CN103884391B - A kind of double feedback gas flow transducer - Google Patents

Abstract

The invention discloses a kind of double feedback gas flow transducer, including: air-flow probe, differential amplifier circuit, modulate circuit, compensation circuit, controller and power amplification circuit.The present invention uses controller output two-way PWM ripple to power amplification circuit and then the size of regulation and control feedback current, rather than directly utilize differential analog circuitry and carry out the feedback of electric current, corresponding control algolithm is set in the controller and exports suitable feedback quantity, avoid that analog circuit feedback quantity is excessive or too small, repeatedly feedback, the slow shortcoming of response speed, contribute to realizing the Fast-Balance of electric bridge, significantly improve the dynamic property of sensor.Volume flow is revised in real time by the present invention according to the gas pressure intensity in pipeline simultaneously, thus obtain accurate gas volume flow value under actual condition, eliminate the measurement error caused because of air pressure change, meet commercial production and measure the required precision to volume flowmeter.

Description

A kind of double feedback gas flow transducer

Technical field

The invention belongs to gas flow field of sensing technologies, be specifically related to a kind of double feedback gas flow transducer.

Background technology

Gas flow measurement method is segmented into four big classes according to measuring principle at present, is differential pressure flowmeter, speed respectively Degree formula effusion meter, volumetric flowmeter and mass flowmenter.Gas can be simply divided into again according to the output type of gas flow Volume flowmeter and mass-flow gas meter.Owing to the volume of gas is the function of temperature and pressure, and by medium temperature, pressure Impact, therefore the certainty of measurement of volumetric flow of gas is the highest；And the quality of gas the most in time, temperature, pressure change And change, so the measurement result of gas mass flow is more accurate.But in some actual application, generally require is high The volumetric flow of gas of precision.

Thermal type gas quality flow meter is a kind of common mass flowmenter, and its operation principle is to exist based on heating element heater Heat transfer in gas flowing.When gas flows through heating element heater, heating element heater dispersed heat and gas flow and ambient temperature Relevant.Currently used thermal mass flow meter is to maintain heater element surface temperature constant mostly, comes according to the change of electric current Obtain the flow of gas, be referred to as thermostatic type thermal mass flow meter.

The circuit structure of traditional thermostatic type mass flowmenter is as it is shown in figure 1, include a flow velocity probe and a temperature Probe, is distributed in the two-arm of Hui Sidun electric bridge, changes the electric current in electric bridge by the feedback of differential analog circuitry and realizes flow velocity spy The temperature constant of head.Temperature probe compensates for the temperature of fluid medium, it is to avoid flow measurement is at constant flow Time affected by gas temperature.The measuring circuit of thermostatic type mass flowmenter has easy of use, and frequency response is high, low noise etc. Series of advantages, therefore uses extensively.But in the applications such as automobile, the response speed of thermal flowmeter still can not meet to be wanted Ask, need to improve further.

Traditional thermal flowmeter is primarily present problems with in terms of dynamic property: one is to use differential analog circuitry real Existing current feedback, differential feedback amount is easily disturbed by extraneous factor, feedback current amount situation too much, very little often occurs, so that Electric bridge reach balance time due to repeatedly feedback and elongated；Two is the temperature-compensating platinum resistance RS resistance that temperature probe uses Relatively big, during electric bridge rebalancing, by the current change quantity of thermo-compensator RS much smaller than by measuring platinum resistance The current change quantity of RH, both voltage differences are less, and the response speed of electric bridge is slow, and dynamic property is poor.

Summary of the invention

For the above-mentioned technical problem existing for prior art, the invention provides a kind of double feedback gas flow sensing Device, is obtained the volume flow of gas, and obtains reality according to the air pressure correction in pipeline by the measuring method of gas mass flow High-precision volumetric flow units under the operating mode of border, uses microprocessing unit to avoid single differential analog circuitry to be easily subject in the feedback loop The shortcoming that external interference, response speed are slow, and it is first additionally to increase temperature-compensating during a feedback circuit increases bridge balance The voltage of part, improves the dynamic property of sensor, and certainty of measurement is high.

A kind of double feedback gas flow transducer, including:

Air-flow is popped one's head in, and for gathering flow signal and the pressure signal of gas in gas pipeline, it includes being installed on gas Measurement resistance, thermo-compensator and pressure sensing element in pipeline；Wherein, measure resistive voltage and be flow signal, pressure Pressure signal described in strong sensing element output；

Differential amplifier circuit, for measurement resistive voltage and thermo-compensator voltage are carried out differential amplification, poor Divide and amplify signal；

Modulate circuit, for carrying out conditioning shaping to described pressure signal；

Compensating circuit, it is connected to be collectively forming Hui Sidun electric bridge with measurement resistance and thermo-compensator, for survey Amount resistive voltage carries out temperature-compensating；

Controller, for constructing two-way pwm signal according to described differential amplification signal, and then according to the survey after compensating Pressure signal after amount resistive voltage and conditioning shaping, calculates the gas flow in gas pipeline；

Power amplification circuit, to drive the compensation circuit described in control after carrying out power amplification to two-way pwm signal.

Described measurement resistance and thermo-compensator all use platinum resistance.Described controller uses microprocessor.

Described compensation circuit includes two audion Q1～Q2 and three resistance R1～R3；Wherein, the collection of audion Q1 Electrode is connected with one end of resistance R1 and the colelctor electrode of audion Q2 and connects supply voltage VCC, the emitter stage of audion Q1 and electricity One end of resistance R2 is connected with one end of thermo-compensator, the other end ground connection of thermo-compensator, the emitter stage of audion Q2 It is connected with one end of the other end, the other end of resistance R2 and the resistance R3 of resistance R1, the other end of resistance R3 and measurement resistance One end is connected, and measures the other end ground connection of resistance；The base stage of two audion Q1～Q2 receives two-way respectively after power amplification Pwm signal.

Described controller is according to the gas flow in following formula calculating gas pipeline:

$q_{\mathrm{vw}}=\frac{a}{{\mathrm{\ρ}}_n}{[\frac{1}{B}\frac{U_H}{(T_H-T_n)(1+\mathrm{\β}{T}_H)}-\frac{A}{B}]}^2$

Wherein: a=P_nT_w/P_wT_n, P_nAnd T_nIt is respectively pressure and temperature, the P of current gas in pipelines_wAnd T_wIt is respectively this gas Body is corresponding pressure and temperature, ρ under setting operating mode_nFor setting the density of this gas under operating mode, A and B is default warp Testing constant, β is the temperature coefficient measuring resistance, T_HFor measuring the surface temperature of resistance, U_HFor compensate after measurement resistive voltage, R_H0It it is the resistance measuring resistance at 0 DEG C.

Described controller determines the dutycycle of pwm signal S1 according to following control strategy, and then constructs and export PWM letter Number S1 is to be controlled audion Q1:

When not having gas to flow through in pipeline, then | e (t) |≤τ, α₁(t)=α；

When there being gas to flow through in pipeline, if | e (t)-e (t-1) | is≤τ, then α₁(t)=α₁(t-1)；If | e (t)-e (t-1) | ＞ τ, then α₁(t)=η*i_Q1(t)+α；

Wherein: e (t) and e (t-1) is respectively current time and the signal value of previous moment differential amplification signal, α₁(t) and α₁(t-1) being respectively current time and the dutycycle of previous moment pwm signal S1, α is default dutycycle (it is slightly larger than 0), η For default proportionality coefficient, τ is default quality coefficient, i_Q1T () is the electric current of current time audion Q1 emitter stage.

Described electric current i_Q1T () is tried to achieve based on following formula:

$i_{Q1}\left(t\right)=\frac{T_6}{T_5+T}{i}_{Q1}(t-1)+\frac{T_5+T}{T_6+T}e\left(t\right)-\frac{T_5}{T_6+T}e(t-1)$

Wherein: i_Q1(t-1) being the electric current of a upper moment audion Q1 emitter stage, T is the sampling period, T₅And T₆It is default Leading phase compensation parameter.

Described controller determines the dutycycle of pwm signal S2 according to following control strategy, and then constructs and export PWM letter Number S2 is to be controlled audion Q2:

When not having gas to flow through in pipeline, then | e (t) |≤τ, α₂(t)=α；

When there being gas to flow through in pipeline, if | e (t)-e (t-1) | is≤τ, then α₂(t)=α₂(t-1)；If | e (t)-e (t-1) | ＞ τ, then α₂(t)=ω*i_Q2(t)+α；

Wherein: e (t) and e (t-1) is respectively current time and the signal value of previous moment differential amplification signal, α₂(t) and α₂(t-1) being respectively current time and the dutycycle of previous moment pwm signal S2, α is default dutycycle (it is slightly larger than 0), ω is default proportionality coefficient, and τ is default quality coefficient, i_Q2T () is the electric current of current time audion Q2 emitter stage.

Described electric current i_Q2T () is tried to achieve based on following formula:

$i_{Q2}\left(t\right)=\frac{T_4}{T_3+T}{i}_{Q2}(t-1)+\frac{T_3+T}{T_4+T}e\left(t\right)-\frac{T_3}{T_4+T}e(t-1)$

Wherein: i_Q2(t-1) being the electric current of a upper moment audion Q2 emitter stage, T is the sampling period, T₃And T₄It is default Leading phase compensation parameter.

The present invention compensates measurement resistance, thermo-compensator that resistance R2, R3 of circuit pop one's head in air-flow collectively form Hui Sidun electric bridge, compensate for the ambient temperature impact on measurement result, it is ensured that the measurement of gas flow is unrelated with ambient temperature.

When not having air-flow to flow through in pipeline, Hui Sidun electric bridge reaches balance, each element voltage value stabilization, differential amplification electricity The output result on road is zero.Two transistor bases do not have electric current to input, and are closed, two feedback circuit all feedback-less Amount.When there being air-flow to flow through in pipeline, air-flow and the heat transfer measured between resistance RH change, and the surface temperature of RH reduces, RH Voltage reduce, the difference result of RH and thermo-compensator RS is not zero by differential amplifier circuit, and two feedback circuits start Conducting, the electric current of power amplification circuit output correspondence is to the base stage of audion Q1 and Q2, the power increasing RH and the electric current flow through. When the heat that air-flow is taken away and RH power-balance, RH surface temperature keeps stable, and magnitude of voltage now is by microprocessing unit Reason obtains volumetric flow of gas, and exports to external equipment and show.When in pipeline, air-flow becomes 0 again, make at feedback circuit Under with, Hui Sidun electric bridge recovers initial balance, and the temperature of RH also recovers initial temperature.

Increase the electric current by RH after audion Q2 conducting, increase the power of RH self, make heat production power and the gas of RH The heat that stream is taken away reaches balance, and RH surface temperature keeps stable.When air-flow becomes 0 again, at the electric conduction of audion Q2 Under stream effect, RH returns to initial surface temperature, and electric bridge reaches balance again, and difference result is zero again.

The electric current by temperature-compensating platinum resistance RS is increased after audion Q1 conducting.In order to improve the sensitivity of sensor, Requiring the surface temperature immediate stability of RH when having air-flow to flow through, when not having an air-flow, electric bridge can restore balance rapidly.Therefore, three pole The electric current of pipe Q1 is for increasing the voltage of RS, and then can increase the voltage difference of RS Yu RH when having air-flow to flow through, thus improves Q2's Collector current, shortens the time that RH reaches steady statue and electric bridge restores balance, improves the dynamic property of gas sensor.

Therefore the method have the advantages that

(1) present invention use controller output two-way PWM ripple to power amplification circuit so that regulation and control feedback current size, Rather than directly utilize differential analog circuitry and carry out the feedback of electric current, it is suitable that the output of corresponding control algolithm is set in the controller Feedback quantity, it is to avoid the shortcoming that analog circuit feedback quantity is excessive or too small, repeatedly feedback, response speed are slow, contribute to realizing The Fast-Balance of electric bridge, significantly improves the dynamic property of sensor.

(2) present invention causes much larger than measuring cell to improve compensating element, resistance in traditional thermal flowmeter The shortcoming that dynamic responding speed is slow, one feedback circuit being connected with compensating element, of extra increase, during increasing bridge balance The voltage of compensating element, thus realize the fast of bridge balance when the fast and stable of RH surface temperature and airless when air-flow flows through Quick-recovery, improves dynamic responding speed.

(3) present invention uses the method measuring gas mass flow to obtain the volume flow of gas, and according in pipeline Volume flow is revised by gas pressure intensity in real time, thus obtains accurate gas volume flow value under actual condition, eliminates Because the measurement error that air pressure change causes, meet commercial production and measure the required precision to volume flowmeter.

Accompanying drawing explanation

Fig. 1 is the structural representation of tradition thermal type gas quality flow meter.

Fig. 2 is the structural representation of the double feedback gas flow transducer of the present invention.

Fig. 3 is the circuit theory diagrams of differential amplifier circuit.

Detailed description of the invention

In order to more specifically describe the present invention, below in conjunction with the accompanying drawings and detailed description of the invention is to technical scheme And related work principle is described in detail.

As in figure 2 it is shown, a kind of double feedback gas flow transducer, including: air-flow probe 1, differential amplifier circuit 2, conditioning Circuit 3, controller the 4, first power amplification circuit the 5, second power amplification circuit 6 and compensation circuit 7.

Air-flow is popped one's head in 1 integral measuring platinum resistance RH, temperature-compensating platinum resistance RS and gas pressure intensity sensing element 1a, for Time the detection flow of gas in pipelines and pressure；Wherein, the voltage measuring platinum resistance RH and temperature-compensating platinum resistance RS is the most defeated Delivering to the positive-negative input end of differential amplifier circuit 2, the outfan of gas pressure intensity sensing element 1a is connected with modulate circuit 3, measures The voltage of platinum resistance RH is also transported to controller 4.

The outfan of differential amplifier circuit 2 is connected with controller 4, and wherein differential amplifier circuit 2 is for measuring platinum resistance The voltage of RH and temperature-compensating platinum resistance RS carries out differential amplification.

The outfan of modulate circuit 3 is connected with controller 4, and wherein modulate circuit 3 is for gas pressure intensity sensing element 1a Measurement result process, export corresponding voltage signal.

Controller 4 carries two-way PWM ripple to the first power amplification circuit 5 and the second power amplification circuit 6, and processes To volumetric flow of gas can be transported to external equipment and show.

The outfan of the first power amplification circuit 5 is connected with the base stage of the audion Q1 compensated in circuit 7.

The outfan of the second power discharge circuit 6 is connected with the base stage of the audion Q2 compensated in circuit 7.

Wherein the first power amplification circuit 5 and the second power amplification circuit 6 for being converted to the electricity of correspondence by two-way PWM ripple Stream signal also exports.

Compensate circuit 7 and include two audion Q1 and Q2 and three resistance R1, R2, R3, wherein resistance R2 and R3 and air-flow Measurement platinum resistance RH and temperature-compensating platinum resistance RS in probe constitute Hui Sidun electric bridge.

The emitter stage of audion Q1 is directly connected with temperature-compensating platinum resistance RS；

The emitter stage of audion Q2 is connected with Hui Sidun electric bridge one end；

Controller 4 is the microprocessor of built-in multichannel AD conversion module.Multichannel A/D D/A converter module can be to defeated Enter signal and carry out sampling the most repeatedly；Microprocessor can select TMS320F28335, these microprocessor transmission process data Speed is fast, substantial amounts of sampled data can be carried out high speed processing and transmit.

As it is shown on figure 3, differential amplifier circuit 2 by two operational amplifier L1 and L2 and seven resistance R4, R5, R6, R7, R8, R9, R10 are constituted.Input signal V1 and V2 are to measure platinum resistance RH and the voltage of temperature-compensating platinum resistance RS respectively, and V3 refers to poor Dividing result, V4 refers to differential amplifier circuit 2 output signal to central processing unit 4.It is poor that amplifier L1 and resistance R4, R5, R6, R7 are constituted Branch divides, if four resistances are equal, then and V3=V1-V2.Amplifier L2 and resistance R8, R9, R10 constitute amplifier section $V_4=V_3(1+\frac{R_{10}}{R_9}).$

When not having air-flow to flow through in gas pipeline, bridge balance, measure platinum resistance RH and temperature-compensating platinum resistance RS Voltage difference e (t) is approximately zero；When there being air-flow to flow through in gas pipeline, measure the reduction of platinum resistance RH surface temperature and cause voltage Reducing, two feedback circuit conductings, e (t) exports two-way PWM after controller.PWM2 is through the second power amplification circuit to three Pole pipe Q2, increases the electric current by Hui Sidun electric bridge, mainly increases the electric current by RH, so that the power of RH increases, and gas The heat that stream is taken away reaches balance with the heat production power of RH, and RH surface temperature keeps stable, and when air-flow is 0 again, electric bridge is extensive Arrive initial poised state again.PWM1, through the first power amplification circuit to audion Q1, mainly increases the electric current by RS, from And expand e (t) so that in the moment that RH resistance changes, the emitter current of Q2 is relatively big, improves the sensitivity of pneumatic sensor.

Traditional thermostatic type mass flowmenter uses differential analog circuitry to realize current feedback, and each differential feedback amount is not Fixed, feedback current amount situation too much, very little often occurs, so that RH temperature reaches steady statue or electric bridge reaches newly to balance Time due to repeatedly feedback and elongated.Additionally, the temperature-compensating platinum resistance RS resistance that temperature probe uses is relatively big, at electric bridge weight In new equilibrium process, by the current change quantity of thermo-compensator RS much smaller than the curent change by measuring platinum resistance RH Amount, the response speed of electric bridge is slack-off, bad dynamic performance.The present invention uses controller to be calculated PWM ripple, it is ensured that feedback quantity closes Suitable, it is to avoid situation about repeatedly feeding back, and additionally increase a feedback circuit being connected with temperature-compensating platinum resistance RS, it is used for increasing The current change quantity of RS in equilibrium process.

Wherein, the thermostatic control strategy of PWM2 is as follows:

When gas flow rate constant, measure platinum resistance in work temperature_HUnder dynamical equation be:

$\frac{\mathrm{mcL}}{\stackrel{\‾}{H}\stackrel{\‾}{R_H}}\frac{d}{\mathrm{dt}}{r}_H+\frac{r_H}{\stackrel{\‾}{R_H}}=2(L-1)\frac{i_H}{\stackrel{\‾}{I_H}}---\left(1\right)$

In formula: c is the specific heat measuring platinum resistance, m is the quality measuring platinum resistance, and L was ratio of specific heat, had with present flow rate Close,For work temperature_HThe resistance of lower measurement platinum resistance,For work temperature_HThe electric current of lower measurement platinum resistance, above respectively Parameter is constant.r_HFor measuring platinum resistance change in resistance amount, i_HFor the current change quantity by measuring platinum resistance.

Owing to temperature-compensating platinum resistance RS is much larger than measuring platinum resistance RH, the therefore emitter current i approximation of audion Q2 Current change quantity i equal to RH_H。

Measure the voltage U of platinum resistance RH_HMeet:

$U_H=\stackrel{\‾}{U_H}+u_H---\left(2\right)$

$U_H=I_H{R}_H=(\stackrel{\‾}{I_H}+i_H)(\stackrel{\‾}{R_H}+r_H)---\left(3\right)$

In formula: U_H、I_H、R_HIt is respectively and measures the voltage of platinum resistance, electric current and resistance, u_HFor voltage variety,For work Make temperature T_HThe voltage of lower measurement platinum resistance, for constant.

Formula (2) and formula (3) are substituted into formula (1) obtain:

$\frac{\mathrm{mcL}}{\stackrel{\‾}{H}\stackrel{\‾}{U_H}}\frac{{\mathrm{du}}_H}{\mathrm{dt}}+\frac{u_H}{\stackrel{\‾}{U_H}}=\frac{\mathrm{mcL}}{\stackrel{\‾}{H}\stackrel{\‾}{I_H}}\frac{d{i}_H}{\mathrm{dt}}+2(L-1)\frac{i_H}{\stackrel{\‾}{I_H}}---\left(4\right)$

Formula (4) is carried out Laplace transform obtain:

$G_2\left(s\right)=\frac{u_H\left(s\right)}{i_H\left(s\right)}=K_1\frac{T_{1}s+1}{T_{2}s+1}---\left(5\right)$

In formula: $K_1=\frac{2\stackrel{\‾}{U_H}(L-1)}{\stackrel{\‾}{I_H}},T_1=\frac{\mathrm{mcL}}{2\stackrel{\‾}{H}(L-1)},T_2=\frac{\mathrm{mcL}}{\stackrel{\‾}{H}}.$

Increase controller G_c2S () carries out leading phase compensation, the electric current i of controller output_HRealized by the dutycycle of PWM2. G_c2S () transmission function is as follows:

$G_{c2}\left(s\right)=\frac{i_H\left(s\right)}{e\left(s\right)}=\frac{T_{3}s+1}{T_{4}s+1}---\left(6\right)$

In formula, e (s) is the pull-type conversion of temperature-compensating platinum resistance RS and the voltage difference measuring platinum resistance RH.

Formula (6) turns to the differential equation:

$T_4\frac{d{i}_H\left(t\right)}{\mathrm{dt}}+i_H\left(t\right)=T_3\frac{\mathrm{de}\left(t\right)}{\mathrm{dt}}+e\left(t\right)---7$

The differential representation form of formula (7) is as follows:

$T_4\frac{i_H\left(t\right)-i_H(t-1)}{T}+i_H\left(t\right)=T_3\frac{e\left(t\right)-e(t-1)}{T}+e\left(t\right)---\left(8\right)$

In formula: T is the sampling period, i_H(t) and i_H(t-1) it is the electric current of t and (t-1) moment audion Q2 emitter stage, e (t) With the voltage difference that e (t-1) is respectively t and (t-1) moment RS Yu RH.

Formula (8) alterable obtains:

$i_H\left(t\right)=\frac{T_4}{T_3+T}{i}_H(t-1)+\frac{T_3+T}{T_4+T}e\left(t\right)-\frac{T_3}{T_4+T}e(t-1)---\left(9\right)$

When gas pipeline does not has air-flow to flow through, bridge balance ,≤τ, e (t) are approximately 0 to | e (0) |, the dutycycle of PWM2 α₂(0)=α₂₀, α₂₀Slightly larger than 0；

When there being air-flow to flow through in gas pipeline, measure platinum resistance RH voltage and reduce, | e (t) | >=τ.

If e (t)-e (t-1)≤τ, then α₂(t)=α₂(t-1)；

If e (t)-e (t-1) > τ, then obtained, by formula (9), the electric current i that audion Q2 emitter stage should circulate_H(t), PWM2's Duty cycle alpha₂T () meets such as following formula:

α₂(t)=ω·i_H(t)+α₂₀(10) in formula: ω is proportionality coefficient, and τ is relevant with control accuracy.

Change i_HIt is | e (t) |≤τ till≤τ or bridge balance until satisfied | e (t)-e (t-1) |.

The control strategy of PWM1 is as follows:

The dynamical equation of temperature-compensating platinum resistance RS is as follows:

Δu_S(t)=i_Q1(t)·[R₁//(R₃+R_H)+R₂]//R_S(11)

Resistance in view of RS in circuit mono-arm is significantly larger than the resistance of RH mono-arm, and therefore formula (11) can be reduced to:

$\mathrm{\Δ}{u}_S\left(t\right)=\frac{i_{Q1}\left(t\right)\·R_S}{2}---\left(12\right)$

Formula (12) is carried out pull-type change obtain:

$G_2\left(s\right)=\frac{\mathrm{\Δ}{u}_S\left(s\right)}{i_{Q1}\left(s\right)}=K_2---\left(13\right)$

In formula: K₂=R_S/2。

Increase controller G_c1S () carries out leading phase compensation, the electric current i of controller output_Q1Real by the dutycycle of PWM1 Existing.G_c1S () transmission function is as follows:

$G_{c1}\left(s\right)=\frac{i_{Q1}\left(s\right)}{e\left(s\right)}=\frac{T_{5}s+1}{T_{6}s+1}---\left(14\right)$

Can obtain by differential representation:

$i_{Q1}\left(t\right)=\frac{T_6}{T_5+T}{i}_{Q1}(t-1)+\frac{T_5+T}{T_6+T}e\left(t\right)-\frac{T_5}{T_6+T}e(t-1)---\left(15\right)$

In formula: i_Q1 (t) and i_Q1 (t-1) is the electric current of t and (t-1) moment audion Q1 emitter stage.

When gas pipeline does not has air-flow to flow through, bridge balance ,≤τ, e (0) are approximately 0 to | e (0) |, the dutycycle of PWM1 α₁(0)=α₁₀, α₁₀Slightly larger than 0；

When there being air-flow to flow through in gas pipeline, measure platinum resistance RH voltage and reduce, | e (t) | >=τ.

If | e (t)-e (t-1) | is≤τ, then α₁(t)=α₁(t-1)；

If | e (t)-e (t-1) | > τ, then obtained, by formula (15), the electric current i that audion Q1 emitter stage should circulate_Q1(t), The duty cycle alpha of PWM1₁T () meets such as following formula:

α₁(t)=η·i_Q1(t)+α₁₀(16) in formula: η is proportionality coefficient, and τ is relevant with control accuracy.

i_Q1Impact on electric bridge is less than the iH impact on electric bridge, so i_Q1Meet such as following formula:

$i_{Q1}\≤\frac{1}{10}\stackrel{\‾}{I_S}---\left(17\right)$

In formula:For the electric current of temperature-compensating platinum resistance RS under work temperature H, for constant.

Change i_Q1I.e. | e (t) |≤τ till meeting e (t)≤τ or bridge balance.

Larger difference is there is between the operating mode pressure actual due to gas in pipelines and setting pressure, and during measuring The result of output also can be had an impact by the fluctuation of air pressure, it is therefore desirable to measured value is carried out pressure correction, thus obtains under operating mode Actual volumetric flow of gas.

The gas pressure intensity measured in pipeline is as follows to the correction of measured value:

In gas flow measurement, the heat transmitted between air-flow and heating element heater refers mainly to Forced Convection Heat Transfer and is produced Heat exchange, the heat Q therefore transmitted is represented by:

Q=hA_S(T_H-T_r) in (18) formula: Q is air-flow and measures the heat of heat exchange between platinum resistance, and h is right for forcing Stream mean heat transfer coefficient, A_SFor the surface area of probe, T_HFor measuring the surface temperature (DEG C) of platinum resistance, T_rTemperature for air-flow (℃)。

Measuring platinum resistance and keep constant temperature, therefore its electrical power is equal with the heat that flowing gas heat convection is taken away:

$\frac{{U_H}^2}{R_H}=h{A}_S(T_H-T_r)---\left(19\right)$

In formula: U_HFor measuring the voltage of platinum resistance, R_HFor measuring the resistance of platinum resistance.

hA_SIt is represented by:

hA_S=A+B(q_m)^1/2(20) in formula: A, B are empirical, can be measured by experiment, q_mQuality stream for air-flow Amount.

Can be obtained by formula (19) and (20):

$q_m={[\frac{1}{B}\frac{U_H}{(T_H-T_r)R_H}-\frac{A}{B}]}^2---\left(21\right)$

Resistance R of platinum resistance_HWith surface temperature T_HRelevant, it is represented by:

R_H=R_H0(1+βT_H) in (22) formula: R_H0Being the resistance of platinum resistance at 0 DEG C, β is the temperature coefficient of platinum resistance.

Pneumatic sensor is in constant temperature mode of operation, platinum resistance resistance R_HWith surface temperature T_HIt is constant, therefore gaseous mass Flow q_mOnly with gas flow temperature T_rWith platinum resistance voltage U_HRelevant, when gas flow temperature is stablized, q_mIt is U_HMonotropic function.

The volumetric flow of gas set under operating mode is represented by:

$q_{\mathrm{vn}}=\frac{a_{\mathrm{qm}}}{{\mathrm{\ρ}}_n}={\frac{1}{{\mathrm{\ρ}}_n}[\frac{1}{B}\frac{U_H}{(T_H-T_n)(1+\mathrm{\β}{T}_H)}-\frac{A}{B}]}^2---\left(23\right)$

In formula: ρ_nFor setting the gas density under operating mode.

In actual condition, owing to the reason gas density of gas pressure intensity is different from setting operating mode, can be by preferable gas Body state equation is modified:

${\mathrm{\ρ}}_w={\mathrm{\ρ}}_n\frac{P_w{T}_n}{P_n{T}_w}={\mathrm{\ρ}}_n/a---\left(24\right)$

In formula: ρ_wFor the gas density under actual condition, P_n、T_nAnd P_w、T_wIt is respectively actual condition and sets under operating mode Gas pressure intensity and temperature, a is correction factor.

Volumetric flow of gas actual after can being revised by formula (23) and (24) and between relation:

$q_{\mathrm{vw}}=\frac{q_m}{{\mathrm{\ρ}}_n}=\frac{q_m}{{\mathrm{\ρ}}_n/a}=\frac{a}{{\mathrm{\ρ}}_n}{[\frac{1}{B}\frac{U_H}{(T_H-T_n)(1+\mathrm{\β}{T}_H)}-\frac{A}{B}]}^2=a{q}_{\mathrm{vm}}---\left(25\right)$

Volumetric flow of gas actual after correction can be directly obtained from the output voltage measuring platinum resistance.

Claims (8)

1. a double feedback gas flow transducer, it is characterised in that including:

Air-flow is popped one's head in, and for gathering flow signal and the pressure signal of gas in gas pipeline, it includes being installed on gas pipeline Interior measurement resistance, thermo-compensator and pressure sensing element；Wherein, measure resistive voltage and be flow signal, pressure sense Answer the pressure signal described in element output；

Differential amplifier circuit, for measurement resistive voltage and thermo-compensator voltage are carried out differential amplification, obtains difference and puts Big signal；

Modulate circuit, for carrying out conditioning shaping to described pressure signal；

Compensating circuit, it is connected to be collectively forming Hui Sidun electric bridge with measurement resistance and thermo-compensator, for measuring electricity Resistance voltage carries out temperature-compensating；

Controller, for constructing two-way pwm signal according to described differential amplification signal, and then according to the measurement electricity after compensating Pressure signal after resistance voltage and conditioning shaping, calculates the gas flow q in gas pipeline by following formula_vw；

Wherein: a=P_nT_w/P_wT_n, P_nAnd T_nIt is respectively pressure and temperature, the P of current gas in pipelines_wAnd T_wIt is respectively this gas Pressure corresponding under setting operating mode and temperature, ρ_nFor setting the density of this gas under operating mode, A and B is default experience Constant, β is the temperature coefficient measuring resistance, T_HFor measuring the surface temperature of resistance, U_HFor the measurement resistive voltage after compensating, R_H0 It it is the resistance measuring resistance at 0 DEG C；

Power amplification circuit, to drive the compensation circuit described in control after carrying out power amplification to two-way pwm signal.

Gas flow sensor the most according to claim 1, it is characterised in that: described measurement resistance and temperature-compensating electricity Resistance all uses platinum resistance.

Gas flow sensor the most according to claim 1, it is characterised in that: described controller uses microprocessor.

Gas flow sensor the most according to claim 1, it is characterised in that: described compensation circuit includes two three poles Pipe Q1～Q2 and three resistance R1～R3；Wherein, one end of the colelctor electrode of audion Q1 and resistance R1 and the current collection of audion Q2 Extremely being connected and meet supply voltage VCC, the emitter stage of audion Q1 is connected with one end of resistance R2 and one end of thermo-compensator, The other end ground connection of thermo-compensator, the emitter stage of audion Q2 and the other end of resistance R1, the other end of resistance R2 and electricity One end of resistance R3 is connected, and the other end of resistance R3 is connected with the one end measuring resistance, measures the other end ground connection of resistance；Two The base stage of audion Q1～Q2 receives two-way pwm signal after power amplification respectively.

Gas flow sensor the most according to claim 4, it is characterised in that: described controller is according to following control plan Slightly determine the dutycycle of pwm signal S1, and then structure output pwm signal S1 be to be controlled audion Q1:

When not having gas to flow through in pipeline, then | e (t) |≤τ, α₁(t)=α；

When there being gas to flow through in pipeline, if | e (t)-e (t-1) | is≤τ, then α₁(t)=α₁(t-1)；If | e (t)-e (t-1) | is ＞ τ, then α₁(t)=η * i_Q1(t)+α；

Wherein: e (t) and e (t-1) is respectively current time and the signal value of previous moment differential amplification signal, α₁(t) and α₁(t- 1) being respectively current time and the dutycycle of previous moment pwm signal S1, α is default dutycycle, and η is default ratio system Number, τ is default quality coefficient, i_Q1T () is the electric current of current time audion Q1 emitter stage.

Gas flow sensor the most according to claim 5, it is characterised in that: described electric current i_Q1T () is based on following calculation Formula is tried to achieve:

Wherein: i_Q1(t-1) being the electric current of a upper moment audion Q1 emitter stage, T is the sampling period, T₅And T₆It is default surpassing Front phase compensation parameter.

Gas flow sensor the most according to claim 4, it is characterised in that: described controller is according to following control plan Slightly determine the dutycycle of pwm signal S2, and then structure output pwm signal S2 be to be controlled audion Q2:

When not having gas to flow through in pipeline, then | e (t) |≤τ, α₂(t)=α；

When there being gas to flow through in pipeline, if | e (t)-e (t-1) | is≤τ, then α₂(t)=α₂(t-1)；If | e (t)-e (t-1) | is ＞ τ, then α₂(t)=ω * i_Q2(t)+α；

Wherein: e (t) and e (t-1) is respectively current time and the signal value of previous moment differential amplification signal, α₂(t) and α₂(t- 1) being respectively current time and the dutycycle of previous moment pwm signal S2, α is default dutycycle, and ω is default ratio system Number, τ is default quality coefficient, i_Q2T () is the electric current of current time audion Q2 emitter stage.

Gas flow sensor the most according to claim 7, it is characterised in that: described electric current i_Q2T () is based on following calculation Formula is tried to achieve:

Wherein: i_Q2(t-1) being the electric current of a upper moment audion Q2 emitter stage, T is the sampling period, T₃And T₄It is default surpassing Front phase compensation parameter.