Up-down-stream temperature distribution secondary differential moves flow-measuring method, sensor, reaches and use
Technical field
The present invention relates to the mass rate detection range, especially relate to a kind of based on up-down-stream temperature distribution secondary differential take offence physique method of measuring mass flow, sensor, and flowmeter.The present invention can be widely used in motor car engine flowmeter, wheel leakage protective device, gas metering flowmeter, Industry Control flow and take into account transmitter, anemoscope, family expenses full electronic gas meter, flow meter, industries such as Medical Instruments.
Background technology
The thermal type gas quality flow measurement is to utilize heat transfer theory, and exchange heat concerns the technology of measuring flow between the outer calandria of object that heats in fluid in promptly flowing and the heat source fluid or measuring tube.It mainly is divided into wind gage formula anemometer and heat-measuring type calorimetric dual mode.The wind gage principle of work is to be based upon on King ' the s Law theoretical foundation that proposed in 1914, and this metering system is to flow the heat dissipation degree of heater strip down as beasurement base with fluid.The measuring principle of heat-measuring type is then surveyed the flow velocity size with the Temperature Distribution of surveying heating element thermal source both sides in the process fluid flow.
In the tradition calorimetric formula principle, usually adopt the hot fluid sensor to comprise well heater and temperature sensor two parts, be symmetrically distributed a pair of or several in the heater strip upstream and downstream to platinum matter responsive to temperature silk, and, adopt microbridge formula hanging structure between heater strip and the responsive to temperature silk in order to improve the thermal insulation between the unit component.Say that from structure the impact strength of this sensor is very weak, measured medium requires pure, no granule foreign, and can not bear bigger instantaneous impact flow.
Tradition calorimetric formula principle is the temperature gap by a pair of temperature sensor of measurement upstream and downstream, thereby determines rate of flow of fluid.But this temperature gap is along with saturation point can appear in the increase of flow velocity, and drop then, and as shown in Figure 1, curve is by an ascent stage, and a saturation point F and a decline stage characterize.Among the figure, transverse axis is represented flow velocity V, longitudinal axis representation temperature difference Δ T.As shown in Figure 1, effective range is limited in the saturation point F under this metering system.Simultaneously, the position of saturation point F is relevant with the spacing between temperature sensor and the heater strip, and for the nearer sensor of spacing, saturation point F takes place when speed is big, has relatively large measurement range, but the curve rising slowly, and sensitivity is not good enough; And for spacing sensor far away, saturation point F is then in hour generation of speed, and measurement range is less, but has the bigger rate of rise at the low speed segment curve, and is therefore more sensitive at low speed segment.In a word, the measurement range of this pattern is very little, only is applicable to low flow rate conditions.
For this reason, people have carried out long-term exploration, have proposed diversified embodiment.For example, Chinese patent literature discloses a kind of flow velocity detector application number: CN00801406.X, it has the diaphragm portion that is provided with the space and forms thin wall shape in the part of pedestal, the heater that forms and forms in these heater both sides in this diaphragm portion thermistor body, it is characterized in that, above-mentioned thermistor body becomes to connect the comb teeth shape of a plurality of crank-like, this thermistor body is arranged to, makes the concave and convex direction of above-mentioned comb teeth shape be roughly parallel to the flow direction of detected fluid.This scheme adopts remains traditional calorimetric formula signal processing method, only is the structure of the thermistor body of sensing is improved, and has improved the thermometric precision of thermistor body.But, all there is not too big help for the saturated phenomenon of heat distribution measurement and the low speed instability of hot wire type's measurement etc., therefore fundamentally do not overcome the defective that prior art exists.
The somebody discloses the patent publication No. of " heat pulse time difference type flow detection method " by name: CN1603762A, this scheme puts into thermal flow rate sensor in the parallel pipeline of flow velocity, heating thermometric unit or heating element are added electric impulse signal, measure its corresponding temperature pulse signal; To measuring, also obtain the temperature pulse signal of the thermometric unit in downstream again at the detector unit in heating element downstream; Two pulse signal curves are compared, by detecting value time lag of pulse signal rising edge, just measurement gas flow velocity.At first heat pulse time difference method and up-down-stream temperature distribution secondary differential of the present invention move based on diverse measuring principle, and the former is the measurement to time span based on being worth time lag, and the latter changes the voltage signal amplitude that produces based on Temperature Distribution.Secondly, the heat pulse time difference method adopts electric impulse signal heating power supply, and is effective to reducing power consumption; But, because heat transfer process depends primarily on the factors such as the gentle body heat transmissibility factor of space length of thermal element and downstream thermometric unit, measure value time lag that produces because rate of flow of fluid changes, when fluid hangs down flow velocity, value time lag that flow velocity causes is very small, can be flooded by the dry acoustical signal of generations such as the gentle body heat transmissibility factor of other peripheral environment factor.So, insensitive at low speed segment, be difficult to be applicable to low flow rate conditions.
Summary of the invention
The present invention mainly is that solution existing in prior technology measurement range is little, and output characteristics is prone to saturation point, to the very reasonable technical matters that waits of Signal Processing; Move after a kind of saturation point is provided, improved the range ability and the linearity, Signal Processing is reasonably based on up-down-stream temperature distribution secondary differential take offence physique method of measuring mass flow, sensor, and flowmeter.
It is that to solve the precision that existing in prior technology measures not high that the present invention also has a purpose, causes error easily, to the technical matters of the insensitive grade of low speed segment; A kind of measuring accuracy height is provided, can have effectively eliminated error, highly sensitive based on up-down-stream temperature distribution secondary differential take offence physique method of measuring mass flow, sensor, and flowmeter.
It is that solution existing in prior technology thermal inertia is bigger that the present invention has a purpose again, and Frequency Response is general, the technical matters of the bigger grade of power consumption; Provide a kind of employing MEMS technology to realize low-power consumption, high frequency sound, significantly reduce chip thermal inertia based on up-down-stream temperature distribution secondary differential take offence physique method of measuring mass flow, sensor, and flowmeter.
Above-mentioned technical matters of the present invention is mainly solved by following technical proposals: based on the up-down-stream temperature distribution secondary differential physique method of measuring mass flow of taking offence, it is characterized in that: a. applies the constant power source excitation on the element of heating of sensor, measures the Temperature Distribution of the element upstream and downstream of heating under the airless state respectively by the detector unit that is symmetricly set on the elements on either side of heating; B. when the gas flows through sensor, upstream temperature detecting element mensuration region Temperature Distribution changes and output produces the upstream temperature difference signal, and the downstream temperature detecting element is measured region Temperature Distribution variation and output produces the downstream temperature difference signal; C. deduct the downstream temperature difference signal with the upstream temperature difference signal, thereby draw the moving signal of up-down-stream temperature distribution secondary differential, measure the flow quality flow of the sensor of flowing through by the corresponding relation of secondary differential wave and air flow mass rate.
The present invention creatively handles the voltage signal of output by the second difference flowing mode.The temperature variation curve of upstream and downstream all reduces gradually with the increase of flow, the difference curve range of decrease that upstream temperature changes greatly, the difference curve fall that downstream temperature changes is little.Thus the upstream and downstream temperature difference is carried out second order difference and obtain secondary difference curve output characteristics, saturation point is passed backward, can significantly improve the flow rate test scope.The arranged direction of the element of heating of sensor and the direction of air-flow are perpendicular, and make when airless, and the Temperature Distribution of upstream and downstream is symmetrical substantially.The temperature that records one distance Curve of this moment roughly becomes normal distribution.
As preferably, above-mentioned secondary differential wave is amplified through signal, and be digital signal by analog signal conversion, this digital signal is carried out calculation process according to the corresponding relation of secondary differential wave and air flow mass rate in CPU (central processing unit), draw the air flow mass rate of the sensor of flowing through.
As preferably, described whole sensor adopts MEMS mode processing and fabricating.MEMS is meant micro electro mechanical system (MEMS) technology, and the micrometer structure device of making by the MEMS technology strengthens the sensitivity that temperature variation is measured, and improves the linearity that gas mass flow is measured.
Can describe with following mathematical model based on the take offence principle of physique method of measuring mass flow of up-down-stream temperature distribution secondary differential: the upstream temperature detecting element airless and have the difference of detected temperature under the air-flow two states deduct the downstream temperature detecting element airless and have detected temperature under the air-flow two states difference; Thereby realize the secondary temperature difference, for a simple one dimension heat type fluid sensor, the temperature of its heater strip can be expressed as:
①
T in the formula
h-heater strip temperature P-heating power
k
F-fluid thermal conductance w
h-heater strip width
l
h-heater strip length δ-thermal boundary layer
V-mean flow rate α-Liu body heat diffusivity
Wherein k can be expressed as
②
K in the formula
Si-backing material thermal conductivity t
d-diaphragm thickness
Then the temperature difference between the upstream temperature sensor is expressed as
ΔT
up=T
h[exp(γ
1l
u1)-exp(γ
1l
u2)] ③
Wherein
④
Equally, the temperature difference between the downstream temperature sensor is expressed as
ΔT
down=T
h[exp(γ
2l
d1)-exp(γ
2l
d2)] ⑤
Wherein
⑥
L in the formula
U1, l
U2-heater strip is to the distance of upstream temperature sensor
l
D1, l
D2-heater strip is to the distance of downstream temperature sensor
The secondary temperature difference then can be expressed as:
ΔT=ΔT
down-ΔT
up ⑦
Though the sensor secondary temperature difference output signal curve shape upstream and downstream difference curve that obtains thus all reduces gradually with the increase of flow, and owing to adopt the temperature difference mode, the downstream difference curve is insensitive to the decline of actual temperature, so its fall is very little; Thus, again the upstream and downstream temperature difference is carried out second order difference and obtain the secondary difference curve.Can see that this curve low speed segment is more sensitive, the high regime saturation point is moved after can be significantly, therefore, can significantly improve the flow rate test scope.In addition, by the first time difference can offset a part of error.
Adopt said method based on the up-down-stream temperature distribution secondary differential physique amount flow sensor of taking offence, comprise the element of heating, be symmetricly set on the detector unit of the elements on either side of heating, be upstream temperature detecting element and downstream temperature detecting element, it is characterized in that the described element of heating links to each other with the constant power source excitation, the upstream temperature detecting element links to each other with two signal input parts of differential operational circuit respectively with the downstream temperature detecting element, and the output terminal of described differential operational circuit is connected with CPU (central processing unit).
As preferably, described heating element adopts the semi-conducting electrode of polycrystalline silicon material; Described upstream temperature detecting element and downstream temperature detecting element adopt integrated electric heating heap device; And whole sensor adopts the MEMS structure.
As preferably, described heating element and the upstream temperature detecting element and the downstream temperature detecting element that are positioned at its both sides are arranged on the monocrystalline silicon membrane in parallel to each other, and described monocrystalline silicon membrane is fixed on the glass substrate.
This measuring method based on the sensor of MEMS technology is the variation that is converted into heat propagation by the variation that fluid is flowed, variation with heat propagation is converted into voltage signal again, thereby realize being distributed in two pairs of different detector units in position of heating element upstream and downstream, measure the difference of upstream and downstream temperature variation by the voltage electric signal of detector unit output by detection.The sensor of this working method is without any need for moving-member, and is simple in structure, is easy to realize microminiaturized.
The maximum characteristics of MEMS technology are by its sensitivity of scaled micro raising and Frequency Response with device or system, and significantly reduce device quality and inertia, realize low-cost manufacturing the in enormous quantities.MEMS technology is incorporated in the design of thermal flow rate sensor, can realize the microminiaturized and accurate control heated filament of temperature sensor and the micron order spacing between the thermoelectric pile easily, meanwhile, the microminiaturized feature of MEMS device can significantly reduce the thermal inertia of chip, realizes low-power consumption, high frequency sound requirement.Therefore, MEMS technology hot type flow sensing chip will promote the industrial applications process.
That adopts the sensor moves mass-flow gas meter based on up-down-stream temperature distribution secondary differential, comprise the sensor that is fixed thereon based on the up-down-stream temperature distribution secondary differential braking technique, the constant power source excitation that links to each other with sensor, the output terminal that it is characterized in that described sensor links to each other with the differential operational circuit, and described differential operational circuit links to each other with CPU (central processing unit) by the A/D change-over circuit.
As preferably, described CPU (central processing unit) is connected with display unit by the display driver unit, and CPU (central processing unit) also is connected with output interface by output module.
As preferably, described CPU (central processing unit) also is connected with load module, and described load module links to each other with entry terminal.
As preferably, the glass substrate of described sensor is arranged on the holder, and described holder is inserted on the duct wall of flowmeter, is provided with O-ring seal between holder and pipe hole, is fixed with cover plate by fixed body on pipe hole.
Therefore, the present invention has following advantage: 1. by upstream and downstream temperature variation difference is carried out the secondary differential operational, guarantee the influence of the low speed segment linearity less; 2. under normal pressure and standard temperature test condition, toward pusher, range ratio has enlarged more than 10 times, has improved the range ability and the linearity with the saturation point of the relation curve of the flow velocity of gas mass flow and output voltage; 3. the measuring accuracy height can effectively be eliminated error, and is highly sensitive; 4. adopt the MEMS technology to realize low-power consumption, high frequency sound, significantly reduce the thermal inertia of chip.
Description of drawings
Accompanying drawing 1 is a kind of flow velocity V of this prior art---temperature difference Δ T graph of a relation;
Accompanying drawing 2 is of the present invention a kind of at no flow and the thetagram that has under the flow two states.
Accompanying drawing 3 is a kind of flow of the present invention---graphs of a relation of output voltage values;
Accompanying drawing 4 is a kind of working state figures of sensor provided by the invention;
Accompanying drawing 5 is a kind of partial enlarged drawings of sensor provided by the invention;
Accompanying drawing 6 is user mode figure of a kind of flowmeter provided by the invention;
Accompanying drawing 7 is sectional structure synoptic diagram of a kind of flowmeter provided by the invention;
Accompanying drawing 8 is structural representations of a kind of differential operational circuit provided by the invention.
Among the figure, the element 1 of heating, upstream temperature detecting element 2u, downstream temperature detecting element 2d, constant power source excitation 3, differential operational circuit 4, CPU (central processing unit) 5, A/D change-over circuit 6, display driver unit 71, display unit 72, output module 81, output interface 82, load module 91, entry terminal 92, sensor 10, monocrystalline silicon membrane 11, glass substrate 12, holder 13, pipeline 14, O-ring seal 15, fixed body 16, cover plate 17, press welding block 18, metal interconnected 19, curve A, curve B, the temperature variation curve C of upstream, the temperature variation curve D in downstream, secondary difference curve E, saturation point P, the voltage output signal U, flow L.
Embodiment
Below by embodiment, and in conjunction with the accompanying drawings, technical scheme of the present invention is described in further detail.
Embodiment:
Based on the up-down-stream temperature distribution secondary differential physique method of measuring mass flow of taking offence, it is characterized in that: a. applies constant power source excitation 3 on the element 1 of heating of sensor, measures the Temperature Distribution of the element upstream and downstream of heating under the airless state respectively by the detector unit that is symmetricly set on the elements on either side of heating; B. when the gas flows through sensor, upstream temperature detecting element 2u mensuration region Temperature Distribution changes and output produces the upstream temperature difference signal, and downstream temperature detecting element 2d measures region Temperature Distribution variation and output produces the downstream temperature difference signal; C. deduct the downstream temperature difference signal with the upstream temperature difference signal, thereby draw the moving signal of up-down-stream temperature distribution secondary differential, measure the flow quality flow of the sensor of flowing through by the corresponding relation of secondary differential wave and air flow mass rate.
Above-mentioned secondary differential wave is amplified through signal, and be digital signal by analog signal conversion, this digital signal is carried out calculation process according to the corresponding relation of secondary differential wave and air flow mass rate in CPU (central processing unit), draw the air flow mass rate of the sensor of flowing through.Described whole sensor adopts MEMS mode processing and fabricating.
As shown in Figure 2, curve A is the temperature curve under no flow status, and curve B is at the temperature curve that has under the flow status.As seen same position, when flow was arranged, the temperature of upstream descended, and the temperature in downstream rises.The arranged direction of the element of heating of sensor and the direction of air-flow are perpendicular, and make when airless, and the Temperature Distribution of upstream and downstream is symmetrical substantially.Temperature-the distance Curve that records (curve A) of this moment roughly becomes normal distribution.Arrow is an airflow direction among the figure.
As shown in Figure 3, the temperature variation curve C of upstream and the temperature variation curve D in downstream reduce gradually with the increase of flow, the difference curve range of decrease that upstream temperature changes greatly, the difference curve fall that downstream temperature changes is little.Thus the upstream and downstream temperature difference is subtracted each other and obtain secondary difference curve E output characteristics, saturation point is passed backward, can significantly improve the flow rate test scope.
As shown in Figure 4, be adopt said method based on the up-down-stream temperature distribution secondary differential physique amount flow sensor of taking offence, comprise the element 1 of heating, be symmetricly set on the detector unit of element 1 both sides of heating, be i.e. upstream temperature detecting element 2u and downstream temperature detecting element 2d.The element 1 of heating links to each other with constant power source excitation 3, and upstream temperature detecting element 2u links to each other with two signal input parts of differential operational circuit 4 respectively with downstream temperature detecting element 2d, and the output terminal of described differential operational circuit 4 is connected with CPU (central processing unit) 5.Arrow is an airflow direction among the figure.Heating element 1 adopts the semi-conducting electrode of polycrystalline silicon material; Described upstream temperature detecting element 2u and downstream temperature detecting element 2d adopt integrated electric heating heap device; And whole sensor adopts the MEMS structure.
As shown in Figure 5, heating element 1 is arranged on the island shape monocrystalline silicon membrane 11 in parallel to each other with the upstream temperature detecting element 2u and the downstream temperature detecting element 2d that are positioned at its both sides, and described monocrystalline silicon membrane 11 is fixed on the glass substrate 12.The two ends of detector unit are fixing by press welding block 18.Heating element 1 is fixed on the glass substrate 12 by metal interconnected 19.
As shown in Figure 6, be adopt the sensor based on the moving mass-flow gas meter of up-down-stream temperature distribution secondary differential, comprise the sensor 10 that is fixed thereon based on the up-down-stream temperature distribution secondary differential braking technique, the constant power source that links to each other with sensor 10 encourages 3.The output terminal of sensor 10 links to each other with differential operational circuit 4, and described differential operational circuit 4 links to each other with CPU (central processing unit) 5 by A/D change-over circuit 6.CPU (central processing unit) 5 is connected with display unit 72 by display driver unit 71, and CPU (central processing unit) 5 also is connected with output interface 82 by output module 81.CPU (central processing unit) 5 also is connected with load module 91, and described load module 91 links to each other with entry terminal 92.
As shown in Figure 7, the glass substrate 12 of sensor is arranged on the holder 13, and described holder 13 is inserted on the duct wall of flowmeter, is provided with O-ring seal 15 between holder 13 and pipeline 14 holes, is fixed with cover plate 17 by fixed body 16 on pipe hole.
As shown in Figure 8, be the differential amplifier circuit figure that two inputs are arranged.Wherein an end is imported upstream temperature detecting element magnitude of voltage, other end input downstream temperature detecting element magnitude of voltage.U1 links to each other with upstream temperature detecting element 2u, and U2 links to each other with downstream temperature detecting element 2d.When temperature variation, because of two tube current Changing Patterns are identical, two pipe collector voltage drift amounts are also identical, thereby make the both-end output voltage be always zero.That is to say, rely on the complete symmetry of circuit, the zero point drift of two pipes is offseted at output terminal, therefore, zero point drift is suppressed.The two-way input end all links to each other with U3, by above-mentioned differential amplifier circuit output secondary differential wave.
Sensor among the present invention goes for multiple industry, and for example, motor car engine flowmeter, wheel leakage protective device, gas metering flowmeter, Industry Control flow are taken into account transmitter, anemoscope, family expenses full electronic gas meter, flow meter, Medical Instruments etc.
Can by known solution realize all that about correlation techniques such as signal Processing, MEMS structures this paper repeats no more among the present invention.
Specific embodiment described herein only is that the present invention's spirit is illustrated.The technician of the technical field of the invention can make various modifications or replenishes or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.
Although this paper has used the element 1 of heating morely, upstream temperature detecting element 2u, downstream temperature detecting element 2d, constant power source excitation 3, differential operational circuit 4, CPU (central processing unit) 5, A/D change-over circuit 6, display driver unit 71, display unit 72, output module 81, output interface 82, load module 91, entry terminal 92, sensor 10, monocrystalline silicon membrane 11, glass substrate 12, holder 13, pipeline 14, O-ring seal 15, fixed body 16, cover plate 17, press welding block 18, metal interconnected 19, curve A, curve B, the temperature variation curve C of upstream, the temperature variation curve D in downstream, secondary difference curve E, saturation point P, the voltage output signal U, terms such as flow L, but do not get rid of the possibility of using other term.Using these terms only is in order to describe and explain essence of the present invention more easily; They are construed to any additional restriction all is contrary with spirit of the present invention.