CN1847802A - Flow detecting method and device - Google Patents
Flow detecting method and device Download PDFInfo
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- CN1847802A CN1847802A CN 200510011567 CN200510011567A CN1847802A CN 1847802 A CN1847802 A CN 1847802A CN 200510011567 CN200510011567 CN 200510011567 CN 200510011567 A CN200510011567 A CN 200510011567A CN 1847802 A CN1847802 A CN 1847802A
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Abstract
The present invention relates to flow detecting method and device, and is especially flow detecting method and device for fine pipeline in industrial, medical and biochemical instrument. The detecting method includes acquiring two temperature values T1 and T2 of fluid in constant section pipe with two infrared probes S1 and S2 spaced by certain interval, performing cross correlation calculation on T1 and T2 to find out time deviation corresponding to the maximum cross correlation value or the time for the fluid to flow through two infrared probes, dividing the interval by the time and multiplying the flow rate and the cross section area of the pipeline to obtain the flow rate value. The detecting device includes a pipe, an electromagnetic induction coil, an electromagnetic induction heating stainless steel tube, two infrared probes, a heating power driver and a micro computer unit. The present invention may be used for measurement of micro flow rate.
Description
Technical field
The present invention relates to a kind of flow rate testing methods and device, the method and apparatus of the tubule road flow detection in particularly industry, medical treatment, the biochemical instrument.
Background technology
In traditional industry, flow detection meter complex structure, the flow of being surveyed generally is big flow, adopts the mechanics principle of fluid more.In the tiny flow quantity context of detection, hot detection method has very big dirigibility and advantage, detects flow by detected temperatures traditionally, and main method is:
1, adopts a heating resistance element, a thermistor element detected temperatures.The temperature rise and the flow of liquid are inversely proportional to.Flow is big, and fluid temperature is low, and flow is little, the fluid temperature height.Because the heat conduction meeting of pipeline consumes a part of heat, the liquid heat capacity difference of variable concentrations, this method obviously is difficult to guarantee high precision.A kind of improvement of this kind method is that heating resistor and temperature detection resistance are reduced to a resistance, and it has double action simultaneously.And often as a brachium pontis of electric bridge.But still can't overcome above-mentioned shortcoming.
2, another kind of sensitivity for raising method 1 changes a temperature detecting resistance into two temperature detecting resistances, as the Jap.P. JP10019621 of EUROPEAN PATENT OFFICE's announcement.Principle adopts autothermal process as shown in Figure 6, and two heating resistors also are temperature detecting resistances simultaneously, two resistance are connected to electric bridge as two brachium pontis, when fluid flows through, and the temperature difference of two thermistors, their temperature signal is converted to electric signal, the delivery rate signal.Fluid flows through and can bring the temperature difference, but the temperature difference is difficult to reflect accurately flow, and the difference of fluid concentrations, thermal capacity can be brought bigger error, the turbulent flow of fluid and the factors such as assembling of electric resistance sensor, make the relation between the flow velocity and the temperature difference bring too many disturbing factor, so be difficult to that still high precision is arranged though such sensor has carried out all multifactor corrections.
The medicine that develops rapidly, life science instrument field detect microfluid needs a kind of more effective, simple in structure, high-precision flow detection meter.There is above-mentioned defective in existing flowmeter, fails to satisfy the requirement of medicine, the detection of life science microfluid.
Summary of the invention
The objective of the invention is to propose a kind of simple in structure, flow rate testing methods and device that precision is high, be fit to the flow detection of small fluid and micro-fluid chip more.Method of the present invention is applicable to the flow detection in industry, medical treatment, the biochemical instrument.Device of the present invention is subjected to factor affecting such as type of fluid, density, thermal capacity little, can directly use, and does not need to demarcate.Can be integrated in micro-fluid chip inside, also can be serially connected with in the scientific instrument such as biochemistry, medicine as device separately.
The present invention adopts and measures the mistiming that the uneven temperature fluid successively flows through two points for measuring temperature, calculates the method for flow velocity and flow by the mistiming.Be eliminate fluid interference such as the unavoidable heat conduction that occurs, thermal diffusion when flowing through two points for measuring temperature, the present invention adopts related algorithm to eliminate above-mentioned interference to obtain result accurately to the temperature data from two temp probes.
Related algorithm in the signal Processing field especially the seizure for motor message be a kind of very useful algorithm, it can effective recognition goes out to mix certain noise, a certain signal of certain variation has taken place.The formula of correlation computations:
R
T1T2(N)=∑ f
T1(n) f
T2(n-N); Formula 1
f
T1(n), f
T2(n) being a pair of discrete series signal with similar characteristic, when the value of the N of R (N) when obtaining maximal value, is f
T2(n) with respect to f
T1(n) the lag or lead value on sequence.
The present invention adopts the related algorithm in the signal Processing, comes calculated flow rate by means of the supercomputing performance of microprocessor (DSP).And the structural manufacturing process of sensor required to simplify greatly and reduce.In order to adopt this efficient algorithm, can make the liquid that flows through be in the non-uniform temperature state at first with the heating of heating element convection cell grow degree, in fluid, add the thermal perturbation signal.
For convection cell produces thermal perturbation, the present invention adopts the isolation induction heating mode of good airproof performance, by electromagnetic induction coil and the heating of stainless steel cartridge heater convection cell.Type of heating is the grow degree, has comprised temperature-rise period and temperature-fall period, and the temperature variation curve of fluid can be random function curve arbitrarily.
The collection of microcontroller processor real-time is along the temperature value T1, the T2 that flow to direction two infrared temperatures probe at regular intervals.T1 and T2 are carried out cross-correlation calculation, and the cross-correlation maximum time corresponding off-set value τ that calculates promptly is that fluid flows through two needed times of temp probe.Obtain flow speed value with the distance between two infrared temperature probes divided by τ.The sectional area that multiply by pipeline with flow speed value obtains flow value.
The output of flow reading can be analog and digital signal.
The device of using the inventive method mainly comprises body, electromagnetic induction coil, electromagnetic induction heating stainless steel cylinder, infrared temperature probe, heating power driver, microprocessor controller.
Body is that body [G] is a constant section duct, with the tubule that heat, electric poor conductor material (as organic glass or pottery) are made, inner wall smooth.Electromagnetic induction coil outside body liquid go into end, single or multiple lift coiling in axial direction.The electromagnetic induction heating stainless steel cylinder is a thin cylinder made from stainless steel material, and barrel bore is identical with internal diameter of tube body, is embedded in the body from the coaxial heart of body one end.The electromagnetic induction heating stainless steel cylinder aligns vertically with the external electromagnetic inductive coil, and length is identical.Stainless steel cylinder is heating liquid under the effect of the alternating electromagnetic field that electromagnetic induction coil produces.Electromagnetic induction coil is operated in the high frequency state, is generally tens kilo hertzs.The effect of heating power driver is that an interchange input rectifying is a direct current, and the high-frequency alternating current (tens kilo hertzs) that is reverse into certain power again is applied to the electromagnetic induction coil two ends.Rectification can realize by 4 diode full-bridge rectification: diode two two-phases polyphone, and then in parallel, two polyphone branch road middle parts are input, the two ends after the parallel connection are output.Inversion can adopt 4 MOS power tubes to realize, 4 metal-oxide-semiconductors are connected to full-bridge circuit: metal-oxide-semiconductor two two-phases polyphone, two brachium pontis behind the polyphone are in parallel again, two ends up and down after the parallel connection connect the galvanic both positive and negative polarity of rectification output respectively, draw lead from the middle part of two brachium pontis and connect electromagnetic induction coil.The following metal-oxide-semiconductor of the last metal-oxide-semiconductor of left side brachium pontis and the right brachium pontis is open-minded during work; Two other metal-oxide-semiconductor ends, and is then positive right negative to the alive direction of an electromagnetic induction coil left side.Otherwise the last metal-oxide-semiconductor of the right brachium pontis and the following metal-oxide-semiconductor of left side brachium pontis are open-minded; Two other metal-oxide-semiconductor ends, then to the negative right side, the alive direction of an electromagnetic induction coil left side just.Under the High-speed Control of microprocessor, high frequency, alternately, the above-mentioned two kinds of on-off modes of switching of symmetry, then realize high-frequency ac drive controlling to electromagnetic induction coil.Because in four metal-oxide-semiconductors, the diagonal angle duty is identical, so microprocessor (MCU) only need be sent the two-way drive signal, each road drive signal is opened the gate pole that special chip is connected to two metal-oxide-semiconductors in diagonal angle fast by the metal-oxide-semiconductor gate pole.The two-way drive signal that microprocessor is sent is to adopt width modulation (PWM), and promptly frequency is constant, only changes dutycycle.Dutycycle is big more, and the time ratio that four metal-oxide-semiconductors are opened is big more, and the power of output is big more.Opening of two-way drive signal replaces, when the dutycycle of two paths of signals all near 50% the time, then electromagnetic induction coil with peak power to induction heating stainless steel cylinder transmission power, so, can change heating power by changing dutycycle.
In axial direction on the tube body wall of distance electromagnetic induction heating stainless steel cylinder certain distance (as 5 centimetres), offer from the outside one from the large aperture by the with the level through hole of step to the small-bore transition, the center and the conduit axis of through hole intersect vertically, large aperture and infrared temperature probe match, one infrared temperature probe embeds wherein, and the small-bore is more bigger than infrared temperature probe incidence window.In the infrared temperature probe incidence window point tube, with epoxide-resin glue the infrared probe sealing and fixing in stepped hole.With the tube wall of the body of this infrared temperature probe certain distance on, offer the through hole with the level of another same structure, another infrared temperature probe embeds this through hole.Because common organic glass body or pottery have absorption can bring temperature measurement error to infrared, (Φ 2.54mm) is bigger for incidence window so pop one's head in than infrared temperature in the small-bore of stepped hole, makes the infrared radiation that sends from fluid directly enter infrared probe.This a pair of infrared probe performance is answered basically identical.The requirement response speed is fast, and the response time is below 0.1 second, but temperature-measuring range 0-100 degree centigrade.The output area of low temperature infrared temperature sensor that satisfies above-mentioned requirements is below 2 millivolts, in order to make the analog to digital converter of microprocessor, can directly change, the feeble signal that infrared temperature sensor is exported need adopt differential operational amplifier to amplify 1000-2000 doubly.The a pair of voltage output pin of infrared temperature probe and a pair of input pin of differential operational amplifier link to each other, and the bias voltage pin connects the output terminal of potentiometer.Suitable bias voltage can make the output of infrared temperature probe that better linearity is arranged, and helps improving measuring accuracy.The bias voltage operated by rotary motion is about 2 volts.The positive 5 volts of power supplys of potentiometer one termination, an end ground connection, the bias voltage input of middle adjustable voltage output termination infrared temperature probe makes the infrared temperature probe obtain 2 volts of bias voltages that the left and right sides is suitable by regulator potentiometer.
In the whole flow detection, liquid to be detected flows into from the end that body is wound with electromagnetic induction coil, and the other end flows out.220 volts of alternating currents are directly inputted to analog line driver, analog line driver is at first the alternating current of 50HZ low frequency, rectification is the two ends up and down that 300 volts direct current is added in 4 power MOS pipes of full-bridge inverting main circuit, microprocessor is according to the random function data that prestore, change corresponding pwm signal into, divide the two-way drive signal to go to control the power output of full-bridge main circuit.Data in the random function are big more, and corresponding heating power is big more, and the fluid temperature that flows through the electromagnetic induction heating stainless steel cylinder is high more, otherwise, then low more.The liquid that is loaded with temperature signal is successively popped one's head in through the infrared temperature that two longshore currents are installed to direction, and two infrared temperatures probes change the infrared radiation of the liquid that flows through into the voltage signal output of faint (millivolt level) in real time.The faint voltage signal of two-way carries out analog to digital conversion through the two-way AD that the amplifying circuit of 2000 times of two-way inputs to microprocessor respectively.Microprocessor at first being retained in two arrays from the analog-to-digital value of two-way (temperature), carries out flow rate calculation first behind the result that the data preservation of two arrays is gathered for 100 times.Because the fluid that is the temperature dipping and heaving is successively through two infrared temperature probes, so the array of two storage temperature data has similarity and priority in time.Microprocessor adopts cross correlation algorithm to two arrays, calculates the mistiming of temperature signal in two arrays, just can calculate flow velocity, can further calculate flow according to flow velocity.After finishing calculating first, microprocessor joins the two-way temperature data of gathering in real time respectively the end of two arrays, the top data of deletion array, guaranteeing under the constant situation of array length like this, array is upgraded, and array of every renewal, microprocessor carries out once new correlation computations, thereby provides flow rate in real time.
Description of drawings
Fig. 1 is the structural representation of apparatus of the present invention.
The G body, L1 electromagnetic induction coil, L2 electromagnetic induction heating stainless steel cylinder, S1, S2 infrared temperature probe, H heating power driver, MCU microprocessor controller.
Fig. 2 is apparatus of the present invention heater circuit schematic diagram.
M1, M2, M3, M4 power MOS pipe, K are that the metal-oxide-semiconductor gate pole is opened driver, MCU (TMS320F240) microprocessor controller, A1, A2 operational amplifier, S1, S2 infrared temperature probe, L1 electromagnetic induction coil.
The temperature curve that Fig. 3 obtains from two temp probes for the specific embodiment of the invention.
Transverse axis: acquisition time t (second), the longitudinal axis: temperature value T (degree centigrade), f1: from the temperature curve of S1, f2: from the temperature curve of S2.
Fig. 4 specific embodiment of the invention is carried out the result schematic diagram of correlation computations to two similar temperature curves.
Transverse axis: time t (second), the longitudinal axis: correlation R (N) (no unit).
Fig. 5 the inventive method flow detection calculation process block diagram.
S1[], S2[] ([]: in mathematics, particularly in the relevant course of computing machine, usually array a is expressed as a[], be used for and number a difference): the temperature array of gathering from temp probe S1, S2,
f
T1(n) f
T2(n+N): array S1[], S2[] fragment,
R (N): correlation computations result,
MAX{R (N) }: the maximal value MAX{R (N) that asks correlation results },
T: the temperature sampling cycle, the value of m:R (N) N when getting maximal value,
Tm: the array sequence moves the m time corresponding,
L: the distance between temp probe S1 and S2,
V: the flow velocity of liquid, Q: the flow of liquid.
Fig. 6 is a Jap.P. JP10019621 principle schematic.
R1, R2: the heating and the temperature difference detect resistance.
Embodiment
Below in conjunction with the drawings and the specific embodiments, the invention will be further described.
As shown in Figure 1, the body G of apparatus of the present invention adopts the tubule that hot poor conductor material-organic glass or stupalith are made.The tubule internal diameter is less than 10mm (as diameter 7mm), external diameter 15mm.Electromagnetic induction heating stainless steel cylinder L2 is a thin cylinder made from thin stainless steel material, length 80mm, internal diameter identical with plexi-glass tubular G internal diameter (as 7mm), heating stainless steel cylinder L2 wall thickness is less than 0.5mm (as 0.3mm), and coaxial heart is embedded in the plexi-glass tubular G.Electromagnetic induction coil L1 adopts the fine enamelled wire coiling.The design of heating power should guarantee that when the maximum range of flow measurement the temperature of liquid can reach the temperature rise that is not less than 10 degree, and the temperature fluctuation of liquid is obvious like this, helps microprocessor and calculates flow exactly.1800uL/s calculates by the design maximum flow, and the maximum heating power of electromagnetic induction heating should reach 100 watts.The temperature that liquid is flow through in generalized case control fluctuates to being lower than within 50 degrees centigrade of scopes at normal temperature, can further reduce for the liquid heating-up temperature amplitude that temperature is had specific (special) requirements.On the pipe G wall of distance electromagnetic induction stainless steel cartridge heater L2 certain distance (as 5 centimetres), open one from the large aperture by the with the level through hole of step to the small-bore transition, the center and the conduit axis of through hole intersect vertically, large aperture and infrared temperature probe match, embed infrared temperature probe S1, the small-bore is than infrared temperature probe incidence window bigger (incidence window diameter 2.54mm).In the infrared temperature probe incidence window point tube, infrared temperature probe component outward appearance is a right cylinder, diameter 7-8mm, high 4.5mm, the incidence window at probe top is the infra-red-transmitting glass window with flat transmissive performance (2-23um infrared wavelength), and the infrared-sensitive micro unit is encapsulated in cylinder body-centered portion.Again with the tube wall of the body G of the certain distance of infrared temperature probe S1 certain distance (as 5 centimetres) on, offer the through hole with the level of another same structure, another infrared temperature probe S2 embeds this through hole.Top drilling and the liquid of S1, S2 directly communicate, and make the infrared radiation that sends from fluid directly enter infrared probe from the top.Be adhesively fixed in stepped hole with epoxide-resin glue around the infrared temperature probe.The end of body G dress heating stainless steel cylinder L2 is an inlet, and the other end is a liquid outlet.
Electromagnetic induction heating is based on electromagnetic induction principle: the alternating magnetic field that electromagnetic induction coil L1 produces is coupled by magnetic field, energy is imported into electromagnetic induction heating stainless steel cylinder L2, and electromagnetic induction heating stainless steel cylinder L2 produces vortex current and produces Joule heat under the effect of eddy electric field.
The radius of electromagnetic induction heating stainless steel cylinder L2 is 3.5mm, and the section radius of design electromagnetic induction coil L1 is 4.5mm, and then coupling coefficient (k) is the ratio of sectional area in theory, i.e. k=π * 3.5*3.5/ (π * 4.5*4.5)=0.6.Consider that electromagnetic induction heating stainless steel cylinder L2 has certain thickness (0.3mm), will effectively increase magnetic flux, coupling coefficient is revised as 0.7 from 0.6.
Induction electromotive force that electromagnetic induction heating stainless steel cylinder L2 produces and the voltage relationship of electromagnetic induction coil L1 are: E=V*k*1/N, k is a coupling coefficient, N is the number of turn of electromagnetic induction coil, the number of turn of electromagnetic induction heating stainless steel cylinder is 1, E is an induction electromotive force, and V is the added voltage of electromagnetic induction coil.Stainless resistivity (ρ) is 1 Ω mm
2About/m.Resistance (R) for eddy electric field is ρ * l/s.
R=1* π * 0.007/0.3*80=0.9 * 10
-3Ω is so the power of heating is: P=E
2/ R, promptly
P=(V*k/N)
2/ R, (formula 2)
Design peak power 100W gets P=100W.(V*k/N)
2/ R=100; Get the N=700 circle, V=300V can realize above-mentioned requirements.
In order to choose suitable enameled wire line footpath, need do further calculating to alternating magnetic field frequency and current fluctuation.
Air core solenoid inductance formula is:
(formula 3)
u
0Be the magnetic permeability in the vacuum: 4 π * 10
-7H/m, N: the electromagnetic induction coil number of turn, S: cross-sectional area, l: solenoid length.
Calculate above: N=700, S=π * 4.5*4.5 * 10 in this example
-6m
2, l=80mm;
Above-mentioned parameter substitution formula 3 calculates inductance L=4.9mH, and considering has the stainless steel metal tube in the solenoid, so if the 2-3 of inductance value air core solenoid times.So power taking sense
L＝4.9mH×3＝14.7mH。
Under the effect of alternating magnetic field, the electric current in the electromagnetic induction coil is linear rising and decline, is triangular wave.
Δ l is excessive in real work, can cause copper loss to increase, thus generally limit Δ l/ I＜1, continuous to guarantee electric current.I＝100/300＝0.33A；Δl＝0.3A。I
Max=I+ Δ l=0.63A substitution formula 4:
Calculate Δ T=14.7us; Working method for full-bridge circuit:
So frequency of operation
The maximum current I of electromagnetic induction coil L1
Max=0.63A, amass agreement according to electric current in the engineering and copper section: current density is less than 6A/mm
2Get 5A/mm at this
2, calculate enameled wire line footpath: diameter of phi=0.4mm; On the length of 80mm around 700 circles, need be around 4 layers, inner three layers every layer 200 circle, outermost layer be around 100 circles, the center symmetry.
From top calculating, draw: electromagnetic induction coil L1 supply voltage 300V, current peak 0.63A, 34 kilo hertzs of alternating voltage frequencies, electromagnetic induction coil L1 winding diameter 0.4mm, the number of turn 700 circles, electromagnetic induction coil L1 and the in axial direction long 80mm of electromagnetic induction heating stainless steel cylinder L2, internal diameter are respectively 9 and 7mm.Design maximum average power 100W.From Fig. 1, provided electromagnetic induction coil L1 and electromagnetic induction heating stainless steel cylinder, their same length (about 80mm), electromagnetic induction heating stainless steel cylinder L2 is at body G inwall, and electromagnetic induction coil is around the body G outside of diging up certain wall thickness.Body external diameter 15mm, the internal diameter that electromagnetic induction coil requires is 9mm, digs up the radially step groove of 3mm, axial width 80mm, and electromagnetic induction coil is around in wherein.
Heating is only required that the fluid temperature (F.T.) that flows through behind the stainless steel cartridge heater has fluctuations, for example select for use one section random function value (can be artificially manually to write irregular 50 integers, be stored in the microprocessor that the scopes of number are between 0-100; The random function random () that also can use C language function library tape generates).This 50 number is passed out to (PWM) D/A successively, the output control heating intensity of D/A, each counts 0.5 second retention time, and the fluid temperature that flows through is constantly changed.
As shown in Figure 2, the heating power driving circuit is a bridge circuit.Power driving circuit is made up of rectification and high-frequency inversion two parts.The full-bridge rectification partial circuit is that 4 withstand voltage 300V current capacities that surpass are formed greater than 4 diodes of 0.5A.Diode two two-phases polyphone, and then in parallel, two polyphone branch road middle parts are input, the two ends after the parallel connection are output.Inversion adopts 4 MOS power tube M1, M2, M3, M4 to realize, 4 metal-oxide-semiconductors are connected to full-bridge circuit: metal-oxide-semiconductor two two-phases polyphone, two brachium pontis behind the polyphone are in parallel again, two ends up and down after the parallel connection connect the galvanic both positive and negative polarity of rectification output respectively, draw lead from the middle part of two brachium pontis and connect electromagnetic induction coil.220 volts of alternating currents are directly inputted to analog line driver, analog line driver is at first formed the alternating current of 50HZ low frequency by four diodes rectifier bridge rectification is the two ends up and down that 300 volts direct current is added in 4 power MOS pipes of full-bridge inverting main circuit, about the full-bridge inverting main circuit middle part of two brachium pontis draw lead directly connect body G outward around electromagnetic induction coil L1.The gate pole control signal of 4 power MOS pipes is provided by microprocessor.Microprocessor (MCU) only need be sent the two-way drive signal, and each road drive signal is opened the gate pole that special chip (K) is connected to two metal-oxide-semiconductors in diagonal angle fast by the metal-oxide-semiconductor gate pole.The two path control signal that microprocessor is sent is opposite at level, is one group of M1 and M4 so these four metal-oxide-semiconductors are divided into two groups by the diagonal angle, one group of M2 and M3, and the identical duty of each group gate electrode drive signals is identical; And these two groups of metal-oxide-semiconductors can not be open-minded simultaneously, and promptly M1M4 opens then that M2M3 must end, otherwise, as the same.Open and replace by high frequency for these two groups,, just realized the high-frequency electromagnetic induction heating, realize power adjustments by PWM (width modulation) as 37 kilo hertzs of calculating above.As mentioned above, the value of this PWM is the irregular data that designs according in advance, such as this scope of organizing irregular number is 0-100; Then 100 watts of heating of 100 corresponding electromagnetic induction coil peak power power, 50 corresponding half-power heating.
The right part of Fig. 2 is the connecting circuit figure of infrared temperature probe.The pin of three lines of infrared temperature probe: a pair of and temperature input proportional substantially voltage output pin of infrared radiation (V+, V/-), with a bias voltage adjustment pin (R), infrared temperature probe V+ links to each other with inverting input with the in-phase input end of differential operational amplifier A1, A2 respectively with V/-, and bias voltage pin R connects the output terminal of potentiometer.The positive 5 volts of reference power sources of potentiometer one termination (Verf), an end ground connection, the bias voltage input of middle adjustable voltage output termination infrared temperature probe.Obtain 2 volts of bias voltages that the left and right sides is suitable by regulator potentiometer.The voltage signal of two-way infrared temperature probe output amplifies through connected differential operational amplifier A1, A2, delivers to then to be converted to digital signal in the analog to digital converter of microcontroller MCU and to calculate.The inclined to one side threshold voltage of infrared temperature probe is provided with and regulates is that adjusting by potentiometer provides, and the infrared temperature with 2 volts left and right sides bias voltages is popped one's head in and had better output characteristics.The infrared temperature probe has noncontact, fast, the highly sensitive characteristics of response.As adopt the TP336 infrared temperature probe of roither-laser company, and can use temperature-measuring range-20 to+100 degrees centigrade, time constant 16ms, photosensitive region diameter 0.5mm, 2-22um wave band have the infrared transmission window of flat transmissive performance.The position of infrared temperature probe as shown in Figure 1, S1, S2 are inlaid in the body G wall from the outside, the top of S1, S2 is infrared incidence window, for the incidence window that incides infrared probe that the temperature radiation that makes liquid has no to block, opens the through hole of 2.5 millimeters of diameters in the top stage of probe.With fixedly infrared temperature probe and sealing of epoxide-resin glue.Because the temperature rise and fall maximum of design is 10 degrees centigrade, so the working range of infrared temperature probe is the normal temperature state.Above-mentioned infrared temperature probe when the liquid of measuring 30-50 degree centigrade, export voltage signal probably at 0.1-1mV/, the size of this voltage signal has just characterized the height of temperature.The analog to digital converter changing voltage is preferably in about 2V normally, so need amplify about 2000 times to the direct output of infrared temperature probe, one-level is amplified 40 times of amplifier units in series with 50 times of one-level amplifications and finished 2000 times amplification.Amplify the microcontroller processor is directly linked in the back near 2 volts signal analog to digital converter (ADC).Microprocessor starts chip internal ADC with certain frequency (0.1 second time interval) and carries out analog to digital conversion and read transformation result, and the result is kept among the RAM in the chip, has finished the collection of temperature data.The result who gathers preserves the result of two-way temperature signal correspondence with the form of two arrays, is that the back correlation computations is used, and is respectively two-way temperature T 1 and the T2 that this patent is mentioned from the voltage signal numerical value of infrared temperature probe S1, S2.
For the enforcement of microprocessor related algorithm, if one section fluid temperature that fluid flows through stainless steel cartridge heater L2 after being heated as shown in Figure 3: flow through the curve such as the f1 of the temperature (T1) of temp probe S1, flow through the curve such as the f2 of the temperature (T2) of temp probe S2.Secondly at first f2 should lag behind f1 a period of time (tm) in time, and f2 should exist to a certain extent similar to f1.In order to guarantee second point, requiring pipe G is straight, the pipe of inner wall smooth, and internal diameter is less than 10mm.In order accurately to try to achieve above-mentioned tm with microprocessor, need eliminate fluid to flow to the S2 way from S1, the noise that adds in desirable temperature curve because other factors are disturbed adopts related algorithm at this.To curve f1, f2 gathers certain point number (as the n point) respectively, obtains two array (f of two curve correspondences like this
T1(n), f
T2(n)).Utilize related algorithm: translation curve f backward
T1(n), perhaps translation f forward
T2(n), work as f
T2(n) and f
T1When (n) registration is maximum, the integrated value that obtains (add up and) will be a maximal value.By the pairing sequence f of the maximal value that calculates integration
T2(n) translation figure place, it is poor just can to obtain correct time, the curve of supposing the correlation computations result as shown in Figure 4, integration maximal value time corresponding value tm as can be seen, tm is exactly f
T2(n) lag behind f
T1(n) time.The flow velocity that just obtains liquid divided by mistiming tm with the distance (L) of S1 and S2 (v), and then can obtain flow (Q).
Calculation procedure of the present invention as shown in Figure 5.
(1), (2) step: with microprocessor (TMS320F240) control electromagnetic induction coil L1 heating, the two-way AD of microprocessor carries out data acquisition to two-way temperature signal T1, T2.Suppose that the curve that flows through temp probe S1, S2 temperature (T1, T2) is respectively f1, f2, as shown in Figure 3.The sample frequency of two-way AD is 10Hz, and every sampling interval is 0.1 second, will obtain the array of 100 points so in 10 seconds to two-way temperature S1 (T1), S2 (T2), and note is S1[0:99], S2[0:99].Below the array of adopting is calculated.
(3) step:
Make f
T1(n)=S1[0:49]; f
T2(n+N)=S2[0+N:49+N].
N: be the shift value of array (curve), the span of N is from 0 to 50.
N＝0：f
T2(n+N)＝S2[0:49]；
N＝50：f
T2(n+N)＝S2[50:99]；
(4) step:
Make N=0 to 50, calculate
(5) step: obtain integration summation sequence R (N), the N=m of maximal value correspondence in retrieval R (N) sequence.Draw tm=m * 0.1; Tm: be the retardation time of being asked, the 0.1st, sampling time interval, unit are seconds.Flow velocity v=L/tm; L: be the distance between temp probe S1, the S2.Flow Q=v * s; S: be that pipeline section is long-pending.
(6) step: after finishing collection calculating for the first time, S1, S2 gather next temperature data.
(7) step was added in array S1[0:99 to a new number of gathering respectively], S2[0:99] the end, everybody moves forward successively in the array, two top numbers of array are disallowable.Repeat the aforementioned calculation process once more, calculate flow velocity, flow.The computing velocity of microprocessor (TMS320F240) is very fast, can finish aforementioned calculation in the 1ms, so the aforementioned calculation time can be ignored, can give outflow in real time.
50 random numbers of control heating power can be reused.
Embodiment of the invention temp probe spacing 5cm, the flow range that internal diameter 7mm is fit to measure is 0-1800uL.
The present invention can change measurement range by changing internal diameter size and temp probe S1, S2 spacing and sample frequency.
The course of work of the present invention is as follows.
When flow detection, liquid to be detected flows into from the A end of the body G of apparatus of the present invention, and B holds outflow.Be wound with 700 circle electromagnetic induction coil L1 on the 80mm length outside near the A end the body G, the electromagnetic induction heating stainless steel cylinder L2 that length 80mm thickness 0.3mm is arranged in the corresponding body G, electromagnetic induction coil L1 and electromagnetic induction heating stainless steel cylinder L2 form heating component, 100 watts of power.220 volts of alternating currents are directly inputted to analog line driver H, analog line driver is at first the alternating current of 50HZ low frequency, rectification is 300 volts a direct current, be added in the two ends up and down of 4 power MOS pipes of full-bridge inverting main circuit, microprocessor MCU is according to the random function data that prestore, change corresponding pwm signal into, divide the two-way drive signal to go to control the power output of full-bridge main circuit.Data in the random function are big more, and corresponding heating power is big more, and it is high more to flow through the electromagnetic induction coil fluid temperature, otherwise, then low more.Under the control of microprocessor MCU, heating intensity constantly changes by the random number rule, thereby makes the fluid temperature that flows through in body G dipping and heaving at random, and maximum the fluctuating reaches 10 degrees centigrade.The liquid that is loaded with the temperature fluctuation signal is successively through infrared temperature probe S1 and the S2 of two longshore currents to direction spacing 50mm, and two infrared temperature probe S1 and S2 change the infrared radiation of the liquid that flows through into the voltage signal output of faint (millivolt level) in real time.The weak voltage signal of output is a linear corresponding relation with the temperature of the liquid that flows through basically.The faint voltage signal of two-way carries out analog to digital conversion through the two-way AD that the amplifying circuit of 2000 times of two-way inputs to microprocessor MCU respectively.Microprocessor MCU is constantly being retained in two array S1[from the analog-to-digital temperature value of two-way (T1, T2)], S2[] in, microprocessor MCU adopts cross correlation algorithms to two arrays again, calculates two array S1[], S2[] in the difference on time series of temperature signal.The spacing of two infrared measurement of temperature points (50mm) just calculates flow velocity divided by the time series difference, and flow velocity multiply by the long-pending flow value that promptly obtains of pipeline section.
Claims (6)
1, a kind of flow rate testing methods is characterized in that gathering temperature value T1, T2 that fluid in the constant section duct successively flows through two infrared temperatures probes at regular intervals [S1 and S2], T1 and T2 is carried out cross-correlation calculation, the formula of correlation computations:
R
T1T2(N)=∑ f
T1(n) f
T2(n-N), correlation R (N), f
T1(n), f
T2(n) be a pair of discrete series signal with similar characteristic; The cross-correlation maximum time corresponding off-set value τ that calculates, be that fluid flows through two infrared temperature probe [S1 and S2] needed times, obtain flow speed value with the distance between the infrared temperature probe [S1 and S2] divided by τ, the sectional area that multiply by pipeline with flow speed value obtains flow value.
2, flow rate testing methods according to claim 1, before it is characterized in that detecting, it is preceding to flow through two infrared temperature probes [S1 and S2] at fluid, and first convection cell carries out the heating of grow degree, adds the thermal perturbation signal in fluid.
3, use pick-up unit of the present invention, it is characterized in that mainly comprising body [G], electromagnetic induction coil, electromagnetic induction stainless steel cartridge heater [L2], infrared temperature probe [S1 and S2], heating power driver, microprocessor controller [MCU]; Body [G] is a constant section duct, in axial direction on the tube wall of the body [G] of distance electromagnetic induction stainless steel cartridge heater [L2] certain distance, offer one from the large aperture by the with the level through hole of step to the small-bore transition, the center and the conduit axis of through hole intersect vertically, large aperture and infrared temperature probe [S1] match, infrared temperature probe [S1] embeds wherein, and the small-bore is more bigger than infrared temperature probe incidence window; In the infrared temperature probe incidence window point tube; With the tube wall of the body [G] of infrared temperature probe [S1] certain distance on offer another through hole with the level of same structure, infrared temperature probe [S2] embeds this through hole; The a pair of voltage output pin of infrared temperature probe [S1 and S2] and a pair of input pin of differential operational amplifier link to each other, and the bias voltage pin connects the output terminal of potentiometer.
4, pick-up unit according to claim 3 is characterized in that the tubule of body [G] for making with heat, electric poor conductor material, inner wall smooth; Electromagnetic induction stainless steel cartridge heater [L2] is a thin cylinder made from stainless steel material, barrel bore is identical with body [G] internal diameter, be embedded in the body [G] from body [G] end is coaxial, electromagnetic induction coil on stainless steel cartridge heater [L2] outer tube body [G], single or multiple lift coiling in axial direction; Stainless steel cartridge heater [L2] and external electromagnetic inductive coil same length vertically, basic alignment.
5, pick-up unit according to claim 3 is characterized in that electromagnetic induction coil is operated in the high frequency state; The heating power driver is a bridge circuit, is made up of rectification and high-frequency inversion two parts; The full-bridge rectification partial circuit is made up of 4 diodes, two two-phases polyphone, and then in parallel, two polyphone branch road middle parts are input, the two ends after the parallel connection are output; High-frequency inversion adopts 4 MOS power tubes [M1, M2, M3, M4] to realize, 4 metal-oxide-semiconductors are connected to full-bridge circuit: metal-oxide-semiconductor two two-phases polyphone, two brachium pontis behind the polyphone are in parallel again, two ends up and down after the parallel connection connect the galvanic both positive and negative polarity of rectification output respectively, draw lead from the middle part of two brachium pontis and connect electromagnetic induction coil.
6, pick-up unit according to claim 3, it is characterized in that two infrared temperatures probes [S1 and S2] change the infrared radiation of the liquid that flows through into the voltage signal output of millivolt level in real time, the two-way voltage signal carries out analog to digital conversion through the two-way AD that the amplifying circuit of 2000 times of two-way inputs to microprocessor [MCU] respectively; Microprocessor [MCU] is constantly being retained in two array S1[from the analog-to-digital temperature value of two-way], S2[] in, microprocessor [MCU] is again to two array S1[], S2[] adopt cross correlation algorithm, calculate two array S1[], S2[] in the difference on time series of temperature signal; The spacing of two infrared measurement of temperature points [S1 and S2] calculates flow velocity divided by the time series difference, and flow velocity multiply by the long-pending flow value that promptly draws of pipeline section.
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