CN111795730A - Gas thermal mass flowmeter - Google Patents
Gas thermal mass flowmeter Download PDFInfo
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- CN111795730A CN111795730A CN202010745966.3A CN202010745966A CN111795730A CN 111795730 A CN111795730 A CN 111795730A CN 202010745966 A CN202010745966 A CN 202010745966A CN 111795730 A CN111795730 A CN 111795730A
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- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
- G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
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Abstract
The invention provides a gas thermal mass flowmeter, relates to the field of gas flow measurement, and aims to solve the problem that the existing gas thermal mass flowmeter is influenced by gas components when calibration gas and measurement gas are inconsistent in the use process to cause measurement accuracy deviation. The gas thermal mass flowmeter comprises a flowmeter body, an MEMS sensing element, a control module, a battery power supply module and a flow straightener, wherein the flowmeter body is provided with a gas flow channel for gas to flow, the MEMS sensing element is installed on the flowmeter body, a detection part of the MEMS sensing element extends into the gas flow channel, the detection part comprises a mass flow sensor, the MEMS sensing element further comprises a thermophysical property sensor, the thermophysical property sensor comprises two thermosensitive elements, and one thermosensitive element is configured to be in contact with the measured gas; the mass flow sensor and the thermophysical property sensor are both electrically connected with the control module. The thermal mass flowmeter for the gas provided by the invention can realize measurement independent of gas components.
Description
Technical Field
The invention relates to the field of gas flow measurement, in particular to a gas thermal mass flowmeter.
Background
The advantage of a gas thermal mass flow meter is that its metering results are not affected by changes in ambient temperature and pressure, but when mass flow is converted to standard volumetric flow metering, if the calibration gas is not in agreement with the actual measured gas, the metering results will be affected by changes in the composition of the gas. Thus, when used for purposes of trade metering, would conflict with existing metering specifications. For industrial gas measurement, the repeatability required by measurement can be obtained by adopting a simple gas conversion factor, but for the requirement of trade measurement, the gas conversion factor can not completely ensure the precision required by measurement, so that the problem that the precision between calibration and gas use of a gas thermal mass flowmeter is necessary for the application of the gas thermal mass flowmeter in the field of trade measurement is effectively solved.
Disclosure of Invention
The invention aims to provide a gas thermal mass flowmeter, which aims to solve the technical problem that the measurement precision is deviated due to the influence of gas components when a calibration gas and a measurement gas are inconsistent in the use process of the conventional gas thermal mass flowmeter.
The invention provides a gas thermal mass flowmeter, which comprises a flowmeter main body, an MEMS sensing element, a control module, a battery power supply module and a fluid straightener.
The flowmeter body has a gas flow passage through which gas flows.
The MEMS sensing element is mounted to the flowmeter body, and a detection portion of the MEMS sensing element protrudes into the gas flow channel, the detection portion includes a mass flow sensor, the MEMS sensing element further includes a thermophysical sensor, the thermophysical sensor includes two thermosensitive elements, one of the thermosensitive elements is configured to be in contact with a gas to be measured.
The mass flow sensor and the thermophysical property sensor are electrically connected with the control module.
The battery power supply module is used for supplying power to electric components in the gas thermal mass flow meter.
The flow straightener is mounted at the inlet of the flow meter body.
Further, the MEMS sensing element include the installation department and with installation department fixed connection's shaft-shaped portion, the installation department be used for with flowmeter main part fixed connection, the probe site is in shaft-shaped portion keeps away from the one end of installation department, thermophysical property sensor is located shaft-shaped portion with between the installation department.
Further, a closed space is arranged between the rod-shaped portion and the mounting portion, the thermophysical property sensor is located in the closed space, and an opening used for gas exchange with the outside is formed in the closed space.
Further, a first closed space and a second closed space are arranged between the rod-shaped portion and the mounting portion in parallel, the first closed space is provided with the thermal property sensor, the first closed space is filled with reference gas, the second closed space is provided with an opening for gas exchange with the outside, the second closed space is provided with the thermal property sensor, and the thermal property sensor in the second closed space is configured to be in contact with gas in the airflow channel; the first enclosed space and the second enclosed space are the same in spatial dimension.
Further, shaft portion includes first section and second section, first section be used for with installation department fixed connection, the second section be used for with detection portion fixed connection, wherein, the radial cross-section of first section is circular, the axial cross-section of second section is the V-arrangement, the pointed end orientation of second section the air current passageway, just two sides of second section with the extending direction of air current passageway is parallel.
Further, the detection part still includes the sheet metal, the sheet metal set firmly in the rod-like portion is kept away from the one end of installation department, the face of sheet metal with airflow channel's extending direction is parallel, mass flow sensor inlays and adorns in the sheet metal.
Further, the airflow passage is in a venturi tube shape, and the detection part of the sensing element extends into the central position of the throat part of the venturi tube-shaped airflow passage.
Further, the gas thermal mass flow meter further comprises a display module configured to display a measurement value of the gas thermal mass flow meter.
Furthermore, the gas thermal mass flowmeter further comprises a sealed first box body and a sealed second box body, the first box body is fixedly connected to the flowmeter main body, and the battery power supply module is positioned in the first box body; the second box body is fixedly connected to the flowmeter main body, and the MEMS sensing element is located inside the second box body.
Further, the gas thermal mass flowmeter also comprises a fluid rectifier, and the fluid straightener and the fluid rectifier are sequentially arranged along the flowing direction of the gas in the gas flow channel.
Furthermore, the thermophysical property sensor also comprises a silicon substrate, wherein the silicon substrate is provided with a first surface and a second surface which are arranged oppositely, the two thermosensitive elements are fixedly arranged on the first surface, and the second surface is provided with a thermal isolation cavity.
The gas thermal mass flowmeter has the advantages that:
the principle of measuring the gas flow by using the gas thermal mass flowmeter is as follows: first, among the two thermistors defining the thermophysical sensor, the one that is in direct contact with the gas to be measured is the first thermistor, and the one that is not in contact with the gas to be measured is the second thermistor. When the gas flows in the gas flow channel, the first thermosensitive element is in direct contact with the measured gas, when the component of the measured gas changes, the first thermosensitive element measures the change, then a corresponding signal is output to the control module, and the control module feeds the output signal back to the mass flow sensor; the mass flow sensor then heats the first thermistor to correct for thermal conduction and resultant metering drift due to changes in gas thermophysical property values, and compares the measured values to calibrated values for real-time calibration to achieve gas composition independent measurements. The mass flow sensor works by adopting a calorimetric flow sensing principle irrelevant to the change of the ambient temperature and the pressure.
In a static fluid environment, the gas thermal conductivity k can be measured through the power consumption of heating a first thermosensitive element, and the constant pressure specific heat capacity Cp can be measured through the temperature of an adjacent second thermosensitive element increased by the diffusion coefficient D, and the calculation formula is as follows: d ═ k/ρ Cp, where ρ is the gas density. The first and second heat sensitive elements operate in a differential circuit mode to eliminate electrical instability and temperature effects of the heat sensitive elements, thereby improving fluid thermal performance measurement accuracy.
The gas thermal mass flowmeter has the functions of measuring the thermal property of gas in real time and automatically correcting, measures the mass flow of the gas by the mass flow sensor during the continuous measurement period of the standard volume measurement deviation of the calibration gas caused by the change of the gas components or the thermal property value, measures by adopting the thermal property sensor and carries out real-time measurement correction, so that the measurement result according to the converted standard volume is independent of the components of the gas.
In addition, the arrangement of the battery power supply module can realize the power supply of the electric parts in the gas thermal mass flow meter, an external power supply is not needed, and the modularization and integration of the gas thermal mass flow meter are realized. And, through set up the fluid straightener in the entrance of flowmeter main part, can eliminate torrent and unstable undulant of fluid, be favorable to improving measurement accuracy.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a gas thermal mass flowmeter provided by an embodiment of the invention;
fig. 2 is an exploded view of a gas thermal mass flow meter according to an embodiment of the present invention;
fig. 3 is a schematic half-sectional structure view of a flowmeter body of the thermal mass flowmeter according to the embodiment of the present invention;
fig. 4 is a schematic structural diagram of a first form of MEMS sensing element of a gas thermal mass flow meter according to an embodiment of the present invention;
fig. 5 is a partial schematic structural diagram of a first form of MEMS sensing element of a gas thermal mass flow meter according to an embodiment of the present invention;
fig. 6 is a schematic internal structural diagram of a first form of MEMS sensing element of a gas thermal mass flow meter according to an embodiment of the present invention;
fig. 7 is a schematic diagram showing an internal structure of a second form of MEMS sensing element of the gas thermal mass flow meter according to the embodiment of the present invention;
fig. 8 is a schematic structural diagram of a thermophysical sensor of a gas thermal mass flowmeter according to an embodiment of the present invention.
Description of reference numerals:
100-a flow meter body; 110-an air flow channel; 120-a mounting port; 130-a first flange; 140-a second flange; 150-a fluid straightener; 160-fluid rectifier;
200-MEMS sensing elements; 210-a detection section; 211-a mass flow sensor; 212-a sheet; 220-a rod-shaped portion; 221-first stage; 222-a second segment; 230-a mounting portion; 231-connecting holes; 240-epoxy resin; 250-a cable line; 261-an enclosed space; 262-opening; 263-first enclosed space; 264-a second enclosed space; 270-a thermophysical property sensor; 271-a first thermosensor; 272-a second heat sensitive element; 273-a silicon substrate; 274-a thermally isolated cavity; 275-window; 276-wire bond pads;
300-a first cartridge; 310-a first box body; 320-a first box cover;
400-a second container; 410-a second box body; 420-a second box cover;
500-a battery power module;
600-a data cable;
700-a control module; 710-connection terminal;
800-display module.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Fig. 1 is a schematic structural diagram of a gas thermal mass flow meter according to this embodiment, fig. 2 is an exploded structural view of the gas thermal mass flow meter according to this embodiment, and fig. 3 is a schematic half-section structural diagram of a flow meter main body 100 of the gas thermal mass flow meter according to this embodiment. As shown in fig. 1 to 3, the present embodiment provides a gas thermal mass flowmeter, including a flowmeter main body 100, a MEMS sensing element 200 and a control module 700, wherein the flowmeter main body 100 has a gas flow channel 110 for flowing gas, the MEMS sensing element 200 is mounted on the flowmeter main body 100, and a detection portion 210 of the MEMS sensing element 200 extends into the gas flow channel 110.
Fig. 4 is a schematic structural diagram of a first form of the MEMS sensing element 200 of the gas thermal mass flow meter provided in this embodiment, fig. 5 is a schematic partial structural diagram of the first form of the MEMS sensing element 200 of the gas thermal mass flow meter provided in this embodiment, and fig. 6 is a schematic internal structural diagram of the first form of the MEMS sensing element 200 of the gas thermal mass flow meter provided in this embodiment. As shown in fig. 4 to 6, in particular, the detecting part 210 includes a mass flow sensor 211, the MEMS sensing element 200 further includes a thermal property sensor 270, the thermal property sensor 270 includes two thermal elements, one of the thermal elements is configured to contact with the measured gas, and the mass flow sensor 211 and the thermal property sensor 270 are both electrically connected to the control module 700.
The principle of measuring the gas flow by using the gas thermal mass flowmeter is as follows: first, of the two thermistors defining the thermal property sensor 270, the one directly contacting the gas to be measured is the first thermistor 271, and the one not contacting the gas to be measured is the second thermistor 272. During the gas flowing in the gas flow channel 110, the first heat sensitive element 271 is in direct contact with the measured gas, when the composition of the measured gas changes, the first heat sensitive element 271 measures the change, and then outputs a corresponding signal to the control module 700, and the control module 700 feeds back the output signal to the mass flow sensor 211; the mass flow sensor 211 then heats the first thermistor 271 to correct for thermal conduction and resulting metering drift due to changes in gas thermal property values, and compares the measured values to calibrated values for real-time calibration to achieve gas composition independent measurements. The mass flow sensor 211 works on the basis of the calorimetric flow sensing principle independent of ambient temperature and pressure changes.
It should be noted that, in a static fluid environment, the gas thermal conductivity k can be measured by the power consumption of heating the first thermosensitive element 271, and the constant pressure specific heat capacity Cp can be measured by the temperature of the adjacent second thermosensitive element 272 increased by the diffusion coefficient D, and the calculation formula is: d ═ k/ρ Cp, where ρ is the gas density. The first and second heat sensitive elements 271, 272 operate in a differential circuit mode to eliminate electrical instability and temperature effects of the heat sensitive elements, thereby improving fluid thermal performance measurement accuracy.
The gas thermal mass flowmeter has the functions of measuring the thermal property of gas in real time and automatically correcting, measures the mass flow of the gas by the mass flow sensor 211 during the continuous measurement period of the standard volume measurement deviation of the calibration gas caused by the change of the gas components or the thermal property value, and measures and carries out real-time measurement correction by the thermal property sensor 270, so that the measurement result is independent of the components of the gas according to the converted standard volume.
The gas thermal mass flowmeter records the measured gas thermophysical property (gas component) change in real time and sends the measured data to the control module 700, the control module 700 compares the value in the calibration state stored in the memory thereof with the current measured value, if any difference exceeds the preset limit value, the automatic correction program is triggered, and an alarm is simultaneously generated and stored in the independent memory of the control module 700. The corresponding code will be displayed on the local display screen of the gas thermal mass flow meter. The measured data is further stored in a solid-state memory of the gas thermal mass flow meter, and the measured value is sent to a designated data center in a state that the flow meter is networked. The database formed by the data provides basis for future use or upgrading of heat value metering.
It should be noted that, in this embodiment, the control module 700 should provide an interface for NB-IoT, GPRS, and other wireless or wired transmission devices; the method provides a communication channel for wireless transmission equipment such as Bluetooth, Zigbee and infrared transmission equipment, and the specific communication mode is selected according to specific requirements.
Referring to fig. 1 and fig. 2, in the present embodiment, a first flange 130 is disposed at one end of the flowmeter body 100, and a second flange 140 is disposed at the other end. So configured, connection and maintenance of the flowmeter body 100 to the corresponding pipe are facilitated. In other embodiments, the flowmeter body 100 can also be connected to the corresponding conduit by threads.
Preferably, the flowmeter body 100 is made of cast aluminum alloy or stainless steel. By the arrangement, the long-term field use of the gas thermal mass flowmeter can be ensured.
Referring to fig. 3, in the present embodiment, the flowmeter main body 100 is provided with a mounting opening 120, and the detecting portion 210 extends into the airflow channel 110 through the mounting opening 120. Specifically, the air flow passage 110 has a venturi shape, and the detecting portion 210 of the sensing element extends into a central position of a throat portion of the venturi-shaped air flow passage 110.
In operation, the gas thermal mass flowmeter flows through the gas flow channel 110, and the gas flow channel 110 is configured in a venturi shape, so that the gas has the highest flow velocity when flowing to the throat of the gas flow channel 110. The detecting part 210 of the sensing element extends into the central position of the throat part, so that the detecting part 210 can timely and accurately detect the flow change of the gas, the measurement sensitivity of the MEMS sensing element 200 is improved, and the measurement requirement on the low-flow gas is met.
With reference to fig. 4 to 6, in the present embodiment, the MEMS sensing element 200 may include a mounting portion 230 and a rod portion 220 fixedly connected to the mounting portion 230, wherein the mounting portion 230 is used for fixedly connecting to the flowmeter main body 100, the detecting portion 210 is located at an end of the rod portion 220 far from the mounting portion 230, and the thermal property sensor 270 is located between the rod portion 220 and the mounting portion 230.
By disposing the thermal property sensor 270 between the rod portion 220 and the mounting portion 230, the thermal property sensor 270 is far from the airflow channel 110, interference of the gas flowing process to the thermal property sensor 270 is reduced, and the measurement accuracy of the thermal property sensor 270 is ensured.
Referring to fig. 5, the mounting portion 230 is provided with a plurality of connecting holes 231. When it is necessary to mount the MEMS sensing element 200 to the flowmeter body 100, the rod portion 220 may be sealingly connected to the mounting port 120 of the flowmeter body 100, and the mounting portion 230 may be fastened to the flowmeter body 100 with screws respectively passing through the respective connection holes 231, wherein a seal ring may be provided between the mounting portion 230 and the flowmeter body 100.
This connection not only avoids the gas in the gas flow channel 110 from leaking from the joint between the MEMS sensing element 200 and the flowmeter main body 100, but also realizes the detachable connection between the MEMS sensing element 200 and the flowmeter main body 100, which is convenient for maintenance.
With continued reference to fig. 4 and 6, in the present embodiment, the epoxy resin 240 with corrosion resistance can be used to seal the connection of the cable 250. The epoxy resin 240 with the anti-corrosion performance is not easy to volatilize, and the sealing reliability of the connection of the cable 250 can be ensured by the arrangement.
Referring to fig. 4 to 6, in the present embodiment, a closed space 261 is disposed between the rod portion 220 and the mounting portion 230, the thermal property sensor 270 is located in the closed space 261, and the closed space 261 is opened with an opening 262 for exchanging air with the outside.
By disposing the thermal property sensor 270 in the enclosed space 261, the thermal property sensor 270 is covered by the enclosed space 261, and the adverse effect of the gas flow on the thermal property sensor 270 is further weakened, thereby improving the measurement accuracy of the thermal property sensor 270. When the composition of the gas in the gas flow channel 110 changes, the gas in the gas flow channel 110 can exchange with the medium in the enclosed space 261 by diffusion through the openings 262.
Note that the "closed space 261" is not absolutely closed but relatively closed, and the inner cavity of the closed space 261 can be exchanged with the outside air through the opening 262. The "first closed space 263" and the "second closed space 264" mentioned below are the same.
Preferably, a filter is disposed at the opening 262. Through setting up the filter, realized the filtration to gas for mixed tiny oil droplet, granule or other foreign matters homoenergetic in the gas can be blockked outside enclosed space 261, thereby has reduced the influence of gaseous impurity to thermophysical property sensor 270 measurement process.
With reference to fig. 4 to fig. 6, in the present embodiment, the rod portion 220 may include a first section 221 and a second section 222, specifically, the first section 221 is used for being fixedly connected to the mounting portion 230, the second section 222 is used for being fixedly connected to the detecting portion 210, wherein a radial cross section of the first section 221 is circular, an axial cross section of the second section 222 is V-shaped, a tip of the second section 222 faces the airflow channel 110, and two side surfaces of the second section 222 are parallel to an extending direction of the airflow channel 110.
By arranging the first section 221 of the rod-shaped portion 220 to be a round rod shape, the second section 222 to be a pointed rod shape, and arranging the second end of the pointed rod shape to face the airflow channel 110, both sides of the second section 222 are inclined to form boundary layers for fluid media, so that better fluid flow field characteristics can be obtained during the flowing process of the airflow channel 110.
Referring to fig. 4 to fig. 6, in the present embodiment, the detecting portion 210 may further include a thin plate 212, specifically, the thin plate 212 is fixedly disposed at an end of the rod portion 220 away from the mounting portion 230, a plate surface of the thin plate 212 is parallel to the extending direction of the airflow channel 110, and the mass flow sensor 211 is embedded in the thin plate 212.
The arrangement is such that during the gas flow in the gas flow channel 110, when the gas flows to the position of the thin plate 212, the fluid medium sensed by the mass flow sensor 211 is redistributed to form a laminar flow, thereby producing the best measurement conditions for the metering of the mass flow sensor 211.
Note that "sheet 212" means: thinner than the plate of the rod portion 220.
Specifically, in this embodiment, mass flow sensor 211 may be connected via a ceramic circuit board and embedded in sheet 212. Preferably, sheet 212 is made of stainless steel.
Fig. 7 is a schematic diagram of an internal structure of a second form of MEMS sensing element 200 of the gas thermal mass flow meter according to the present embodiment. As shown in fig. 7, the present embodiment also provides another MEMS sensing element 200, and the MEMS sensing element 200 is different from the MEMS sensing element 200 shown in fig. 4 to 6 described above in the following.
Specifically, referring to fig. 7, a first closed space 263 and a second closed space 264 are arranged side by side between the rod-shaped portion 220 and the mounting portion 230, wherein the first closed space 263 is provided with the thermal property sensor 270, the first closed space 263 is filled with a reference gas, the opening 262 is provided in the second closed space 264, the second closed space 264 is also provided with the thermal property sensor 270, and the thermal property sensor 270 in the second closed space 264 is configured to contact with the gas in the airflow channel 110. Wherein, the first enclosed space 263 and the second enclosed space 264 have the same spatial size.
When the gas thermal mass flowmeter employs the MEMS sensing element 200 shown in fig. 7, in operation, the first closed space 263 will be filled with a reference gas such as methane, air, or nitrogen, so that the thermal property sensor 270 in the first closed space 263 is completely sealed in the reference gas. Further, the thermal property sensor 270 in the first closed space 263 and the thermal property sensor 270 in the second closed space 264 operate using a differential circuit to cancel the electrical drift, thereby ensuring high accuracy for the measurement correction due to the change in the gas composition (thermal property).
In the above process, the deviation and the reference of the thermal property sensor 270 in the first closed space 263 are referenced and corrected by the thermal property sensor 270 in the second closed space 264, and the thermal property parameters of the gas measured by the two thermal property sensors 270 in real time provide feedback to the control module 700, so that when the thermal property (gas composition) of the gas changes, the control module 700 can automatically adjust to correct the standard volume deviation of the measurement caused by the change.
It should be noted that, for the gas thermal mass flowmeter for city gas metering, it is preferable to fill the first closed space 263 with methane.
Referring to fig. 1, in the present embodiment, the gas thermal mass flowmeter may further include a display module 800, and specifically, the display module 800 is configured to display a measurement value of the gas thermal mass flowmeter. The display module 800 is arranged, so that a user can visually see the measurement result of the gas thermal mass flowmeter, and the gas thermal mass flowmeter is very convenient.
Preferably, the Display module 800 is an LCD (Liquid Crystal Display).
Referring to fig. 1, in the present embodiment, the gas thermal mass flowmeter may further include a battery power module 500, and specifically, the battery power module 500 is used to supply power to the electric components in the gas thermal mass flowmeter. With the arrangement, all the electric components (such as the display module 800 and the control module 700) in the gas thermal mass flow meter can work by using the electric energy supplied by the battery power module 500, and an external power supply is not required, so that the integration of the gas thermal mass flow meter of the embodiment is realized.
With reference to fig. 1 and fig. 2, in the present embodiment, the gas thermal mass flowmeter may further include a sealed first case 300 and a sealed second case 400, wherein the first case 300 is fixedly connected to the flowmeter main body 100, and the battery power module 500 is located inside the first case 300; the second case 400 is also fixedly attached to the flowmeter body 100, and the MEMS sensing element 200 is located inside the second case 400.
By the arrangement, the battery power supply module 500 and the MEMS sensing element 200 are installed in a closed mode, the battery power supply module 500 and the MEMS sensing element 200 are protected, and pollution of external impurities to the battery power supply module 500 and the MEMS sensing element 200 is avoided to a certain extent, so that the service lives of the battery power supply module 500 and the MEMS sensing element 200 are prolonged.
Referring to fig. 2, in particular, a control module 700, a connection terminal 710 and a display module 800 are further disposed in the second box 400. The connection terminal 710 is connected to the control module 700, and the display module 800 is connected to the control module 700. To ensure data security, user data access may be provided by a local data port with data cable 600 in the event of a disruption in telecommunications for a variety of reasons. This data port may also be used for local GPRS connections and external power connections in case the battery power module 500 is unable to support the required communication power consumption.
Referring to fig. 1 and fig. 2, in the present embodiment, the first box body 300 includes a first box body 310 fixedly connected to the flowmeter body 100, and a first box cover 320 detachably and fixedly connected to the first box body 310, wherein the first box body 310 has an installation opening, and the first box cover 320 covers the installation opening of the first box body 310. Similarly, the second box 400 includes a second box body 410 fixedly connected to the flowmeter main body 100, and a second box cover 420 detachably and fixedly connected to the second box body 410, wherein the second box body 410 has an installation opening, and the second box cover 420 covers the installation opening of the second box body 410.
Preferably, the first cover 320 is integrally formed with the second cover 420.
Specifically, in the present embodiment, the first case 300 and the second case 400 are made of the same material as the flowmeter body 100. Meanwhile, the second box cover 420 is provided with a glass window and sealed by an additional anti-counterfeiting and anti-theft mechanism. For example: for protection, tamper-proof and theft-proof purposes, the glass window of the second cover 420 may be coated with a transparent metal film to prevent electromagnetic radiation or other external interference.
With continued reference to fig. 1 and 2, in the present embodiment, the gas thermal mass flowmeter may further include a fluid straightener 150 and a fluid rectifier 160 both mounted to the flowmeter body 100, and specifically, the fluid straightener 150 and the fluid rectifier 160 are disposed in sequence along the flow direction of the gas in the gas flow channel 110.
The gas will pass through the flow straightener 150 before entering the gas flow channel 110, turbulence and unstable fluctuations are eliminated by the flow straightener 150, and then the gas will pass through the flow straightener 160 during the course of continuing to flow, and the flow straightener 160 is used to ensure the repeatability and accuracy of the measurement. So set up, improved this embodiment gas thermal type mass flowmeter's measurement accuracy.
In this embodiment, the distance between the flow straightener 150 and the flow straightener 160 is 1/6-1/2, preferably 1/3, of the diameter of the airflow passage 110. When it is required to minimize the pressure loss of the gas through the gas flow channel 110, the gas thermal mass flow meter may be provided with only the fluid straightener 150 without the fluid straightener 160.
Fig. 8 is a schematic structural diagram of a thermal property sensor 270 of the gas thermal mass flow meter according to the present embodiment. As shown in fig. 8, in this embodiment, the thermal property sensor 270 may further include a silicon substrate 273, specifically, the silicon substrate 273 has a first surface and a second surface opposite to each other, wherein the first thermosensitive element 271 and the second thermosensitive element 272 are fixedly disposed on the first surface, and the second surface is opened with a thermal isolation cavity 274.
And, the first side is provided with a thin film composed of low stress silicon nitride and silicon dioxide made by a low pressure chemical vapor deposition method, the thin film covers the first and second heat sensitive elements 271 and 272, and the thermal isolation chamber 274 is opposite to the thin film and is located below the thin film. In an actual manufacturing process, the first heat sensitive element 271 may be brought into direct contact with gas through the window 275 by performing an etching process on the thin film formed by the above-described passivation to open the window 275.
Preferably, the first thermosensitive element 271 and the second thermosensitive element 272 have the same size and resistance, and the material of the first thermosensitive element 271 and the second thermosensitive element 272 is platinum, nickel or doped polysilicon. This arrangement provides the thermal property sensor 270 with higher sensitivity.
The thermal property sensor 270 may eliminate any deviation associated with the electrical characteristics by comparing the thermal conductivity values obtained by the first thermistor and the second thermistor at the same time, thereby obtaining a stable thermal conductivity value. To measure thermal diffusivity, one of the two thermal elements will be pulsed or periodic voltage applied, while the difference in temperature conduction time that the other thermal element receives beside the heating thermal element is directly related to thermal diffusivity.
It should be noted that the metering and correction method does not require a pre-established database of gas compositions, because as long as the thermal property sensor 270 measures a deviation of the thermal property of the off-gas from a value under calibration, the mass flow sensor 211 packaged on the same MEMS sensing element 200 will execute an algorithm to correct the measured deviation to be consistent with the conditions under calibration, meeting the requirements of the current metering legislation.
With reference to fig. 8, wire bonding pads 276 are disposed at four corner positions of the silicon substrate 273, and the first and second thermosensitive elements 271 and 272 are connected to the corresponding wire bonding pads 276.
In this embodiment, the control module 700 has a function of acquiring raw data from the MEMS sensing element 200, and amplifies and converts analog data into digital data through a high-precision analog-to-digital converter (ADC) and an amplifier, so that a Microcontroller (MCU) can process the digital data and compare the digital data with calibrated data to output a correct flow measurement value. At the same time, the control module 700 will also obtain the gas thermophysical value from the thermophysical sensor 270 and compare it to the stored gas thermophysical value at calibration. Upon detecting a change in the gas thermophysical property value that exceeds a predetermined threshold, the microcontroller will invoke a preset algorithm to modify to obtain a flow measurement value that complies with existing measurement regulations. For data security, each change value and corresponding data may be stored in multiple solid state memories of the control module 700 at the same time. The remote data communication is preferably performed using industry standard protocols (e.g., NB-IoT or GPRS) or other standards local to the flowmeter installation. Wherein, the number of the solid-state memories is not less than three. Other functions of the control module 700 include detecting power status, flow anomalies, and other user-interesting and pre-programmed tasks of the battery power module 500.
It should be noted that if the gas thermal mass flow meter is connected to a network, the control module 700 will respond to a remote query or automatically transmit any data to a designated data center or service center while displaying on the display module 800. The control module 700 will also perform power status monitoring and evaluation and send its status to a designated data center at a fixed time, send an early warning when the battery power module 500 may be out of charge, either preprogrammed into the gas thermal mass flow meter or remotely processed.
It should be noted that although the MEMS sensing element 200 in this embodiment can only measure the thermophysical properties of the fluid and cannot analyze the chemical composition of the fluid, the commercial metering of most fluid metering requirements, including city gas, only requires fairness and compliance of the final metering, and does not require detailed knowledge of gas chemistry. Therefore, as long as the MEMS sensing element 200 can correctly measure the change of the fluid medium characteristic and perform real-time correction with reference to the characteristic of the calibration medium, the influence of the change of the gas component on the metering can be eliminated according to the standard of the current metering regulation, thereby realizing the metering independent of the gas characteristic. Further, for the example of natural gas measurement, the measured natural gas thermal property value parameter can be further used for price evaluation based on the natural gas thermal value, because for urban gas consumers, the actual consumption is the thermal value of the natural gas rather than the standard volume of the natural gas, and the technical disclosure provides a technical approach for upgrading the future urban gas metering.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (11)
1. A gas thermal mass flow meter, comprising:
a flow meter body (100), the flow meter body (100) having a gas flow passage (110) for gas to flow;
a MEMS sensing element (200), the MEMS sensing element (200) being mounted to the flowmeter body (100) with a probe (210) of the MEMS sensing element (200) protruding into the gas flow channel (110), the probe (210) comprising a mass flow sensor (211), the MEMS sensing element (200) further comprising a thermophysical sensor (270), the thermophysical sensor (270) comprising two thermosensors, wherein one of the thermosensors is configured to be in contact with a gas being measured;
a control module (700), the mass flow sensor (211) and the thermophysical sensor (270) both being electrically connected to the control module (700);
a battery power module (500), the battery power module (500) being configured to power electrical components in the gas thermal mass flow meter; and
a fluid straightener (150), the fluid straightener (150) being mounted at an inlet of the flow meter body (100).
2. The gas thermal mass flow meter according to claim 1, characterized in that the MEMS sensing element (200) comprises a mounting portion (230) and a rod portion (220) fixedly connected to the mounting portion (230), the mounting portion (230) being for fixed connection to the meter body (100), the detecting portion (210) being located at an end of the rod portion (220) remote from the mounting portion (230), the thermophysical property sensor (270) being located between the rod portion (220) and the mounting portion (230).
3. The gas thermal mass flow meter according to claim 2, characterized in that a closed space (261) is provided between the rod portion (220) and the mounting portion (230), the thermal property sensor (270) is located in the closed space (261), and the closed space (261) is opened with an opening (262) for exchanging gas with the outside.
4. The gas thermal mass flow meter according to claim 2, wherein a first closed space (263) and a second closed space (264) are provided side by side between the rod-shaped portion (220) and the mounting portion (230), the first closed space (263) is provided with the thermo-physical sensor (270), the first closed space (263) is filled with a reference gas, the second closed space (264) is provided with an opening (262) for gas exchange with the outside, the second closed space (264) is provided with the thermo-physical sensor (270), and the thermo-physical sensor (270) in the second closed space (264) is configured to be in contact with a gas in the gas flow passage (110);
the first enclosed space (263) and the second enclosed space (264) are both of the same spatial size.
5. A gas thermal mass flow meter according to claim 2, characterized in that the rod-shaped part (220) comprises a first section (221) and a second section (222), the first section (221) being adapted for fixed connection with the mounting part (230) and the second section (222) being adapted for fixed connection with the probe part (210), wherein the first section (221) is circular in radial cross-section, the second section (222) is V-shaped in axial cross-section, the tip of the second section (222) is directed towards the gas flow channel (110), and both sides of the second section (222) are parallel to the extension direction of the gas flow channel (110).
6. A gas thermal mass flow meter according to claim 2, characterized in that the detecting part (210) further comprises a thin plate (212), the thin plate (212) is fixedly arranged at one end of the rod part (220) away from the mounting part (230), the plate surface of the thin plate (212) is parallel to the extending direction of the gas flow channel (110), and the mass flow sensor (211) is embedded in the thin plate (212).
7. A gas thermal mass flow meter according to any of claims 1-6, characterized in that the gas flow channel (110) is venturi-shaped, and the detecting part (210) of the sensing element protrudes into the central position of the throat of the venturi-shaped gas flow channel (110).
8. A gas thermal mass flow meter according to any of the claims 1-6, characterized in that it further comprises a display module (800), said display module (800) being configured to display the measurement values of the gas thermal mass flow meter.
9. A gas thermal mass flow meter according to any of the claims 1-6, characterized in that it further comprises a sealed first case (300) and a sealed second case (400), said first case (300) being fixedly connected to said meter body (100), said battery power module (500) being located inside said first case (300); the second box body (400) is fixedly connected to the flowmeter main body (100), and the MEMS sensing element (200) is located inside the second box body (400).
10. The gas thermal mass flow meter according to any of the claims 1-6, further comprising a flow straightener (160), the flow straightener (150) and the flow straightener (160) being arranged in sequence in the flow direction of the gas in the gas flow channel (110).
11. The gas thermal mass flow meter according to any of claims 1-6, wherein the thermophysical sensor (270) further comprises a silicon substrate (273), the silicon substrate (273) having a first side and a second side opposite to each other, the two thermal elements being fixed to the first side, and the second side being opened with a thermal isolation chamber (274).
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| CN111795730B (en) | 2021-10-22 |
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Address after: 311121 1 / F, building 4, No. 6, Longquan Road, Cangqian street, Yuhang District, Hangzhou City, Zhejiang Province Patentee after: Sixiang micro electromechanical (Hangzhou) Co.,Ltd. Address before: 311121 northwest of 1st floor, building 1, No.22 Longtan Road, Cangqian street, Yuhang District, Hangzhou City, Zhejiang Province Patentee before: Sixiang micro electromechanical (Hangzhou) Co.,Ltd. |