DE19617961C2 - Method for measuring the flow rate of gaseous or liquid media by means of ultrasound and a measuring device suitable for carrying out the method - Google Patents

Description

The invention relates to a method for measuring the current flow rate of gaseous or liquid media by means of ultrasound, in which within one or more of the medium through which the measurement flows and in one another reference path connected to the medium, in which the medium rests and in the same characteristic physical constraints prevail, the terms a signal emitted by an ultrasound transmitter determined and then in a signal processing device from this the flow velocity of the medium in the respective signal direction can be derived. The invention also concerns one to carry out this procedure suitable measuring device.

To measure the flow rate of media Devices used according to mechanical, electrothermal work, laser-optical or ultrasound processes. Except for working according to the electrothermal process the devices, the non-mechanical devices need one expensive electronics, an elaborate housing and elaborate Evaluation programs to calculate the target values, what a Reason for the relatively low spread of such devices is.

Ultrasonic measuring devices are still for more demanding Measuring tasks gladly used because they are the simultaneous Determining the direction and speed of a medium allow what they are especially for use in the Meteo rology suitable. They also allow the measurement of Turbulence.

Ultrasonic measuring devices for measuring a flow rate speed are constructed so that one or more measuring sections  are present in which the duration of the signal of a Ultrasound transmitter between a transmitter and a receiver or the phase shift between emitted and received signal is measured. The duration of an acousti signal in a medium is from the speed of movement of the medium in the signal direction and on the specific  Speed of sound in this medium dependent. The The speed of sound in turn is subject to the influence of Temperature and possibly the influence of others Properties of the medium.

Work to compensate for the influence of temperature Previously known devices according to the following procedure: To one Measurement basically becomes a measurement in the opposite direction connected and both terms or phase shifts are subtracted so that the purely windge component due to speed remains. To this Purpose is a double use of sender and receiver each necessary according to signal direction. High quality is therefore used Piezo elements that cause high costs.

From US-PS 5 343 744 z. B. an arrangement with three 120 ° offset transducers known, one of which as sound generator and the other two as receivers By ring-shaped switching after a certain Measurement time becomes the signal runtime in the three measurement sections measured in both directions and then arithmetic nically processed.

From DE-PS 26 51 142 is a flow rate knife for a medium flowing in one direction only known a single test section, in which also in the already explained in the alternating direction will.

Similar devices and methods are the subject of DE-OS 38 43 678 and DE-AS 24 29 822.

Because of the required switching and the start-up properties of the piezo elements already mentioned high-quality evaluation devices required. The response times of the Piezo elements move in ms range while a Resolution of the signal in the ns range is required so that the transit time differences from the envelopes of the wave packets  of the signal must be analyzed, which is a compli adorned control electronics required. After all, that is Accuracy of such a measurement places narrow limits, so that special devices are used for different measuring ranges Need to become.

From DE-C 44 22 367 is a flow meter for conventional Lichen flow measurement in one flow channel in two Directions known. The disadvantage is that this device based on the measurements in two directions with a zero Flow correction factor must work, because the transducers work as sender and receiver at the same time, not in have the same properties in both directions. It ent there is a zero flow error, d. H. a deviation of the measured values when zero flow is measured. The zero flow correction factor results from a measurement in both Directions in a reference path.

An arrangement known from WO 93/03334 works analogous to the arrangement from DE-C 44 22 367 with the Difference that the reference distance here in series to Measurement section is located and the signal for the reference section obtained from an echo from a deflection point of the signal becomes. Ultimately, measurements are again taken in both directions.

The measurement of the flow velocity according to DE-A 44 30 230 takes place in two directions, so that this too Device transmitter / receiver components are used have to. A reference distance and a zero recorded with it flow correction factor are not provided.

DE 44 30 223 describes a method and a device known for flow measurement using ultrasound. Here too there is no reference path. The measurement is done again in opposite directions and is therefore with already mentioned disadvantages.  

DE 31 46 477 is a circuit arrangement for measuring solution of the speed of flowing media. This is particularly useful in ventilation systems. Here is a value for the flow velocity from the Measurement formed in only one signal direction. However With this measuring method the influence of the temperature has to be considered view, since in the measurement the speed of sound with which depends to a large extent on the temperature is dependent. A sufficiently precise value for the currents This means that the speed of flow is only there with this method attainable, where almost constant temperature conditions, e.g. B. underground.

The invention has for its object a method and a measuring device working according to the method at the beginning Specify the type mentioned that the complete recording of Direction and flow velocity with high resolution allowed, but the construction of the measuring device with inexpensive Components allowed and no complicated control electronics tronics requires.

According to the invention, the object is achieved by a method at which the flow velocity of the medium from the Difference of the reciprocal values of only in one signal direction measured transit times of the respective measuring section and the Reference route is derived.

In a preferred manner according to the invention, that for the measurements in the reference path and in the or an in-phase signal is used for the measuring sections.

It can also be provided according to the invention that the barrel times at the end of the reference section and the measuring section (s) by measuring the phase shifts of the received be compared to the output signal.  

The solution according to the invention eliminates the previously customary one sequential double use of the sounder / receiver, because the influences of temperature and other variables on the Speed of sound by comparing the transit times in the  open measuring sections with the running time in an essentially Chen closed reference path with otherwise the same Conditions are eliminated.

The invention thus allows the use of inexpensive acoustic microphones as receivers and thereby leads already at a drastic reduction in manufacturing costs a corresponding measuring device. The Vermei also leads double use of the electroacoustic components by avoiding complex taxation electronics to further reduce manufacturing cost, as well as the relatively straightforward signal processing tung. For obtaining three-dimensional information three transmitter / receiver pairs are no longer necessary, son only a simple sounder and four standard microphones.

The invention opens up the possibility of using a sub broken, continuous signal in only one at a time To work the measuring direction between the sounder and the receiver, what unmistakable in terms of signal processing Brings advantages.

It can preferably also be provided that the frequency of the emitted ultrasound signal by the signal processing processing device is controlled so that in the reference path no phase shift between the emitted and the received ultrasound signal. So can be advantageous the sensitivity is always kept in the optimal range because the signals are always in their increasing range can be evaluated. It also becomes the maximum achievable measuring range maintained by over step the phase shift from a period of Output signal is limited.

The signal measured at the output of the reference path becomes For this purpose led to a controller that is controlled by a Frequency generator generated frequency with which the sounder  is acted on accordingly. The control signal of the controller is also a measure of the temperature of the medium because the runtime change in the reference route essentially depends only on the temperature.

The control signal can therefore according to a corresponding Signal processing used directly for temperature display become.

In a preferred manner, the sounder is in its reso operating range.

Deviating from the signal processing described above this also take place in such a way that the Runtimes at the end of the reference route and the measurement route (s) by measuring the frequency of the signal received can be determined in which the phase shift between the frequency of the output Si, which can be changed within limits signal and the signal received in each case becomes zero.

The measurement is also carried out with a continuous Output signal, which is preferably continuous in frequency is continuously changed between two cutoff frequencies.

According to the invention, the process sequence can be provided be that the length of the reference section and the measuring sections before starting a measurement in a still medium Comparison of the transit times or the phase shifts of the received at the end of the reference path and the measuring paths Signals is calibrated.

Should be a continuous measurement over a longer period of time Alternatively, a permanent potash can also be used bration by means of laser-optical processes or Microwave measurement can be made.

To detect a possible error on the reference route or the To be able to uncover measuring sections can also according to the invention  be provided that the amplitudes at the end of the Reference path and the measuring paths received signals are compared with each other and if the ampli tude of a signal versus an average of the received an error signal is triggered.

The measuring device for performing the method comprises a each equipped with a receiver, from the medium flowed through measuring section and one with a receiver equipped with the medium, from but this does not flow through the reference route, whereby for all measuring sections and one for the reference section effective sound generator is provided.

In a preferred manner according to the invention, the measuring sections and the reference path has the same length.

Preferably, the sound generator in the directions of the Measuring sections and the reference section are in phase Have radiation characteristics. As such is suitable a cylindrical piezo element to which i. ü. only moderate qua requirements must be made.

For a three-dimensional measurement of the flow vector the measuring device according to the invention be constructed so that the Receiver of the measuring sections and the sound generator to the corner points of an imaginary tetrahedron are arranged.

To reflect the signal and thus feedback To avoid the sound generator, the ref border line as a monomodal acoustic, d. H. reflections be a freelance leader (single mode).  

In practice, the structure could e.g. B. be designed so that a thin aluminum cylinder together with the sounder and a receiver is placed in a cap.

Is the meter z. B. for the measurement of wind speed provided, the union tube can also by be sealed by an ultrasound-permeable membrane, so that the sounder is protected against environmental influences. To the Compensation of the measurement conditions can in the hollow cylinder Publ tions are provided so that a connection to the vice exercise air is created.

Anbrin is recommended for a handheld version additional handle on the union tube.

The sounder is preferred in resonant areas operated if a phase difference measurement is carried out in accordance with the method he follows. Here there is the additional advantage that straightforward Piezo elements have a wide resonance spectrum, so sat a measurement in a large measuring range is made possible by for example, upper frequencies of a resonant fundamental frequency can be used to multiply the measuring range.

Due to the possibility of the phase position at the receiver of the Refe to move the reference distance to zero, the Phase angle in the other measuring sections also always in Range of signal zero crossing, in the one with the highest Measurement accuracy can be measured.

The measuring range can be compared to conventional devices Be expanded many times over.

Opened by the advantages of the measuring device according to the invention a wide range of uses. With the high measuring precision is the measuring device for meteorological and aeronautical Uses and suitable for environmental tasks.  

For the construction industry, wind measurement on cranes comes into play Consideration.

In aeronautical systems, the measuring device can also be used Determination of flight data, e.g. B. airspeed, Aircraft sliding and pitch angles are used then the flow velocity in a quasi stationary medium and a moving frame of reference becomes.

In particular, the price advantages also leave use of the measuring device in a non-professional Area become possible, such. B. as a handheld device for surfers, Hang glider and athletes.

In addition to the use for air and gases, the flow Measurement in low viscosity fluids possible.

The invention is illustrated below with the aid of an embodiment game are explained in more detail.

Show in the accompanying drawings

Fig. 1 shows the basic structure of a measuring device according to the invention to wind measurement in a perspective view;

Fig. 2 is a block diagram of the control and evaluation electronics of the measuring device when using the phase difference measurement according to the method and

Fig. 3 is a block diagram showing control and evaluation electronics of the measuring device when using the frequency measurement method.

The exemplary embodiments relate to a wind measuring device, the wind vector according to the inventive method  in terms of wind speeds in three spatial Directions is fully captured.

The measuring device contains three receivers 1 , 2 , 3 and a sound generator 4 . The receivers 1 , 2 , 3 are all equidistant from the sound generator 4 and together span an axis cross, which in the present case is to be understood as orthogonal. The three receivers 1 , 2 , 3 and the Schallge 4 sit at the corner points of an imaginary tetrahedron. The equally long measuring sections L1, L2, L3 are indicated by dashed lines.

The structure is formed by a ring 5 , on the underside of which the receivers 1 , 2 , 3 are placed at a distance of 120 °, and by a support 6 which holds the ring 5 in place .

A reference path LR is formed from a tube 7 designed as a monomodal acoustic conductor, in which at the lower end, likewise at the same distance from the sound generator 4 as the receivers 1 , 2 , 3 , the receiver 8 of the reference path LR is accommodated. The reference path LR is thermally and mechanically protected within a cylindrical union tube 9 , in which parts of the electronics can be accommodated. The reference path LR is connected to the surrounding atmosphere via the opening 10 in the union tube 9 and via the openings 11 in the tube 7 .

The sound generator 4 is covered with an ultrasound-permeable window in the form of a film 12 , which protects the sound generator 4 against environmental influences and completes the reference route LR.

The procedural sequence of signal processing at a Measurement can be represented as follows:

For the reference section and each measuring section L (LR, L1, L2, L3) the transit time T (TR, T1, T2, T3) is determined. The  the following calculation is based on the consideration of the Measuring section L1.

The running time TR in the reference path LR depends only on the speed of sound sv, which is the result

sv = LR / TR

results.

The transit time T1 of the measuring section L1 represented by the receiver 1 also depends on the air speed v1 in the direction of this measuring section according to the relationship

L1 / T1 = sv + v1.

The wind speed v1 results from the combination of both equations

v1 = L1 / T1 - LR / TR.

According to a first method variant, TR should always have a fixed number n of periods Tg of generator frequency fg

Tg = 1 / fg

consist.

In the event of a temperature change, there is also a change in the transit time TR in the reference path LR, which can be characterized as a phase shift tR, so that applies

TR = n × Tg + tR

and accordingly for the measuring section L1

T1 = n × Tg + t1.

With

L = L1 = LR

will total

v1 = L / (n × Tg + t1) - L / (n × Tg + tR)

Simply by measuring the phase shifts t1 and tR therefore the wind speed v1 towards the first Determine measuring section L1.

By now changing the generator frequency fg and thus the number of periods Tg by feedback, the phase shift tR = zero can always be achieved, so that with

v1 = L / (n × Tg + t1) - L / n × Tg

the wind speed v1 is derived solely from the measurement of the Phase shift t1 can determine what a comfortable Signal processing and working in a large measuring area richly allowed, since only small phase shifts are measured, where there is no risk that they will Exceed length of a period Tg. The latter is significant sam for the phase comparison method, since the number n of Periods remain unchanged.

The wind speeds v2, v3 are analogous in the others To determine directions.

Fig. 2 shows the block diagram of such signal processing. The sound generator 4 is connected to a frequency generator 13 and is excited to continuously emit radiation. As sound generator 4 in this embodiment, for. B. uses a cylindrical piezo element, the Emmis sionscharakteristik to in-phase radiation both in the direction of the receiver 8 of the reference path LR and in the direction of the receiver 1 , 2 , 3 of the measuring distances L1, L2, L3 leads. The receiver signals are amplified in the amplifiers 14-17 and, for a phase comparison method in the triggers 18-21, converted into rectangular pulses which serve as primary signals for the comparators 22-25. In the comparators 22 , 23 and 24 , the signal from the reference path LR is compared with the respective signal of the corresponding measuring path L1, L2, L3 and the dif ferential signal for further signal processing is passed to the resistance transducers 26 to 28 . Their output signals are proportional to the amounts of the components X, Y and Z of the wind vector, based on the axis cross spanned by the sound generator 4 and the receivers 1 , 2 , 3 . If necessary, the components X, Y, Z can be converted into a spatially rotated axis cross according to geographical points of view or a axis cross that is not at right angles to one another, for which the known geometric relationships are to be used for the conversion.

The output signal of the comparator 25 also serves to feed back the phase position of the signal of the receiver 8 of the reference link LR to the frequency generator 13 . For this purpose, the signal is applied to a controller 29 , the manipulated variable of which controls the frequency generator 13 in such a way that a phase shift = zero is maintained between the signal from the sounder 4 and the signal from the receiver 8 and thus at the output of the comparator 25 . This ensures optimal sensitivity regardless of the change in temperature.

The control signal at the output of the controller 29 then serves simultaneously as a measure of the temperature of the atmosphere, which can be taken from the resistance transformer 30 .

Another possibility for determining the signal transit times is described below with reference to FIG. 3.

The transit times T (T1, T2, T3, TR) for the measuring sections and the reference section (L1, L2, L3, LR) are not determined from measurements of the amount of the phase shifts, but rather from a measurement of a variable frequency at which the phase shift occurs at the respective Receiver 1 , 2 , 3 , 8 just becomes zero. The flow rate can then be determined from the measured frequency in the following way:

The frequency fg of the frequency generator 13 is proportional to the voltage U of a sawtooth generator 31 changed within limits and given to the sound generator 4 . The frequency fR, f1, f2, f3 at which the phase shift tR, t1, t2, t3 on the respective receiver 8 , 1 , 2 , 3 becomes zero is then measured in each case.

Then again refer to the measuring section L1 with

T1 = n × Tg1 (at t1 = 0) = n / f1

v1 = L × f1 / n - L × fR / n or

v1 = L / n (f1 - fR).

Since the frequency to be measured is available as a signal proportional to the voltage U (UR, U1, U2, U3) on the sawtooth generator 31 , the equation can also be written as

v1 = cL / n (U1 - UR),

where c is a device constant that u. a. the resonance ver holding the piezo crystal.

The signal evaluation is shown in Fig. 3 again as a block diagram. The signal picked up by the receivers 1 , 2 , 3 , 8 is compared by comparators 32-35 with the signal output by the frequency generator 13 . Reaches the phase shift tR, t1, t2, t3 the value zero, then the respective time is passed on by a logic circuit 36 to the analog / digital converter 37 , which at this moment is predetermined by the sawtooth generator 31 and is applied to the frequency generator 13 Voltage UR, U1, U2, U3 passes a processor for further processing. The flow velocity of a medium can thus be determined in three directions regardless of temperature.

To set the sensitivity range, ie the mean value of the voltage U of the sawtooth generator 31 , the temperature is either determined in the reference path LR before the start of the measuring process and then the mean value of the voltage U is regulated via feedback to an actuator 38 or a separate one on which Actuator 38 acting temperature sensor used.

Claims (18)

1. A method for measuring the flow rate of gaseous or liquid media by means of ultrasound, in which within one or more measuring paths through which the medium flows and in a further reference connected to the medium, in which the medium rests and in which the same characteristic physical Boundary conditions prevail, the transit times of a signal emitted by an ultrasound transmitter are determined and the flow velocity of the medium in the respective signal direction is then derived in a signal processing device, characterized in that the flow velocity of the medium is derived from the difference between the reciprocal values of the transit times measured in only one signal direction the respective measuring section and the reference section is derived. 2. The method according to claim 1, characterized in that for the measurements an in-phase signal is used in the reference section and in the measuring section or sections becomes. 3. The method according to claim 1 or 2, characterized in that the running time at the end of the reference section and the measuring section (s) by measuring the phase shift exercises of the received signal or signals can be determined with respect to the output signal. 4. The method according to any one of the preceding claims, characterized net that the frequency of the ultrasound signal emitted by the signal processing device is regulated so that there is no phase shift between the reference path sent and the received ultrasound signal.   5. The method according to claim 4, characterized in that the control signal of the Control path of the signal processing device simultaneously as a measure of the temperature of the Me diums is processed. 6. The method according to any one of the preceding claims, characterized in net that the sound generator is operated in its resonance range. 7. The method according to claim 1 or 2, characterized in that the running time at the end of the reference section and the measuring section (s) by measuring the frequency of the received signal are determined, in which the phase shift between the The frequency of the output signal, which can be varied within limits, and the received signal Signal becomes zero. 8. The method according to any one of the preceding claims, characterized net that is measured with a continuous ultrasonic signal. 9. The method according to any one of the preceding claims, characterized in net that the length of the reference section and the measuring sections before the start of a measurement in a dormant medium by comparing the transit times or the phase shifts the signals received at the end of the reference path and the measuring paths are calibrated. 10. The method according to any one of the preceding claims, characterized in net that the amplitudes of those received at the end of the reference path and the measuring paths Signals are compared with each other and if the amplitude of a signal deviates compared to an average value of the received signals or a predetermined value signal is triggered. 11. Measuring device for carrying out the method according to claim 1, each with a receiver equipped, flowed through by the medium and a measurement section equipped with a receiver, connected to the medium, but not flowed through by this reference path, characterized in that for all measuring sections (L1, L2, L3) and for the reference section (LR) a single effective sound generator ( 4 ) is provided. 12. Measuring device according to claim 11, characterized in that the measuring sections (L1, L2, L3) and the reference path (LR) have the same length. 13. Measuring device according to claim 11 or 12, characterized in that the sound transmitter ( 4 ) in the directions of the measuring sections (L1, L2, L3) and the reference section (LR) has an in-phase radiation characteristic. 14. Measuring device according to one of claims 11 to 13, characterized in that the receivers ( 1 , 2 , 3 ) measuring sections (L1, L2, L3) and the sound generator ( 4 ) are arranged at the corner points of an imaginary tetrahedron. 15. Measuring device according to one of claims 11 to 14, characterized in that the reference path (LR) is designed as a monomodal acoustic conductor. 16. Measuring device according to one of claims 11 to 15, characterized in that the reference path (LR) is designed as a hollow cylinder ( 7 ). 17. Measuring device according to claim 16, characterized in that the hollow cylinder ( 7 ) is provided with openings ( 11 ). 18. Measuring device according to one of claims 11 to 17, characterized in that the sound generator ( 4 ) is covered by an ultrasound-permeable membrane ( 12 ).