KR20030043951A - Several gas flow measuring devices and signal processing methods - Google Patents

Abstract

The gas flow receiver is installed in the flow tube, wherein the pressure near the upstream orifice is higher than the pressure sensed at the corresponding cross section of the flow tube, while the pressure near the downstream orifice is detected at the corresponding cross section of the flow tube. An asymmetric flow-induced bulkhead that causes an asymmetrical flow in the flow tube that is in a lower state. Gas flowmeters using a thermo-window-type transducer that receives a gas flow rate from an upstream orifice are arranged so that the gas flow rate is reversed in direction while passing through a pair of transducers so that the gas flow rate is not affected by vibration or acceleration. Are manufactured so as not to. Before digital conversion using an ADC, the converter output is amplified by a noise amplifier that injects a secondary signal. In order to obtain samples with a level of precision greater than the minimum quantization value of the ADC, the digital signal is averaged over the sampling period.

Description

Multiple gas flow measurement devices and signal processing methods {SEVERAL GAS FLOW MEASURING DEVICES AND SIGNAL PROCESSING METHODS}

Typically, a gas flow meter consists of a gas flow receiver (GFR) (also called a gas passage), a tube through which gas passes and a differential pressure transducer connected to the GFR. The transducer measures the differential pressure generated by the flow resistant member lying in the tube. In applications such as spirometry, GFRs with simple shapes and easy cleaning and / or disposal are most preferred. Some GFRs used in industry and medicine have tubes with flow-resistant members formed in the form of planar bulkheads (flow obstructions designed to create local differential pressures while allowing flow). The closest product to the present invention used for measuring spirometry is a GFR with a crest-shaped flow resistant member disclosed in US Pat. No. 5038773.

The special shape of the GFR used to measure spirometry should not exceed the maximum allowable back pressure defined by the spirometry standard and the need to increase the differential pressure generated by the flow resistant member to achieve higher flowmeter sensitivity. This is a compromise of the need to do so. For example, the American Thoracic Society Standards for Spirometry (1994) requires that the back pressure be 150 Pa · s / l or less over the entire operating range. Thus, for this particular use, GFR is preferred where the ratio of differential pressure / back pressure is maximum.

Another problem to be solved in the aforementioned flowmeter is related to the reproducibility of the conversion characteristics of the GFR, which defines the flow-to-differential pressure conversion. For this purpose, the simpler the shape of the GFR, the easier it is to manufacture, and the better the reproducibility of the inner shape of the tube and the size of the surface, thereby ensuring the reproducibility of the transformation. Simplification of the tube shape reduces manufacturing costs, which is particularly important for disposable tubes.

U.S. Patent No. 5038773 shows that GFR with flow resistant members made in the form of planar bulkheads has inherently nonlinear flow-to-differential pressure conversion properties. Typically, the differential pressure generated by this type of GFR is close to the secondary function of the flow rate and causes the following problems. Since the flow rate needs to be measured in the dynamic range of 10 ³ , i.e. 15 ml / s to 15 l / s (spiracity measurement), the differential pressure formed by the GFR should be measured in the dynamic range of 10 ⁶ = (10 ³ ) ² . On the other hand, according to the American Thoracic Society's current spirometry standard, the maximum flow impedance of GRF is limited to about 150 Pa · s / l, so the maximum back pressure formed is (150 Pa · s / l) × (15 l / s). Limited to 2 kPa. Therefore, the minimum detectable differential pressure of the pressure transducer should be at the level of several mPa. This need, coupled with the need to operate in a sixth order (6 power) dynamic range, is a challenge for differential pressure transducers to overcome. Medical Graphics has proposed a flow meter in US Pat. The electronic module of the spirometer has a sophisticated structure and includes a submodule that provides analog signal conversion before being digitized by an analog-to-digital converter (ADC).

The use of transducers in the form of thermoanemometers connected in parallel to the GFR for flow measurement has previously been reported [U.Bonne, K. Frisch, "Mikroanemometer for gas flow measurement. fuer die Durchflussmessung von Gasen ", Technisches Messen, 1994, Vol. 61, No. 7, pp.285-294; TR Onstein, RG Johnson, RE Higashi, DW Burns, JO Holmen, EA Satren, GM Johnson, RE Beeking, SD Johnson, "environmentally rugged, wide dynamic range microstructures airflowsensor", solid-state sensors and actuators conference ( 1990), pp. 158-160]. There are also special thermopyroelectric transducers with a linear operating range of about four orders of magnitude and a total operating range of six orders of magnitude or more (Frolov G.A., Gendin A.V. Grudin0 OM, Katsan II, Krivoblotskiy SN, Lupina BI, "Micromechanical Thermal Sensors for Gas Parameters Measurements," 1996 Proceedings of 1996 ASME international engineering congress and exposition, DSC-Vol. 59, micro-electro-mechanical systems, pp. 61-65. It can be used in all operating ranges, attracting attention as a flowmeter application Another advantage of thermo-windometer detectors is that resolution can be improved down to as low as a few mPas without compromising the sensor's dynamic characteristics. For example, Honeywell's mass flow AWM-series detectors with the above-described resolutions have a response time of about 3 ms.

Thermo-windometer transducers include a functional member that is sensitive to gas flow through a specially constructed gas flow assembly (US Pat. No. 4548078). This gas flow rate is proportional to the pressure drop across the transducer and therefore may be used for differential pressure measurements. The physical principle of gas flow measurement is based on the disturbance of the symmetrical temperature distribution caused by the flow in the gas around the heater. This disturbance caused by the heated volume of gas moving in the flow direction is usually detected by a pair of temperature sensing members. Typically, the flow rate sensing member includes one or two heaters to warm the gas in a particular region of the flow channel. The flow sensing member also includes at least two temperature sensing members for measuring the deviation of the temperature distribution in the heated gas volume. The gas heating function and the temperature sensing function may be separated, for example, as a detector (US Pat. No. 4548078) having a central heater and two temperature sensing members opposite the heater. Alternatively, the flow sensor may use only two self-heating temperature sensing members that measure the temperature difference while heating the gas [H.E. De Bree, P. Leussink, T. Korthorst, H. Jansen, TS J. Lammerink, M. Elwenspek, "μ Flow: a novel device for measuring acoustic flows ", sensors and actuators A (1996), Vol. 54, No. 1, pp. 552-557] . In order to achieve the present invention, it is not enough to consider the differences between such configurations.

Thermo-windometer flow or differential pressure transducers are sensitive to acceleration acting in a direction parallel to the gas flow in the transducer flow channel. This effect, caused by the movement of a heated volume of gas, which is less dense than the surrounding cold gas, results in a temperature difference detected by the two temperature sensing members. Acceleration acting in a direction perpendicular to the gas flow also causes a shift in the heated volume of the gas, but in a direction that does not significantly change the temperature difference measured in the two temperature sensing members. Thus, the transducer has low sensitivity to gas flow and acceleration in the vertical direction. In general, one sensor cannot distinguish between a resultant signal induced by acceleration and a signal induced by flow rate. Sensitivity to acceleration of such differential pressure transducers degrades the accuracy of the transducer and hence the accuracy of the gas flow meter exposed to mechanical disturbances such as vibration, rotation and displacement.

Another problem is the need to detect and process differential pressure signals that are about 1000 times smaller than the differential pressure signals formed by nearly linear GFRs (e.g., Fleisch or Lilly tubes in a pulmonary system). Occurs. During flow meter operation (e.g., checking the spirometer), vibration or shock may occur on device members such as pneumatic hoses connecting the GFR and the differential pressure sensor. These parasitic signals are negligibly small compared to the differential pressure signals generated by linear GFR, but are nevertheless severe compared to the useful signals produced by nonlinear GFR. Interference caused by these pseudo signals reduces the accuracy of the flow meter. In particular, in portable small devices, such vibration immunity is considered an important characteristic of the flow meter. If signal filtering techniques for suppressing parasitic signals do not violate any standards in the field of application, such techniques can be used. For example, the spirometry standard specifies the response rate required to measure flow rate variables of patient breathing that must be maintained by the spirometry.

Flowmeters comprising two nonlinear functional members, such as GFR and thermo-windometer detectors, have a complex and inherently nonlinear conversion characteristic that converts the flow rate into an output voltage, which must be linearized. In order to linearize the flowmeter, a calibration curve F (V) must be defined which defines the correspondence between the flow rate F and the measured voltage V. The present invention also proposes a linearization scheme of an essentially non-linear flow meter comprising a GFR having a flow resistant member that produces a differential pressure close to the square of the flow rate.

Existing spirometers typically include an analog-to-digital converter (ADC) that digitizes the analog signal from the converter for subsequent processing. In order to provide the necessary resolution in the wide operating range of the above six orders of magnitude, an ADC having a resolution of 16 to 18 bits or more should be used. On the one hand, a 12-bit ADC which is relatively inexpensive, simple and widespread is desirable. Thus, the problem of analyzing low flow rates (in flowmeters with nonlinear GFR) arises not only because of the limited sensitivity of the differential pressure transducer, but also because of the limited resolution of the desired electronic circuit.

The present invention generally relates to a gas flow meter comprising one or more differential pressure transducers for measuring a pressure drop across a flow resistant member located within a gas passage. More specifically, the present invention improves the precision of flowmeters used for measuring spirometry by the special design of gas passages by increasing vibrational immunity and by providing special signal processing methods and linearization methods that can be applied to flowmeters or other transducer signals. It is about.

DETAILED DESCRIPTION The present invention will be better understood with reference to the following detailed description of the non-limiting preferred and other embodiments and the accompanying drawings.

1 is a schematic diagram of a flow meter including a gas flow receiver, a differential pressure transducer, an analog electronic module, and an ADC module.

2 is a gas flow receiver (prior art) with a star-shaped partition.

3 is a gas flow receiver with an asymmetric flow resistant member according to the present invention.

4 shows the measured back pressure and flow rate for two types of GFR.

5 shows the ratio η of the differential pressure generated by the asymmetrical and symmetrical flow resistant member to the flow rate.

FIG. 6 shows the deviation of the measured syringe volume from the actual values during discharge and inflow at various average flow rates for GFR with symmetric star-shaped obstructions.

7 shows the deviation of the measured syringe volume from the actual values during discharge and inflow, at various average flow rates for GFR with asymmetric flow resistant members of the present invention.

8 is a schematic side view of a GFR.

9 is a schematic front view of the flow resistant member in a GFR tube (observed along the long axis of the tube).

10 and 11 show the configuration of the differential pressure transducer and the flow transducer of the present invention including a flow sensing member in the form of two thermo-empirometers. The gas flowing channel connects the two members in series (FIG. 10) or in parallel (FIG. 11).

12 shows a schematic diagram of a single flow rate sensing member subjected to acceleration.

FIG. 13 shows an embodiment of a more complicated configuration comprising three flow sensing members connected in a triangular form.

14 shows a configuration in which gas flows through only one of two equally aligned flow rate sensing members.

FIG. 15 shows the unfiltered output signal (FIG. 15A) and the filtered output signal (FIG. 15B) of the flow meter at low flow rate.

16 shows a block diagram of an electronic module of the flow meter.

17 and 18 are flowcharts illustrating a signal processing method of the present invention.

19 shows the flowmeter's response to sudden flow rate fluctuations.

20 shows the calibration curve of the flow meter.

It is an object of the present invention to propose the following solution.

Increase the effectiveness of GFR by improving the differential pressure / back pressure ratio.

Simplify the shape of the GFR for excellent reproducibility and ease of manufacture.

· Improve the immunity of the flow meter against vibration and shock of the device including the thermo-windometer type differential pressure and flow rate transducer and its members.

Improve flowmeter resolution and resulting accuracy at low flow rates.

Accurately linearize the gas flow meter

1. One of the objectives of the present invention is solved by the new shape of the flow resistant member of the GFR. This flow resistant member, when viewed along the axial direction of the GFR tube, is made in the form of a gas flow obstruction having an asymmetrical shape. This flow resistant member is designed to simultaneously obtain a low total back pressure and a high local differential pressure measured between two points inside the GFR. Local differential pressure is generated by placing an obstruction between two points inside the GFR where the differential pressure is measured and, typically, in the case of bidirectional flow measurement, is installed as close as possible to the center point of the line connecting these two points.

According to the general aspect of the present invention, there is provided a flow tube having a side wall and guiding the flow therethrough while inducing a minimum resistance, an upstream sensing tube having an upstream orifice connected to the flow tube through the side wall and the flow tube through the side wall; A gas flow receiver is provided, consisting of a downstream sense tube having a downstream orifice connected thereto. The receiver is installed in the flow tube between the upstream orifice and the downstream orifice, wherein the accentuated pressure near the upstream orifice is higher than the pressure sensed at the corresponding cross section of the flow tube and near the downstream orifice. An asymmetric flow-induced septum which causes an asymmetrical flow in the flow tube where the emphasis pressure is lower than the pressure sensed at the corresponding cross section of the flow tube, the orifices being capable of suppressing pressure fluctuations due to turbulence induced by the It is positioned relative to the bulkhead to sense the pressure pressure without actually sensing it.

The partition is preferably installed on the side walls between the orifices. The partition wall may be formed to exhibit high drag and generate maximum stress pressure with respect to its magnitude. The flow tube may have a smaller cross section between the orifices and may be tapered similarly to each other on both sides of the small cross section.

2. In order to improve the vibration immunity of the thermo-windometer differential pressure transducer, two or more thermo-windometer flow sensing members are connected and used so that the parasitic components of the signal induced by the acceleration are removed separately from the components caused by the flow rate. Therefore, the signal caused by the flow rate can be identified.

Generally, this object is achieved by using a plurality of flow sensing members connected to flow and acceleration in different directions (angles) in different flow sensing members. Many other embodiments are possible. For example, two thermopneumatic flow rate sensing members are connected in a special way such that gas passes through each member in the opposite direction. The output signals of the two flow sensing members are processed electronically to eliminate the signal components caused by acceleration while doubling the signal components caused by the flow rates.

Another combination may also include at least one flow sensing member through which no gas passes. Acceleration acts on this reference member, thereby generating an output signal that is used to remove components caused by the acceleration of the member through which the gas passes.

According to the general aspect of the present invention, each of the plurality of gas flow transducer members is sensitive to vibration or acceleration in at least one direction and generates an output signal proportional to the gas flow rate and disturbance component due to the vibration or acceleration, A gas flow transducer device having vibrational or accelerated immunity is provided. The transducer members are disposed on the cavity support, and a plurality of gas flow passages direct the gas flow from the inlet to the outlet through at least one of the transducer members. The members are arranged on the cavity support and are connected to the passage such that at least one of the disturbing component and the gas flow rate are measured separately by the transducer member. A circuit is provided which receives the output signal of each transducer member and outputs a vibrational or accelerated immune output signal corresponding to the gas flow rate with the disturbance component substantially removed.

The gas flow passage may make the gas flow rate equal through the transducer member, and the gas flow may be separated between the transducer members or may pass through the transducer member in series. Two transducer members are provided which are sensitive to vibration or acceleration along only one axis and arranged parallel to each other, and the gas flow path is preferably arranged such that the gas flow rate passes through the transducer member in the opposite direction.

The gas flow may be blocked at at least one transducer member that measures only disturbing components.

The at least one transducer member is preferably connected with a gas flow such that at least one transducer member maintains the same gas component and temperature as the other transducer members.

The transducer member is preferably composed of a transducer in the form of a thermo-empirometer.

3. In order to improve the resolution of flowmeter at low flow rate limited by quantization noise of ADC, the following signal processing method is proposed.

Choice 1

3.1) The output analog signal of the differential pressure transducer shall have a high frequency component at the frequency f> 1 / Δt. Where Δt is the ADC sampling rate and the amplitude of this high frequency component must exceed one quantization unit of the ADC.

3.2) If the output analog signal of the differential pressure transducer does not have a high frequency component at frequency f> 1 / Δt and the amplitude exceeds one quantization unit of the ADC, then an artificially generated vibration signal or noise that meets this criterion is digitized by the ADC. Must be mixed with the signal before

3.3) The average output signal voltage is calculated by the arithmetic mean of the various samples from the ADC output during the time τ = N · Δt (where N> 2), resulting in better resolution than the quantization unit of the ADC.

3.4) The flow rate corresponding to the average signal voltage in 3.3) is calculated from the calibration curve of the flow meter.

Choice 2.

The output analog signal of the differential pressure converter as described above in 3.1) and 3.2) can be subsequently processed as follows.

3.5) The flow rate corresponding to the digitized output signal voltage sample is calculated from the calibration curve of the flow meter.

3.6) The average flow rate is calculated during the time τ = N · Δt (where N> 2).

According to the general aspect of the present invention, there is provided a method for evaluating an analog signal value using an analog-to-digital converter (ADC) having a level of precision greater than the minimum quantization value of the ADC. This way

Summing a secondary signal having a DC component of zero, a substantially uniform and symmetrical amplitude distribution, and a peak-to-peak amplitude greater than the minimum quantization value, to the analog signal,

Recording and storing the digital output of the ADC,

Averaging the digital output values recorded during the sampling time to obtain an evaluated high precision digital value having a precision greater than the precision of the digital output value.

The secondary signal is provided by noise generated in the amplifier circuit used to amplify the analog signal, which preferably is a gas flow transducer signal and other types of signals.

The sampling time changes depending on the amplitude of the analog signal. It is preferable that the sampling time is long for low amplitude values and the sampling time is short for high amplitude values.

4. In order to suppress parasitic signals caused by vibration or shock of the flow meter or its members without degrading the frequency response of the device, the output analog signal of the differential pressure transducer under high frequency component conditions as described in 3.1) and 3.2) is Can be treated as follows.

4.1) The entire operating range of the meter may be divided into at least two (preferably two or more) non-overlapping subranges. The number of subranges is theoretically up to the number of quantization units in the ADC. As such, the averaging time may vary for each subrange.

4.2) Where flow rates are measured in accordance with 3.3), 3.4) or 3.5) above, the averaging time shall be monotonically reduced from the lower range of the lower flow rate to the lower range of the higher flow rate.

According to a general aspect of the present invention, there is provided a method of measuring the amplitude of a signal, determining a long averaging time for low amplitude values and a short averaging time for high amplitude values as a function of amplitude, to provide a filtered output signal. A signal filtration method is provided that includes averaging the amplitude over time.

The function may be a step function. If the amplitude is above a preset reference value, the filtered output signal may be an instantaneous value of amplitude. The measuring step preferably includes converting the analog gas flow transducer signal into a digital signal providing an amplitude.

5. Invented a calibration function F (V) of the general form of a flow meter that includes a flow resistant member that produces a differential pressure close to the secondary function of the flow rate.

Where N is 3 or more, the variable α _i > 1 (preferably, α _i value is close to 2), and Ai is a coefficient experimentally determined to give the best linearity for a particular flow meter. To increase accuracy, the entire operating range of the flowmeter is divided into several (at least two) subranges, and the test function is calculated separately for each subrange in the same way.

According to a general aspect of the present invention, a method is provided for processing a non-linear transducer output signal for a measured physical variable to obtain a calibrated output signal representing the physical variable at a predetermined magnitude. This way,

Maintaining the transducer under a plurality of validated physical variable conditions,

Recording the output value under each condition,

Where V is the transducer output signal, N is greater than or equal to 3, the variable A _i is a coefficient determined from the recorded value, and α _i is a real number, the analysis expressed as follows for the nonlinear function relating the output value to the physical variable obtaining analytical solution,

Using the analysis solution to determine a black output signal for the transducer output signal.

It is preferable that (alpha) _i is larger than 1, and it is not necessary to be an integer.

The determining step is

Using the analysis solution to calculate a physical variable value for each possible value of the transducer output signal,

Creating a table of physical variable values indexed by digital outputs,

Converting the converter output signal to a digital output value, and

Obtaining the value of the black output signal from the table using the digital output value.

The analysis solution can be accurate for each value recorded and the analysis function can be divided into subranges.

The transducer output signal can be derived from a gas flow signal having a secondary transfer function, and the gas flow transducer is preferably a transducer device in the form of a thermo-windometer.

In a preferred embodiment, the gas receiver has a partition installed in the flow tube to cause an asymmetrical flow, the downstream orifice while the pressure pressure near the upstream orifice is higher than the pressure sensed in the corresponding cross section of the flow tube. The near pressure pressure results in an asymmetrical flow in the flow tube that is lower than the pressure sensed in the corresponding cross section of the flow tube. For example, by arranging the transducers parallel to each other such that the gas passes continuously through a pair of transducers in the opposite direction, a gas flow meter using a thermo-emergency transducer that receives the gas flow rate from the upstream orifice may produce vibration or acceleration It is manufactured to have. The resulting transducer signal is processed such that the effects of vibration or acceleration are eliminated. The converter output is amplified by a noise amplifier that injects a secondary signal before digital conversion using an ADC. To obtain a sample with a level of precision greater than the minimum quantization value of the ADC, the digital signal is averaged over the sampling period. The sampling period is varied as a function of the amplitude of the analog signal of the transducer so that the sampling period is long for low amplitudes and short for high amplitudes. Changes in the sampling period provide signal filtration. Since the flow meter exhibits a nonlinear response, it records samples at multiple tested flow rates, solves for the nonlinear function, uses the analysis solution to obtain test values for all sample values, and tests that correspond to the sample values during operation. By contrasting the values, a calibrated output signal representing the flow rate is obtained. The features of the preferred embodiments have been briefly described in general, and the following will describe each of the features in more detail.

The present invention discloses various advanced features that can be applied to gas flow meters. These features improve the flowmeter's characteristics. The combination and implementation of the inventions described below can achieve the maximum effect.

<Tube for converting gas flow rate to differential pressure>

1 shows a schematic diagram of a flow meter comprising a GFR 1, a differential pressure transducer 2, an analog electronic module 3 and an ADC module 4. The flow resistant member 5 of the gas flow receiver (GFR) of the present invention simultaneously measures the overall low back pressure and the locally high differential pressure measured between two points inside the GFR 1 in bidirectional flow measurement such as the spirometry. It is designed to be obtained. Local differential pressure is created by placing an obstruction 5 in the GFR 1, which places the obstruction as close as possible to the central point of the line connecting the two points between the two points in the GFR 1 for which the differential pressure is to be measured. . In some cases, it may be desirable to position the obstruction or partition to be deflected at a central point.

In order to demonstrate the idea of the present invention, two experimental GFRs were prepared. Each of the star-shaped symmetric bulkheads 7 and the asymmetric bulkheads 5 of the present invention was placed at the center of the same-shaped tube having an inlet diameter of 21 mm, a diameter of 19 mm and a length of 120 mm (Fig. 2 and 3). The shape of the flow resistant member was chosen such that a back pressure of less than 150 Pa · s / l (based on the ATS standard for spirometry) was formed. The six beams of the star-shaped bulkhead 7 are each 1 mm wide. The diameter of the central part of this bulkhead is 4 mm. The asymmetric partition 5 has the shape of a circular segment 4 mm in height. The star-shaped partition 7 has a thickness of 1 mm, and the partitioned partition 5 has a thickness of 0.1 mm to 0.2 mm.

Each GFR was connected to the same differential pressure transducer 2 and tested separately. Back pressure was measured by a separate pressure sensor. Three-liter assay syringes, called "SpiroCal" from Burdick, were used to generate the gas flow during the experiment. 4 shows the air flow rate dependence of back pressure for two GFRs. FIG. 5 shows the ratio η = ΔP ₁ / ΔP ₂ as a function of pressure, where ΔP ₁ and ΔP ₂ are each formed by a GFR having an asymmetric bulkhead 5 and a star-shaped symmetric bulkhead 7 of the present invention. Foreclosure. The GFR of the present invention produces a lower back pressure and a higher differential pressure than a GFR having a symmetric partition 7.

To investigate the sensitivity of the two tubes to the gas velocity distribution across the tube cross section, the following two step experiments were conducted. In the first step, each tube (after test) was connected to a syringe, and gas was introduced into the syringe through the tube from the atmosphere at various flow rates by the stroke of the piston. The inflow volume was determined by summing the flow rate measurements over time and compared to the actual volume of the syringe. In the second step, each tube was rotated 180 ° to reverse the direction, and the same experiment was conducted except that the opposite side of the tube was connected to the syringe, and the gas was discharged by the discharge piston stroke. Thus, the gas flow direction in the tube was the same, but the gas flow rate distribution in the connection and the resulting flow rate was different. In the first stage, the entrance of the GFR was directly connected to an infinite volume of atmospheric gas, but in the second stage, the gas flow rate into the GFR was formed by a connection tube of 40 mm length and 30 mm inner diameter. The deviation (expressed in%) from the actual value of the syringe volume obtained experimentally measured in the region of "emission" and "inflow" at various average flow rates is shown in FIGS. 6 and 7. In the GFR equipped with the star-shaped partition wall 7, the volume difference measured up to 8.5% occurred due to the change of direction, and the sensitivity to the gas velocity distribution over the cross section of the tube can be confirmed. In the case of the tubes of the invention, this difference does not exceed 1%, indicating substantially that the sensitivity of the gas velocity distribution over the tube cross section is lower.

The GFR of the present invention is simpler in shape than a star-shaped symmetric partition wall or crest-shaped flow resistant member. For this reason, a manufacturing process can be simplified and the reproducibility of a conversion characteristic can be improved.

The above-described embodiment can confirm the advantages of the solution of the present invention. In addition, according to this invention, the asymmetric flow-resistant member of another shape can also be used. GFR including the flow resistant member of the present invention in the form of asymmetrical circular compartments of 3 mm and 5 mm in height was also tested. Experimental results are shown in FIGS. 4 and 5, and each is represented by a circle and a triangle symbol. This variant also shows that the sensitivity of the gas velocity distribution over the cross section of the tube is low.

Increasing the thickness of the circular compartment obstruction from 0.2 mm to 1.2 mm results in a significant change in the conversion properties of the GFR. The observed deviations of back pressure and local differential pressure did not exceed 5%.

8 and 9 show some possible designs of the GFR, but not all possible GFR shapes. Special choices of GFR should be made to best fit the given application and manufacturing technique. 8, various cross sections of the flow resistant members 8, 9, 10 in the GFR 1 are shown. GFR 1 may also include tubing 11 attached at an angle. 9 is a front view of the planar bulkheads 12, 13, and 14 used as the flow resistant member.

In a preferred embodiment, the flow measured is bidirectional. In the case where the flow is unidirectional, it may be desirable for the asymmetric bulkhead to be at a location different from the center between the sensing tube orifices.

<Differential pressure and gas flow transducer with immunity to vibration / acceleration>

10 and 11 show two possible configurations of the transducer of the present invention, in which two flow rate sensing members 15 are connected in parallel (FIG. 10) and in series (FIG. 11). In both cases, the gas passing through the channel passes through the flow resistant member in the opposite direction. Thus, the heated volume of gas 16 (shown by hatched circles) around the heater 17 in the two flow resistant members 15 also moves in the opposite direction, resulting in an inverted output signal component. As shown in FIG. 12, when accelerated in a direction parallel to the gas flow rate, the heated volume of gas 16 moves in the same direction with respect to the two flow resistive members 15, thereby producing the same output signal for both detectors. Causes an increase. The output signals V _{detector 1} and V _{detector 2} of the two flow resistive members 15 are processed in the electronic circuit 3 to subtract one from the other. The following three equations summarize this situation.

V _detector1 = V _{flow rate} + V _acceleration

V _detector2 =-V _{flow rate} + V _acceleration

V _{detector 1} -V _{detector 2} = 2, V _{flow rate}

Where V _{flow rate} and V _acceleration are the sensor output voltage components generated by the gas flow rate and the applied acceleration, respectively.

If the two linear flow sensing members 15 are identical, the sensitivity to acceleration of the entire transducer can theoretically be reduced to zero. In practice, immunity to acceleration can be limited by the test of non-identity and sensitivity of the two sensor elements 15.

The choice of configuration shown in FIGS. 10 and 11 depends on the particular application. The transducer with two flow sensing elements 15 connected in series has twice the flow impedance than the single member, and the second transducer (Fig. 11) has twice the flow impedance.

To experimentally demonstrate the inventive concept, a transducer prototype was assembled based on two AWM2200 mass flow detectors (Honeywell) connected in series with a plastic hose. The performance of the assembled prototype was compared with a single AWM2200 detector. The electronic circuit of the converter had the same sensitivity to differential pressure. After that, both devices were rotated in the gravitational field. The single AWM2200 detector had a sensitivity to acceleration of 14 mV / g, while the converter prototype of the present invention was fully immune to the same acceleration within the resolution of the electronic circuit (<1 mV). The two transducers tested have the same sensitivity to gas flow rate.

The configuration of the present invention of the accelerated immune converter 2 can be realized in various ways. The best results can be obtained by using the same flow sensing member. Such a flow sensing member is a commercially available detector as described above or a specially designed functional sensing member.

Among other possible configurations, three flow sensing members are arranged in the same plane and connected in a triangular form is shown in FIG. 13. In this case, the output signal of each flow sensing member is as follows.

V _{detector 1} = V _{flow rate} + V _acceleration ㆍ cos (60 °-β)

V _{sensor 2} = V _{flow rate} + V _acceleration ㆍ cos (60 ° + β)

V _{sensor 3} =-V _{flow rate} -V _acceleration ㆍ cos (β)

Here, β is the effective angle of acceleration as shown in FIG.

This system of three equations with three unknown variables V _{flow rate} , V _{acceleration,} and β can be solved to remove the influence of signal components caused by acceleration.

14 shows another possible combination of two flow sensing members. The gas passage 18, with one end open to the main gas passage, allows the reference sensor to be exposed to the same gas component, pressure and temperature without undergoing gas flow. If the gas component, pressure and temperature conditions are constant, detector 2 may be isolated without using passage 18. In this case, summarizing the acquisition of the detector output signal and the flow signal, the following three equations are given.

The output signal of the sensor,

V _detector1 = V _{flow rate} + V _acceleration

V _Detector2 = V _Acceleration

V _{detector 1} -V _{detector 2} = V _{flow rate}

Thus, processing of the output signal can eliminate the acceleration inducing component of the signal.

Note the following points:

In addition to the aforementioned acceleration compensation, compensation for changes in temperature, gas components and atmospheric pressure can also be implemented in a number of ways typically used in mass flow controllers. On the other hand, the acceleration suppression of the present invention is effective regardless of the specific embodiments shown in Figs. 10, 11, 13 and 14, and is independent of possible compensation methods of gas temperature, gas composition and atmospheric pressure.

<Signal Processing to Improve Flowmeter Accuracy>

The method of the present invention for improving the flowmeter resolution at low flow rates by special signal processing (otherwise, if a high resolution ADC is not available, is limited by the quantization noise of the ADC), results in a nonlinear GFR (1). It was experimentally examined using a mass flow sensor AWM2200 from Honeywell, which was connected to GFR 1 by the flow meter and the two plastic hoses 6 including. Detector excitation and signal amplification were done by a circuit recommended by the manufacturer. The reason why the flowmeter sensitivity is significantly reduced at low flow rates is due to the close dependence of the differential function of the differential pressure on the flow rate produced by the GFR (1). The limited resolution of the ADC 4 limits the minimum detectable flow rate. At the same time, parasitic signals due to vibration are sufficient to degrade the flowmeter's accuracy at low flow rates. As an example, FIG. 15A shows the effect when the vibration is intentionally applied to the pneumatic hose 6. It has been found that the minimum detectable flow rate defined by ADC 4 (flow rate corresponding to +1 mV or -1 mV, quantization unit of ACD) is about 50 ml / s (if no signal processing according to the invention). In the above embodiment, the electronic module included a typical 12 bit ADC 4 (AD7890-4). A digital signal with a sampling rate Δt of 2ms was sent to a personal computer for visualization, storage and processing.

The rational and useful frequency band of the electronic module for detecting different flow rates, specified in the ATS standard, need not be greater than 100 Hz to 150 Hz. In order to artificially increase the high frequency noise component of the analog output signal by the present invention (described above in 3.2), the frequency band of the electronic module is intentionally increased to 10 kHz. The increased high frequency noise component of the analog output signal, determined by the noise close to the white noise of the circuit's operational amplifier, has an amplitude of about 3 mV equal to the three quantization units of the ADC 4. Such additional noise is shown in Fig. 15A. A schematic block diagram of the device is shown in FIG. 16. In this embodiment examined experimentally, additional noise is generated in the analog circuit module.

Flowcharts illustrating signal processing in a microprocessor based module are shown in FIGS. 17 and 18. In order to suppress the signal caused by the vibration of the hose 6 without degrading the dynamic characteristics of the flowmeter, the following filtration parameters are used. The working flow range of the flowmeter is divided into four subranges.

0 ≤ flow rate ≤ 0.5 l / s

0.5 l / s ≤ flow rate ≤ 1 l / s

1 l / s ≤ flow rate ≤ 2 l / s

2 l / s ≤ flow rate ≤ 15 l / s

The averaging time τ is 72 ms (N ₁ = 36) for the first subrange, 30 ms (N ₂ = 15) for the second subrange, 12 ms (N ₃ = 6) for the third subrange, and fourth subrange. For the range, 6 ms (N ₄ = 3) was selected. According to the first preferred embodiment (FIG. 17), after the analog voltage output of the converter is converted to digital form by the ADC, the corresponding flow rate is found from the calibration curve of the flow meter. Store the flow rate reading in the buffer so that at least the last N _i reading is in the buffer. Analyze where the current flow falls in the four subranges. According to the analysis result, if the current flow rate falls in the lower range i (i = 1 ... 4), the flow rate is averaged using the last N _i displayed value stored in the buffer.

The effect of the signal processing described is shown in Fig. 15B. Averaging the signal improves the flow rate resolution from 50 m / s to about 5 ml / s. The suppression factor of the signal generated by vibration is about 7-8.

Another possible filtration process is shown in FIG. 18. The difference between this signal processing and the above-described signal processing is as follows.

Four sub-ranges are defined as voltages (not flow rates).

-Averaged to voltage converted to digital format.

The flow rate corresponding to the average voltage is obtained from the calibration curve of the flow meter.

The filtration process described above is very important at low flow rates, but may be unnecessary at high flow rates due to the rapid increase in signal approximately proportional to the square of the flow rate. For example, as the flow rate increases from 50 ml / s to 2 l / s, the signal increases by a factor of 1600 = 40 &lt; 2 &gt;, which is above the order of magnitude higher than the usual parasitic signal due to vibration. On the other hand, the high frequency response of the flowmeter is mainly necessary at high flow rates (e.g., spirometry) and is degraded by the long averaging time τ. Thus, the use of several subranges with low averaging times at high flow rates maintains satisfactory reaction rates at medium and high flow rates. FIG. 19 shows the flowmeter's response to the flow shock generated by the “Spy Locale” 3 liter syringe. At high flow rates, the filtered signal b has the same shape as the unfiltered signal a. The fall time is estimated to be less than 10 ms. The filtration effect at low flow rates can be considered to be due to the effective suppression of the vibrational acoustic signals generated by the piston impacting the bottom of the syringe.

The parameters of this filtration method, such as the number of flow rate subranges, the averaging time and the amplitude of the analog signal noise component, can be selected to optimize the operation of the flow meter for a particular application. The irradiated physical process parameters that result in this choice are the required frequency response and flow operating range of the flow meter and the strength and frequency range of the suppressed parasitic signal.

<Flowmeter linearization method>

Typically the calibration of the flow meter includes the following steps.

-Measure the flow meter output voltage at multiple reference flows.

Calculation of the analytical function that fits the actual calibration curve of the flow meter.

Save analytic function as

-Clearly showing all possible ADC readings corresponding to flow rate.

Variables in the analytic function to calculate the flow rate for each ADC reading during flow meter operation.

Typically, a high precision flow rate generator is used to calibrate the flowmeter at various reference flow rates. The number of such reference flows should not exceed 10-20. Otherwise, the test process is too long. On the other hand, even the 12-bit ADCs typically used in flow meters measure 4096 voltage levels within the device's operating range. Therefore, it is very important to find an analytical function that allows you to accurately trend the flow meter's actual calibration curve and determine the flow rate corresponding to all possible ADC readings. Curve trending methods are well known and are not discussed here.

The form of the analysis function F (V) which optimally trends the flowmeter mentioned above is shown as follows.

Where V is the output voltage of the flow meter, N is at least 3, A _i is an experimentally determined coefficient, and α _i is typically a real number (not necessarily an integer) greater than one.

In order to verify the linearization method of the present invention, a flowmeter prototype was used. This flow meter is based on the above-described GFR 1 which includes a tube having a length of 120 mm, a mouth side inner diameter of 21 mm, and a center diameter of 19 mm. An asymmetric planar partition 5 having the shape of a circular section 4 mm in height (FIG. 3) was used as the flow resistant member. This partition, 0.2 mm thick, is located in the center of the tube and produces a differential pressure (secondary transfer function) close to the square of the flow rate. In order to measure the differential pressure caused by the flow rate, the mass flow sensor AWM2200 (Honeywell) was connected to the GFR 1 with two plastic hoses 6. The flowmeter also included a 12-bit ADC AD7890-10 operating in the range of ± 10V.

According to the present invention, the operating flow rate range of the flowmeter was divided into two subranges, 0l / s to 2l / s and 2l / s to 15l / s. The coefficient A _i of the calibration curve F (V) was obtained for N = 5 and α _i = 2. Two functions, each defined for two subranges, are shown in FIG. 20. After the assay, the calibration curve was saved in a computer file in the form of a table.

In order to verify the accuracy of the flow meter, the GFR was connected to a "spiro-local" 3 liter assay syringe. Thereafter, air was introduced and discharged into the syringe at various flow rates by the piston stroke. The discharged and introduced air volume was measured with a flow meter and compared with the actual volume of the syringe. The difference between these two volumes (in%) shown in FIG. 7 did not exceed 2%. As a result, the accuracy of the flowmeter was confirmed to be less than or better than 2%, and satisfies the requirements specified in the ATS standard for measuring spirometry.

In practice, the selection of the variables N and α _i may differ from the selection in the embodiments described herein depending on the application. For example, when N = 6, the operation to find the coefficient A _i is more complicated, but the linearization process is successful.

To better trend the calculated calibration curve to the actual flow rate response of the flow meter, the variable α _i can be selected. At low flow rates, the sum: The first member of makes a major contribution. By converting this equation, Get In this case, the variable α ₁ defines the conversion of the flow rate at the low flow rate to the output voltage, and mainly depends on the structure of the GFR 1. Typically, the GFR 1 with the flow resistant member 5 in the form of a partition creates a differential pressure that changes (secondary transfer function) to a state close to the square of the flow rate. For this type of GFR (1), α ₁ = 2 reasonably approximates the calibration curve. Nevertheless, slight deviations of the value 2 low value of the variable α ₁ as well as the variable α _i (1 <i <N) are also included in the linearization method of the present invention.

Depending on the requirements of accuracy and the flow rate operating range, the number of subranges can vary from one to two or more. This choice depends on the particular application.

As described above, according to the present invention, it is possible to improve the differential pressure / back pressure ratio to increase the effectiveness of the GFR, and to simplify the shape of the GFR to improve reproducibility and manufacturability. In addition, it is possible to provide a flowmeter with improved immunity to vibration or shock and resolution at low flow rates.

Claims (32)

A plurality of gas flow transducer members each sensitive to vibrations or accelerations in at least one direction and generating an output signal proportional to gas flow rate and disturbance components due to said vibrations or accelerations, said gas flow transducer members being disposed on a common support; A plurality of gas flow passages having a constant cross-sectional area for guiding a gas flow through at least one of the gas flow transducer members from inlet to inlet to outlet; And A circuit for receiving the output signal of each gas flow transducer member and outputting an output signal corresponding to the gas flow rate, the effect of vibration or acceleration being excluded with the disturbance component substantially removed; The gas flow transducer member is disposed on a common support and connected to the gas flow passage so that at least one of the gas disturbance component and the gas flow rate can be measured separately by the plurality of gas flow transducer members. A gas flow rate converter having vibration or acceleration immunity. 2. The gas flow transducer with vibration or acceleration immunity according to claim 1, wherein the gas flow passage serves to keep the gas flow constant throughout the gas flow transducer member. 3. The gas flow transducer of claim 2, wherein the gas flow rate is divided between the gas flow transducer members. 3. The gas flow transducer with vibration or acceleration immunity of claim 2, wherein the gas flow passes through the gas flow transducer members in series. 5. The gas flow transducer member of claim 4, wherein two gas flow transducer members are provided that are sensitive to vibration or acceleration along one axis and are arranged parallel to each other, wherein the gas flow path is opposite the gas flow transducer members. Gas flow rate transducer device with vibration or acceleration immunity, characterized in that arranged to pass through. 2. The gas flow transducer member of claim 1, further comprising a gas flow obstruction member in said at least one of said gas flow transducer members, said at least one of said gas flow transducer members measuring only said disturbing component. Gas flow transducer device having vibration or acceleration immunity. 7. The vibration according to claim 6, wherein said at least one of said gas flow transducer members is connected to said gas flow rate so that the conditions of gas composition and temperature are the same as the other members of said gas flow transducer member. Or a gas flow transducer device having accelerated immunity. 8. Gas with vibration or acceleration immunity according to any of claims 1, 4, 6 and 7, wherein the gas flow transducer member is sensitive to vibration or acceleration along only one axis. Flow transducer device. 9. The gas flow rate with vibration or acceleration immunity according to any one of claims 1 to 4 and 6 to 8, wherein the gas flow rate converter device is composed of two gas flow rate transducer elements. Transducer device. 10. The gas flow transducer with vibration or acceleration immunity according to any one of claims 1 to 9, wherein the gas flow transducer member is configured as a transducer in the form of a thermo-windometer. A flow tube having sidewalls and guiding flow therethrough while inducing minimum resistance; An upstream sensing tube having an upstream orifice connected with the flow tube through the sidewall; A downstream sensing tube having a downstream orifice connected with the flow tube through the sidewall; And Is provided in the flow tube between the upstream orifice and the downstream orifice, and the pressure in the vicinity of the downstream orifice is higher than the pressure detected in the corresponding cross section of the flow tube. An asymmetric flow-induced septum causing an asymmetric flow in said flow tube that is lower than the pressure sensed in the corresponding cross section of said flow tube, And the orifices are positioned relative to the bulkhead to sense the pressure pressure without substantially sensing pressure fluctuations due to turbulence caused by the bulkhead. The gas flow container according to claim 11, wherein the partition wall is installed on sidewalls between the orifices. 13. The gas flow container according to claim 11 or 12, wherein the partition wall is formed to exhibit high drag and to generate maximum stress pressure with respect to its magnitude. 14. A gas flow receiver according to any one of claims 11 to 13, wherein the flow tube has a smaller cross section between the orifices and similarly tapered on both sides of the small cross section. An analog-to-digital converter (ADC) is used to evaluate an analog signal value with higher accuracy than the minimum quantization value of the ADC Summing a second signal having a zero (zero) DC component, a substantially uniform and symmetrical amplitude distribution and a peak-to-peak amplitude greater than the minimum quantization value to the analog signal; Recording and storing the digital output of the ADC; And And averaging the digital output values recorded during the sampling period to obtain a high precision digital evaluation value having a higher precision than the digital output value. 16. The method of claim 15, wherein the secondary signal is provided by a noise signal with a higher precision than the minimum quantization value of the ADC. 17. The method of claim 16, wherein the noise signal is generated in an amplifier circuit used to amplify the analog signal. 18. The analog signal value according to any one of claims 15 to 17, wherein the analog signal is a gas flow rate converter signal, and the gas flow rate converter is a transducer device in the form of a thermo-windometer. How to evaluate with high precision. 18. An analog signal as claimed in any one of claims 15 to 17, wherein the sampling period varies as a function of the amplitude of the analog signal, the sampling period being long for low amplitude values and short for high amplitude values. A method of evaluating a value with higher precision than the minimum quantization value of the ADC. Measuring the amplitude of the signal; Determining an averaging period tau as a function of the amplitude such that the averaging period tau is long when the amplitude is small and tau is short when the amplitude is large; And Averaging the amplitude over the averaging period to provide a filtered output signal. 21. The method of claim 20, wherein the function is a step function. 22. The method of claim 20 or 21, wherein the amplitude is equal to or greater than a preset reference value and the filtered output signal is an instantaneous value of the amplitude. 23. The method of any of claims 20 to 22, wherein said measuring step comprises converting an analog gas flow transducer signal into a digital signal providing said amplitude. 24. The method of claim 23, wherein the gas flow transducer is a transducer device in the form of a thermo-empirometer. A method of processing a non-linear transducer output signal over a measured physical variable to obtain a calibrated output signal representing a physical variable at a given scale. Maintaining the transducer under a plurality of validated physical variable conditions; Recording the output value under each of the conditions; Where V is the transducer output signal, N is greater than or equal to 3, the variable A _i is a coefficient determined from the recorded value, and α _i is a real number, expressed as follows for the nonlinear function that associates the output value with the physical variable To find the solution, And determining the calibration output signal for the transducer output signal using the analysis solution. 26. The method of claim 25 wherein α _i is greater than one. 27. The method of claim 26 wherein α _i is not an integer. 27. The method of any of claims 25 to 26, wherein the determining step Calculating a value of the physical variable for each of the possible values of the transducer output signal using the analysis solution; Creating a table of physical variable values indexed into digital output values; Converting the converter output signal to a digital output value; And And obtaining the value of the calibrated output signal from the table using the digital output value. 29. A method as claimed in any of claims 25 to 28, wherein said analysis is correct for each of said recorded values. 30. The method of any one of claims 25 to 29, wherein the analysis solution is separated into subranges. 30. A method according to any one of claims 25 to 29, wherein said transducer output signal is derived from a gas flow transducer signal having at least one of a secondary and a secondary approximation of a transfer function. . 32. The method according to claim 31, wherein said gas flow transducer is a transducer in the form of a thermo-emometer.