of the fluid sensor via at least one fluid conduit during use. Thus, the pressure compensation chamber is filled with fluid at the same or a similar elevated pressure as the fluid flowing along the flow channel at the location of the pressure compensation conduit, while the sensor housing accommodates fluid at the same or a similar elevated pressure as the fluid flowing along the flow channel at the location of at least one sensor port. Thus, the pressure compensation chamber compensates for the internal pressure within the housing, and thus the housing only has to resist the relatively small difference between the fluid pressure at the location of the pressure compensation conduit and the fluid pressure at the location of at least one fluid conduit. This reduces the risk of leakage or sensor failure compared to sensor housings that need to withstand the difference between the elevated internal fluid pressure and the atmospheric pressure. The reduced burden on the housing also allows for the simplification of the structure and manufacture of the fluid sensor and can facilitate the use of lighter, smaller, and less complex components. This can be particularly beneficial when the fluid sensing device is intended for use in a compact device such as a micro MFC.

[0034] In other embodiments, fluid may be supplied to the pressure compensation chamber from a fluid source rather than the fluid flow channel via at least one pressure compensation conduit. The at least one pressure compensation conduit may extend between the pressure compensation chamber and one or more fluid conduits separate from the fluid flow channel. In cases where the fluid sensing device includes a housing, the housing may include a plurality of fluid conduits, and the at least one pressure compensation conduit may extend between the pressure compensation chamber and one or more of the plurality of fluid conduits. For example, the fluid sensing device may be configured as part of a manifold or a flow controller having a housing. The housing may include a first fluid inlet connected to an inlet of the fluid flow channel, a first fluid outlet connected to an outlet of the fluid flow channel, and a second fluid inlet, wherein the at least one pressure compensation conduit extends between the pressure compensation chamber and the second fluid inlet. In such examples, the fluid sensing device may include a first fluid line connected to the first fluid inlet or the first fluid outlet, and a second fluid line extending between the first fluid line and the second fluid inlet. With this arrangement, the fluid in the first fluid line enters the pressure compensation chamber during use via the second fluid line, the second fluid inlet, and the at least one pressure compensation conduit. Thus, the pressure compensation chamber is filled with fluid at a pressure similar to that of the fluid flowing along the first fluid line to compensate for the internal pressure within the housing. Additionally, this arrangement can facilitate cleaning of the fluid sensing device by allowing the pressure compensation chamber to be flushed via the second fluid inlet and the at least one pressure compensation conduit. In cases where a single pressure compensation conduit is provided, during cleaning, fluid can be flushed out of the chamber via the at least one fluid conduit and the fluid flow channel. In cases where a plurality of pressure compensation conduits are provided, during cleaning, at least a portion of the fluid can be flushed out of the chamber via an additional pressure compensation conduit. For example, the housing may include a first pressure compensation conduit extending between the pressure compensation chamber and the second fluid inlet, and a pressure compensation conduit extending between the pressure compensation chamber and the second fluid outlet. In such examples, fluid can be flushed through the pressure compensation chamber via the first pressure compensation conduit and the second pressure compensation conduit.

[0035] Preferably, the fluid sensor is mounted on a printed circuit board that forms part of the pressure compensation chamber. It has been found that this provides a particularly compact arrangement and obviates the need for a separate electrical connector that extends from the fluid sensor and passes through the wall of the pressure compensation chamber. Such electrical connectors are difficult to seal effectively and thus represent potential leak points. This arrangement also has the advantage of close proximity between any control electronics on the printed circuit board and the fluid sensor to reduce noise or other interference to the signals generated by the fluid sensor. The printed circuit board may form the wall of the pressure compensation chamber. The printed circuit board should have sufficient strength to withstand the difference in fluid pressure within the pressure compensation chamber on its underside and atmospheric pressure on its upper side.

[0036] Preferably, the pressure compensation chamber further includes a reservoir, against which the printed circuit board is sealed to enclose the reservoir and thereby define the pressure compensation chamber. With this arrangement, the printed circuit board forms the upper wall, or lid, of the pressure compensation chamber.

[0037] Preferably, the fluid sensing device further includes an elastomeric seal between the printed circuit board and the reservoir, wherein the printed circuit board is removably sealed against the reservoir by the elastomeric seal. With this arrangement, the elastomeric seal can compensate for variations in manufacturing tolerances between the reservoir and the printed circuit board. The elastomeric seal also allows removal of the printed circuit board and replacement of the printed circuit board when needed, without the need to apply a separate sealant to reseal the printed circuit board against the reservoir. The elastomeric seal can be a rubber seal or any other suitable elastomer, such as NBR, FPM, or EPDM. The elastomeric seal can be seated in a groove extending around the reservoir. The elastomeric seal is preferably continuous. That is, the elastomeric seal preferably surrounds the reservoir to form a continuous seal.

[0038] In other examples, the printed circuit board can be permanently sealed against the reservoir by a sealant applied after the printed circuit board is positioned against the reservoir.

[0039] Preferably, the fluid sensing device further includes a housing.

[0040] At least one fluid conduit, pressure compensation conduit, and / or pressure compensation chamber can be formed by separate components held within the housing. Preferably, the housing includes a solid body in which the at least one fluid conduit and the at least one pressure compensation conduit are formed. The solid body can include a plurality of holes, and the at least one fluid conduit and the at least one pressure compensation conduit are formed by these holes. Preferably, the reservoir is defined by a cavity in the solid body. The cavity can be defined in the outer surface of the solid body. The fluid flow channels can be formed in whole or at least in part by one or more of the plurality of internal holes. The plurality of internal holes are preferably formed in the solid body by a subtractive manufacturing process, such as drilling or another machining operation.

[0041] In the case where the fluid sensing device includes an elastomeric seal between the printed circuit board and the reservoir, the elastomeric seal can be seated in a groove in the outer surface of the solid body that extends around the cavity such that the elastomeric seal forms a continuous seal around the cavity.

[0042] In some embodiments, the printed circuit board is the main printed circuit board on which the control electronics and the fluid sensor are mounted. With this arrangement, all or substantially all of the electrical components of the fluid sensing device can be provided on a single PCB.

[0043] In other embodiments, the printed circuit board is a secondary printed circuit board, and the fluid sensing device further includes a primary printed circuit board on which control electronics are mounted. The primary printed circuit board may be spaced apart from the secondary printed circuit board and electrically connected to the secondary printed circuit board by one or more electrical connectors. With this arrangement, the primary printed circuit board is at atmospheric pressure on both its top and bottom sides and, unlike the secondary printed circuit board, does not need to be strengthened to withstand the pressure in the pressure compensation chamber. This can reduce the size, weight, complexity, and cost of the primary circuit board. Additionally, and somewhat counterintuitively, in cases where a secondary printed circuit board is provided in addition to the primary printed circuit board, the overall size of the fluid sensing device can be reduced by reducing the space occupied by the fluid sensor on the primary printed circuit board. With this arrangement, the primary printed circuit board only needs to accommodate electrical connectors for the fluid sensor, such as pins, rather than the entire fluid sensor. Thus, other electrical components can occupy the space on the primary PCB that was originally required for the fluid sensor, allowing for a more compact overall arrangement. The primary printed circuit board may be spaced apart from the secondary printed circuit board in a direction substantially perpendicular to the plane of the secondary printed circuit board. In such embodiments, the primary printed circuit board and the secondary printed circuit board may be substantially parallel. The primary printed circuit board may be spaced apart from the secondary printed circuit board in a direction substantially parallel to the plane of the secondary printed circuit board. In such embodiments, the primary printed circuit board and the secondary printed circuit board may be arranged substantially perpendicular to each other.

[0044] At least one sensor port may be flush with at least one fluid conduit. At least one sensor port may extend into at least one fluid conduit. Some fluid leakage may be admitted between at least one sensor port and at least one fluid conduit. Preferably, the at least one fluid conduit is isolated from the pressure compensation chamber. Preferably, the fluid sensing device further includes a sensor seal between the at least one sensor port and the at least one fluid conduit, wherein the at least one fluid conduit is isolated from the pressure compensation chamber by the sensor seal. The sensor seal may include an O-ring that extends around at least one sensor port and / or at least one fluid conduit. In a preferred embodiment, at least one sensor port extends into at least one fluid conduit, and the sensor seal may include an O-ring that extends around at least one sensor port to isolate at least one fluid conduit from the pressure compensation chamber. The sensor seal is preferably an elastomeric sensor seal.

[0045] The at least one fluid conduit may comprise a single fluid conduit. The at least one sensor port may comprise a single sensor port. In such examples, the fluid sensor may be configured to measure the fluid pressure in a single fluid conduit using a single sensor port. Preferably, the at least one fluid conduit comprises a first fluid conduit extending from a first position along the fluid flow channel and a second fluid conduit extending from a second position along the fluid flow channel. Preferably, the at least one sensor port comprises a first sensor port in fluid communication with the first fluid conduit and a second sensor port in fluid communication with the second fluid conduit.

[0046] The at least one pressure compensation conduit may comprise a plurality of pressure compensation conduits extending from different positions. For example, different positions along the fluid flow channel. The at least one pressure compensation conduit may comprise a single pressure compensation conduit. The at least one pressure compensation conduit may comprise a single pressure compensation conduit in fluid communication with the fluid flow channel. By this arrangement, the fluid flow channel is in fluid communication with the pressure compensation chamber via only a single pressure compensation conduit.

[0047] In certain preferred embodiments, the fluid flow channel includes a flow restrictor disposed between the first position and the second position. The flow restrictor may comprise an obstacle that is inserted into the fluid flow channel to create a pressure drop. The flow restrictor may comprise an orifice plate or a nozzle. The flow restrictor may comprise a reduction in the diameter of the outer wall of the fluid flow channel. The diameter reduction may comprise a step change in the diameter of the outer wall. The diameter reduction may comprise a gradual change in the diameter of the outer wall. The reduction may be provided only around a portion of the circumference of the fluid flow channel. Around the circumference of the fluid flow channel, the reduction may be uniform. Preferably, the reduction comprises a taper extending around the entire circumference of the outer wall around the flow channel. The fluid sensing device may include a laminar flow element that includes a flow stabilizing rod that extends along the fluid flow channel at least from the first position to the second position. In such examples, the flow restrictor may comprise an increase in the diameter of the flow stabilizing rod. The increase may comprise a step change in the diameter. The increase may comprise a gradual change in the diameter. The increase may be provided only around a portion of the circumference of the flow stabilizing rod. Around the circumference of the flow stabilizing rod, the increase may be uniform. Preferably, the increase comprises a taper extending around the entire circumference of the flow stabilizing rod. In such embodiments, the diameter of the flow channel may be constant in the region of the flow restrictor such that the flow restrictor is defined only by the increase in the diameter of the flow stabilizing rod. This can be beneficial as it allows for the pressure drop across the flow restrictor to be changed as needed for a given flux simply by changing the laminar flow element. The flow restrictor may comprise a reduction in the diameter of the outer wall of the fluid flow channel and an increase in the diameter of the flow stabilizing rod.

[0048] The fluid sensor can be configured to measure a first pressure in the first fluid conduit and a second pressure in the second fluid conduit. Then, the flow rate through the fluid flow channel can be determined based on the pressure difference.

[0049] The first fluid port and the second fluid port can be isolated from each other within the housing. The first fluid port and the second fluid port can be in fluid communication within the housing. In some embodiments, the first fluid conduit, the sensor housing, and the second fluid conduit together form a bypass channel, and a portion of the fluid flow along the fluid flow channel is diverted along the bypass channel during use. The fluid sensor can be configured to measure the bypass flow rate through the bypass channel. Then, the flow rate through the fluid flow channel can be determined based on the bypass flow rate through the flow channel.

[0050] The fluid sensor can be a pressure sensor. The fluid sensor can be configured to sense a first fluid pressure at a first location along the fluid flow channel and a second pressure at a second location along the fluid flow channel. The fluid sensor can be configured to sense the first fluid pressure at the first location via the first fluid conduit and the second pressure at the second location via the second fluid conduit. The fluid sensor can include a first sensor port that is positioned in the first fluid conduit and is configured to sense the first fluid pressure at the first location. The fluid sensor can include a second sensor port that is positioned in the second pressure conduit and is configured to sense the second fluid pressure at the second location. A first sensor seal can be provided around the first sensor port to form a seal between the outer surface of the first sensor port and the inner surface of the first pressure conduit. A second sensor seal can be provided around the second sensor port to form a seal between the outer surface of the second sensor port and the inner surface of the second pressure conduit. In this way, fluid in the first sensor port and / or the second sensor port can be prevented from bypassing the first sensor portion and / or the second sensor portion. The fluid in the first pressure conduit and the second pressure conduit enters the housing of the fluid sensor via the first sensor portion and the second sensor portion.

[0051] The fluid sensor can be configured to output a sensor signal. The sensor signal can include a first fluid pressure signal and a second fluid pressure signal. The fluid sensor can be configured to calculate the pressure difference between the first fluid pressure and the second fluid pressure. The fluid sensor can be configured to output a sensor signal that includes a pressure difference signal, the pressure difference signal including a plurality of calculated pressure difference values. The fluid sensor can be configured to calculate the flow rate through the fluid flow channel based on the sensed first fluid pressure value and the second fluid pressure value. The fluid sensor can be configured to output a sensor signal that includes a flow rate signal, the flow rate signal including a plurality of calculated flow rate values.

[0052] The fluid sensor can be a mass flow sensor. The fluid sensing device can include a bypass channel configured to divert flow around a flow restrictor in a fluid flow channel. The fluid sensor can be a mass flow sensor configured to measure a bypass flow through the bypass channel. The first fluid conduit and the second fluid conduit can be connected to form part of the bypass channel.

[0053] The fluid sensor can include a single sensing head. Signals from the sensing head can be amplified with different gains. This can increase the effective measurement range of the flow rates that can be accurately measured by the fluid sensing device and facilitate accurate flow rate readings from the fluid sensor even at very low flow rates. The fluid sensor can include multiple sensing heads within a single sensor. Signals from each sensing head can be amplified with different gains. This can increase the effective measurement range of the flow rates that can be accurately measured by the fluid sensing device and facilitate accurate flow rate readings from the fluid sensor even at very low flow rates.

[0054] The fluid flow channel can be bounded and defined by an outer wall of the fluid flow channel. In such embodiments, one or both of the at least one pressure compensation conduit and the at least one fluid conduit can extend through the outer wall of the fluid flow channel.

[0055] The at least one pressure compensation conduit can extend between the pressure compensation chamber and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel at the location of the at least one pressure compensation conduit enters the pressure compensation chamber via the at least one pressure compensation conduit during use.

[0056] The at least one fluid conduit can extend between the at least one sensor port and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel at the location of the at least one fluid conduit enters the housing of the fluid sensor via the at least one fluid conduit during use.

[0057] The pressure compensation chamber can be remote from the fluid flow channel. This means that the pressure compensation chamber is located away from the fluid flow channel. The fluid flow channel can extend adjacent to the pressure compensation chamber. The fluid flow channel can extend along the length of the pressure compensation chamber. At least one pressure compensation conduit can form part of a separate fluid flow path to the fluid flow channel. In some embodiments, the pressure compensation chamber does not form part of the same fluid flow path as the fluid flow channel.

[0058] At least one pressure compensation conduit may be accessed into the fluid flow channel at a pressure compensation location along the length of the fluid flow channel such that the fluid pressure in the pressure compensation chamber is the same as the fluid pressure at the pressure compensation location in the fluid flow channel.

[0059] At least one fluid conduit may be accessed into the fluid flow channel at a fluid sensing location along the length of the fluid flow channel such that the fluid pressure at at least one sensor port is the same as the fluid pressure at the fluid sensing location in the fluid flow channel.

[0060] The at least one pressure compensation conduit may be configured such that a portion of the fluid flowing along the fluid flow channel at the location of the at least one pressure compensation conduit is diverted from the fluid flow channel during use to enter the pressure compensation chamber via the at least one pressure compensation conduit.

[0061] The at least one fluid conduit may be configured such that a portion of the fluid flowing along the fluid flow channel at the location of the at least one fluid conduit is diverted from the fluid flow channel during use to enter the housing of the fluid sensor via the at least one fluid conduit.

[0062] The at least one pressure compensation conduit may extend between the pressure compensation chamber and at least one pressure compensation location along the length of the fluid flow channel between the inlet and the outlet.

[0063] The at least one fluid conduit may extend between the at least one sensor port and at least one fluid sensing location along the length of the fluid flow channel between the inlet and the outlet.

[0064] The fluid sensing device may be used in any suitable assembly. For example, the fluid sensing device may form part of a fluid manifold.

[0065] According to a fourth aspect of the present invention, there is provided a mass flow controller comprising: a fluid control valve; control electronics; and a fluid sensing device according to the first aspect, wherein the control electronics are configured to control the fluid control valve based on a sensor signal provided by the fluid sensing device. The fluid control valve may be a proportional valve.

[0066] In certain embodiments, the fluid sensing device of the mass flow controller further comprises: a main printed circuit board on which the control electronics are mounted; and an auxiliary printed circuit board on which the fluid sensor is mounted and which forms part of the pressure compensation chamber. The main printed circuit board may be spaced apart from the auxiliary printed circuit board in a direction perpendicular to the plane of the auxiliary printed circuit board and may be electrically connected to the auxiliary printed circuit board by one or more electrical connectors.

[0067] The mass flow controller can be a micro mass flow controller. As used herein, the term "micro mass flow controller" refers to a mass flow controller having a housing with a maximum dimension in any direction of less than 100 mm, preferably less than 80 mm. The micro flow controller can have a maximum length of less than 80 mm and a maximum height of less than 50 mm.

[0068] Within the scope of the present application, it is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, in the claims, and / or in the following description and drawings (and in particular in their individual features) can be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless the features are incompatible. The applicant reserves the right to change any originally filed claim or to file any new claim accordingly, including the right to amend any originally filed claim to depend on and / or incorporate any feature of any other claim, although not originally presented in this way. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The further features and advantages of the present invention will be further described hereinafter only by way of example and with reference to the accompanying drawings, in which:

[0070] Figure 1 is a partial perspective cross-sectional view of a mass flow controller that includes a fluid sensing device according to a first embodiment;

[0071] Figure 2 is Figure 1 a top view of the mass flow controller of

[0072] Figure 3 is a cross-sectional view taken along line III-III through Figure 2 of

[0073] Figure 4 is a cross-sectional view taken along line IV-IV through Figure 2 of

[0074] Figure 5 is Figures 1 to 4 a top perspective view of the solid body of the mass flow controller of

[0075] Figure 6 is Figures 1 to 4 a schematic cross-section of the fluid sensing device of the mass flow controller of

[0076] Figure 7 is a partial perspective cross-sectional view of a mass flow controller that includes a fluid sensing device according to a second embodiment. Detailed implementation mode

[0077] Figures 1 to 6 A first mass flow controller 100 is shown, which includes a fluid sensing device 120 according to a first embodiment of the present invention. The mass flow controller 100 includes a housing 101 having a fluid inlet 102 and a fluid outlet 103. The housing 101 houses a fluid control valve 104 (such as a proportional valve) and control electronics 105 mounted on a main PCB 106. In this example, the housing 101 includes a solid body 107 and a cover 108, which is removably fixed to the solid body 107 by screws 109. The fluid control valve 104 is positioned along a fluid flow path extending between the fluid inlet 102 and the fluid outlet 103 and is configured to regulate the flow through the mass flow controller 100 based on a control signal from the control electronics 105 in order to achieve or maintain a desired flow rate. As Figure 1 shown, the fluid inlet 102 and the fluid outlet 103 can be threaded to allow easy connection to threaded connectors. Alternatively, the fluid inlet and outlet can have plug-in fittings, or can have flange-mounted manifolds through which fluid lines can be connected without threaded connections.

[0078] The fluid sensing device 120 includes a fluid flow channel 121, which is surrounded and defined by an outer wall 122 of the channel 121 and forms part of the fluid flow path through the mass flow controller 100. The fluid flow channel 121 extends between a channel inlet 123 and a channel outlet 124, the channel inlet being in fluid communication with the fluid inlet 102 of the mass flow controller 100, and the channel outlet being in fluid communication with the fluid outlet 103 of the mass flow controller 100. In this example, the cross-section of the fluid flow channel 121 is circular, but other cross-sectional shapes may also be appropriate. The fluid sensing device further includes a flow restrictor 125, which is positioned along the length of the fluid flow channel 121 and is configured to create a pressure difference in the fluid flowing along the channel 121. In this example, the flow restrictor 125 includes a gradually decreasing diameter of the outer wall 122 of the fluid flow channel 121 such that the cross-sectional area of the fluid flow channel 121 decreases in this region and the flow rate of the fluid increases as the fluid passes through the flow restrictor 125. This creates a pressure drop across the flow restrictor 125. In other examples, the flow restrictor can include a step change in the diameter of the outer wall and / or a change in the diameter of the outer surface of a laminar element positioned in the flow channel 121 as described below.

[0079] The fluid sensing device 100 further includes a fluid sensor 130 mounted on an auxiliary printed circuit board 140. The main PCB 106 is spaced apart from the auxiliary printed circuit board 140 in a direction perpendicular to the plane of the auxiliary printed circuit board 140 and is electrically connected to the auxiliary printed circuit board 140 through an electrical connector 141. The main printed circuit board 106 is removably mounted on the solid body 107 by the same screws 109 as the cover 108. Since the main printed circuit board 106 supports the control electronics 105 of the mass flow controller 100, it can be regarded as the "main" PCB. The auxiliary printed circuit board 140 on which the fluid sensor 130 is mounted can be regarded as the "auxiliary" PCB. In other examples, such as the embodiment discussed in conjunction with Figure 7 the mass flow controller may include a single PCB, and both the control electronics 105 and the fluid sensor 130 are directly mounted on the single PCB.

[0080] As Figure 6 best seen in, the fluid sensor 130 is in fluid communication with a first position 131 of the fluid flow channel 121 upstream of the flow restrictor 125 via a first fluid conduit 132 and is in fluid communication with a second position 133 of the fluid flow channel 121 downstream of the flow restrictor 125 through a second fluid conduit 134. However, in other examples, the fluid sensor may be in fluid communication with only a single position of the fluid flow channel. The fluid sensor 130 is configured to generate a sensor signal indicative of the flow rate of the fluid passing through the fluid flow channel 121 such that the control electronics 105 can correspondingly control the fluid control valve 104 to achieve a desired flow rate through the mass flow controller 100.

[0081] In this example, the fluid sensor 130 is a pressure sensor and includes a first sensor port 135 positioned in a first fluid conduit 132 and a second sensor port 136 positioned in a second fluid conduit 134. The first sensor port 135 and the second sensor port 136 are each provided with an opening through which fluid can enter and / or leave the housing 137 of the fluid sensor 130. The first sensor port 135 enables the fluid sensor 130 to sense or measure a first fluid pressure P1 at a first location 131, and the second sensor port 136 enables the fluid sensor 130 to sense or measure a second fluid pressure P2 at a second location 133. The first sensor port 135 and the second sensor port 136 extend into the first fluid conduit 132 and the second fluid conduit 134, respectively. An O-ring 138 is provided around each of the first sensor port 135 and the second sensor port 136 to form a resilient seal between the first sensor port 135 and the first fluid conduit 132 and between the second sensor port 136 and the second fluid conduit 134, respectively, to prevent fluid leakage.

[0082] Due to the flow restrictor 125, the flow rate at the second location 133 tends to be higher than the flow rate at the first location. Accordingly, the second fluid pressure P2 tends to be lower than the first fluid pressure P1. The pressure difference ΔP across the flow restrictor 125 can be calculated based on the sensed values of P1 and P2, and the flow rate through the fluid flow channel 121 can be determined based on the principle that the flow rate of fluid through the flow restrictor is proportional to the pressure difference across the flow restrictor. The pressure difference ΔP can be determined by the fluid sensor 130 or by the control electronics 105. In the case where the pressure difference ΔP is determined by the control electronics, the sensor signal can include a first pressure signal of the first fluid pressure P1 over time and a second pressure signal of the second fluid pressure P2 over time. In the case where the pressure difference ΔP is determined by the fluid sensor, the sensor signal can include a pressure difference signal of the pressure difference ΔP over time. The fluid sensor can be configured to determine the flow rate, in which case the sensor signal can include a flow rate signal.

[0083] In other examples, the fluid sensor 130 can be a mass flow sensor. For example, the first fluid conduit 132 and the second fluid conduit 134 can be connected to form a bypass channel (not shown) where a portion of the fluid flow is diverted by the flow restrictor 125, and the fluid sensor is configured to measure the bypass flow rate at the bypass channel. Then, the fluid flow rate along the fluid flow channel can be calculated based on the bypass flow rate.

[0084] As Figures 3 to 5Best seen in, the solid body 107 is formed from a solid block of material in which a plurality of holes are defined to form respective conduits, and the other components of the mass flow controller 100 are accommodated by the solid block of material. The fluid sensing device 120 further includes a pressure compensation chamber 142 that is in fluid communication with a third location 143 along the fluid flow path 121 via a pressure compensation conduit 144. The pressure compensation chamber 142 is defined by a reservoir in the form of a cavity 145 in the outer surface of the solid body 107 and an auxiliary printed circuit board 140 that closes the cavity 145. The auxiliary printed circuit board 140 is held in place against the cavity 145 by a pair of screws 146 that extend into threaded holes 1071 in the solid body 107. The auxiliary printed circuit board 140 is sealed against the cavity 145 by an elastomeric seal 147 that sits in a continuous groove 148 formed in the outer surface of the solid body 107 and extending around the cavity 145. The elastomeric seal 147 prevents fluid leakage between the auxiliary printed circuit board 140 and the solid body 107. In this way, the auxiliary printed circuit board 140 forms the upper wall of the pressure compensation chamber 142. Thus, the lower side of the auxiliary printed circuit board 140 on which the fluid sensor 130 is mounted is exposed to the elevated pressure in the pressure compensation chamber 142, while the upper side of the auxiliary printed circuit board 140 is exposed to atmospheric pressure. This means that the auxiliary printed circuit board should be constructed to withstand the difference between atmospheric pressure and the elevated pressure in the pressure compensation chamber 142 during operation. However, it also means that the components of the mass flow controller located above the auxiliary printed circuit board 140, such as the main printed circuit board 106, are at atmospheric pressure and do not need to be constructed to withstand elevated pressure. The first fluid conduit 132, the second fluid conduit 134, and the pressure compensation conduit 144 extend to the bottom of the cavity 145. The pressure compensation conduit leads to the pressure compensation chamber. The first fluid conduit 132 and the second fluid conduit 134 each have cup-shaped reservoirs 1321, 1341 at their cavity ends and seal seats 1322, 1324 around the cup-shaped reservoirs 1321, 1341 in which O-rings around each sensor port are sealed to isolate the first fluid conduit and the second fluid conduit from the pressure compensation chamber.

[0085] In this example, the third location 143 from which the pressure compensation conduit 144 extends is downstream of both the first location 131 and the second location 133 from which the first fluid conduit 132 and the second fluid conduit 134 extend. However, in other examples, the pressure compensation conduit 144 can be connected to different locations along the fluid flow path 121, such as a location upstream of one or both of the first location 131 and the second location 133.

[0086] To improve flow sensing accuracy, the fluid sensing device 120 further includes an optional laminar flow element 150 that is located in the fluid flow channel 121. The laminar flow element 150 includes a flow stabilizer rod 151 and a support 152. The flow stabilizer rod 121 is centrally mounted in the fluid flow channel 121 by the support. The flow stabilizer rod 151 extends at least from a first position 131 through the flow restrictor 125 along the fluid flow channel 121 to a second position 133 to promote laminar flow and suppress turbulent flow in the fluid flow channel 121. In this example, the flow stabilizer rod 151 extends from a position upstream of the first position 131 to a position downstream of the second position 133. The support 152 of the laminar flow element 150 is fastened within the fluid flow channel 121 at the upstream end of the flow stabilizer rod 151. The support 152 can be fixedly fastened in the flow channel 151 or can be removably fastened. In this example, the support 152 includes threads 156 on its outer surface 154 that engage corresponding threads on the outer wall 122 of the flow channel 121. Thus, the support 152 is removably fastened within the flow channel 121 at a position upstream of the first position 131 by a threaded connection.

[0087] The support 152 of the laminar flow element 150 includes a plurality of fluid flow orifices 155 that are spaced apart at regular intervals around the circumference of the support 152 and are spaced from the outer surface 154 of the support. The fluid flow orifices 155 allow fluid to pass through the support 152 and promote more uniform flow of the fluid along the fluid flow channel 121. The support 152 can have any suitable shape. In this example, the shape of the outer surface 154 of the support 152 corresponds to the shape of the outer wall 122 of the flow channel 121 and is fastened by a threaded connection. This prevents or reduces the amount of fluid that can pass between the outer surface 154 of the support 152 and the outer wall 122 of the flow channel 121. Because the shape of the outer surface 154 corresponds to the shape of the outer wall 122 of the flow channel 121, substantially all of the fluid flowing along the fluid flow channel flows through the fluid flow orifices 155. In other examples, one or more outer orifices can be formed between the outer surface of the support and the outer wall of the flow channel such that fluid can pass around the outer surface of the support.

[0088] As Figure 6Best seen in [description omitted], the outer wall 122 of the fluid flow passage 121 and the outer surface 153 of the flow stabilizer rod 151 together define an annular portion 126 through which fluid in the fluid flow passage 121 flows. The outer surface 153 of the flow stabilizer rod 151 is substantially continuous. That is, the outer surface 153 of the flow stabilizer rod 151 is substantially free of any grooves, protrusions, or other surface features that might otherwise impede flow attachment. The outer surface 153 of the flow stabilizer rod 151 may be smooth. In this example, the diameter of the outer surface 153 is substantially constant along the entire length of the flow stabilizer rod 151. Accordingly, the cross-sectional area of the annular portion 126 that varies with the radial distance between the outer wall 122 of the fluid flow passage 121 and the outer surface 153 of the flow stabilizer rod 151 decreases solely as the diameter of the outer wall 122 of the flow passage 121 decreases over the flow restrictor. In other examples, the diameter of the outer surface 153 may vary along the length of the flow stabilizer rod 151. The diameter of the outer surface 153 may increase or decrease along its length provided that the radial distance between the outer wall 122 of the fluid flow passage 121 and the outer surface 153 of the flow stabilizer rod 151 decreases to define the flow restrictor. In an example where the diameter of the outer surface of the flow stabilizer rod increases, the diameter of the outer wall of the flow passage may decrease, remain the same, or increase in the region of the flow restrictor provided that the increase in the diameter of the outer surface of the flow stabilizer rod is sufficient such that the radial distance between the outer wall of the fluid flow passage and the outer surface of the flow stabilizer rod still decreases over the flow restrictor.

[0089] During operation of the mass flow controller 100, fluid enters the housing 101 through the fluid inlet 102 and enters the fluid flow channel 121 via the channel inlet 123. When the fluid reaches the laminar flow element 150, the fluid passes through the plurality of fluid flow orifices 155 in the support 152 and enters the annular portion 126 of the fluid flow channel 121 defined between the flow straightening rod 151 and the outer wall 122 of the fluid flow channel 121, where the fluid travels along the length of the flow straightening rod 151, passes through the flow restrictor 125, and exits the fluid flow channel 121 at the channel outlet 124. The fluid enters the housing 137 of the fluid sensor 130 via the first fluid conduit 132 and the second fluid conduit 134. The fluid sensor 130 monitors the first fluid pressure P1 at the first location 131 and the second fluid pressure P2 at the second location 133, and outputs the sensed P1 value and P2 value as a sensor signal to the control electronics 105. The control electronics 105 determines the pressure drop ΔP across the flow restrictor 125 by subtracting P2 from P1. The control electronics 105 calculates the flow rate through the fluid flow channel 121 based on the pressure drop ΔP and compares it with the desired flow rate in a conventional manner. If the calculated flow rate is greater than or less than the desired flow rate, the control electronics 105 then controls the fluid control valve 104 to adjust the flow rate as needed. Since the pressure compensation chamber 142 is in fluid communication with the fluid flow channel via the pressure compensation conduit 144, the pressure compensation chamber 142 is filled with fluid at the same pressure P3 as at the third location 143 along the fluid flow channel 121. With this arrangement, the outer surface of the housing 137 of the fluid sensor 130 is exposed to an elevated pressure that varies with the pressure P3 at the third location 143 of the fluid flowing along the flow channel 121. At the same time, the inner surface of the housing 137 is exposed to an elevated pressure that varies with the pressure P1 at the first location 131 and the pressure P2 at the second location 133 of the fluid flowing along the flow channel 121. This means that the housing of the fluid sensor only has to resist a relatively small difference between the pressure P3 at the third location and the first pressure P1 at the first location and the second pressure P2 at the second location, rather than the full difference between atmospheric pressure and the first fluid pressure P1 and the second fluid pressure P2.

[0090] By enclosing the housing 137 of the fluid sensor 130 within the pressure compensation chamber 142, the outer surface of the housing 137 is exposed to a fluid pressure that can be equivalent to the fluid pressure inside the housing 137. Thus, the pressure differential across the housing 137 is smaller. This means that the housing 137 does not need to be constructed to withstand large internal pressures, since these internal pressures will be matched by large external pressures. Accordingly, the complexity, size, and weight of the fluid sensor can be reduced relative to conventional fluid sensing devices. In fact, with the arrangement of the present invention, a fluid sensor having a housing that can only withstand a pressure differential of 1 bar or less can be used.

[0091] Figure 7 FIG. 2 shows a second embodiment of a mass flow controller 200 which includes a fluid sensing device 220 according to the second embodiment of the present invention. The mass flow controller 200 has a structure and function similar to that of the mass flow controller 100 of the first embodiment, and like reference numerals are used to denote like features. As in the first embodiment, the fluid sensing device 220 includes a laminar flow element 250 having a flow stabilizer rod 251 which is centrally positioned in the fluid flow channel 221 and extends from a position upstream of the first position 231 to a position downstream of the second position 233. The mass flow controller 200 also includes control electronics 205 which are mounted on a PCB 206. However, unlike the first embodiment, the fluid sensor 230 together with the control electronics 205 are directly mounted on the main PCB 206. Thus, the main PCB 206 is the only PCB in the mass flow controller 200. In the absence of an auxiliary printed circuit board, the main PCB 206 forms the upper wall of the pressure compensation chamber 242, is held in place by a pair of screws 209 extending into threaded holes in the solid body 207, and is sealed against the solid body 207 by an elastic seal (not shown). Thus, the underside of the main PCB 206 is exposed to the elevated pressure in the pressure compensation chamber 242 while the upper side of the main PCB 206 is exposed to atmospheric pressure. This means that the main PCB 206 should be constructed to withstand the difference between atmospheric pressure and the elevated pressure in the pressure compensation chamber 242 during operation.

[0092] Further, in the mass flow controller 200 of the second embodiment, the third position 243 from which the pressure compensation conduit 244 extends is upstream rather than downstream of both the first position 231 and the second position 233.

[0093] Although the invention has been described above with reference to one or more preferred embodiments, it should be understood that various changes or modifications can be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A fluid sensing device, comprising: a fluid flow channel having an inlet and an outlet; at least one fluid conduit in fluid communication with the fluid flow channel; a fluid sensor having a housing and at least one sensor port in fluid communication with the at least one fluid conduit and providing access to the housing; a pressure compensation chamber in which the housing of the fluid sensor is enclosed; and at least one pressure compensation conduit in fluid communication with the pressure compensation chamber and the fluid flow channel, wherein the at least one pressure compensation conduit extends between the pressure compensation chamber and a location along the fluid flow channel such that fluid flowing along the fluid flow channel enters the pressure compensation chamber via the at least one pressure compensation conduit at the location of the at least one pressure compensation conduit during use, and wherein the at least one fluid conduit extends between the at least one sensor port and a location along the fluid flow channel such that fluid flowing along the fluid flow channel enters the housing of the fluid sensor via the at least one fluid conduit at the location of the at least one fluid conduit during use.

2. The fluid sensing device according to claim 1, wherein the fluid sensor is mounted on a printed circuit board that forms part of the pressure compensation chamber.

3. The fluid sensing device according to claim 2, wherein the pressure compensation chamber further includes a reservoir, and the printed circuit board is sealed against the reservoir to enclose the reservoir and thereby define the pressure compensation chamber.

4. The fluid sensing device according to claim 3, further comprising an elastic seal between the printed circuit board and the reservoir, wherein the printed circuit board is removably sealed against the reservoir by the elastic seal.

5. The fluid sensing device according to claim 3 or claim 4, further comprising a housing including a solid body in which the at least one fluid conduit and the at least one pressure compensation conduit are formed, wherein the reservoir is defined by a cavity in the solid body.

6. The fluid sensing device according to any one of claims 2 to 4, wherein the printed circuit board is a main printed circuit board on which control electronics and the fluid sensor are mounted.

7. The fluid sensing device according to any one of claims 2 to 4, wherein the printed circuit board is an auxiliary printed circuit board, and the fluid sensing device further includes a main printed circuit board on which control electronics are mounted, the main printed circuit board being electrically connected to the auxiliary printed circuit board by one or more electrical connectors.

8. The fluid sensing device according to any one of claims 1 to 4, further comprising a sensor seal between the at least one sensor port and the at least one fluid conduit, wherein The at least one fluid conduit is isolated from the pressure compensation chamber by the sensor seal.

9. The fluid sensing device according to any one of claims 1 to 4, wherein, the at least one fluid conduit includes a first fluid conduit extending from a first position along the fluid flow channel and a second fluid conduit extending from a second position along the fluid flow channel, and wherein the at least one sensor port includes a first sensor port in fluid communication with the first fluid conduit and a second sensor port in fluid communication with the second fluid conduit.

10. The fluid sensing device according to claim 9, wherein, the fluid flow channel includes a restrictor disposed between the first position and the second position, and wherein the fluid sensor is configured to measure a first pressure in the first fluid conduit and to measure a second pressure in the second fluid conduit.

11. The fluid sensing device according to claim 10, wherein, the first fluid conduit, the sensor housing, and the second fluid conduit together form a bypass channel, a portion of the fluid flow of the fluid flow channel is diverted along the bypass channel during use, and wherein the fluid sensor is configured to measure the bypass flow through the bypass channel.

12. The fluid sensing device according to any one of claims 1 to 4, wherein, the fluid flow channel is bounded and defined by an outer wall of the fluid flow channel, and wherein the at least one pressure compensation conduit and the at least one fluid conduit extend through the outer wall of the fluid flow channel.

13. The fluid sensing device according to any one of claims 1 to 4, wherein, the at least one pressure compensation conduit extends between the pressure compensation chamber and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel enters the pressure compensation chamber via the at least one pressure compensation conduit at the location of the at least one pressure compensation conduit during use.

14. The fluid sensing device according to any one of claims 1 to 4, wherein, the at least one fluid conduit extends between the at least one sensor port and a location along the fluid flow channel such that a portion of the fluid flowing along the fluid flow channel enters the housing of the fluid sensor via the at least one fluid conduit at the location of the at least one fluid conduit during use.

15. The fluid sensing device according to any one of claims 1 to 4, wherein, the pressure compensation chamber is remote from the fluid flow channel.

16. The fluid sensing device according to any one of claims 1 to 4, wherein, a portion of the fluid flowing along the fluid flow channel is diverted from the fluid flow channel at the location of the at least one pressure compensation conduit during use to enter the pressure compensation chamber via the at least one pressure compensation conduit.

17. The fluid sensing device according to any one of claims 1 to 4, wherein, A portion of the fluid flowing along the fluid flow channel is withdrawn from the fluid flow channel at the location of the at least one fluid conduit during use to enter the housing of the fluid sensor via the at least one fluid conduit.

18. The fluid sensing device according to any one of claims 1 to 4, wherein, the at least one pressure compensation conduit extends between the pressure compensation chamber and at least one location along the length of the fluid flow channel between the inlet and the outlet.

19. The fluid sensing device according to any one of claims 1 to 4, wherein, the at least one fluid conduit extends between the at least one sensor port and at least one location along the length of the fluid flow channel between the inlet and the outlet.

20. A mass flow controller, comprising: a fluid control valve; control electronics; and the fluid sensing device according to any one of claims 1 to 19, wherein the control electronics is configured to control the fluid control valve based on a sensor signal provided by the fluid sensing device.

21. The mass flow controller according to claim 20, wherein, the fluid sensing device further comprises: a main printed circuit board on which the control electronics is mounted; and an auxiliary printed circuit board on which the fluid sensor is mounted and the auxiliary printed circuit board forms part of the pressure compensation chamber, wherein the main printed circuit board is spaced apart from the auxiliary printed circuit board in a direction perpendicular to the plane of the auxiliary printed circuit board and is electrically connected to the auxiliary printed circuit board by one or more electrical connectors.

22. The mass flow controller according to claim 20 or claim 21, wherein, the mass flow controller is a micro mass flow controller.

Images