CN101949893B - Reduction of temperature influence caused by pressure of sound velocity in gas - Google Patents
Reduction of temperature influence caused by pressure of sound velocity in gas Download PDFInfo
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Abstract
The invention discloses equipment for determining the proportion of gas in a gas mixture, comprising a measuring chamber, an ultrasonic wave source and an ultrasonic wave detector and a temperature sensor. The measuring chamber is provided with a chamber limiting structure containing a high heat conduction material, a gas inlet and a gas outlet, wherein the material is metal; the ultrasonic wave source and the ultrasonic wave detector are mounted to enable the ultrasonic wave source to transmit the ultrasonic wave to the ultrasonic wave detector through the measuring chamber; and the temperature sensor is mounted to enable the sensor to sense the temperature in the measuring chamber, wherein the measuring chamber has a tubular cavity with a radius r0 of 1-8mm so as the make the distance between gas in the measuring chamber and an inner wall of a tube, and the measuring chamber is designed so as to make the gas to be measured to tightly contact a rigid surface of an object with thermal inertia and good heat conduction, thus the heat can free move to a surrounding structure from the gas.
Description
Present patent application is that international filing date is the dividing an application for the application for a patent for invention of " reducing of the temperature impact that the pressure of sound velocity in gas is caused " that on June 17th, 2005, national applications number be 200580050144.7 denomination of invention.
Technical field
Present invention relates in general to the measurement of the velocity of sound in gaseous mixture.More specifically, the present invention relates to ultrasonic detector for example is applied to gas concentration in the environment of leading factor that temperature impact that pressure wherein causes is measuring accuracy or the measurement of gas flow.
Background technology
In some of ultrasound examination used such as the measurement gas potpourri in the concentration or ratio of gas composition, the pressure of gaseous mixture changes has large impact to measuring accuracy.There is well-known relation in the velocity of sound with specific between the parameter of gas, but and based on the current ratio of this relation and velocity of sound measured value Calculation of Gas composition.In addition, sound velocity in gas has strong dependence to temperature, and for correct Calculation of Gas composition, also needs gas is carried out timely and accurate temperature survey.
In medical breathing apparatus, determine accurately that for the dosage of gas composition in the monitoring and controlling gaseous mixture or for the health status that monitors the patient for example the patient sucks or the airborne gas ratio of breathing out is vital.But, when patient respiratory, significant pressure occurs in breathing apparatus change, therefore, according to perfect gas law, gas temperature changes widely.Therefore, in order accurately to determine the ratio of gas componant, usually need to carry out point-device temperature survey, and need closely to carry out on the time temperature survey and acoustic velocity measutement so that they describe the instantaneous physical state of gas.
When measuring temperature in practice, always there is to a certain degree delay in temperature measurement result with respect to true Current Temperatures.The time constant for the temperature sensor of measuring is depended in this delay.Sample frequency and usually very short to compare with temperature measurement result be inapparent and insignificant is depended in delay in ultrasonic sensor.Therefore, measure simultaneously the velocity of sound and temperature and will always cause wrong in a way temperature, the gas concentration that this makes the mistake again and calculates.
Prior art
In the prior art, this measures the method for problem to have different processing.The example that prior art is arranged in following publication, described publication are by reference in conjunction with in this application.
At Nuclear Instruments and Methods in Physics Research A264 (1988) 219-234, North-Holland, in the people's such as the G.Hallewell in Amsterdam technical report A SONAR BASED TECHNIQUE FOR THE RATIOMETRIC DETERMINATION OF BINARY GAS MIXTURES, the background theories of this measurement is arranged.
US 6 202 468 discloses a kind of equipment and method of determining the relative scale of gas in potpourri by measuring magnetic susceptibility and the velocity of sound.
US 4 155 246 discloses a kind of gas analysis system that uses the sound wave skew of tubulose gas column top.
US 4 932 255 discloses the method and apparatus that surface acoustic wave that a kind of use is arranged in the substrate top of air-flow is measured air-flow.Thermally conductive pathways around substrate periphery has reduced thermal gradient.In this piece prior art, the Transmission Design of mating surface sound wave thermally conductive pathways, in order to reduce the thermal gradient that produced by sensor.
US 5 351 522 discloses a kind of gas sensor based on ultrasound examination with L shaped measuring chamber.This piece prior art is for the minimized problem of standing sound wave that makes in measuring chamber.
JP 2,002 257 801 discloses a kind of ultrasonic gas analyte sensors, and the problem on the impact of sound wave that caused by specific gas flow rate and diffusion is avoided in its processing.Measuring chamber with diffusion hole is arranged in the gas passage pipe with gas access and outlet.
The elongated resistive temperature sensor that EP 1 336 841 discloses a kind of ultrasonic propagation district by means of being arranged in the acoustics gasometer is determined the method for the temperature of this gasometer.
US 5 060 506 discloses a kind of binary gas potpourri of measuring such as the method and apparatus for the treatment of with gas ratio in the oxygen/nitrogen potpourri.This gaseous mixture is transmitted through sample hose, and in sample hose, ultrasound wave is advanced with the burst of the continuous impulse under the right resonance frequency of emitter/receiver.Section rest time between burst, thus rest time section the dissipation of length sufficient to guarantee transient state of duration do not form standing wave.The delay that is caused by the transit time of gaseous sample by sound produces the electric pulse that is converted into simulating signal, and then simulating signal is by temperature correction.Gained voltage and transit time are proportional, and therefore proportional with gas composition.Sample hose be housed inside than within large cylinder to strengthen air-flow and heat insulation be provided, heat insulation is intended to improve the precision of temperature compensation.
US 4 938 066 discloses a kind of method and apparatus of processing the problem of length expansion in sonic transducer, the ultrasonic transducer of this sonic transducer emission acoustic impluse, acoustic impluse is from the nearly surface reflection of invar (invar) bar and from the second surface reflection of this invar bar far-end.Be used to calculate the velocity of sound from the mistiming between the detection of the reflected impulse of respective surfaces and the known length of this bar.
US 6 481 288 discloses a kind of method and apparatus that adopts spherical measurement chamber to measure the velocity of sound.
Goal of the invention
Overall purpose of the present invention and the problem that will solve be in the gaseous mixture that further improves in the environment of leading factor that temperature impact that pressure wherein causes is measuring accuracy based on the measurement mechanism of sound speed detection and the precision of method.
Especially there is the following aspect of this purpose and this problem:
-reduce the pressure variation to the impact of the temperature of the part of the current gaseous mixture that stands to measure.
-the suitable acoustic pattern of the ultrasonic transmitter in measurement mechanism is provided.
-reduce the impact of the thermal expansion of the material in measurement mechanism.
-determine the gas concentration in gaseous mixture.
-determine the flow rate in air-flow.
Summary of the invention
According to the present invention, the realization of this solution of problem and this purpose is to complete by the temperature variation of the part of the current gas that stands to measure of balance or gaseous mixture and the temperature variation that suppresses thus gas.In other words, the present invention offsets by the thermograde in the sensor device that makes measured entity (being the measuring object of gaseous mixture form) and cause and becomes to putting down this problem that solves.
Described in background, gas temperature changes rapidly at the pressure During, and this is during for example the typical case in medical breathing apparatus uses in the present invention, occur in piping system relatively with patient's suction or the ventilation of breathing out.There is following process in the temperature variation of gas: make the temperature variation of gas become to putting down or balance towards medial temperature by the heat interchange between ambient substance and gas.
The present invention is based on the inventor to the understanding of the following fact: the speed of the flat process that becomes can be increased to a degree, makes the impact that changes the thermograde that causes by pressure in gas be minimized, and even can ignore.According to the present invention, the acoustics gasmetry is designed so that thus that heat interchange is exaggerated and the speed of the flat process that becomes is complementary with pre-provisioning request to the balanced time lag of temperature variation in gas.This and prior art form contrast, and in the prior art, for example measuring speed is increased or unexpected temperature variation is compensated in calculating in order to processes the measurement problem that the temperature variation by the pressure initiation causes.In the present invention, measuring chamber itself is customized to and reduces or even eliminate these measurement problems.
According to the present invention, amplify heat interchange by making the rigid surperficial close contact with material good heat conductive measured gas and thermal inertia, make heat to be free to travel to surrounding structure from gas.In an enforcement of concept of the present invention, the present invention is by providing following measuring chamber to realize: this measuring chamber is designed to be suitable for amplifying the current part of the gas in this chamber and the structure of the heat interchange between the limiting structure of chamber of being present in.The technique effect of this scheme is: when the fast energy pulse that produces with the pressure version is introduced in the system of pipeline and institute's connection device, measuring chamber will serve as the low-pass filter of energy pulse, and the material in measuring chamber will show near the little variation medial temperature.Because the heat interchange between chamber matter and gas is exaggerated, so like this gas also will be low pass filtering, and temperature variation will become flat very soon, and consequently temperature variation becomes and can ignore in the case.
Preferably, the chamber limiting structure is suitable for providing heat interchange, makes temperature variation be balanced to the interior predeterminated level of predetermined time lag.This time lag for example is defined as the time constant of the heat interchange of chamber limiting structure.The chamber limiting structure for example is suitable for providing required heat exchanger effectiveness according to the predetermined maximum error of gas concentration.This is implemented as the method that measurement mechanism is customized in concept of the present invention.
In fact the become speed of flat process of temperature variation depend on some parameters, such as the thermal conductivity of gas, the geometric distance from gas atom to the ambient substance surface, thermal inertia and the thermal conductivity of ambient substance.Found that geometric distance and thermal conductivity are about dominant parameters of the present invention.
According to a first aspect of the invention, equalized temperature is realized by designing such measuring chamber: the shape of this measuring chamber lumen is relevant to the properties of materials that limits the chamber.According in this respect, the characteristic about the gaseous mixture that will use in application-specific of the present invention is custom made with the chamber limiting structure combination of shape, size and material.Preferably, this customization is designed to: about the characteristic of gaseous mixture and the combination of the shape of measuring chamber, size and material in State selective measurements equipment, the predetermined maximum that makes the time lag of the heat interchange between gaseous mixture and measuring equipment be less than or equal to (≤) heat interchange can allow time lag.But the maximum of heat interchange can allow gas in value that time lag preferably changes according to the occurrence temperature of gaseous mixture and gaseous mixture the maximum permissible error of definite ratio calculate.In one embodiment, maximum can allow time lag also to calculate according to being applied to from the time lag of the traffic filter on the signal of the ultrasonic detector in measurement mechanism.
According to second aspect, by being arranged on, ultrasonic transducer make the impact that transmitter expands be eliminated in measuring chamber, reduced the impact that in the measurement mechanism, material expands.
According to the third aspect, by means of the sealing of the acoustic damping between the effective surface of the end face that is placed on the measuring chamber opening and transmitter (dampening seal) member, reduced to originate from the structure-borne sound (structure borne sound) of ultrasonic transducer.The sealing member is preferably made with silicon rubber.
According to a forth aspect of the invention, by allowing ultrasound wave in resilience between the transmitter surface and detect n echo, improved wherein between ultrasonic transducer the resolution apart from the measurement in short small size measuring chamber.The longer distance thereby ultrasonic pulse is advanced.
According to a fifth aspect of the invention, designed hyperacoustic pattern of the gas that is transmitted through in measuring chamber, in order to reduce transient state and cause harmonious temporary steady-state process.This is by the row burst of repetition transmitted and each is listed as to realize since 1/4 recurrence interval.This makes the frequency that is applied to transmitter be not equal to the resonance frequency of transmitter on mathematical meaning.
Other side of the present invention is explained in the detailed description of embodiment.
The invention advantage
Except above-mentioned technique effect and advantage, the present invention also brings following technique effect and advantage.
The simple temperature sensor that has than large time constant can use in measurement mechanism, and this is because the speed of temperature variation is reduced by the equalized temperature effect.
Measurement mechanism of the present invention is to the alternative technical scheme based on a kind of more environmental protection of the sensor of carbon burning battery (fuel cell, electrochemical cell).Sensor based on the carbon burning battery must annually be changed once, and produces quite a large amount of scrap leads.
In addition, the present invention has realized a kind of alternative scheme of the paramagnetism sensor of costliness but also mechanical sensitivity not only.
Explaination and explanation
In this article, use term " balance " and synonymous expression to describe exchange heat energy as " equilibrium ", " becoming flat " etc. so that the action of the thermograde in the measured part of inhibition gas.
Gas and gaseous mixture are the expression of describing measured gas entity.The so-called binary gas that typical gas mixture during the medical treatment breathing apparatus is used is comprised of normal air mixture and certain other gas such as oxygen or nitrogen.
The present invention relates to determine and monitor the concentration of gas composition in gaseous mixture.But this there are various alternatives express, such as gas ratio, gas relative scale, gas componant etc.
In being used for determining the method for binary gas potpourri (i.e. the potpourri of two kinds of gases) gas ratio, can use following well-known relation.The velocity of sound in gaseous mixture can be described according to following equation:
The c=velocity of sound [m/s] wherein
Cp=constant pressure specific heat [kJ/kgK]
Cv=constant volume specific heat [kJ/kgK]
Rm=gas law constant 8314.5[J/kmolK]
T=temperature [K]
The M=molecular weight
And wherein the cp of gas, cv and M (molecular weight) have replaced to the respective value of the potpourri of taking from the gas in the physical characteristics gas meter.The amount cp that replaces
*, c
v* and M
*The ratio that depends on gas.The current concentration of one of gas can be by finding the solution M in known mode own
*Equation calculate.
Time constant normally makes the instrument indication produce from the required time of given number percent of the final reading of input signal, the i.e. relaxation time of instrument.Under such as the instrument of the thermometer situation of (it is indicial response to response that the step of applying signal changes), time constant equals to make total 63.2% (namely when transient error is reduced to the 1/e of original signal variation) required time that changes of this instrument indication.Also be called lag coefficient.[source: the online dictionary of Webster].In the present invention, time lag can for example be defined as time constant.In the description of the embodiment of the present invention, be illustrated as measuring chamber according to this and defined time constant tau.
Description of drawings
Further explain the present invention with reference to accompanying drawing, in the accompanying drawings:
Fig. 1 shows the schematic diagram according to the measuring system of the embodiment of the present invention.
Fig. 2 shows the embodiment of the present invention that solid structure flanges is arranged in the ensonified zone of measuring chamber wherein.
Fig. 3 shows the embodiment of the present invention that porous structure is arranged in the ensonified zone of measuring chamber wherein.
Fig. 4 shows the exploded view according to the measurement mechanism assembly of the embodiment of the present invention.
Fig. 5 shows the xsect of the measurement mechanism assembly in the embodiment of Fig. 4.
Fig. 6 shows the skeleton view of measurement chamber pipe, and
Fig. 7 shows the cross-sectional side view according to the embodiment of Fig. 5.
Fig. 8 shows the sketch map of the embodiment with balance upstream gas channel part.
Fig. 9 schematically shows the mode that according to an aspect of the present invention transmitter is installed to measuring chamber;
Figure 10 A-D illustrates the mode of n the echo that detects ultrasonic pulse; And
Figure 11 A-D illustrates the mode of stimulated emission transmitter according to an aspect of the present invention;
Figure 12 shows the curve map of the temperature disturbance that is caused by the pressure transient of introducing; And
Figure 13 shows the curve map that reduces that disturbs in the relative temperature of drawing on the normalized time with the time constant.
Embodiment
Measuring chamber
In a preferred embodiment, the present invention is by means of realizing for the measuring chamber that temporarily holds the gas that will measure.Preferably, this chamber is installed into and makes air-flow measure intermittently sampling by this chamber and on the gas that flows.Functional requirement to measuring chamber is that chamber restriction material should serve as thermal buffer and with gas molecule, efficient heat interchange be arranged.The heat exchanger effectiveness of realizing is higher, and the speed of equalized temperature process increases manyly, and effect of the present invention is better.
Fig. 1 schematically shows according to measurement mechanism 1 of the present invention.The measuring chamber 2 that is limited by chamber limiting structure 5 has chamber 4, and chamber 4 has wherein that ultrasound wave propagates into the space of the gas of ultrasonic receiver from ultrasonic transmitter.In the embodiment in figure 1, ultrasound wave is propagated between two the first and second ultrasonic transducer 6A, 6B with transmitter and receiver function that relatively install in known mode own.This chamber is provided with gas access 8 and gas vent 10, and gas access 8 and gas vent 10 are designed to make gas from the chamber 4 of air flow path 12 by measuring chamber 2.Temperature sensor 14 is designed to detect the temperature of gas in this chamber.Temperature must be measured in suitable district (being the district that sound transmission passes through).This can be for example by means of comprising that the temperature sensor that is tightened up and passes the thin platinum line of measurement zone realizes.But alternative scheme is sensing and sound measurement district, some temperature at place of known relation and the temperature in Calculation of Gas are arranged.Preferably, should select to have the temperature sensor of as far as possible little time constant.This exemplary platinum temperature sensor has little time constant and is to realize suitable selection of the present invention.Yet the present invention has following effect: make temperature variation become flat by means of efficient temperature exchange, make temperature variation be low pass filtering and therefore can use the simple temperature sensor that has than large time constant.Currently preferred embodiments are provided with standard NTC type thermistor (NTC=negative temperature coefficient).
Also there is the block diagram according to the electronic control circuit of an embodiment in Fig. 1.Central processing unit CPU 16 is provided with the program code that aims at the present invention's customization, and is coupled to temperature sensor 14 via temperature signal input end 18 and temperature signal amplifier 20.The first ultrasonic transducer 6A is coupled to the input end 24 of timer level 26 via ultrasonic receiver signal amplifier 22.The second ultrasonic transducer 6B drives via ultrasonic transmitter the output 28 that signal amplifier 30 is coupled to timer level 26.Timer is grade coupled to be realized to CPU (central processing unit) 16 or by means of CPU (central processing unit) 16, and has following function: deposit and compare from the time of arrival of the detector signal that receives ultrasonic transducer 6A, the mistiming between signal and the output time that is used for the driving signal of stimulated emission ultrasonic transducer 6B.Digital-to-analog (D/A) converter 36 is coupled to CPU (central processing unit), so that export for example measurement result or generation alarm signal on display.Signal from ultrasonic transducer 6A, 6B also is transmitted through or is applied in unshowned traffic filter, and this traffic filter has the common specific time lag that reaches with the time constant table.CPU (central processing unit) 16 further is coupled to I
2C bus 32 is so that be communicated with other circuit block.Power supply 34 is coupled to described parts on demand.This sensor device is operating as thus and sends ultrasonic pulse by the gaseous mixture (for example potpourri of air and oxygen) in this chamber, and measures the travel-time of this pulse.The measured time is corresponding to the timer value in processor (for example several 4534).In conjunction with measured gas temperature, according to pre-programmed concern Calculation of Gas concentration, and with for example corresponding to 21%-100% oxygen O
2The form of aanalogvoltage produce output signal.
The chamber 4 of chamber 2 is limited and is defined by physical cell limiting structure 5, and physical cell limiting structure 5 designs with suitable shape and suitable material and has and the contacted surface of air-flow of passing through this chamber.
The thermal conductivity of this structure is determined rate of heat exchange, and depends on physical size, shape and the properties of materials of this structure.Thermal conductivity in International System of Units with watt every meter Kelvin (Wm
-1K
-1) tolerance, the thermal conductivity of each material can be learnt from table.For shape and physical size, thermal conductivity for example with indirect method such as independent parameter being carried out modeling and experiment measuring is estimated.The material of this structure should have high heat conductance thus, and preferably such as thermal conductivity is 236Wm
-1K
-1Aluminium or thermal conductivity be about 50Wm
-1K
-1The metal of steel.Also can consider other material, for example be added with the heat-conducting plastic of metal fragment (chip).The weight of hot padded coaming should be about weight, volume and the molecular density of gas componant in other design parameter and this chamber and is selected, and it is enough making heat exchanger effectiveness.According to the present invention, should adopt available design parameter, so that the chamber limiting structure is suitable for providing heat interchange, make the temperature variation of gas be balanced to the interior predeterminated level of predetermined time lag.In the case, the tolerance that the time constant of the heat interchange of time lag or chamber limiting structure is defined as to the heat exchanger effectiveness of this chamber is useful.
Concept of the present invention comprises the method that measuring equipment is customized according to of the present invention.The method is indirectly on following meaning: the parameter that it approaches to customize according to the expectation quality of measurement result, and return to seek requirement to the parameter that is used for customizing.
Therefore, but determined gas in the gaseous mixture the maximum permissible error of definite ratio.But should permissible error depend on application, its in the present invention in the application in breathing apparatus for example at definite oxygen concentration (O
2In the scope of 5% error concentration).Estimated the value of the maximum generation pressure variation of gaseous mixture.In this exemplary application, the maximum pressure variation that occurs is as at 50cmH
2In the scope of O.In patient's actual ventilation, modal pressure changes at 25-30cmH
2In the scope of O.Yet for example, when the patient coughed, pressure changed and can reach up to about 100cmH
2The extreme value of O.
Estimate the calculating of value by means of the institute that changes according to the generation pressure of gaseous mixture, estimate the value of the maximum occurrence temperature variation of gaseous mixture.In order to carry out this estimation, determine the model of conduction process, and be the equation of the item of the work done during compression that comprises that pressure that expression changes is done with this model tormulation.In an exemplary embodiment, this equation is expressed as:
Wherein T is temperature, and p is pressure, and ρ is density, and Cp is constant pressure specific heat, and λ is thermal conductivity.Following mechanics and thermal parameters value are applicable to the air of 25 ℃:
| Parameter | Value |
| ρ | 1.18[kg/m 3] |
| C p | 1000[J/kgK] |
| λ | 0.024[W/mK] |
Table 1
In this model example, density p is near steady state value, and this is because the less pressure, temperature variation of research.Now at the pressure transient Δ p=5000[Pa without any heat transmission term and introducing]=50cmH
2In the situation of O, solving equation 2, obtain being plotted in the value in the curve map of Figure 12.This is corresponding to infinitely-great measuring chamber size or thermal conductivity λ=0.In Figure 12, the interference of temperature variation is plotted as the function of time, wherein time value on transverse axis, take degree centigrade as the temperature disturbance value of unit on vertical axes.As shown in curve map, Δ p=5000[Pa]=50cmH
2The input pressure transient state of O is brought approximately the very fast-descending of the temperature of 4 degrees centigrade.
Therefore, in this example, 50cmH
2The pressure of O reduce to cause 4 degrees centigrade (℃) temperature variation that reduces this form in scope.But so in the value that can change according to the occurrence temperature of gaseous mixture and gaseous mixture gas the maximum permissible error of definite ratio, come the maximum of the heat interchange between Calculation of Gas potpourri and measuring equipment can allow time lag.In the present example, the maximum that is expressed as time constant of the heat interchange between gaseous mixture and measuring equipment can allow time lag to be about 0.050 second.For these requirements, measuring equipment is customized to the maximum of calculating that the time lag that makes the heat interchange between gaseous mixture and measuring equipment is less than or equal to (≤) heat interchange can allow time lag.
Use the basic result of the method that is used for customization, the method also comprises the steps: about the characteristic of gaseous mixture and the combination of the shape of measuring chamber, size and material in State selective measurements equipment, and the maximum of calculating that makes the time lag of the heat interchange between gaseous mixture and measuring equipment be less than or equal to (≤) heat interchange can allow time lag.
In embodiments of the present invention, it is usually favourable traffic filter being applied to from the time lag (preferably time constant) of on the signal of ultrasonic detector and also considering wave filter when measuring equipment is customized.Therefore, an embodiment of the method also comprises the steps: according to the pre-provisioning request to response time of measuring equipment, selects to be applied to the time lag from the traffic filter on the signal of the ultrasonic detector in measuring equipment.Therefore, this embodiment comprises: also come the maximum of the heat interchange between Calculation of Gas potpourri and measuring equipment can allow time lag according to being applied to from the time lag of the traffic filter on the signal of the ultrasonic detector in measuring equipment.
In the embodiment of the time lag of also considering traffic filter, the maximum of the heat interchange between Calculation of Gas potpourri and measuring equipment can allow time lag to comprise the following steps:
The value that changes according to the occurrence temperature of gaseous mixture come gas in the Calculation of Gas potpourri the value of generation error of definite ratio;
Calculating changes by pressure the maximum that causes and can allow detected temperatures to change;
Determine that the maximum occurrence temperature that is changed the gaseous mixture that causes by pressure changes and the maximum relation that can allow between the detected temperatures variation;
Determine the time lag of the heat interchange between gaseous mixture and measuring equipment and be applied to from the relation between the time lag of the traffic filter on the signal of the ultrasonic detector in measuring equipment;
Determine the relation between described temperature relation and described time lag relation; And
Come the maximum of the heat interchange between Calculation of Gas potpourri and measuring equipment can allow time lag according to the described relation between described temperature relation and described time lag relation.
As mentioned above, be time constant to the preferred measure of time lag, namely reach 63.2% required time of total heat interchange according to definition.
After having determined the requirement to the heat exchange characteristics of measuring equipment, concept of the present invention comprises the distinct methods of realizing enough heat exchanger effectiveness.
In one embodiment, realize required rate of heat exchange by the surface and the distance between gas molecule that reduce about other design parameter or minimize the material that limits the chamber.More specifically, be in the chamber gas or by the gas in chamber around material.In the variant of this embodiment, the surface area of hot padded coaming is exaggerated in the ensonified zone of chamber.
For example, as shown in the embodiment of Fig. 2, measuring chamber 2 can be provided with the flange 38 of the hot padded coaming that is arranged in ensonified zone.Preferably, between transmitter 6A, 6B, be parallel to direction of sound propagation 40 and mounting flange 38, in order to avoid reduce acoustic pressure.Similarly, the primary air direction 42 by measuring chamber should be parallel to flange, in order to avoid disturb the flow rate by this chamber.Therefore in Fig. 2, airflow direction 42 is in paper, and perpendicular to direction of sound propagation 40.To be provided with thickness approximately 1 millimeter (mm) and interrupted inner distance approximately the experiment test that carries out of the measuring chamber of the steel flange of 2 millimeters (mm) show: the temperature variation in ventilator work is balanced to the insignificant degree of temp-related effect.Do not need to measure and compensates, only need to measure relatively lentamente basic gas temperature, in order to obtain the precise results that gas concentration is calculated.
In another exemplary embodiment shown in Figure 3, chamber 2 is provided with the porous structure 44 of solid material in its ensonified zone, and as velvet or spongy structure, it is for example made by steel or certain other metal or similar Heat Conduction Material.Gas flow is crossed and around porous structure 44, has been realized thus the small distance from the gas molecule to the body structure surface.This porous structure should be arranged so that ultrasound wave without any remarkable interference and advance by this porous structure with little flow resistance.
In the 3rd exemplary embodiment, chamber is shaped as the pipe of minor diameter, and this has caused from the chamber gas molecule to the small distance of inside pipe wall.Preferably, the inner tube shape is cylindrical shape, but also can consider other xsect.In the actual enforcement of this embodiment, a part of air-flow is diverted measuring chamber from primary air, so that heat cushions and measure suitable gas volume.This concept is applied to the currently preferred embodiment of the present invention shown in Fig. 4-7.Determined model in order to seek the suitable parameters of tubular chamber.The relative level to the interference of measuring accuracy that this model causes based on the temperature variation that caused by pressure transient of research.Suppose that relative temperature interference level T (r, t) is index according to following equation and reduces:
Wherein r0 is the inside radius of cylinder, and r is the radius in space (being pipe-type combustion chamber) in cylinder, g (r/r
0) be the Temperature Distribution in the space in cylinder, τ is time constant.
Timeconstantτ is
Wherein ρ is density, and Cp is constant pressure specific heat, and λ is thermal conductivity, and they have the value described in top table 1.
Curve map in Figure 13 shows the example of this relation of form of the curve that reduces that disturbs in the relative temperature of drawing on the normalized time with the time constant.After 1 time constant, interference level has been reduced to approximately 36% of initial level.
In the situation that use in Modeling Calculation these equations show different pipe radius r 0 (millimeter) and with do not compare according to the nominal level of any equalized temperature of the present invention the relation between timeconstantτ (tau) [s] relative temperature interference level afterwards that causes due to the pressure variation.In following table, after the pressure transient of introducing respectively at two time point t=0.01[s] and t=0.1[s] list these parameters.For example, it is the free constant tau=0.0765 of pipe of 3.0mm that radius has been shown in this table, and has 0.877 relative temperature interference level after 0.01 second, has 0.271 relative temperature interference level after 0.1 second.
Table 2
Can find out, for 50%O
2And 50%N
2Gaseous mixture, determine O2 concentration error be that every degree celsius temperature changes approximately 2.5% unit.Therefore, radius be 3.0mm and after 0.01 second relatively interference level be in 0.877 previous example, determine that the error of O2 concentration is Δ XO2=2.5 * 0.877 ≈ 2.2%.
At the O of the present invention at breathing apparatus
2In application in sensor, must take into account extreme value up to about 100cmH in customization procedure
2The pressure of O changes.This will produce in the mode identical with above-mentioned calculating up to the about temperature variation of 8 degrees centigrade, and this is again by calculating 2,5[O
2The percentage unit error of concentration/degree celsius temperature changes] * 8[degree centigrade] produce the O that the temperature variation that causes due to pressure causes
2Up to the about error interference of 20 percentage units.By means of signal filtering, this interference can be reduced to approximately 3% more tolerable level.That is, wave filter should be reduced to error and reduce the sub-fraction that the factor is 3%/20%=0.15.Traffic filter is applied on signal from ultrasonic sensor thus.Traffic filter is about originating from O
2The signal of the real change of concentration and limit the speed of ultrasonic sensor.For large filter time constant τ f, the temperature variation that pressure causes is to O
2Concentration as influencing factor is less.For this configuration, therefore the error through measuring O2 concentration is subject to the impact of the thermal time constant τ of measuring chamber on the one hand, is subject on the other hand the impact of traffic filter timeconstantτ f.Above use has, the concise and to the point traffic filter of describing and being applicable to is determined the more detailed version of method for customizing of the required size of measuring chamber, can determine traffic filter timeconstantτ f, measuring chamber timeconstantτ and with wave filter reduce maximum interference degree reduce the factor corresponding reduce relation between factor η.Concern (not shown in detail) according to this, can determine in this example for reducing the factor 0,15, the timeconstantτ f of the timeconstantτ of measuring chamber≤0.235 * traffic filter.In fact, concern τ≤0.235 * τ f for example as description disturbance reduce the factor and time constant than between funtcional relationship be a bit being found on the curve map of η (τ f/ τ).Be the slow wave filter of 20 seconds for time constant, the maximum time constant of measuring chamber will be 0.235 * 20=4.7 second.Calculating is as the interior diameter of the metal tube of decisive customized parameter and suppose that gaseous mixture is air, and resulting requirement is that maximum inner diameter is 47 millimeters.
Need to consider different design factors and parameter when execution is of the present invention, so that according to the invention provides the enough heat exchange effects of efficient.In an embodiment of concept of the present invention, selected structural design is customized about for example diameter, wall thickness, weight or thermal conductivity by means of following method.The pressure that measurement may occur in application-specific of the present invention changes, and wherein pays special attention to be not suitable for the situation of pressure.Carry out the emulation that one or more selected design parameters bear results to for example time constant and temperature interference level, and definite maximum temperature interference level.Temperature deviation or temperature interference level are converted into the error of gained Calculation of Gas concentration or gas flow.But the maximum permissible error that is expressed as alternatively thus deviation or interference level is scheduled to for gained measure gas concentrations level, for example maximum 3% error of O2 concentration.After this, calculate selected design parameter according to predetermined maximum gas concentration error, for example the diameter of pipe.If for example required thermal conductivity is the selected design parameter that will customize, also carry out corresponding calculating according to for example predetermined pipe diameter.This concept is similar with the modeling example that provides above.
Fig. 4 shows the exploded view of the critical piece of the embodiments of the invention of realizing as the measurement mechanism assembly, and this measurement mechanism assembly comprises sensor shell 46 with sightless measuring chamber in Fig. 4, has the circuit board 48 of the connector that is connected to outside wiring and be designed to covering sensor shell 46 and the over cap 50 of circuit board 48.Sensor shell 46 is designed to be arranged on main gas flow pipe 52, thereby covers primary air and partly insert in primary air via the opening 54 in gas flow tube 52.The part of air-flow is imported in the measuring chamber of sensor shell 46 thus.
Fig. 5 shows the xsect that is arranged on the measurement mechanism assembly on main gas flow pipe 52 according to Fig. 4.Sensor shell 46 is provided with lip member 56, and this lip member is projected in main gas flow pipe 52 and with gas and is directed to measuring chamber 2.Measuring chamber 2 is spatially limited by cylindrical duct 58, and cylindrical duct 58 comprises the respect to one another elongated entrance and exit 60 that is used for gas that the valve jacket (mantle) along cylinder is located.The elongated shape of design entry and outlet is so that the impact of the ultrasonic propagation pattern that can occur relatively with the unexpected regional change of air-flow minimizes.More specifically, reduce or even avoided the acoustic impluse resilience at regional change place, thereby can avoid the destructive interference to the sound transmission pattern that caused by such acoustic impluse resilience.At work, gas flows into and the outflow tube chamber along lip member and via entrance and exit 60.In Fig. 5, only an entrance and exit as seen.Ultrasonic transducer 6A, 6B are positioned at each end opening place of this pipe, make the effective surface of transmitter cover this pipe at the end opening of each respective end.Packing ring 62 with damping sealing member function seals the leakage between the effective surface of the chamber of preventing pipe 58 and transmitter.Between O shape circle 64 chamber of being sealed in pipes 58 and sensor shell 46, and neck shape sealer 66 is sealed between sensor shell 46 and main gas flow pipe 52.Elasticity shackle (shackle) sheet 68 in each side with transmitter 6A, the 6B chamber of being fixed to pipe 58.Can know from Fig. 5 and see, the most of parts in sensor shell occur in pairs, around the symmetric mode chamber of being arranged on pipe 58.Circuit board 48 is placed on the top of sensor shell 46, and is last, and the protected lid 50 of assembly covers.
Fig. 6 and Fig. 7 have been shown in further detail chamber pipe 58.Chamber pipe 58 at one end is provided with flange 82, and when pipe 58 was arranged in sensor shell, flange 82 had the position hold function.Each end at pipe 58 is useful on the recess 84 that holds seal with O ring spare 64 (with reference to Fig. 5).Elongated entrance and exit 60 is as mentioned above along the valve jacket setting of managing 58.Preferably about temperature variation and signal to noise ratio (S/N ratio) and optimize the size of chamber pipe.This exemplary embodiment is for the suction passage of such breathing apparatus and design, and it is that the representative gases flow rate of 0-200 liter/min of clock, exemplary operation gas temperature and the scope that scope is 15-50 ℃ are 0-140cmH that this breathing apparatus has by the scope in the primary air of this suction passage
2The typical pressure of O changes.This embodiment of chamber pipe preferably has interior diameter in the 9mm scope and the overall diameter in the 12mm scope, thereby has caused between the material thickness of approximately 3mm of locular wall major part and gas molecule and inside surface the approximately ultimate range of 4.5mm.This material is to have 50Wm
-1K
-1The stainless steel of the thermal conductivity in scope.In being applied to the embodiment of the present invention of air-flow larger environment for the measuring chamber cavity volume wherein, preferably provide for concept is used for the equilibrium temperature gradient and the upstream gas channel part that designs according to the present invention.The exchange velocity of having eliminated thus gas part in the chamber surpasses the risk of the speed of equalized temperature in the chamber.Such upstream gas channel part preferably utilizes cross sectional dimensions less Heat Conduction Material for the primary air size to design thus.Fig. 8 shows the sketch map of this embodiment, and wherein equalized temperature channel part 90 is positioned at the upstream of measuring chamber 4 and is designed to make its temperature T 0 to become flat before inflow gas enters measuring chamber.In the embodiment of the Fig. 5 that explains in the above, lip member 56 consists of such equalized temperature channel part together with surrounding structure.
The problem of processing on the other hand the measuring chamber expansion according to sonic transducer of the present invention.Measure velocity of sound c by means of sonic transducer and be based on and measure the acoustic impluse required time t of known distance s that advances, and calculate c=s/t and carry out.Therefore need to carry out accurate and stable measurement to measuring distance.For example, when coming measure gas concentrations by the sound speed detection in the gaseous mixture of air and oxygen, on the measuring distance of 18mm, 10 microns variations of measuring distance have caused approximately 1% error of oxygen concentration unit.The expansion of measuring distance can occur because the pressure in the chamber or thermal expansion transmitter and measuring chamber changes.
Thermal expansion occur in the enclosed construction of chamber and ultrasonic transducer self in.According to the present invention, the material that is used for the chamber enclosed construction is processed by the material of selecting to have alap linear temperature expansion coefficient about other design parameter.For example, have 22.2 (m/m.K * 10
-6) thermal linear expansion coefficient aluminium or have 13.0 (m/m.K * 10
-6) steel can be used for the chamber.
Ultrasonic transducer comprises the layer of different materials, effective ultrasound wave emitting surface, damping material layer and the silicone rubber layer on adaptation material wherein, and they all are arranged on and are generally used for leaning on the edge of recess and install on the flange of transmitter.All these layers all expand or shrink according to environment or temperature variation gas or because ultrasound wave produces, and cause measuring error thus.According to the present invention, and as shown in the schematic diagram of Fig. 9, this effect makes the effective surface 94 of corresponding transmitter 6A/6B cover tubular chamber 4 by transmitter is installed end opening is eliminated.Can ignore the change in size of the material that consists of transmitter thus, this is because the position of effective surface keeps constant.Effective surface 94 leans on the thin acoustic damping seal of packing ring 62 forms between the end xsect of locular wall 97.Damping seal packing ring 62 preferably by for example approximately the silicone rubber of 0.7 millimeters thick make.Damping sealing member packing ring 62 is processed a fourth aspect of the present invention, namely eliminates structure-borne sound.Because its thickness is little, silicone seal has the insignificant length expansion that is caused by pressure and temperature.
In addition, transmitter is equipped with elastic device 102, and elastic device 102 is pressed in transmitter on damping seal packing ring 62.In Fig. 9, with explaining, this elastic device is fixed on shackle or is with on 104, shackle or be with 104 fastening by rigidity with respect to cell structure.In the embodiment shown in fig. 6, shackle sheet 68 self is presented as elastic device.This elastic device should be designed to surpass the elastic force of the maximum pressure pulse produce in measuring chamber, and eliminates thus the expansion of pressure correlation of measuring distance and the displacement of transmitter.
The advantage of this embodiment is that it has realized the small size measuring chamber.Small size has been simplified the temperature survey that interrelates with gas concentration measurement, and this is because little ensonified zone has caused more uniform gas temperature.This has realized again can be on one point rather than measurement gas temperature in whole district.Can use this concept as illustrated in the embodiment of the present invention, perhaps combine with other configuration of ultrasonic transducer and use independently this concept.
The other method that the process chamber material expands is measuring chamber to be designed to spherical, makes the thermal expansion of chamber closure equate in all directions.The shortcoming of this embodiment is that spheroid is to provide the geometric configuration about the minimum possibility surface area of this volume.Therefore this embodiment is provided preferably with extra hot padded coaming, so that enough heat interchange efficiently of the gas componant of realization and chamber.This can for example realize by means of the porous structure in chamber, flange or thicker locular wall.
Another aspect of the present invention relates to following problem: in the situation that short measuring distances is still realized gratifying ultrasonic measurement resolution.According to the present invention, this by allow acoustic impluse before traveling time is read out transmitter between resilience solve.Detection and timing to the reflected signal of the longer distance of having advanced have been realized thus.Figure 10 A-10D illustrates the present invention.Figure 10 A illustrates emission ultrasonic transducer 106 as an example, and it sends ultrasonic pulse and arrives reception transmitter 108 through for example measuring distance 110 of 6 centimetres.Figure 10 B illustrate with first the emission amplitude 1 the emission and with second than short arc (being caused by the energy loss during advancing by gas) 2 receptions acoustic impluses.In Figure 10 C, transmit and receive transmitter with for example 2 centimetres locate than short spacing.As shown by arrows, acoustic impluse is allowed to resilience or echo twice between transmitter, and after the transmitter spacing three times of having advanced received transmitters sense.As shown in Figure 10 D, be subjected to damping during preferably making the acoustic impluse emission of receiver in the time period 1, in order to offset interference oscillatory.This pulse is resilience for the first time in the time period 2, resilience for the second time in the time period 3, received transmitters sense thereupon.Usually, detect n echo, and signal damping with due regard to.Yet, in a preferred embodiment, according to the design of measuring chamber, detect the second echo.N the echo that detects ultrasonic pulse for example second echo makes the ultrasound wave longer distance of advancing, and so improved the Measurement Resolution of small size measuring chamber.
Of the present inventionly process on the other hand again following problem: the proper signal pattern that realizes sensor device.According to the embodiment of the present invention, it is the ultrasonic pulse of 200Hz that the emission transmitter is operating as the emission repetition frequency.Like this, this transmitter is energized to vibrate and the pulse of launching is actually the spike train burst that for example comprises 3 pulses, and each burst has the duration in 2.25 cycles, thereby corresponding to 0.0050 second.In order to reduce transient state and to cause harmonious temporary steady-state process, the transmitter driving voltage only is controlled as has high voltage and vibration during the rising period of transmitter vibration.That is, when transmitter output has positive derivative and therefore the first vibration of driving voltage has the length of 1/4 recurrence interval only.This is shown in Figure 11 A-11D.Figure 11 A is the screen message dump of exemplary oscilloscope measurement, and it illustrates how resilience between the transmitter surface in measuring chamber of acoustic impluse, is detected by receiving transmitter.This sound is subjected to damping and disappears fully after 2.4 milliseconds, and new impulse ejection can begin.In Figure 11 B, on illustrate the ultrasonic pulse that detects, under illustrate the driving voltage input of emission transmitter.Measure from emission by means of the timer in microprocessor as above and begin to receive time of the second echo to for example receiver.Figure 11 C shows the part enlarged drawing of the excited oscillation in Figure 11 B.The first vibration only 1/4 recurrence interval long, and vibration subsequently has the length of 1/2 recurrence interval, so the signal that applies departs from the resonance frequency of transmitter on mathematical meaning.This is also shown in the graph of a relation of excited oscillation and the output of emission transmitter.According to Figure 11 D, driving voltage is input to transmitter with the form since the burst of the square wave oscillation 112 of 1/4 recurrence interval, has high voltage thus during the positive derivative part of transmitter output signal 114.Can use this concept as illustrated in the embodiment of the present invention, perhaps combine with other configuration of ultrasonic transducer and use independently this concept.
Flow meter applications of the present invention
Concept of the present invention also can be applicable to by means of hyperacoustic gas flow measurement.Utilized the velocity of sound poor of measurement zone upstream and downstream based on hyperacoustic flowmeter.The mean value of upstream measurement and measured downstream value has provided the indirect measurement to gas composition and gas temperature.For be applied in the flowmeter survey district according to temperature buffer of the present invention, measured value is only the tolerance that the gentle body of flow is formed.This can for example be used for the functional residual volume (FRC) of definite patient's lung.The time of particular measurement sampling needn't synchronize with temperature survey.
Label
1 measurement mechanism 46 sensor shell
2 measuring chamber 48 circuit boards
4 chamber 50 over caps
5 Room limiting structure 52 main gas flow pipe
Opening in 6A, 6B ultrasonic transducer 54 main gas flow pipe
8 gas access 56 lip member
10 gas vent 58 cylindrical duct
12 air flow path 60 entrance and exits
14 temperature sensor 62O shape circles
16 central processing unit CPU 66 neck shape sealers
18 temperature signal input end 68 elastic hook ring plates
20 temperature signal amplifier 82 flanges
22 ultrasonic receiver signal amplifier 84 recesses
24 timer level input end 90 channel parts
The effective surface of 26 timer level 94 transmitters
28 timer level output 102 elastic devices
30 drive signal amplifier 106 emission ultrasonic transducers
34 power supply 34 110 measuring distances
38 flange 112 square wave oscillations
40 direction of sound propagation 114 transmitter output signals
42 primary air directions
44 porous structures
Claims (11)
1. equipment of be used for determining the ratio of gaseous mixture gas comprises:
Measuring chamber has the chamber limiting structure, gas access and the gas vent that comprise the material with high heat conductance, and wherein, described material is metal;
Ultrasound source and ultrasonic detector are installed into and make described ultrasound source ultrasound wave can be transferred to described ultrasonic detector through described measuring chamber;
Temperature sensor is installed into and makes the temperature of described sensor in can the described measuring chamber of sensing,
Wherein, described measuring chamber (2) has radius r 0 and is the tubular cavity of 1-8mm, thereby cause gas molecule from described chamber to the small distance of the inwall of described pipe, and wherein, described measuring chamber is designed such that the rigid surperficial close contact of material measured gas and thermal inertia and good heat conductive, is free to travel to surrounding structure so that heat energy is enough from gas.
2. equipment according to claim 1, wherein, described tubular cavity is columnar.
3. equipment according to claim 1, wherein, described measuring chamber is shaped as the interior diameter that has in the 9mm scope and the pipe of the overall diameter in the 12mm scope.
4. equipment according to claim 1, wherein, the material of described chamber limiting structure is to have at 50Wm
-1K
-1The stainless steel of the thermal conductivity in scope.
5. equipment according to claim 1, wherein, described measuring chamber is shaped as cylindrical duct, and described cylindrical duct comprises, respect to one another elongated the entrance and exit location along the valve jacket of described cylindrical duct.
6. equipment according to claim 1, wherein, described measuring chamber comprises the hot padded coaming that is arranged in the ultrasonic propagation district.
7. equipment according to claim 6, wherein, described measuring chamber comprises the flange of the hot padded coaming in described ultrasonic propagation district.
8. equipment according to claim 7, wherein, described flange is arranged to parallel with primary air direction and ultrasonic propagation direction through described measuring chamber, and described primary air direction and described ultrasonic propagation perpendicular direction.
9. equipment according to claim 6, wherein, described measuring chamber comprises the porous structure of the hot padded coaming in described ultrasonic propagation district.
10. equipment according to claim 1, also comprise the upstream gas channel part that utilizes Heat Conduction Material to design.
11. equipment according to claim 1 also comprises and utilizes that Heat Conduction Material designs, as to have cross sectional dimensions less for the size of main air flow passage upstream gas channel part.
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| KR101956955B1 (en) * | 2011-11-22 | 2019-03-11 | 인피콘, 인크. | Multi-chambered acoustic sensor for determining gas composition |
| CN108152370B (en) * | 2017-12-20 | 2020-10-02 | 国网河北省电力有限公司电力科学研究院 | SF (sulfur hexafluoride)6And N2Device and method for rapidly detecting component proportion of mixed gas |
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| EP1343004A2 (en) * | 2002-03-06 | 2003-09-10 | NGK Spark Plug Co., Ltd. | Gas sensor and gas concentration detection device |
| EP1464957A2 (en) * | 2003-03-26 | 2004-10-06 | Maquet Critical Care AB | Acoustic analysis of gas mixtures |
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| JP2002257801A (en) * | 2001-03-05 | 2002-09-11 | Daiichi Nekken Co Ltd | Ultrasonic type gas analitical sensor |
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| EP1343004A2 (en) * | 2002-03-06 | 2003-09-10 | NGK Spark Plug Co., Ltd. | Gas sensor and gas concentration detection device |
| EP1464957A2 (en) * | 2003-03-26 | 2004-10-06 | Maquet Critical Care AB | Acoustic analysis of gas mixtures |
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