GB1583490A

GB1583490A - Apparatus for measuring the flow rate of a medium

Info

Publication number: GB1583490A
Application number: GB29845/77A
Authority: GB
Original assignee: Nord Micro Elektronik Feinmechanik AG
Current assignee: Nord Micro Elektronik Feinmechanik AG
Priority date: 1976-07-20
Filing date: 1977-07-15
Publication date: 1981-01-28
Also published as: IT1114636B; FR2359427A1; DE2632553A1; DE2632553B2

Description

(54) APPARATUS FOR MEASURING THE FLOW RATE OF A MEDIUM (71) We, NORD-MICRO ELEK TRONIK FEINMECHANIK AKTIENGESELLSCHAFT, (formerly known as NORD-MICRO ELEKTRONIK FEINMECHANIK GmbH) of Victor Slotosch-Strasse 20, D-6000 Frankfurt/tl Main 60, Federal Republic of Germany, a German Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an apparatus for measuring the flow rate of a medium, whereby by means of a sound source and a sound receiver the vortex systems behind an obstacle are scanned and the determined vortex frequency is indicated as a measure of the flow rate of the medium.

It is, for example, known from British Patent 925,541 to measure by means of sound the flow rate of a medium which contains the elements scattering the measuring jet, e.g. gas bubbles. The measuring jet in part flows upstream and in part downstream.

The acoustic frequency difference at the transmitter and at the receiver is measured.

The measured result is independent of the velocity of sound in the medium to be measured.

U.S. Patent 3,214,728 disclosed another measuring method in which a turbulence generator is used, detectors being arranged in its wake or vortex system. According to one embodiment of this Patent Specification, turbulence is recognised by the turbulence generator introducing into the flow a temperature which differs from the temperature of the medium, and the turbulence which occurs can be determined by small dynamic temperature changes. Therefore the measuring system is independent of the temperature of the flowing medium. It therefore has an advantage compared with those measuring arrangements in which the velocity of sound exerts a limited influence and in which consequently operate independently of the temperature of the medium under investigation.

A further effect is known from the flow teaching applied. A flag attached to a flagpole flutters to a greater or lesser extent depending on the wind speed. This is due to the fact that a vortex system is formed at the flag-pole and the flag positioned downstream thereof, whereby vortices occurring in staggered manner alternately at either side of the flag bulge out said flag to one side or the other.

Such vortex systems occur at any flow obstacle located in a flow. The frequency with which individual vortices occur behind said flow obstacle can be expressed by the following equation: S f =-. v d whereby f is the frequency, s the Strouhal number, d the effective diameter of the flow obstacle and v the flow rate. In this case, the frequency of the turbulence which occurs is independent of the temperature of the flowing medium.

The measuring arrangement according to German Patent Specification No. 2004 398 utilises this effect and this Specification discloses a circuit for a corresponding measuring apparatus. However, said measuring apparatus is only suitable for measuring the flow rate in a predetermined uniform direction, thus permitting the measurement e.g. of the flow rate of a medium in a pipe or duct if the flow is of a laminar nature. However, difficulties are encountered in the free atmosphere if it is desired to measure the direction and magnitude of a possibly nonlaminar flow. The present invention is intended to eliminate this difficulty.

The aim of the present invention is to measure both the speed and direction of a flow, and a development of the invention also makes it possible to determine only individual directional components of a free flow.

The latter problem occurs in particular with missiles relative to which it is important to measure the relative velocity between the particular missile and the direction component of a surrounding flow in the longitudinal axis of said missile, whereby it is necessary to take account of tolerances dependent on the aerodynamic profile.

According to the invention, there is provided apparatus for measuring the flow rate of a medium, whereby by means of a sound source and a sound receiver the vortex systems behind an obstacle are scanned and the determined vortex frequency is indicated as a measure of the flow rate of the medium, wherein two rod shaped flow obstacles are arranged substantially parallel to one another and with a spacing relative to one another, the sound transmitter and the sound receiver are located substantially mid-way between the obstacles, and in an area of undisturbed flow a direction detector is provided which is aligned parallel to the common plane containing the flow obstacles.

According to one embodiment of the invention, the flow obstacles can be linked with a member automatically aligned in the flow direction such as e.g. a wind sock.

According to a further embodiment of the invention, the flow obstacles are arranged in a wind tunnel which has at least one side wall, whereby the side walls carry the sound transmitter and/or receiver.

In the latter embodiment of the invention, it is possible to determine the velocity of the flow component occurring in the longitudinal direction of said tunnel.

The apparatuses provided according to the invention do not only solve the problem indicated hereinbefore. Compared with the measuring arrangement according to German Patent Specification No. 2,044,398 the invention provides the considerable advantage that all the parts of the known arrangement do not have to be duplicated, and it is in fact possible to use only one sound transmitter and one sound receiver and consequently only one evaluation circuit for the vortex frequency measured. Furthermore, the indication of the flow rate can be simplified to a single scale running from 0 to n to which it is merely necessary to add an optical indication of the flow direction. It is thus possible to obtain a relatively simple apparatus for measuring the speed of e.g. helicopters or submarines.

The invention is explained in exemplified manner hereinafter with reference to the accompanying drawings, wherein: Figure tin purely diagrammatic manner is a plan view of a measuring apparatus according to the invention; Figure 2 is a block diagram of an evalua tion device; Figure 3 is a diagrammatic view of a direc tion determination device; Figure 4 is a view of an indicator; Figure 5 is the associated circuit; Figure 6 is a view of a modified embodi ment of an indicator; and Figure 7 is the associated circuit.

In the arrangement shown in Figure 1, a wind tunnel 3, through which an air flow is directed in accordance with arrows 4 qr 5, is formed between wall faces 1 and 2. On opposite wall faces in the centre of wind tunnel 3 are provided an ultrasonic transmitter 6 and an ultrasonic receiver 7.

In a wind tunnel 3 and at equal distances from the axis of the transmitter and receiver are provided two flow obstacles 8 and 9 which in the represented embodiment are constructed as rods having a circular crosssection.

The wind tunnel 3 can have a random cross-section. However, it is advantageous to construct it in such a way that in the axial direction of the flow obstacles it is longer than at right angles thereto.

The vortices occurring at the flow obstacles pass through the measuring zone 10 independently of the flow direction. Therefore, the measured vortex frequency is an absolute measure for the flow passage through the cross-section of tunnel 3, whereby optionally by means of a second measuring arrangement flow direction information can be linked therewith.

To obtain an accurate measuring result it is absolutely necessary for the dimensions of both flow obstacles to be precisely the same.

Figure 2 shows a block diagram for evaluating the measured results.

An oscillator 11 produces the fundamental frequency necessary for operating the ultrasonic system. Oscillator 11 is connected via an amplifier 12, with the transmitting head 6 of the ultrasonic transmitter.

The acoustic signal from the transmitting head 6 is disturbed from the vortex emanating from one of the flow obstacles. Therefore the receiving head 7 receives a signal whose frequency differs from the output frequency.

This signal is supplied to a high frequency amplifier 13 and from there to a demodulator 14. From the demodulator the input signal passes to a pulse shaper 15 which shapes the signal pulses in such a way that they can be completely satisfactorily processed by a following mono-stable toggle stage 16. From toggle stage 16 the signal can be applied via an output 17 to an electronic measuring device. The signal at output 17 is a digital signal with a predetermined frequency per speed unit.

For the indication of the signal on a normal indicator the signal is supplied to an integrator and an output amplifier 18, from where the signal can be fed to an output 19 which can supply an electronic analogue measuring system.

However, in the represented embodiment the signal is supplied from the output amp Lifer to a control circuit 20 for the servosystem 21 of an indicator 22. By means of a supply line the control circuit 20 receives a signal which provides information on. the flow direction. To this end a direction indicator 23 is provided which is aligned parallel to the common plane containing the obstacles 8, 9 and whose output signal is supplied via an amplifier 24 to the control circuit 20.

An embodiment of a direction detector is shown in purely diagrammatic manner in figure 3. Between walls 30 and 31 is formed a wind tunnel 32 which is open at both sides and constructed in a symmetrical manner, whereby its central part is narrower than. the entry area. In said narrower central part are provided two pressure sensors 33 and 34, which can be semi-conductors, connected to a circuit 35 which emits an output signal as a function of the flow direction at amplifier 24.

The operation of such semi-conductor pressure sensors is known per se and permits in a satisfactory manner a compensation of the temperature and atmospheric pressure.

As the direction detector is only required to supply basic information on the flow direction, its construction can be particularly simple.

In place of the represented pressure sensor it i:s naturally also possible to use some other suitable known device for measuring the flow direction, e.g. devices which operate in a purely mechanical or aerodynamic manner..

However, for measuring at particularly low flow rates the direction detector configuration shown has proved particularly adVan- tageous because due to the narrow crosssection of the wind tunnel 32, the average velocity in this area is considerably increased.

Figure 6 diagrammatically shows a plan view of an indicator 40 for the flow rate whose scale has a central zero mark 41.

Depending on whether the indicator pointer 42 is deflected to the left or right, it is possible to establish whether the relative flow direction is negative or positive. The magnitude of the deflection is determined by the measured speed. A control circuit for controlling this indicator corresponding to part 2Q in figure 2 is, for example, shown in figure 7. This control circuit comprises an analogue switch and an inverter for the speed information. In order to be able to compare positive and negative output voltages, the servocircuit must be constructed in corresponding manner. The deflection direction conse fluently depends on whether a signal is applied at output u + or at output u-.

Figure 4 shows a more easily readable indicator 50 whose pointer 51 passes over a conventional speed scale. At the front of the indicator are provided two luminous elements 52, 53 which through lighting upnindi- cate whether, for example, a missile is. mov ing forwards or backwards relative to the proportionate flow component.

Figure 5 shows a block diagram of a control circuit which could, for example, be used for such a device. It contains a flip-flo and a driver stage for the direction indication whose outputs are designated by u + and u-.

WHAT WE CLAIM IS: 1: Apparatus for-measuring the flow rate of a medium, whereby by means of a sound source and a sound receiver the vortex systems behind an obstacle are scanned and the determined vortex frequency is indicated as a measure of the flow rate of the medium, wherein two rod shaped flow obstacles are arranged substantially parallel to one another and with a spacing relative to one another, the sound transmitter and the sound receiver- are located substantially mid'way between the obstacles, and in an area of undisturbed flow a direction detector is provided which is aligned parallel to the common plane containing the flow obstacles..

2. Apparatus according to claim 1, wherein the flow obstacles are arranged in a wind tunnel having side walls which carry the sound transmitter and sound receiver.

3. Apparatus according to claim 2, wherein the direction detector is arranged in the same wind tunnel as the flow obstacles.

4. Apparatus according to claim 2, wherein the direction detector is. arranged in a separate wind tunnel..

5. Apparatus according to any of the preceding claims wherein the flow obstacles comprise rods with the same circular crosssection.

6. Apparatus according to any of the preceding claims, wherein the sound transmitter and the sound receiver are connected to an evaluation circuit..

7. Apparatus according to claim 6, wherein the evaluation circuit has a frequency-stable oscillator which supplies the sound transmitter and that the signal from the sound transmitter is supplied to a demodulator and then to a pulse shaper.

8. Apparatus according to claim 6 ot 7, wherein a control device which controls an indicator is provided at the output of the evaluation circuit, the signal from the direction deteetorbeingfedt-o said control device.

9. Apparatus according to any of the preceding claims, wherein the flow path around the direction detector has a crosssectional constriction in which are arranged sensors.

10. Apparatus according to any of the

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Claims

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indicator the signal is supplied to an integrator and an output amplifier 18, from where the signal can be fed to an output 19 which can supply an electronic analogue measuring system.

However, in the represented embodiment the signal is supplied from the output amp Lifer to a control circuit 20 for the servosystem 21 of an indicator 22. By means of a supply line the control circuit 20 receives a signal which provides information on. the flow direction. To this end a direction indicator 23 is provided which is aligned parallel to the common plane containing the obstacles 8, 9 and whose output signal is supplied via an amplifier 24 to the control circuit 20.

An embodiment of a direction detector is shown in purely diagrammatic manner in figure 3. Between walls 30 and 31 is formed a wind tunnel 32 which is open at both sides and constructed in a symmetrical manner, whereby its central part is narrower than. the entry area. In said narrower central part are provided two pressure sensors 33 and 34, which can be semi-conductors, connected to a circuit 35 which emits an output signal as a function of the flow direction at amplifier 24.

The operation of such semi-conductor pressure sensors is known per se and permits in a satisfactory manner a compensation of the temperature and atmospheric pressure.

As the direction detector is only required to supply basic information on the flow direction, its construction can be particularly simple.

In place of the represented pressure sensor it i:s naturally also possible to use some other suitable known device for measuring the flow direction, e.g. devices which operate in a purely mechanical or aerodynamic manner..

However, for measuring at particularly low flow rates the direction detector configuration shown has proved particularly adVan- tageous because due to the narrow crosssection of the wind tunnel 32, the average velocity in this area is considerably increased.

Figure 6 diagrammatically shows a plan view of an indicator 40 for the flow rate whose scale has a central zero mark 41.

Depending on whether the indicator pointer 42 is deflected to the left or right, it is possible to establish whether the relative flow direction is negative or positive. The magnitude of the deflection is determined by the measured speed. A control circuit for controlling this indicator corresponding to part 2Q in figure 2 is, for example, shown in figure 7. This control circuit comprises an analogue switch and an inverter for the speed information. In order to be able to compare positive and negative output voltages, the servocircuit must be constructed in corresponding manner. The deflection direction conse fluently depends on whether a signal is applied at output u + or at output u-.

Figure 4 shows a more easily readable indicator 50 whose pointer 51 passes over a conventional speed scale. At the front of the indicator are provided two luminous elements 52, 53 which through lighting upnindi- cate whether, for example, a missile is. mov ing forwards or backwards relative to the proportionate flow component.

Figure 5 shows a block diagram of a control circuit which could, for example, be used for such a device. It contains a flip-flo and a driver stage for the direction indication whose outputs are designated by u + and u-.

WHAT WE CLAIM IS: 1: Apparatus for-measuring the flow rate of a medium, whereby by means of a sound source and a sound receiver the vortex systems behind an obstacle are scanned and the determined vortex frequency is indicated as a measure of the flow rate of the medium, wherein two rod shaped flow obstacles are arranged substantially parallel to one another and with a spacing relative to one another, the sound transmitter and the sound receiver- are located substantially mid'way between the obstacles, and in an area of undisturbed flow a direction detector is provided which is aligned parallel to the common plane containing the flow obstacles..
2. Apparatus according to claim 1, wherein the flow obstacles are arranged in a wind tunnel having side walls which carry the sound transmitter and sound receiver.
3. Apparatus according to claim 2, wherein the direction detector is arranged in the same wind tunnel as the flow obstacles.
4. Apparatus according to claim 2, wherein the direction detector is. arranged in a separate wind tunnel..
5. Apparatus according to any of the preceding claims wherein the flow obstacles comprise rods with the same circular crosssection.
6. Apparatus according to any of the preceding claims, wherein the sound transmitter and the sound receiver are connected to an evaluation circuit..
7. Apparatus according to claim 6, wherein the evaluation circuit has a frequency-stable oscillator which supplies the sound transmitter and that the signal from the sound transmitter is supplied to a demodulator and then to a pulse shaper.
8. Apparatus according to claim 6 ot 7, wherein a control device which controls an indicator is provided at the output of the evaluation circuit, the signal from the direction deteetorbeingfedt-o said control device.
9. Apparatus according to any of the preceding claims, wherein the flow path around the direction detector has a crosssectional constriction in which are arranged sensors.
10. Apparatus according to any of the

preceding claims, wherein the direction detector has semi-conductor elements as sensors.
11. Apparatus for measuring the flow rate of a medium constructed and arranged substantially as hereinbefore described and with reference to the accompanying drawings.