JPH04231820A - Measured value detector for ultrasonic-wave flow-rate measuring apparatus - Google Patents

Abstract

PURPOSE: To provide a measured value detector wherein defect which ultrasonic flow rate measurement principle has is eliminated. CONSTITUTION: This ultrasonic flow rate measured value detector consists of a straight measuring pipe 1 having a pipe wall which is arranged on a pipe line introducing liquid to be measured. On the peripheral surface of the pipe wall, the following are formed and linked at intervals in the flow direction; a first resonance absorber composed of an absorber disk 111, a first converter disk 21 wherein a first ultrasonic converter 31 for driving a radial resonance frequency is fixed on one side surface, a second converter disk 22 wherein the similar second ultrasonic converter 32 is fixed, and a second resonance absorber 12 composed of an absorber disk. The absorber disks are so designed that the respective radial resonance frequencies are equal to the ultrasonic wave driving frequency.

Description

[Detailed description of the invention]

0001

SUMMARY OF THE INVENTION The present invention provides a straight measuring device which can be inserted into a pipeline conducting the liquid to be measured and which has a free flow cross section and a continuous tube wall. A measurement value detector for an ultrasonic flow rate measuring device consisting of a tube, in which the following are fixed in a form-connected manner to the circumferential surface of the tube wall, successively spaced apart from each other in the direction of flow: a first resonant absorber on the inlet side consisting of at least one absorber disk and on one side at least one first ultrasonic transducer exciting a radial resonant frequency; consisting of a first transducer disk, a second transducer disk to which a second ultrasonic transducer exciting at least one radial resonant frequency is fixed on one side, and at least one absorber disk. on the outflow side, a second resonant absorber is fixed, said absorber disks being designed such that their respective radial resonance frequency is equal to the excitation frequency of said ultrasonic transducer. Consists of a measurement value detector for a flow rate measuring device.

[0002] According to the invention, the drawbacks associated with the ultrasonic flow measurement principle can be overcome by the characteristics and advantages described below. The measured value detector can be designed even for very small nominal diameters of the measuring tube, so that even small and very small flow rates can be measured.

The measurement value detector is furthermore suitable for any type of liquid and is independent of what type of flow form is formed in the liquid. Both laminar and turbulent flows can be measured. Furthermore, flows at the boundary between laminar and turbulent flows, or flows with significantly varying Reynolds numbers, can be directly measured.

[0004] Furthermore, the material of the measurement value detector can be matched to the liquid to be measured taking into account its corrosive properties. Also, the measurement value detector is useful as is for food products. This is also further advantageous in that the measuring tube can be easily cleaned due to its constant inner wall and no materials are deposited there. High-pressure liquids can also be measured with metal or ceramic measuring tubes.

Since the ultrasonic transducer is fixed on at least one side of the transducer disc, it can be replaced from the pipeline without dismantling the measured value detector, ie interrupting a sequence involving, for example, a flow measurement. There's no need to.

[0006] Particularly suitable electronic measuring and operating circuits are those described in WO-90/00723 of the applicant. According to it, an ultrasonic transducer can operate alternately as an ultrasonic transmitter or an ultrasonic receiver to measure the transit time of ultrasonic waves both in the flow direction and in the counter-flow direction. I'm trying to make it possible.

With the inventive configuration of the measurement value detector, it is also possible to adjust the distance between the transducer discs in such a way that the travel time differences that occur during operation can be processed by the connected measurement and activation circuit. .

The ultrasonic transducer is an ultrasonic transducer made of a suitable piezoelectric material, for example a piezoceramic. The transmitting transducer is brought into mechanical resonance by the application of an alternating voltage of a suitable frequency, which means that the electrical frequency coincides with one of the mechanical resonance vibrations, so that this (acoustic) frequency When the ultrasonic signal of the transducer freely oscillates,
It is best realized when transmitted from there.

According to the invention, each ultrasound transducer is fixed to its associated transducer disc, so that the ultrasound transducer excites this transducer disc accordingly. This is done optimally here too when one of the mechanical resonance vibrations of the transducer disc is excited, ie when this resonance vibration coincides with the acoustic frequency of the transducer. In the present invention, the mechanical resonant frequency of each transducer disk is one of its radial resonant frequencies, for example the mode-zero resonant frequency. The transducer disk therefore vibrates in the radial direction, so that at the point where the transducer disk is fastened to the measuring tube, these vibrations are transmitted to the tube wall and from there to the liquid (see FIG. 4).

The receiving ultrasonic transducer is excited by the mechanical vibrations acting on it from the transducer disk so as to deliver an alternating voltage of the same frequency. The mechanical vibrations of the transducer disk with its radial frequency are further
Affected by ultrasonic waves traveling through the liquid via the measuring tube wall.

[0011] In embodiments of the invention, the measurement value detector can be made entirely of metal, for example of a stainless steel alloy, which is suitable for the desired application. However, according to other embodiments, it is also possible to use different metals for the measuring tube, for the transducer disk and/or for the absorber disk. This means that in another embodiment, on the one hand, the transducer disc and the absorber disc are made of the same metal with the lowest possible thermoelastic coefficient and the measuring tube is corrosion-resistant, or on the other hand, the mechanical resonance of the transducer disc is It is particularly advantageous if the Q is large compared to the Q of the resonance of the absorber disc.

According to an embodiment of the invention, the measuring tube has a wall that is thickened in a part of its length between the transducer disks. As a result, acoustic signals propagating in the tube wall starting from one of the transducer discs and having a detrimental effect on the measurement accuracy are attenuated to such an extent that they do not reach the other transducer disc.

In a further embodiment, the thickened wall can also be provided with at least one annular groove, which is preferably filled with a damping material that coats the circumferential surface of the wall. ing. A mechanical longitudinal wave filter is thereby realized by each of these two means.

In particular when the resonant absorber has one or more absorber discs, it is also possible for each resonant absorber to be provided with a damping material filling the intermediate space between these absorber discs. can. In this case, the peripheral surface can also be coated.

According to a further embodiment of the invention, the measurement value detector can be provided with a decoupling disk between each transducer disk and an adjacent absorber disk, in which case these The dimensions and/or mechanical properties of the decoupling disc are similar to the dimensions and/or mechanical properties of the absorber disc.
or have different mechanical properties.

In a further embodiment of the invention, the measured value detectors each have an ultrasonic sensor on the transducer disc, the ultrasonic sensors being actuated as actual value generators at the resonant frequency of the transducer disc. It is inserted into an electronic phase control loop for controlling and generating an excitation signal for the ultrasonic transducer.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained in detail with reference to the drawings. The drawings show a section through the structure of the measured value detector and the structure of some parts of the measured value detector as well as the operating circuit.

The sectional view of FIG. 1 shows a measured value detector as an example. It is suitable material, advantageously,
For example, it is made of metal such as stainless steel. Ceramic or glass materials are also suitable. The material selection depends on the specific application and its parameters, such as the type and properties of the liquid to be measured, pressure range, temperature range, ambient conditions, etc.

In FIG. 1, the measuring tube 1 has an inlet 5 on the left and an outlet 6 on the right, so that the direction of flow corresponds to the arrow. It has no tube wall. A first resonant absorber 11 on the inflow side, consisting of an absorber disk 111, is fixed to its circumferential surface. In this absorber disk,
A first transducer disk 21 follows at a certain distance in the flow direction, and a first ultrasonic transducer 31 is fastened to the side of this transducer disk.

On the outflow side, the transducer disk 21
transducer disk 22 . A second ultrasonic transducer 32 is laterally fixed to this transducer disk. Also spaced apart in the direction of flow,
A second resonant absorber 12 , consisting of an absorber disk 121 , follows preferably at the same spacing as between absorber disk 111 and transducer disk 21 .

The ultrasonic transducers 31, 32 can also be mounted on mutually facing sides of the transducer disk. This is particularly advantageous when construction space is at a premium. Furthermore, for example for reasons of symmetry, a plurality of ultrasound transducers, e.g. four ultrasound transducers, can be used in FIG.
It is also advantageous to provide one transducer disk so that it can be read from.

[0022] The measured value detector is connected by its inflow and outflow sides, for example by corresponding coupling elements, such as flanges.
It is inserted into a pipeline (not shown) through which the liquid to be measured flows.

The two resonant absorbers 11, 12 on the one hand prevent acoustic energy from reaching the connected pipeline, and on the other hand, if this happens, the resulting reflected energy is in the return path” and thus the transducer disk 21,
There is no possibility of reaching 22.

may come from the pipeline (
Frequencies corresponding to the energy (interference), for example in the form of noise, are of course also absorbed.

The absorption properties are firstly based on the fact that the absorber disc has a mechanical resonance at ultrasonic frequencies and therefore absorbs acoustic energy when excited. Depending on the Q of the mechanical resonance of the absorber disk, the absorber disk extracts energy from the ultrasound field even in the steady state. This energy extraction depends on the resonance Q, which can be controlled by appropriate material selection.

FIG. 2 shows that, between the two transducers 21, 22 in the wall of the measuring tube 1, starting from one transducer disc, the other transducer disc is reached, which can lead to measurement errors. Advantageous measures are illustrated which make it possible to prevent the propagation of sensitive longitudinal waves. In other words, in order to avoid measurement errors, the measuring tube is provided with a thick wall 2 over part of its length. Otherwise, the structure of the measured value detector is the same as that shown in FIG.

FIG. 3 shows the use of advantageous measures in the embodiment shown in FIG. 2, by means of which the damping properties of the embodiment of FIG. 2 are improved. For this,
An annular groove 3 formed in the thickened wall 2 is provided. Advantageously, the bottoms of the annular grooves are each of such depth that the wall thickness there is equal to the wall thickness of the measuring tube in the inflow and outflow regions.

FIG. 3 further shows that in a further embodiment the annular groove 3 can be filled with a damping material 4, for example a synthetic resin. The damping material here also covers the circumferential surface of the thickened wall 2, although this is not absolutely necessary. However, by doing so, the damping characteristics can be further improved.

The two embodiments of FIG. 3 prevent longitudinal waves in the measuring tube wall from reaching from one ultrasonic transducer to the other even with transducer disks located close to each other. A mechanical longitudinal wave filter can be realized.

FIG. 4 shows how the transducer disc oscillates in the radial direction (see dashed lines). Ultrasonic transducer 31 is a correspondingly designed disk.

FIG. 5 shows that an annular ultrasound transducer 31' can also be used.

FIG. 6 shows three absorber disks 111, 112, 11, each having the same radial resonance frequency.
3 is shown.

FIG. 7 shows the three absorber disks 1 of FIG.
It has been shown that the intermediate space between 11, 112, 113 can be filled with a damping material 4', which can optionally also cover its circumferential surface. This provides the same effect as the damping material 4 in the device of FIG.

Another embodiment of the invention is schematically shown in FIG. A decoupling disk 71, 72 is inserted between each transducer disk 21, 22 and an adjacent absorber disk 11, 12. These are used to suppress potentially harmful overcoupling of acoustic energy to the absorber disk via the tubing connecting the transducer disk to the absorber disk. The dimensions and/or mechanical properties of the decoupling disk differ from those of the absorber disk.

In any of the embodiments according to FIGS. 1 to 8, the absorber disc and the transducer disc can be preformed parts that are fixed to the measuring tube 1, for example using a press fit. . In this type of construction, as already mentioned, different materials can be used for the measuring tube and disk. However, if the measuring value detector can be made from the same material, on the other hand it is also possible to manufacture the measuring value detector in one piece, for example by precision casting or turning.

Finally, the block diagram shown in FIG. 9 shows how the excitation signal for the ultrasonic transducers is determined so that each transmit transducer always excites the associated transducer disk with its resonant frequency. This explains how this can occur. This is done using a phase control loop 9. The transducer disk 21 is shown in side view, so that the ultrasonic transducers 31 , 33 , 34 , 35 connected in parallel - here four - as well as one ultrasonic sensor 81 are schematically shown. I can see that you are there.

An excitation signal in the form of a (high frequency) sinusoidal voltage is supplied not only to the converters 31 , 33 , 34 , 35 but also to the input of the voltage amplifier 91 . In a corresponding manner, the ultrasonic sensor 81 is connected to the input side of the voltage amplifier 91', to which a capacitor C, which is connected to the circuit zero, is connected in parallel. This capacitor C provides a sufficiently large time constant of the sensor 81 together with the input resistance of the voltage amplifier 91'. The respective output sides of the two voltage amplifiers 91, 91' are led to the respective input sides of a square wave converter 92, 92'. These can be realized, for example, as amplifiers whose input side is overcontrolled.

The respective outputs of the two square wave converters 92, 92' are connected to the respective inputs of a phase comparator 93 having a low-pass filter. A voltage proportional to the phase shift between the excitation signal and the signal of the ultrasonic sensor 81 appears on the low-pass filter. This voltage is supplied to the control circuit 94 along with the signal "90°" for a 90° phase shift. At the output of the control circuit appears a voltage representing information about the resonant frequency. That is, this voltage is supplied to the voltage controlled oscillator 97. The frequency fC of this oscillator corresponds to the frequency of the excitation signal before being multiplied by a constant predetermined factor using frequency divider 98. The input side of the rectangular wave to sine wave converter 99 is connected to the output side of the frequency divider 98. Phase comparator 93 is simply realized by an exclusive OR gate.

In order to avoid having to provide one phase control loop for each ultrasonic transducer that operates alternately as a transmitter or a receiver, a phase control loop 9 is provided.
A switch 95 is provided which opens as soon as the controlled condition is reached. The voltage corresponding to the controlled state is then stored in the storage memory CH during the entire measurement cycle (measurement in the direction of flow and in the direction opposite to flow). Before a new measurement cycle, the correct resonant frequency can be set anew.

[0040] Via the sensor 81, the correct functioning of the associated transducer discs and their transducers can also be monitored.

[0041]

[Effects of the Invention] The measurement value detector for an ultrasonic flow rate measuring device of the present invention is capable of measuring even extremely small flow rates, is suitable for any type of liquid, and has features such as easy replacement of the ultrasonic transducer, etc. It has the following advantages.

[Brief explanation of the drawing]

1 is a schematic cross-sectional view of an embodiment of a measurement value detector with the same wall thickness of the measuring tubes; FIG.

FIG. 2 shows a schematic cross-sectional view of an embodiment of the measurement value detector with thickened walls between the transducer disks;

FIG. 3 is a schematic cross-sectional view of an embodiment of a measurement value detector in which an annular groove in the thickened wall is filled with a damping material;

FIG. 4 is a schematic cross-sectional view of a transducer disc with a disc-shaped ultrasound transducer disc;

FIG. 5 is a schematic cross-sectional view of a transducer disc with an annular ultrasound transducer disc;

FIG. 6 is a schematic cross-sectional view of a resonant absorber with three absorber disks;

7 is a schematic cross-sectional view of the resonant absorber of FIG. 6 with a damping material attached; FIG.

FIG. 8 is a schematic cross-sectional view of a measurement value detector with a decoupling disk;

FIG. 9 is a block circuit diagram of a phase control loop for generating an excitation signal for an ultrasound transducer.

[Explanation of symbols]

Claims (12)

[Claims] 1. For an ultrasonic flow measuring device consisting of a straight measuring tube (1) which can be inserted into a pipeline leading to the liquid to be measured and has a free flow cross section and a continuous tube wall. Measurement value detectors, in which at least one absorber disk (111) is fixed in a form-locking manner on the circumference of the tube wall, continuously spaced from each other in the flow direction. a first resonant absorber (11) on the inflow side consisting of a first transducer disk on one side of which a first ultrasonic transducer (31) exciting at least one radial resonant frequency is fixed; (
21), a second transducer disk (22), on one side of which a second ultrasonic transducer (32) exciting at least one radial resonance frequency is fixed; at least one absorber disk (121); ) is fixed on the outflow side, said absorber disks (111, 121) being shaped in such a way that their respective radial resonance frequency is equal to the ultrasound excitation frequency. A measurement value detector for an ultrasonic flow rate measuring device, characterized in that: 2. The measurement value detector for an ultrasonic flow rate measuring device according to claim 1, comprising a metal measuring tube, a metal transducer disk, and an absorber disk. 3. The measurement value detector for an ultrasonic flow rate measuring device according to claim 2, wherein different metals are used for the measuring tube, the transducer disk and/or the absorber disk. 4. Measurement detector for an ultrasonic flow measuring tube, comprising a transducer disk and an absorber disk made of the same metal with the lowest possible thermoelastic coefficient and a corrosion-resistant measuring tube. [Claim 5] The mechanical resonance Q is the resonance Q of the absorber disk.
Claim 3 comprising a transducer disk that is large compared to the transducer disk.
A measured value detector for the ultrasonic flow measuring device described above. 6. The wall of the measuring tube (1) has a transducer disk (
21. The measured value detector for an ultrasonic flow rate measuring device according to claim 1, wherein a part of the length between the first and second portions is made thicker. Claim 7: The thickened wall (2) has at least one
The measurement value detector for an ultrasonic flow rate measuring device according to claim 6, comprising two annular grooves (3). 8. An annular groove (3) filled with a damping material (4) and/or a peripheral surface of a thickened wall (2) covered by said damping material. 7. The measurement value detector for an ultrasonic flow rate measuring device according to 7. 9. At least two absorber discs (111,
112, 113). The measured value detector for an ultrasonic flow rate measuring device according to claim 1. 10. The circumferential surface of the absorber disk is made of damping material (
10. The measured value detector for an ultrasonic flow rate measuring device according to claim 9, which is coated with 4). 11. Each transducer disk (21,
22) and an adjacent absorber disk (11, 12) in each case a decoupling disk (71, 72), the dimensions and/or mechanical properties of said decoupling disk 2. The measurement value detector for an ultrasonic flow measurement device according to claim 1, wherein the absorber disk has different dimensions and/or mechanical properties. 12. One of the transducer discs (21, 22) is provided with an ultrasonic sensor (81), which ultrasonic sensor (81) acts as an actual value generator in the transducer disc (21, 22).
The ultrasonic transducer (31,
12. Measurement value detector for an ultrasonic flow measuring device according to claim 1, wherein the measurement value detector is inserted into an electronic phase control loop (9) for generating an excitation signal for an ultrasonic flowmeter (32).