CN210321856U - Air heating type flowmeter - Google Patents
Air heating type flowmeter Download PDFInfo
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- CN210321856U CN210321856U CN201921713865.7U CN201921713865U CN210321856U CN 210321856 U CN210321856 U CN 210321856U CN 201921713865 U CN201921713865 U CN 201921713865U CN 210321856 U CN210321856 U CN 210321856U
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Abstract
An air thermal flowmeter comprises a flow sensor, a meter rod and a meter head, wherein the flow sensor is electrically connected with a converter in the meter head; the flow sensor comprises two speed measuring probes and a temperature measuring probe, the temperature measuring probe is positioned at the upstream of the measured fluid, the two speed measuring probes are arranged at the downstream of the temperature measuring probe side by side and are positioned at two sides of the temperature measuring probe equidistantly, and the speed measuring probes and the temperature measuring probe are resistance type temperature sensors and can be of a hot wire type or a hot film type; the survey buret can be connected to table pole one end, and the fluid entry end of surveying the buret is provided with the dewatering part, can set up telescopic scale pole on the bayonet table pole. The utility model discloses a two speed probe and a temperature probe make measuring result not receive fluid temperature's influence, make temperature compensation more reasonable, measured degree of accuracy, sensitivity and corresponding speed when having improved fluid temperature change still can set up water trap at the fluid upstream as required, avoid the influence of drop of water to measuring result.
Description
Technical Field
The utility model relates to a measuring equipment technical field especially relates to an air heat formula flowmeter.
Background
The conventional air thermal flowmeter generally comprises two resistance-type temperature sensors, one is heated, the other measures the temperature of the air to be measured, when the air is static, the two temperature sensors form a temperature difference, when the air flows, based on the heat conduction principle, air molecules can take away part of heat of the heated temperature sensor, in order to ensure the original temperature difference, the heated temperature sensor can be continuously heated, the higher the flow rate of the air is, the higher the heat taken away is, the higher the power consumed by the temperature sensor is, the consumed power and the flow rate of the air form a functional relation, and the power consumed by a mainboard circuit is detected to calculate the flow rate of the air according to the functional relation. Because the power consumption algorithm is used and is irrelevant to the air density, the thermal flowmeter can directly convert the flow of the measured air in a standard state without adding temperature and pressure compensation. Compared with a vortex flowmeter, a turbine flowmeter and a differential pressure flowmeter, the flowmeter has the advantages of wide measurement range, small pressure loss, high reliability, capability of measuring mixed gas, suitability for various pipelines, no overload damage and the like.
However, when the ambient temperature changes, the constant temperature differential thermal flowmeter based on the Wheatstone bridge affects the bridge balance, and shows that the zero point is unstable and the precision of small flow cannot be guaranteed, and a corresponding temperature compensation circuit is required to be added; when the flow of the fluid is small or zero, the heat of the speed measuring probe is not easy to be taken away, and the measurement result is influenced by the convection heat transfer between the speed measuring probe and the temperature measuring probe; when the flow of the fluid is continuously increased, the heating power is correspondingly increased, and when the heating power is overlarge, the difficulty of circuit design is increased, and the stability of the circuit is influenced; in addition, because the heat of the heating element is taken away by flowing air, the heating element can be cooled, the resistance value of the heating element can change along with the flow rate of the gas, the larger the air flow is, the more the heat is taken away, the larger the resistance value change of the speed measuring probe is, and the nonlinear temperature compensation resistor and the difference between the resistors cause the complex debugging process of the circuit, and influence the measuring precision to a certain extent.
In addition, when hot air, especially saturated hot steam, is tested, the saturated steam can adhere to the surface of the probe to form water drops, and the accuracy of the measurement result is affected.
SUMMERY OF THE UTILITY MODEL
The utility model aims at overcoming the shortcoming of above-mentioned prior art, provide an air thermal flowmeter who receives the large-scale range that ambient temperature changes that the influence is little, temperature compensation is reasonable, the response is rapid, the degree of accuracy is high.
The utility model discloses a realize through following technical scheme:
an air thermal flowmeter comprises a flow sensor, a meter rod and a meter head, wherein the flow sensor is arranged at one end of the meter rod, the other end of the meter rod is connected with the meter head, a converter is arranged in the meter head, and the flow sensor is electrically connected with the converter in the meter head; flow sensor includes two speed probes and a temperature probe, temperature probe is located the upper reaches of being surveyed the fluid, two speed probes set up side by side in temperature probe's low reaches, and the equidistance is located temperature probe's both sides, two speed probes are isosceles triangle distribution with a temperature probe promptly, two speed probe's line perpendicular to fluidic direction, two speed probes are located the same cross-section of perpendicular to fluid flow direction, speed probe and temperature probe are resistance-type temperature sensor, two speed probe's parameter is the same, temperature probe's resistance value is greater than speed probe's resistance value. And measuring the air mass flow according to the temperatures of the two speed measuring probes, the temperature of the temperature measuring probe, the currents and the resistances of the two speed measuring probes. During measurement, the speed measuring probe and the temperature measuring probe are positioned at the center of the pipeline as far as possible so as to obtain the most real measurement signal; the fluid flows through the temperature measuring probes and then reaches the two speed measuring probes simultaneously. The two speed measuring probes are provided with different heating temperatures, namely the two speed measuring probes are controlled to be heated to different temperatures, so that a temperature difference is generated between the two speed measuring probes.
The technical scheme of further improvement is that the speed measuring probe and the temperature measuring probe are both hot wire platinum resistors.
The technical scheme of further improvement is that the speed measuring probe and the temperature measuring probe are both hot film type platinum resistors.
The technical scheme of further improvement is that each hot film type platinum resistor is deposited on the same surface of the same ceramic substrate, and a protective layer is packaged on the surface of each resistor.
Further improved technical scheme is, table pole one end is connected with survey buret, the flange joint of thermal type flowmeter on through surveying buret is in the pipeline, the fluid entry end of surveying buret is provided with the dewatering component. In order to ensure that the dewatering component does not influence the influence of the airflow flowing on the sensor probe, the dewatering component is arranged at the position of the inlet of the measuring pipe far away from the sensor probe, so that the airflow at the sensor probe is in a stable state.
The further improved technical scheme is that the water removal part is a pore plate provided with a plurality of through holes, and the through holes are spiral or the wall of the through holes is provided with a plurality of blocking pieces parallel to the axis of the measuring pipe.
The technical scheme of further improvement is that the meter rod is connected on the fluid pipeline in an insertion mode, the flow sensor extends into the center of the fluid pipeline, and the meter rod is provided with a ball valve.
The technical scheme of further improvement is that a scale rod is further arranged on the gauge rod, the scale rod is arranged on the main body of the gauge rod in a telescopic mode and is positioned and fixed through a positioning fastener, and length scales are further arranged on the scale rod.
The utility model adopts two speed measuring probes and one temperature measuring probe, the measuring method of the two speed measuring probes is utilized to ensure that the measuring result is not influenced by the fluid temperature, the influence of the environment temperature change on the measurement is reduced, the temperature compensation is more reasonable, the temperature measuring probe provides reference for the environment temperature, the measuring accuracy, the sensitivity and the corresponding speed when the fluid temperature changes are improved, the two speed measuring probes can be mutually calibrated by combining the temperature measuring probes, the two speed measuring probes can also be used independently by combining the temperature measuring probes, the safety of the system is ensured, and the probes can flexibly select different types; aiming at air steam containing water vapor, a water removal device can be arranged on the measuring tube in an upstream mode according to requirements, and the influence of water drops on a measuring result is avoided; for the plug-in meter rod, a telescopic scale rod is arranged, so that the sensor is positioned in the center of the fluid channel and is suitable for fluid pipelines with different sizes and specifications.
Drawings
Fig. 1 is a schematic front structural view of embodiment 1 of the present invention.
Fig. 2 is a schematic side view of embodiment 1 of the present invention.
Fig. 3 is a schematic structural diagram of a flow sensor in embodiment 1 of the present invention.
Fig. 4 is a schematic plan view of fig. 3.
Fig. 5 is another schematic structural diagram of the flow sensor in embodiment 1 of the present invention.
Fig. 6 is an enlarged view of the structure of the flow sensor of fig. 5.
Fig. 7 is a schematic cross-sectional view a-a of fig. 5.
FIG. 8 is a side (flow direction) mounting diagram of the flow sensor of FIG. 4.
Fig. 9 is a schematic front structural view of embodiment 2 of the present invention.
Fig. 10 is a schematic structural view of a water removal component in embodiment 2 of the present invention.
Reference numerals: 1-a flow sensor; 2-a meter bar; 3-header; 4-measuring tube; 5-a flange; a 6-converter; 7-a fluid conduit; 8-a water removal means; 9-ball valve; 10-positioning fasteners; 11-scale bar; 101-a temperature measuring probe; 102-a speed measuring probe; 103-ceramic substrate; 104-a protective layer; 81-through holes; 82-barrier sheet.
Detailed Description
Example 1
An air thermal flowmeter, as shown in fig. 1 and fig. 2, comprises a flow sensor 1, a meter rod 2 and a meter head 3, wherein the flow sensor 1 is arranged at one end of the meter rod 2, the other end of the meter rod 2 is connected with the meter head 3, a converter 6 is arranged in the meter head 3, and the flow sensor 1 is electrically connected with the converter 6 in the meter head 3; the flow sensor 1 comprises two speed measuring probes 102 and a temperature measuring probe 101, wherein the temperature measuring probe 101 is located at the upstream of a measured fluid, the two speed measuring probes 102 are arranged at the downstream of the temperature measuring probe 101 side by side and are equidistantly located at two sides of the temperature measuring probe 101, namely as shown in fig. 3 and 6, the two speed measuring probes 102 and the temperature measuring probe 101 are distributed in an isosceles triangle shape, a connecting line of the two speed measuring probes 102 is perpendicular to the direction of the fluid, the two speed measuring probes 102 are located on the same cross section perpendicular to the flow direction of the fluid, the speed measuring probes 102 and the temperature measuring probe 101 are both resistance type temperature sensors, the parameters of the two speed measuring probes 102 are the same, and the resistance value of the temperature measuring probe 101 is larger than. The air mass flow is measured according to the temperatures of the two speed probes 102, the temperature of the temperature measuring probe 101, and the currents and the resistances of the two speed probes 102. During measurement, the speed measuring probe 102 and the temperature measuring probe 101 are positioned at the center of the fluid pipeline 7 as much as possible so as to obtain the truest measuring signal; the fluid first flows through the temperature probes 101 and then reaches the two speed probes 102. The two speed measuring probes 102 are provided with different heating temperatures, that is, the two speed measuring probes 102 are controlled to be heated to different temperatures, so that a temperature difference is generated between the two probes.
The specific measurement principle is set forth as follows:
a general thermal type flowmeter is measured based on the following relation:
P/(Tw-Tc)＝D+E·qm k(1)
wherein P is the heating power of the heating circuit, qmIs the mass flow rate of the fluid, E is a parameter related to the physical properties of the fluid medium, D is a constant related to the flow of the fluid, Tw-TcIs the temperature difference between the speed probe 102 and the temperature probe 101, TwTo measure the temperature, T, of the probe 102cIs the temperature of the temperature probe 101 (i.e., the temperature of the fluid). When the temperature is a fixed value, the temperature is constant-temperature differential thermal flowmeter.
While the heat conducted and radiated around the tachometer probe 102, the measuring rod, other probes, etc. is ignored, the heating power P and the heat convection Q between the tachometer probe 102 and the fluid, i.e. the heat convection Q
P＝Q (2)
Heating power P ═ Iw 2Rw(3)
Wherein IwFor the current passing through the tachometer probe 102, RwIs the resistance of the tachometer probe 102.
Q＝hS(Tw-Tc) (4)
Where h is the convective heat transfer coefficient and S is the heat transfer area of the tachometer probe 102.
From the formulae (2), (3) and (4) to obtain
Iw 2Rw＝hS(Tw-Tc) (5)
hS＝A+B·qm 1/2(6)
Where A, B is the constant of the system,
to obtain
When the difference in constant temperature is measured, Tw-TcNot changing, e.g. RwAt constant time, qmIs a current IwAs a function of (c).
However, when the temperature change is large, RwIs not constant and therefore requires temperature compensation.
From the above analysis, it is known that, in the thermal gas flowmeter using the constant temperature difference method, when the measurement is performed, the sensitivity coefficient of the sensor is related to the heat conduction, density, viscosity, and the like of the fluid, and the heat conduction, density, viscosity are related to the ambient temperature, and when the temperature change is large, the measurement result of the flowmeter has a large error. As known by the measuring circuit, when the ambient temperature rises, the tachometer resistor becomes larger, and to ensure the balance of the Wheatstone measuring bridge, the heating current of the Wheatstone measuring bridge becomes larger along with the rise of the temperature, and the output voltage of the flowmeter also increases. Even if there is no airflow variation, the flow meter measurement will change with the ambient temperature, and its output will produce a large error or erroneous result. Therefore, when the common thermal gas flowmeter measures the gas flow, the temperature deviation phenomenon generally exists.
The utility model discloses set up two speed probe, there is following relation:
Iw1 2Rw1＝hS(Tw1-Tc) (8)
Iw2 2Rw2＝hS(Tw2-Tc) (9)
wherein, Iw1、Iw2For the current flowing through the two tachometer probes, Rw1、Rw2The resistors of the two speed measuring probes.
From the formulae (7), (8) and (9) to give
In the measurement, T is measuredw1And Tw2The difference is controlled within a certain range, i.e. it can be made to be approximately linear, or according to the formula Rw＝Rw0(1+aTw+bTw 2) To obtain wherein Rw0The resistance is at 0 ℃, and a and b are temperature coefficients of the resistance and can be consulted or obtained by experimental calibration.
As can be seen from the formula (10), the fluid mass flow rate of the test of the utility model is not affected by the fluid temperature, and is taken as the temperature difference (T) of the two speed measuring probesw1-Tw2) The mass flow of the fluid is related to the current and the resistance of the two speed measuring probes at a certain time, so that when the temperature of the fluid changes greatly, the temperature compensation can be carried out more reasonably according to the formula because the measuring result is not influenced by the temperature of the fluid.
The temperature difference between the two speed measuring probes can be preset to a fixed value, then each constant is calibrated, and the mass flow of the fluid is obtained through the measured current and resistance of the probes. Because each gas has its own thermal characteristics, the calibration is performed by using a gas having the same or similar thermal characteristics as the actual test gas.
The temperature detector is used for detecting the temperature T of the fluid in the pipelinecAlbeit at a fluid temperature TcThe temperature of the fluid can provide reference for the temperature control of the two speed measuring probes, so that the temperature of the two speed measuring probes is controlled within a certain range, when the temperature of the fluid is lower, the temperature of the speed measuring probes can be adjusted to be lower, and conversely, when the temperature of the fluid is lowerWhen the temperature rises more, the temperature of two speed measuring probes also need correspondingly to be increaseed, and the difference in temperature between two speed measuring probes also can carry out corresponding adjustment, avoids that the fluid difference in temperature change is great and the temperature of two speed measuring probes is unchangeable all the time and produces the error, influences the degree of accuracy. For example, if the fluid temperature is 0 ℃, the temperatures of the two temperature probes are controlled to be 40 ℃ and 70 ℃, respectively, but when the fluid temperature is 80 ℃, the temperatures of the two temperature probes are not properly controlled to be 40 ℃ and 70 ℃, and accordingly adjustment is required. And the temperature control of the temperature probe is controlled by a processor or controller in the converter 6. Of course, besides the temperature measurement probe, the converter 6 may be provided with a communication unit for receiving temperature signals from other temperature sensors in the pipeline system.
The two speed measuring probes 102 and the temperature measuring probe 101 need a power supply circuit to supply power, collected signals need a signal conditioning circuit and a processor to be analyzed and processed, the temperature of the probes can be controlled, the signals are processed, real-time mass flow and accumulated flow are calculated, a display unit and a communication unit can be further arranged on the converter 6, data are displayed on a display module, and data are uploaded to an upper computer to be shared. The power supply circuit can adopt a mature constant temperature difference power supply circuit at present, and the signal conditioning circuit adopts an amplifying circuit, a filter circuit and a conversion circuit which are usually adopted at present. The supply circuit, the signal conditioning circuit and the processor are integrated in the converter 6.
The resistance temperature sensors are of various types, and as one embodiment, as shown in fig. 3 and 4, the tachometer probe 102 and the temperature probe 101 are both hot wire platinum resistors. The hot wire type probe has the defects of poor impact resistance, pollution resistance and corrosion resistance, but has small influence on the fluid motion form, large measurement range and good response performance. The platinum resistor has the advantages of large temperature coefficient, sensitive response, very small element size, linear relationship between resistance and temperature, stable physical and chemical properties within the use temperature range, good repeatability and high measurement precision.
In another embodiment of the resistance temperature sensor, as shown in fig. 5 to 8, the tachometer probe 102 and the thermometric probe 101 can both be hot film platinum resistors. Each hot film type platinum resistor is deposited on the same surface of the same ceramic substrate 103, and a protective layer 104 is packaged on the surface of each resistor. The ceramic substrate 103 has good insulation and strength. The ceramic substrate 103 is parallel to the flow direction of the fluid, and the fluid firstly flows through the temperature measuring probe 101 and then simultaneously reaches the speed measuring probes 102 arranged side by side. Compared with a hot wire type platinum resistor, the thin film resistor has greatly improved impact resistance and stain resistance, and the ceramic substrate adopted can be suitable for complex and severe industrial environments and has the characteristics of large measuring range, small environmental influence, quick response, long service life and the like. The purpose of the resistor surface packaging is to improve the shock resistance and pollution resistance of the probe and prolong the service life, but the thickness of the surface packaging protective layer 104 is small, the thermal resistance is as small as possible, the consistency of the temperature of the inside and the surface of the platinum resistor is ensured, and the measurement precision is improved. In order to make the two speed probes 102 respond to the flow as fast as possible during operation, the sensitivity of the probes is high, and the two speed probes 102 have the same specification and model to ensure the synchronization of heat dissipation.
Referring to fig. 1, the meter rod 2 is connected with a fluid pipeline 7, that is, the meter rod 2 is inserted into the fluid pipeline 7, the flow sensor 1 extends into the center of the fluid pipeline 7, and a ball valve 9 is arranged on the meter rod 2. Still be provided with scale pole 11 on the table pole 2, the telescopic setting of scale pole 11 is in the main part of table pole 2 to fix a position fixedly through positioning fastener 10, still be provided with the length scale on the scale pole 11. The insertion depth of the sensor can be adjusted according to the caliber size of the pipeline, so that the device is suitable for pipelines of different specifications and models.
The positioning fastener 10 can be implemented in various ways, such as, for example, 1 and fig. 2, which include a positioning ring lock nut and an insertion depth positioning fastener, or in other ways, such as a positioning and fastening manner of a telescopic rod, for example, a lifting positioning fixing member of a bicycle seat post.
Example 2
The rest is the same as the embodiment 1 except that as shown in fig. 9, the measuring pipe 4 is connected to one end of the meter bar 2, the thermal type flow meter is connected in the pipeline through the flange 5 on the measuring pipe 4, and the fluid inlet end of the measuring pipe 4 is provided with the water removing part 8. In order to ensure that the water removal component 8 does not affect the influence of the air flow on the sensor probe, the water removal component 8 is arranged at the position of the inlet of the measuring tube 4 far away from the sensor probe, so that the air flow at the sensor probe is in a stable state.
The water removing component 8 can be implemented in various ways, one of them is that the water removing component 8 is a hole plate provided with a plurality of through holes 81, the inner wall of the through holes 81 is spiral, the spiral inner wall is favorable for the air flow to pass through, and simultaneously the contact area between the air and the inner wall can be increased, which is favorable for the condensation of water drops. It is also possible to provide a plurality of blocking pieces 82 parallel to the axis of the measuring tube 4 on the wall of the through hole 81, as shown in fig. 10. Or a plurality of blocking pieces 82 vertical to the axis of the through hole 81 are arranged on the hole wall of the through hole 81 of the orifice plate, and the blocking pieces 82 are arranged in a staggered manner. The water removing component 8 may also be other structures or forms capable of removing water vapor, such as a filter screen.
The above detailed description is specific to possible embodiments of the present invention, and the embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or modifications that do not depart from the scope of the present invention should be included within the scope of the present invention.
Claims (8)
1. An air heating type flowmeter is characterized by comprising a flow sensor, a gauge rod and a gauge head, wherein the flow sensor is arranged at one end of the gauge rod, the other end of the gauge rod is connected with the gauge head, a converter is arranged in the gauge head, and the flow sensor is electrically connected with the converter in the gauge head; the flow sensor comprises two speed measuring probes and a temperature measuring probe, wherein the temperature measuring probe is positioned at the upper reaches of a measured fluid, the two speed measuring probes are arranged at the lower reaches of the temperature measuring probe side by side and are positioned at the two sides of the temperature measuring probe at equal intervals, the speed measuring probe and the temperature measuring probe are resistance type temperature sensors, the parameters of the two speed measuring probes are the same, the resistance value of the temperature measuring probe is greater than that of the speed measuring probe, and the speed measuring probe is provided with different heating temperatures.
2. The air thermal flowmeter of claim 1, wherein the tachometer probe and the thermometric probe are each a hot wire platinum resistor.
3. The air-heated flow meter according to claim 1, wherein the tachometer probe and the thermometric probe are both hot film platinum resistors.
4. An air-thermal flow meter according to claim 3, wherein each of said hot-film platinum resistors is deposited on the same surface of the same ceramic substrate, and each resistor surface is encapsulated with a protective layer.
5. An air-heated flow meter according to claim 1, wherein a measuring tube is attached to one end of the meter stem, the flow sensor extending into the center of the measuring tube, the measuring tube being mounted in a fluid conduit, the fluid inlet end of the measuring tube being provided with a water removal feature.
6. An air-thermal flowmeter according to claim 5, wherein said water removing means is a perforated plate provided with a plurality of through holes, said through holes being spiral or having a plurality of blocking pieces provided on the wall of the through holes in parallel with the axis of the measuring tube.
7. An air-thermal flowmeter according to claim 1 wherein said stem is insertedly connected to the fluid conduit, said flow sensor extends into the center of the fluid conduit, and said stem is provided with a ball valve.
8. The air-heating flowmeter as claimed in claim 7, wherein the meter bar is further provided with a scale bar, the scale bar is telescopically arranged on the meter bar body and is positioned and fixed through a positioning fastener, and the scale bar is further provided with length scales.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201921713865.7U CN210321856U (en) | 2019-10-12 | 2019-10-12 | Air heating type flowmeter |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201921713865.7U CN210321856U (en) | 2019-10-12 | 2019-10-12 | Air heating type flowmeter |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113340365A (en) * | 2021-05-25 | 2021-09-03 | 南京禹通自动化科技有限公司 | Thermal flowmeter and flow measuring method |
| CN115900859A (en) * | 2023-01-05 | 2023-04-04 | 杭州泽天春来科技有限公司 | Flue gas flow monitoring device and method |
-
2019
- 2019-10-12 CN CN201921713865.7U patent/CN210321856U/en active Active
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113340365A (en) * | 2021-05-25 | 2021-09-03 | 南京禹通自动化科技有限公司 | Thermal flowmeter and flow measuring method |
| CN113340365B (en) * | 2021-05-25 | 2022-02-18 | 南京禹通自动化科技有限公司 | Thermal flowmeter and flow measuring method |
| CN115900859A (en) * | 2023-01-05 | 2023-04-04 | 杭州泽天春来科技有限公司 | Flue gas flow monitoring device and method |
| CN115900859B (en) * | 2023-01-05 | 2023-08-29 | 杭州泽天春来科技有限公司 | Flue gas flow monitoring device and method |
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