DE10062875A1 - Measurement of mass flow rate of liquids or gases using an ultrasonic transducer, with use of additional pressure gauges enabling determination of fluid density, temperature or viscosity - Google Patents

Abstract

Flowmeter for liquid or gaseous media has a transceiver (1) for transmission and receipt of ultrasound signals (2) into a measurement chamber both with and against the direction of flow. The transceiver comprises at least one piezoelectric ultrasonic transducer (3, 4) for sound generation with a pressure sensor (5, 6) that is used to measure the time of flight of sound wave dependent signals. The time of flight measurement is used to determine the temperature, density or viscosity of the fluid being measured.

Description

The invention relates to a flow meter for liquid or gaseous Media with the further features of the preamble of claim 1.

For a technically perfect transmission and reception operation of a Ultrasonic flow measurement is an independence from disturbance variables necessary requirement. In practice, however, all components have one Ultrasonic measuring path compared to a more or less strong dependence the environmental and medium field sizes. To the differential term of one Transmitting / receiving unit emitted and received ultrasound signals enforce the measuring chamber with and against the direction of flow determine, it is imperative that 0 of the medium, the respective signal propagation times of the opposing ultrasonic signals are the same. In the previously known solutions, this signal equality, the so-called reciprocity principle, through the smallest possible deviations in the Transmission and reception circuit implemented. The previously known Transceiver units are constructed in such a way that only certain elements, such as z. B. the ultrasonic transducer emitting the ultrasonic signals (e.g. piezoelectric elements) are traversed by both signal paths. The remaining parts of the signal path or the components arranged there are run through from one side only, so that all field influences differ Generate phase position. The components of the transmission and reception electronics prove also prove to be extremely sensitive, where coupling of parasitic Capacities can cause large measurement deviations. Furthermore arise Delays in the throughput time due to analog components of 1 nsec per component (so-called gate running time), which also leads to the above-mentioned injury of the principle of equality. So far, only the real one can be measured  Sound propagation time, which has the disadvantage that z. B. neither temperature, Density and viscosity measurements are possible with the ultrasonic measurement. The So far, temperature measurement can only be carried out with a temperature sensor Density is measured via the concentration distribution. To carry out These measurements must be recorded in the ultrasonic counter Measuring devices can be integrated, which leads to a relatively complex structure of the Ultrasound counter leads.

The invention is therefore based on the object of an ultrasonic counter Features of the preamble of claim 1 form such that a completely reciprocal measuring method is created and thus the Sound propagation time can be determined more precisely than previously.

This object is achieved by the entire teaching of claim 1. Advantageous further developments of the flow meter result from the Subclaims 2-24.

The flow meter according to the invention has at least one pressure sensor, with which sound wave dependent signals can be generated for sound propagation time determination are. Using the sound propagation time determination exclusively by at least one Pressure sensor is the measurement of deviations e.g. B. in the arrangement of Ultrasonic transducer independent. The ultrasonic transducers are only for that Sound generation responsible if the measurement is made exclusively using the Pressure sensors are carried out. Due to the independence of the arrangement of the Ultrasonic transducers thus become a completely reciprocal measuring method created.

The temperature, density or viscosity of the medium to be measured.  

The at least one pressure sensor can be used to record the Ultrasound transducer emitted ultrasound signal at the beginning of the to be measured Sound path can be provided.

The pressure sensor therefore records the sound signal before it is used for the Has run through the used measuring distance, and thus determines one defined start time at a defined measuring point.

The sound propagation time can be determined via a first pressure sensor and a second pressure sensor. This can be used to determine the sound propagation time done exclusively by means of the pressure sensors and it will be as above explained, a completely reciprocal measuring method possible.

A first and a second ultrasonic transducer can advantageously be used be provided which define a sound path length L. Within the Sound path L are a first and a second pressure sensor, the are also arranged at a fixed distance M from one another. The first Pressure sensor can be the first ultrasonic transducer and the second Pressure sensor can be directly assigned to the second ultrasonic transducer. However, it is also possible that the pressure sensors at a different angle or with are arranged at different distances from the ultrasonic transducers. By this arrangement of the pressure sensors is in the constellations mentioned possible that both the sound signals generated by the respective ultrasonic transducer associated with the pressure sensor, as well as the after passing through the medium to be measured, sound signals received in convert electrical signals. The sound propagation time is only between the Pressure sensors determined and is therefore from the arrangement of the Ultrasonic transducers or other components in the transmitter / receiver unit independently.  

As an alternative to the sound propagation time determination described above between the Both pressure sensors, it is also possible to determine the sound propagation time between at least one ultrasonic transducer and a pressure sensor.

In this case, the received signal (after the Measuring section) recorded by the ultrasonic transducer. There is the Possibility that only an ultrasonic transducer and a pressure sensor are provided are, the ultrasonic signals the flow of the medium to be measured push through. The time of the ultrasonic signals between the Ultrasonic transducer and the pressure sensor and back measured from which the Difference term can be determined.

Another way of determining the sound propagation time provides that the Pressure sensor at a defined distance (e.g. exactly in the middle) from the two Ultrasonic transducers is arranged. The pressure sensor is used in this arrangement the recording of the signal emitted by the respective ultrasound transducer, the ultrasonic transducers receiving the flow penetrating Serve signal. In this variant, either the distance known between pressure sensor and ultrasonic transducer, or the pressure sensor be placed exactly in the middle between the two transducers, so that the two opposite ultrasound signals cover the same measuring distance, what is necessary for the exact determination of the sound propagation time.

The pressure sensor can be attached to an ultrasound reflector in the area of a Reflection surface or on an irradiated by the ultrasonic signal. wall be arranged so that the ultrasonic signals the medium unhindered can go through.

However, if the pressure sensors are located in the area of the sound path, can these be at least partially permeable to sound, so that the  Ultrasonic transducer emitted sound signal despite the pressure sensor unhindered can spread. So that the pressure sensor is permeable to the ultrasound, the external dimensions of the pressure sensors can be at most three times Correspond to the wavelength of the ultrasonic signal.

The arrangement of the pressure sensors in the flow region of the can advantageously measuring medium, because it means sound paths that are perpendicular to the Current or no directed current (e.g. dead water spaces, niches with Vortex formation and areas with discontinuous or unstable flow conditions) or by media other than the medium to be measured (e.g. by a Sound guide body) run, the sound movement behavior of the emitted and Do not influence the measurement of the ultrasound used. As already briefly above mentioned, can be between the ultrasonic transducer and the Ultrasonic transducer associated pressure sensor are a sound guide, so that the ultrasonic signals emitted by the ultrasonic transducer directly into a well measurable flow of the medium.

Especially in the case where only one ultrasonic transducer and one Pressure sensor is provided, the pressure sensor should be a very fast one Show start-up behavior, since the time of the emitted Ultrasonic signal between the ultrasonic transducer and pressure sensor is measured.

There is also the possibility that an ultrasonic transducer pair as only one Piezoceramic component is formed, which ultrasonic signals on both sides sending out. Due to the transmitter / receiver unit created in this way, the entire Flow meters can be made extremely compact.

With the arrangement of two pressure sensors, the sound propagation time t _Schall1 in one direction (from the first to the second pressure sensor) and the sound propagation time t _Schall2 in the opposite direction (from the second to the first pressure sensor) can be determined. The running time difference dt = t _sound1 - t _sound2 can then be determined on the basis of the running times. The respectively complete signal paths of the two ultrasonic signals running in different directions enable the absolute sound propagation time to be determined and the actual transit time difference dt to be determined. By knowing the absolute sound propagation time, the temperature, density and viscosity can also be determined.

If, on the other hand, only one pressure sensor and one ultrasonic transducer are provided, the sound propagation time from the ultrasonic transducer to the pressure sensor and back is determined, from which the transit time difference dt = t _sound1 - t _sound2 can also be determined. If two ultrasound transducers are provided, which are arranged at a defined distance from the pressure sensor, the transit time from the pressure sensor to the second ultrasound transducer and from the pressure sensor to the first ultrasound transducer is determined and the transit time difference is determined therefrom.

The ultrasonic transducers can be used to generate an oscillator Oscillator frequency are connected via at least one pulse generator. Each ultrasound transducer is expediently a pulse generator assigned that are started by the oscillator.

The time measurement can be carried out with two pressure sensors in such a way that after a wave train _{starts to vibrate,} the sound propagation time t _{Schall1 is} determined by the formula t _Schall1 = (T _g1s2 - T _g1s1 ) + m ₁ .T _OS starting from a first ultrasonic transducer. T _{g1s1 is} the time between a reference signal and the digitized received signal at the first pressure sensor, T _g1s2 is the time between the reference signal after m oscillations and the digitized received signal at the second pressure sensor. m ₁ is a natural number and marks the number of vibrations between the first and second pressure sensor. This number is determined using the sound propagation time that is expected from the measuring system. T _OS is the period of the oscillator and is, for example, 1 µsec. _Conversely , the sound propagation time t _Schall2 can be determined in reverse by the formula t _Schall2 = (T _g2s1 - T _g2s2 ) + m ₂ .T _OS . The transit time difference dt can be determined using the formula dt = ((T _g1s2 - T _g1s1 ) + m ₁ .T _OS ) - ((T _g2s1 - T _g2s2 ) + m ₂ .T _OS ). A clear determination of dt is thus possible if the period of the oscillator T _OS (eg 1 µsec) is greater than the transit time difference dt (eg 600 nsec), since then the value range of -2 <(m ₁ - m ₂ ) <2 does not exceed. With m ₁ = m ₂ , the transit time difference is therefore dt = T _g1s2 - T _g1s1 - T _g2s1 + T _g2s2 . The advantage of the transit time difference measurement is therefore that phase shifts that can arise from the pressure sensors cancel each other out through the subtraction. The dynamic settling behavior of the piezo ceramic of the ultrasonic transducer no longer has to be taken into account in full. This makes it possible to measure in the signal burst at the very beginning if no echo signals have yet overlaid the useful signal from the measuring section.

Accordingly, the time measurement takes place with only one pressure sensor, whereby here however, the reception delay time of the ultrasonic transducer (s) is included in the Differential runtime determination included.

A second oscillator frequency can also be generated by means of the oscillator, with which m can be determined.

The pressure sensors can e.g. B. piezo elements, capacitive sensors act on silicon or strain gauges. The respective pressure sensor can be designed as a differential pressure sensor and thus in a simple manner both the transmitted and the received ultrasonic signals record and convert into electrical signals.  

The pressure sensor can advantageously be used as a composite in the ultrasonic transducer be integrated, which saves additional assembly steps and signal feeds.

The invention is based on advantageous embodiments in the Drawing figures explained in more detail. These show:

Fig. 1 shows a basic construction of the transmitter / receiver unit,

Fig. 2 is a schematic representation of an alternative configuration of the transmitting / receiving unit,

Fig. 3 is a schematic representation of the sound transit time determination from pressure sensor 1 to pressure sensor 2 and

Fig. 4 shows a further alternative embodiment of a basic structure of a transmitting / receiving unit,

Fig. 5 shows a further alternative embodiment of a basic structure of a transmitter / receiver unit and

Fig. 6 shows an arrangement of a transmitter / receiver unit in a vortex measuring chamber.

Fig. 1 shows the transmitter / receiver unit 1 of a flow meter for liquid or gaseous media with a measuring chamber, which is, however, not shown in the drawing figure. The transmitting / receiving unit 1 is used to transmit and receive ultrasonic signals 2 , which pass through the measuring chamber with and against the direction of flow of the medium, which is indicated by the arrow. The transmitting / receiving unit comprises two ultrasonic transducers 3 , 4 for sound generation, which are designed in particular as piezoelectric elements. Furthermore, pressure sensors 5 , 6 are provided, with which sound-wave-dependent measurement signals can be generated for sound propagation time determination. The ultrasonic transducers 3 , 4 are therefore only used for sound generation, the pressure sensors 5 , 6 only for recording the ultrasonic signals emitted by the ultrasonic transducers at the beginning of the sound path and the ultrasonic signals passing through the sound path and converting them into electrical measurement signals. As a result, the ultrasound measurement is not dependent on disturbance variables in the area of the ultrasound transducers and on the sound path between the pressure sensor and the ultrasound transducer, and a completely reciprocal measurement method can take place. For the conversion of the analog electrical measurement signals of the pressure sensors 5 , 6 into digital signals, for. B. an A / D converter 10 is provided.

The first 3 and the second ultrasonic transducer 4 are arranged according to FIG. 1 in such a way that they define a measuring section L, a first 5 and a second pressure sensor 6 also being located within the measuring section L at a fixed distance M from one another. The first pressure sensor 5 is assigned to the first ultrasound transducer 3 and the second pressure sensor 6 is assigned to the second ultrasound transducer 4 . The ultrasonic signals 2 running with and against the direction of flow thus enforce the identical signal path, which is defined by the distance M, so that non-linearities outside of this measuring path play no role in determining the transit time of the ultrasonic waves.

In the alternative structure of the transmitter / receiver unit 1 according to Fig. 2, the pressure sensors 5, 6 is not directly the ultrasonic transducers 3, 4 associated, but are located in the directed flow, while the ultrasonic transducers 3, 4 are arranged in lateral recesses of the flow channel. In this case too, the measurement of irregularities in the area of the ultrasound transducers 3 , 4 or the distance between the respective ultrasound transducer and the pressure sensor is independent, since only the measuring distance M between the pressure sensors 5 , 6 is of importance for the measurement, each of the two opposing ultrasonic waves is penetrated.

These arrangements can be used to determine the sound propagation time t _Schall1 in one direction from the first pressure sensor 5 to the second pressure sensor 6 and the sound propagation time t _Schall2 in the opposite direction from the second pressure sensor 6 to the first pressure sensor 5 . The running time difference dt = t _sound1 - t _sound2 can _then be determined on the basis of the running times. Accordingly, the two measurement signals of the pressure sensors 5 , 6 are used directly in the differential time determination. The phase shift that occurs between the respective ultrasonic transducer 3 , 4 and the respectively assigned pressure sensor 5 , 6 is not taken into account in the time measurement.

An exemplary determination of the sound propagation time using the arrangement according to FIG. 1 or 2 is shown in FIG. 3. T ₀ denotes the starting point at which the oscillator 7 (O _S ) starts the first pulse generator 8 and uses the first ultrasonic transducer 3 to generate a sound burst signal which is detected by the first pressure sensor 5 (S1). A wave train in the sound burst signal is provided with reference number 11 . After the start-up behavior nf _g1 (g1 denotes the first pulse generator 8 ), the time between a reference signal and the first digitized received signal E1 is determined (T _g1s1 ). n is any integer number of wave trains up to the steady state. After a further m oscillations of O _S , the time between the reference signal and the digitized received signal E2 (T _g1s2 ) is measured at the second pressure sensor 6 (S2). The sound propagation time t _Schall1 can now be determined _using the formula t _Schall1 = (T _g1s2 - T _g1s1 ) + m ₁ .T _OS .

T _OS is the period of the oscillator 7 . The sound propagation time t _{Schall2 can} be determined vice versa according to the formula t _Schall2 = (T _g2s1 - T _g2s2 ) + m ₂ .T _OS .

The difference running time, _i.e. the running time difference dt, can be determined by the formula dt = ((T _g1s2 - T _g1s1 ) + nx ₁ T _OS - ((T _g2s1 - T _g2s2 ) + nx ₂ T _OS ), the period time of the oscillator T _OS is greater than the transit time difference dt, since then m does not exceed the value range -2 <(m ₁ - m ₂ ) <2. With m ₁ = m ₂ , the transit time difference is dt = T _g1s2 - T _g1s1 - T _g2s1 + T _g2s2 . Accordingly, the time measurement of phase shifts and dynamic time delays of the pulse generators 8 , 9 and the ultrasonic transducers 3 , 4 and the number m is independent.

As shown in FIGS. 4, 5 and 6, only one pressure sensor 5 in combination with one or two ultrasound transducers 3 , 4 can be provided for determining the sound propagation time. According to FIG. 4, the sound propagation time determination between an ultrasonic transducer 3, and a pressure sensor 5 which is disposed on a reflection surface 13 is performed. With this arrangement, the transit time from the ultrasonic transducer 3 to the pressure sensor 5 and vice versa from the pressure sensor 5 to the ultrasonic transducer 3 is measured and the differential transit time is determined therefrom. For this purpose, the pressure sensor 5 has a very fast start-up behavior.

In Fig. 5, a pressure sensor 5 is placed exactly in the middle between the two ultrasonic transducers 3, 4. The differential transit time results from the sound transit time between the pressure sensor 5 and the ultrasound transducer 4 and between the pressure sensor 5 and the ultrasound transducer 3 . Alternatively, there is also the possibility that the pressure sensor 5 is arranged at a different defined distance from the two ultrasonic transducers 3 , 4 . By means of the knowledge of the distances from the pressure sensor 5 to the respective ultrasonic transducers 3 , 4 , the differential transit time can also be determined. According to the arrangement in FIGS. 4 and 5, the pressure sensors 5 , 6 are arranged in the region of a reflection surface 13 . In FIGS. 2 and 6, the pressure sensors are arranged on an ultrasound reflector 12.

The pressure sensors 5 , 6 , in particular in the arrangement according to FIG. 1, are at least partially permeable to sound, so that the ultrasound signals 2 emitted by the ultrasound transducers 3 , 4 can propagate unhindered. For this purpose, the external dimensions of the pressure sensors correspond at most to three times the wavelength of the ultrasonic signal 2 .

The pressure sensors 5 , 6 are arranged in FIGS. 1 and 2 in the flow area of the medium to be measured, so that sound paths perpendicular to the flow (see FIG. 2) or sound paths without directional flow (e.g. niches with vortex formation) the sound behavior of the Do not influence the sound used for the measurement. Furthermore, between the ultrasound transducer 3 , 4 and the pressure sensor 5 , 6 assigned to the ultrasound transducer 3 , 4 , there can be a sound conducting body that transmits the ultrasound without hindrance.

The vortex measuring chamber 14 shown in FIG. 6 contains an ultrasound transducer 3 , which is designed as a piezoceramic component and emits ultrasound signals 2 on both sides. Alternatively, two ultrasound transducers 3 , 4 can also be combined, each of which emits the ultrasound signals 2 in one direction. The pressure sensor 5 records the emitted ultrasound signals 2 , while the ultrasound signals traversed the sound path are recorded by the ultrasound transducer 3 and / or 4 .

A second oscillator frequency can also be generated by means of the oscillator 7 . The number of vibrations m can thus be determined and the respectively exact transit time t _sound1 or t _{sound2 is obtained} .

The pressure sensors 5 , 6 can be designed as differential pressure sensors or as ultrasound microphones. In a particularly advantageous embodiment variant, the pressure sensors 5 , 6 can be integrated as a composite in the ultrasonic transducer 3 , 4 and can thus be used as a component in the flow meter, which considerably simplifies assembly.

LIST OF REFERENCE NUMBERS

1

Transmitter / receiver unit

2

ultrasonic signals

3

First ultrasonic transducer

4

Second ultrasonic transducer

5

First pressure sensor

6

Second pressure sensor

7

oscillator

8th

First pulse generator

9

Second pulse generator

10

A / D converter

11

wave

12

Ultrasonic Reflector

13

reflecting surface

14

Wirbelmeßkammer

Claims (24)

1. Flow meter for liquid or gaseous media with a measuring chamber, in which at least one transmitting / receiving unit ( 1 ) for transmitting and receiving ultrasonic signals ( 2 ) which pass through the measuring chamber with and against the flow direction is arranged, the transmitting / Receiving unit ( 1 ) comprises at least one ultrasonic transducer ( 3 , 4 ) for sound generation, in particular a piezoelectric element, characterized in that at least one pressure sensor ( 5 , 6 ) is provided with which sound-wave-dependent measurement signals for sound propagation time determination can be generated. 2. Flow meter according to claim 1, characterized in that the temperature, density or viscosity of the medium to be measured can be determined.   3. Flow meter according to one of claims 1 or 2, characterized in that the at least one pressure sensor ( 5 , 6 ) for receiving the ultrasonic signal ( 5 , 6 ) emitted by the ultrasonic transducer ( 2 ) is provided at the beginning of the sound path. 4. Flow meter according to one of the preceding claims, characterized in that the sound transit time is determined by a first pressure sensor ( 5 ) and a second pressure sensor ( 6 ). 5. Flow meter according to one of the preceding claims, characterized in that a first ( 3 ) and a second ultrasonic transducer ( 4 ) are provided which define a sound path L, and within the sound path L, also at a fixed distance M from each other, the first ( 5 ) and the second pressure sensor ( 6 ). 6. Flow meter according to claim 5, characterized in that the first pressure sensor ( 5 ) is assigned to the first ultrasonic transducer ( 3 ) and the second pressure sensor ( 6 ) to the second ultrasonic transducer ( 4 ). 7. Flow meter according to one of claims 1 to 3, characterized in that the sound transit time is determined between at least one ultrasonic transducer ( 3 , 4 ) and a pressure sensor ( 5 , 6 ). 8. Flow meter according to one of the preceding claims, characterized in that the pressure sensor ( 5 or 6 ) is arranged at a defined distance from the two ultrasonic transducers ( 3 , 4 ). 9. Flow meter according to one of the preceding claims, characterized in that the pressure sensor ( 5 , 6 ) is arranged on an ultrasonic reflector ( 12 ). 10. Flow meter according to one of the preceding claims, characterized in that the pressure sensor ( 5 , 6 ) is arranged in the region of a reflection surface ( 13 ). 11. Flow meter according to one of the preceding claims, characterized in that the pressure sensors ( 5 , 6 ) are at least partially permeable to sound. 12. Flow meter according to one of the preceding claims, characterized in that the outer dimensions of the pressure sensors ( 5 , 6 ) correspond to at most three times the wavelength of the ultrasonic signal ( 2 ). 13. Flow meter according to one of the preceding claims, characterized in that the pressure sensors ( 5 , 6 ) are arranged in the flow region of the medium to be measured. 14. Flow meter according to one of the preceding claims, characterized in that between the ultrasonic transducer ( 3 , 4 ) and the pressure sensor ( 5 , 6 ) associated with the ultrasonic transducer ( 3 , 4 ) there is a sound guide element. 15. Flow meter according to one of the preceding claims, characterized in that the pressure sensor ( 5 , 6 ) has a very fast start-up behavior. 16. Flow meter according to one of the preceding claims, characterized in that the ultrasonic transducer ( 3 , 4 ) is designed as a piezoceramic component which emits ultrasonic signals ( 2 ) on both sides. 17. Flow _meter according to one of the preceding claims, characterized in that the sound propagation time t _Schall1 with the flow direction and the sound propagation time t _Schall2 against the flow direction can be determined and based on the transit times the transit time difference
dt = t _sound1 - t _sound2
can be determined. 18. Flow meter according to one of the preceding claims, characterized in that the ultrasonic transducers ( 3 , 4 ) with an oscillator ( 7 ) for generating an oscillator frequency via at least one pulse generator ( 8 , 9 ) are connected. 19. Flow meter according to one of the preceding claims, characterized in that after an _{oscillation behavior of} a wave train ( 11 ) starting from the first ultrasonic transducer ( 3 ), the sound propagation time t _Schall1 by the formula
t _sound1 = (T _g1s2 - T _g1s1 ) + m ₁ .T _OS
can be determined, where T _{g1s2 is} the point in time of the digitized received signal at the second pressure sensor ( 6 ), T _{g1s1 is} the point in time of the digitized received signal at the first pressure sensor ( 5 ), m ₁ corresponds to the number of vibrations between the first and second pressure sensors, and T _OS the period of the oscillator ( 7 ), and the sound propagation time t _Schall2 can be determined vice versa. 20. Flow meter according to claim 19, characterized in that the transit time difference dt can be determined by the formula
dt = ((T _g1s2 - T _g1s1 ) + m ₁ .T _OS - ((T _g2s1 - T _g2s2 ) + m ₂ .T _OS ),
the period of the oscillator T _{OS being} greater than the transit time difference dt and with m ₁ = m ₂ the transit time difference
dt = T _g1s2 - T _g1s1 - T _g2s1 + T _g2s2
is. 21. Flow meter according to one of the preceding claims, characterized in that at least one second oscillator frequency can be generated.   22. Flow meter according to one of the preceding claims, characterized in that at least one of the pressure sensors ( 5 , 6 ) is a differential pressure sensor. 23. Flow meter according to one of the preceding claims, characterized in that at least one of the pressure sensors ( 5 , 6 ) is designed as an ultrasound microphone. 24. Flow meter according to one of the preceding claims, characterized in that at least one of the pressure sensors ( 5 , 6 ) is integrated as a composite in the respective ultrasonic transducer ( 3 , 4 ).