CN201397163Y - Airflow detection circuit of digital airflow meter - Google Patents
Airflow detection circuit of digital airflow meter Download PDFInfo
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- CN201397163Y CN201397163Y CN2009201501933U CN200920150193U CN201397163Y CN 201397163 Y CN201397163 Y CN 201397163Y CN 2009201501933 U CN2009201501933 U CN 2009201501933U CN 200920150193 U CN200920150193 U CN 200920150193U CN 201397163 Y CN201397163 Y CN 201397163Y
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- 238000001514 detection method Methods 0.000 title abstract 2
- 238000001914 filtration Methods 0.000 claims abstract description 28
- 238000012545 processing Methods 0.000 claims abstract description 15
- 230000003321 amplification Effects 0.000 claims abstract description 4
- 238000003199 nucleic acid amplification method Methods 0.000 claims abstract description 4
- 238000012360 testing method Methods 0.000 claims description 18
- 239000003990 capacitor Substances 0.000 claims description 13
- 230000000694 effects Effects 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 9
- 238000007599 discharging Methods 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 claims description 5
- 239000010409 thin film Substances 0.000 claims description 3
- 238000002347 injection Methods 0.000 abstract description 8
- 239000007924 injection Substances 0.000 abstract description 8
- 239000000446 fuel Substances 0.000 abstract description 7
- 230000008054 signal transmission Effects 0.000 abstract 1
- 238000004088 simulation Methods 0.000 abstract 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 24
- 238000010438 heat treatment Methods 0.000 description 21
- 239000012530 fluid Substances 0.000 description 16
- 229910052697 platinum Inorganic materials 0.000 description 12
- 238000000034 method Methods 0.000 description 7
- 238000005259 measurement Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 239000000295 fuel oil Substances 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 239000004579 marble Substances 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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Abstract
The utility model discloses an airflow detection circuit of digital airflow meter. Wherein, the bridge type branch circuit (1) is a linearized bridge branch circuit, the speed measuring resistor R4 isa film strain sheet, the temperature measuring resistor RK is a negative coefficient thermistor; the temperature measuring resistor RK is connected serially with a resistor R2, then both the temperature measuring resistor RK and the resistor R2 are parallel connected with a resistor R3; a proportion amplification branch circuit (2) is in electric connection with a data processing and filtering branch circuit (3); the data processing and filtering branch circuit converts the analog airflow signal from the proportion amplification branch circuit into data signal, obtains an ideal output value by searching tables by program, obtains the data signal output by modulating the duty ratio by controlling pulse width, finally, obtains simulation value output by low-pass filtering branch circuit andsends it to the engine controlling computer. Thereby the digital airflow meter can measure the airflow inhaled by the electronic fuel injection engine at each moment correctly and accurately, and achieves the advantages of automation, convenience, high signal transmission speed and high operating efficiency.
Description
One, technical field
The utility model relates to the air flowmeter that a kind of automobile is used, and specifically relates to a kind of air mass flow testing circuit of automobile air flow meter.
Two, background technology
Air flowmeter is mounted on the inlet channel between automobile gasoline filter cleaner and the air throttle, be used for measuring the air mass flow that sucks in the engine, its output signal is determining the basic fuel injection amount of automobile as the major parameter of control fuel injection amount in the motor car engine fuel oil electric injection system.Electronic fuel injection engine must correctly, accurately be measured the air mass flow that each moment sucks electronic fuel injection engine in order to obtain the combination gas of best fuel oil concentration under various operating conditions, calculates and control the main foundation of distributive value as ECU (Electrical Control Unit).
At present, known air flowmeter is mainly based on hot wire type and hot diaphragm type, these hot types (hot wire type or hot diaphragm type) air flowmeter is to add two metal platinum resistance in measuring pipeline, one of them platinum resistance feeds less current, and (electric current is below 4mA, can not cause resistance heating), be used to measure the detected fluid temperature, be called temperature detecting resistance; Another platinum resistance feeds big electric current (electric current is generally more than 50mA), is used to measure the speed of detected fluid, is called the resistance that tests the speed.According to the thermal diffusion principle, heating object is relevant with the character of the temperature difference, flow rate of fluid and the fluid of heating object and fluid by the heat of fluid removal.If fluid density is ρ, flow velocity is v, and heating object is Q by the heat of fluid removal, and the temperature difference of heating object and fluid is Δ T, and then its relational expression is:
In the formula (1), for the certain fluid of component, k
1, k
2, k
3Be constant.At xsect is in the pipeline of S, mass rate q
m=ρ vS.
In the actual measurement process, the platinum resistance that tests the speed Rh is transfused to the electric current I heating, and under thermal equilibrium state, the heating power of electric current and heating resistor are in equilibrium state by the heat of fluid removal, promptly have: Q=I
2Rh.Therefore, mass rate q
mBecome relation one to one with Rh/ Δ T, can be expressed as:
This shows that the measuring method of mass rate has two kinds: a kind of method is a constant current mode, and promptly when heating current I is constant, the temperature difference T by measuring fluid (ignore Rh with variation of temperature) comes the mass rate of Fluid Computation; Another kind method is the constant difference formula, be to keep the temperature difference T of heating platinum resistance and thermometric platinum resistance constant on the surface, be actually constant with the ratios delta T/Rh of heating platinum resistance Rh, by measuring the mass rate that heating current I comes Fluid Computation by the temperature difference T of a bridge circuit maintenance heating platinum resistance and thermometric platinum resistance.Adopt the constant difference mode, it is constant utilizing bridge circuit to make Δ T/Rh, calibrates mass rate q by experiment
mWith the relation curve of heating current I, just can come the mass rate q of Fluid Computation like this by the current value I of measuring
m
Above-mentioned thermal air flowmeter is used the measuring method of constant current mode mass rate, by simple whiston bridge circuit, temperature-compensation circuit and ratio amplifying circuit air mass flow is detected, the signal value output precision is not high, can not reflect the air input of engine by air variation of moment exactly, very big to the serviceability influence of engine.
Three, utility model content
The purpose of this utility model is to overcome above-mentioned deficiency, can correctly, accurately measure the air mass flow testing circuit of digital air flowmeter that each sucks the air mass flow of electronic fuel injection engine moment and provide a kind of.
The purpose of this utility model realizes by following technical solution: a kind of air mass flow testing circuit of digital air flowmeter, the bridge-type parallel circuit, the ratio that comprise mutual electrical connection are amplified parallel circuit, described bridge-type parallel circuit is a linearization electric bridge parallel circuit, the resistance R that wherein tests the speed 4 is thin film strain-gauge, temperature detecting resistance RK is the negative coefficient thermistor, and this temperature detecting resistance RK is with in parallel with resistance R 3 by temperature detecting resistance RK, resistance R 2 again after resistance R 2 is connected; Described ratio is amplified parallel circuit and is electrically connected with data processing and filtering parallel circuit again, this data processing and filtering parallel circuit are finished the conversion of simulating signal to digital signal to the air flow rate signal that amplifies parallel circuit output through ratio at the data acquisition port, table look-up by program then and obtain desirable output valve, duty by the control pulse-width modulation PWM recently obtains the output of digital signal, obtains analog quantity output by the low-pass filtering electronic circuit at last.
Described data processing and filtering parallel circuit are made up of crystal oscillator Q3 and single-chip microcomputer U2, switch electronic circuit, RC charging and discharging circuit, voltage follower and filtering electronic circuit successively; It comprises single-chip microcomputer U2, crystal oscillator Q3, operational amplifier U1B, triode Q2, resistance R 15-R19, capacitor C 2 and C3.
After adopting the utility model, adopt the constant difference mode, it is constant utilizing linearization electric bridge parallel circuit to make Δ T/Rh, and wherein linearization electric bridge parallel circuit has realized that heating resistor (Rh) is constant with the temperature difference maintenance of temperature detecting resistance (RK).When the mass rate of air changes, the electric bridge out of trim, control circuit is measured unbalance voltage, by changing heating current, make electric bridge be in equilibrium state again, heating current changes into voltage signal by resistance (R2), and passing ratio amplification parallel circuit sends single-chip microcomputer (no longer needing original temperature-compensation circuit) to then.After carrying out the adjustment of data by scm software, produce an output voltage, and marble circuit output and send into the engine control computer (ECU) of automobile after filtration, go out MAF by ECU by computed in software.Thereby just can correctly, accurately measure the air mass flow that each moment sucks electronic fuel injection engine.And operation is convenient automatically, signal conveys speed is fast, high efficiency.
Four, description of drawings
Below in conjunction with accompanying drawing and embodiment the utility model is described in further detail.
Fig. 1 is the air mass flow testing circuit schematic diagram of the digital air flowmeter of the utility model.
Fig. 2 is a circuit block diagram of the present utility model.
Fig. 3 is the data processing among Fig. 1 and the signal processing flow figure of filtering parallel circuit.
Fig. 4 is known bridge circuit figure.
Five, embodiment
With reference to Fig. 1, Fig. 2 as can be known, the air mass flow testing circuit of the digital air flowmeter of the utility model, the bridge-type parallel circuit 1, the ratio that comprise mutual electrical connection are amplified parallel circuit 2, described bridge-type parallel circuit 1 is linearization electric bridge parallel circuit, the resistance R that wherein tests the speed 4 is thin film strain-gauge, temperature detecting resistance RK is the negative coefficient thermistor, and this temperature detecting resistance RK is with in parallel with resistance R 3 by temperature detecting resistance RK, resistance R 2 again after resistance R 2 is connected; Described ratio is amplified parallel circuit 2 and is electrically connected with data processing and filtering parallel circuit 3 again.
With reference to Fig. 1, Fig. 2, Fig. 3, described data processing and filtering parallel circuit 3 successively by single-chip microcomputer U2 (its model: pic12f683) and crystal oscillator Q3, switch electronic circuit 4, RC charging and discharging circuit 5, voltage follower 6 and filtering electronic circuit 7 form, it comprises single-chip microcomputer U2, crystal oscillator Q3, operational amplifier U1B, triode Q2, resistance R 15-R19, capacitor C 2 and C3.Wherein 2 pin of single-chip microcomputer U2 and 3 pin meet crystal oscillator Q3 (another pin ground connection of crystal oscillator Q3), its 5 pin connecting resistance R15, another pin difference connecting resistance R16 of resistance R 15 and the base stage of triode Q2, the equal ground connection of emitter of another pin of resistance R 16 and triode Q2, the collector of triode Q2 is received on the 5V power supply by resistance R 17, and described resistance R 15, R16, R17 and triode Q2 constitute switch electronic circuit 4; One pin of resistance R 18 is received the collector of triode Q2, and its another pin connects 5 pin and the capacitor C 2 of operational amplifier U1B respectively, another pin ground connection of capacitor C 2, and described resistance R 18 and capacitor C 2 constitute RC charging and discharging circuit 5; 6,7 pin of operational amplifier U1B are connected together, 7 pin of operational amplifier U1B meet output terminal 1-5V by resistance R 19, a pin of capacitor C 3 meets output terminal 1-5V, its another pin ground connection, described operational amplifier U1B constitutes voltage follower 6, and described resistance R 19 and capacitor C 3 constitute filtering electronic circuit 7.
The effect of described switch electronic circuit 4 is: the pulse-width modulation PWM waveform of single-chip microcomputer U2 output is amplified, improve the ability that drives load; The effect of RC charging and discharging circuit 5 is: convert square wave to DC voltage; The effect of voltage follower 6 is: the driving force that improves output signal; The effect of filtering electronic circuit 7 is: prevent the interference of external signal to output signal, played the function of digital signal to analog signal conversion.
With reference to Fig. 1, Fig. 3, single-chip microcomputer U2 in described data processing and the filtering parallel circuit 3 finishes the conversion of simulating signal to digital signal to the air flow rate signal that amplifies parallel circuit 2 outputs through ratio at the data acquisition port, table look-up by program then and obtain desirable output valve, dutycycle (number percent of high-low level) by control width modulation (PWM) obtains the output of digital signal, obtains analog quantity output by the low-pass filtering electronic circuit at last.The scm software design utilizes the C language to carry out modularization programming, and software is made up of master routine, A/D sampling routine, digital filter program, operation processing program, PWM written-out program etc.The data that digital filter program obtains sampling average filtering algorithm and handle, and disturb to reduce.According to the obtained different pieces of information of test under varying environment, in addition after the mathematics manipulation, obtain the relation of environment temperature and standard output, operation processing program then carries out ambient temperature compensation according to this relation to be handled, and is exported by D/A then.After system powered on, single-chip microcomputer resetted, and carried out system initialization, then called each functional module program successively, and its control system main program flow is seen Fig. 3.
With reference to shown in Figure 4, power tube Q1 electrifies and banishes big effect.When the circuit energized, resistance R 9 conductings, the power conducting, circuit is powered to electric bridge.When electric bridge is uneven, 2 voltages of locating of A, B are unequal among Fig. 4, its difference is input to the base stage of Darlington transistor Q1 through amplifying after electronic circuit (being made up of operational amplifier U1D and resistance R 7) amplifies, thereby increases the output of its emitter-base bandgap grading, and the voltage that is added on the electric bridge is increased, thereby the electric current by resistance R h increases, resistance R h temperature raises, and its resistance is along with increase, when R1 * R4=Rh * RK, 2 of A, B locate voltage and equate that electric bridge reaches dynamic balance state.If environment temperature changes, then RK changes, and the bridge balance state is destroyed, and by the electric current change of resistance R h, the resistance of resistance R h is along with change, and electric bridge reaches new equilibrium state.
As previously mentioned, mass rate q
mBecome relation one to one with Rh/ Δ T, can be expressed as:
According to heat transfer principle, under the cooling effect of forced convertion, heater element dispersed heat H and heater element in the unit interval are directly proportional with the temperature difference Δ T of air, and be as follows:
H＝hSΔT (4)
In the formula (4), h is the thermal conductivity of heater element; S is the surface area of heater element.
And thermal conductivity be one with air, the relevant parameter of hotting mask.On the other hand, under thermal equilibrium state, heat dissipation capacity equates with thermal value, H=RhI
2Thus, consider various parameters, can get mass rate q
mWith the relational expression of Rh/ Δ T be:
In the formula (5), K is a constant, and K
TAlong with the rising of temperature increases, its temperature coefficient is 0.15～0.18%/℃.So control circuit guarantees in this scheme
Be steady state value, so that the size of flow only is directly proportional with the biquadratic of size of current.
Since the output of air flow sensor should be only with air mass flow be one-to-one relationship and just irrelevant with temperature, therefore do not change for the output that guarantees electric bridge because of the change of environment temperature, we need insert a temperature detecting resistance on the following half-bridge of another brachium pontis, to eliminate the influence of temperature to output.In order to reduce design cost, select for use negative coefficient (NTC) thermistor RK to replace platinum resistance to come measures ambient temperature in this project.For improving the linearization effect of thermistor, can adopt the dual linearizing method of connection in series-parallel resistance.The NTC thermistor is a kind of sintered body of oxide, has negative temperature coefficient, compares with metal platinum resistance, and temperature-coefficient of electrical resistance is big, and sensitivity is about 10 times of metal platinum resistance, and simple in structure, resistivity is little, is suitable for kinetic measurement.
When temperature variation, make resistance R T linear change, wherein, and the resistance of resistance R 2 for connecting, resistance R 3 is for wanting parallel resistor, and resistance R K is the NTC thermistor.As shown in Figure 1:
RT＝(RK+R2)/R3 (6)
Directly constant difference is controlled the output of the voltage at precision resistance R4 two ends on the electric bridge as flowmeter.This method is simple, directly perceived, and the output of air flowmeter is contacted directly with the variation of heating current and is in the same place, and more can accurately reflect the size of fluid flow.Because new linearization electric bridge parallel circuit controlling schemes is optimized the linearization of bridge resistor coupling, thermistor, under the situation of temperature variation, electric current on the resistance R 4 can remain unchanged substantially, be that output voltage is not acted upon by temperature changes, therefore no longer need original temperature-compensation circuit, directly, only need just can reach predetermined effect by a proportional amplifier with the measuring of the voltage output signal at resistance R 4 two ends.
As shown in the figure, principle of work of the present utility model is: linearization electric bridge parallel circuit has realized that the temperature difference of heating resistor and temperature detecting resistance keeps constant.When the mass rate of air changes, electric bridge parallel circuit meeting out of trim, control circuit is measured unbalance voltage, by changing heating current, make the electric bridge parallel circuit be in equilibrium state again, heating current changes into voltage signal by current measurement circuit, and passing ratio amplifies parallel circuit then, sends the single-chip microcomputer (no longer needing original temperature-compensation circuit) of data processing and filtering parallel circuit to.This single-chip microcomputer comprises 10 ADC, 1 10 voltage output DAC, and it is a complete data acquisition micro-system, and 10 A/D change-over periods of its inside are 4 μ s only, and be 15 μ s the Time Created of D/A.After carrying out the adjustment of data by scm software, produce an output voltage through D/A, and marble circuit output and send into automobile ECU after filtration, cross computed in software by the computer expert and go out MAF.
Claims (6)
1, a kind of air mass flow testing circuit of digital air flowmeter, the bridge-type parallel circuit (1), the ratio that comprise mutual electrical connection are amplified parallel circuit (2), it is characterized in that: described bridge-type parallel circuit (1) is a linearization electric bridge parallel circuit, the resistance R that wherein tests the speed 4 is thin film strain-gauge, temperature detecting resistance RK is the negative coefficient thermistor, and this temperature detecting resistance RK is with in parallel with resistance R 3 by temperature detecting resistance RK, resistance R 2 again after resistance R 2 is connected; Described ratio is amplified parallel circuit (2) and is electrically connected with data processing and filtering parallel circuit (3) again, this data processing and filtering parallel circuit (3) are finished the conversion of simulating signal to digital signal to the air flow rate signal that amplifies parallel circuit (2) output through ratio at the data acquisition port, table look-up by program then and obtain desirable output valve, duty by the control pulse-width modulation PWM recently obtains the output of digital signal, obtains analog quantity output by the low-pass filtering electronic circuit at last.
2, the air mass flow testing circuit of digital air flowmeter as claimed in claim 1 is characterized in that: described data processing and filtering parallel circuit (3) are made up of crystal oscillator Q3 and single-chip microcomputer U2, switch electronic circuit (4), RC charging and discharging circuit (5), voltage follower (6) and filtering electronic circuit (7) successively.
3, the air mass flow testing circuit of digital air flowmeter as claimed in claim 2 is characterized in that: described data processing and filtering parallel circuit (3) comprise single-chip microcomputer U2, crystal oscillator Q3, operational amplifier U1B, triode Q2, resistance R 15-R19, capacitor C 2 and C3.
4, the air mass flow testing circuit of digital air flowmeter as claimed in claim 3, it is characterized in that: 2 pin and 3 pin of described single-chip microcomputer U2 meet crystal oscillator Q3, its 5 pin connecting resistance R15, another pin difference connecting resistance R16 of resistance R 15 and the base stage of triode Q2, the equal ground connection of emitter of another pin of resistance R 16 and triode Q2, the collector of triode Q2 is received on the 5V power supply by resistance R 17, described resistance R 15, R16, R17 and triode Q2 constitute switch electronic circuit (4), the effect of switch electronic circuit (4) is with the pulse-width modulation PWM waveform amplification of single-chip microcomputer U2 output, improves the ability that drives load.
5, the air mass flow testing circuit of digital air flowmeter as claimed in claim 3, it is characterized in that: a pin of described resistance R 18 is received the collector of triode Q2, its another pin connects 5 pin and the capacitor C 2 of operational amplifier U1B respectively, another pin ground connection of capacitor C 2, described resistance R 18 and capacitor C 2 constitute RC charging and discharging circuit (5), and the effect of RC charging and discharging circuit (5) is to convert square wave to DC voltage.
6, the air mass flow testing circuit of digital air flowmeter as claimed in claim 3, it is characterized in that: 6,7 pin of described operational amplifier U1B are connected together, 7 pin of operational amplifier U1B meet output terminal 1-5V by resistance R 19, a pin of capacitor C 3 meets output terminal 1-5V, its another pin ground connection, described operational amplifier U1B constitutes voltage follower (6), and described resistance R 19 and capacitor C 3 constitute filtering electronic circuit (7); The effect of voltage follower (6) is the driving force that improves output signal, and the effect of filtering electronic circuit (7) is to prevent the interference of external signal to output signal, has played the function of digital signal to analog signal conversion.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009201501933U CN201397163Y (en) | 2009-04-26 | 2009-04-26 | Airflow detection circuit of digital airflow meter |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009201501933U CN201397163Y (en) | 2009-04-26 | 2009-04-26 | Airflow detection circuit of digital airflow meter |
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| CN201397163Y true CN201397163Y (en) | 2010-02-03 |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101551262B (en) * | 2009-04-26 | 2011-04-13 | 浙江恒光汽车部件有限公司 | Air flow detection circuit of digital air flow meter |
| CN104360100A (en) * | 2014-10-31 | 2015-02-18 | 苏州宏瑞净化科技有限公司 | High-precision anemograph |
| CN110462348A (en) * | 2017-03-30 | 2019-11-15 | 富士金公司 | Mass flow sensor, mass flow meter equipped with the mass flow sensor, and mass flow controller equipped with the mass flow sensor |
| CN112113624A (en) * | 2020-09-24 | 2020-12-22 | 河北紫旭节能环保技术咨询有限公司 | Water flow monitoring equipment |
| CN115452080A (en) * | 2022-08-08 | 2022-12-09 | 重庆川仪自动化股份有限公司 | Thermal gas mass flowmeter signal linearization circuit and method |
-
2009
- 2009-04-26 CN CN2009201501933U patent/CN201397163Y/en not_active Expired - Fee Related
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101551262B (en) * | 2009-04-26 | 2011-04-13 | 浙江恒光汽车部件有限公司 | Air flow detection circuit of digital air flow meter |
| CN104360100A (en) * | 2014-10-31 | 2015-02-18 | 苏州宏瑞净化科技有限公司 | High-precision anemograph |
| CN110462348A (en) * | 2017-03-30 | 2019-11-15 | 富士金公司 | Mass flow sensor, mass flow meter equipped with the mass flow sensor, and mass flow controller equipped with the mass flow sensor |
| CN110462348B (en) * | 2017-03-30 | 2021-08-10 | 富士金公司 | Mass flow sensor, mass flow meter provided with mass flow sensor, and mass flow controller provided with mass flow sensor |
| CN112113624A (en) * | 2020-09-24 | 2020-12-22 | 河北紫旭节能环保技术咨询有限公司 | Water flow monitoring equipment |
| CN112113624B (en) * | 2020-09-24 | 2023-12-05 | 河北紫旭节能环保技术咨询有限公司 | Water flow monitoring device |
| CN115452080A (en) * | 2022-08-08 | 2022-12-09 | 重庆川仪自动化股份有限公司 | Thermal gas mass flowmeter signal linearization circuit and method |
| CN115452080B (en) * | 2022-08-08 | 2024-06-11 | 重庆川仪自动化股份有限公司 | Signal linearization circuit and method for thermal gas mass flowmeter |
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| GR01 | Patent grant | ||
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| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20100203 Termination date: 20110426 |