GB2144227A

GB2144227A - Flow meter

Info

Publication number: GB2144227A
Application number: GB08418187A
Authority: GB
Inventors: Imre Szabo; Gyorgy Danko; Vitez Zsolt Illyefalvi; Karoly Papp
Original assignee: BAKONY FEM ELEKTROMOSKESZULEK; BUDAPESTI MUESZAKI EGYETEM; Budapesti Muszaki Egyetem
Current assignee: BAKONY FEM ELEKTROMOSKESZULEK; BUDAPESTI MUESZAKI EGYETEM; Budapesti Muszaki Egyetem
Priority date: 1983-07-29
Filing date: 1984-07-17
Publication date: 1985-02-27
Also published as: GB8418187D0; IT1174614B; FR2549956A1; JPS60104221A; HU188358B; HUT35092A; IT8422111A0; DE3426361A1

Abstract

A flow meter consists of a resilient diaphragm 3 provided with a measuring orifice 4 and placed transversely in the path of flow. A sensor 8 detects the displacement of the diaphragm 3. A throttle 5 in the orifice 4 is specially shaped to assure a linear correlation between the displacement of the diaphragm 3 and the flow rate of the flowing medium. The diaphragm is spring biased. The throttle may be conical with a straight or concave boundary. Alternatively the throttle is a flat disc and the diaphragm carries a shaped member. In Fig. 3 a plate 5 is fixed. <IMAGE>

Description

SPECIFICATION Flow meter The invention relates to a flow meter with a measuring orifice arranged in the path of the flowing medium and perpendicularly to the direction of flow.

For measuring the flow of different media, a rich assortment of measuring principles and metering devices is known. Recently, new measuring possibilities have been applied: optical, acoustic, ultrasonic and laser-based measuring processes and devices. In general, said devices measure the flow conditions aitered by a body which is arranged in the path of medium flow (see e.g. in GB-PS 1 384 105). GB-PS 1 482699 and 1 1 533717 each describe a device which is capable of detecting oscillations of the body arranged in the path of flow.

The so-called measuring orifices or metering mouths have been known for a long time. These devices are contractions formed in the path of the medium flowing in a pipeline wherein before and after said orifice a differential pressure is produced. The velocity and quantity of the flowing medium may be determined by measuring said differential pressure.

The main drawback of said metering devices is that the correlation between differential pressure and volumetric flow is not linear. Accordingly, evaluation of the results is difficult.

Another well known type of measuring devices is the so-called rotometer, the essential feature of which is that a floating body is arranged in the path of the flowing medium wherein the displacement of said body is proportional with the velocity to be measured. The source of pressure drop is the resistance of the floating body. With this device displacement of the floating body may be directly proportional with the volumetric flow of the liquid, if the pipeline is formed with a widening cross-section in the direction of the displacement of the floating body. However, its drawback is that the floating body is made to reach its state of equilibrium by relatively small forces, while producing large forces involves considerable difficulties.The reason for this is on one hand that increasing the dimensions of the floating body would disproportionately increase the size of the equipment, on the other hand, by increasing the diameter of the floating body a too narrow orifice would be obtained for the free flow cross-section of a given size along the periphery, resulting in the danger of clogging.

According to another device, displacement of the floating body is restricted by a spring, while the change in spring force or displacement of the floating body are giving a quantity being characteristic for the liquid flow (see GB-PS 1 434 165).

There are also known flow meters in which volumetric flow is determined by the extent of displacement of a valve or a transverse plate arranged in the path of flow against spring force, as described in the GB-PS 1 462 878 or 1 476 574. The drawback of said solution is the same, as previously described.

In another well known system the element displacing under the influence of liquid stream is arranged into the measuring orfice. In this case the displacement of the closing or reducing element against the spring force or the pressure drop arising on the reduction is measured as a quantity being proportional with the volumetric flow. With this solution guidance of the reduction element displacing against spring force involves a friction which is disadvantageously influencing measuring results.

Afurther disadvantage is in this case that accurate measuring can be obtained but in pipes with a relatively large diameter (so about of the order of magnitude of 10 cm), the device is most unsuitable for measuring in pipes of small diameters, as a displacement i.e. pressure drop arising under the influence of extremely small forces ought to be measured.

The object of the present invention is to provide a flow meter the internal flow pattern of which is similar to that observed in measuring orfices, however, which is characterizing a changing flow cross-section which enables to establish an optionally selectable, advantageously linear functional correlation between the measured signal and the liquid flow instead of the spontaneously formed quadratic characteristic, even if performing measuring in a pipeline of small diameter.

Accordingly the flow meter according to the invention containing a measuring orifice is made of a resilient diaphragm with a displaceable aperture and there is at least one sensor four detecting the displacement of said diaphragm. The sensors may be connected to measuring electronics.

According to a preferred embodiment of the invention, the measuring orifice is provided with a stationary throttle (hereafter: reduction element), which is advantageously arranged in the measuring orifice.

The reduction element may be designed with a cross-section narrowing in a downstream direction or as a plate arranged perpendicularly to the direction of flow. In the latter case the measuring orifice may be a pipe section with a cross-section that reduces downstream.

According to the invention between the displacement of the measuring orifice (X) and the medium flow rate (+v) a linear correlation can be established: X= C., wherein C is a constant depending on the characteristics of the displacement of the resilient diaphragm and the shape of the throttle reduction.

The diaphragm of the flow meter is supported by a spring, preferably with a spring of linear characteristics. In this case the constant C depends on the common characteristics of the diaphragm and the spring.

The reduction element can be provided with a tuning element ensuring proper positioning down-stream.

According to another preferred embodiment of the invention the aperture of the diaphragm has a circular shape and the reduction element has a concave toroidal outer surface.

The flow meter designed in this manner eliminates all the disadvantages of earlier known devices and, as the differential pressure induced affects a large surface and an advantageous equilibrium of forces can be achieved, quite small liquid flows can be suitably measured. In addition, an optional functional correlation can be realized between volumetric flow and differential pressure. Under pulsating flow conditions the flow meter follows well all the changes as in relation to mass forces the displacement detected is controlled by considerable forces, accordingly, it is well suitable for the mass-measuring of discontinuous flows with gas bubbles, even with "bubbleplugs" with a volumetric ratio over 100 %. Owing to these properties, the flow meter can be advantageously used - among others - for measuring the instantaneous fuel consumption of cars.

The invention will be described in detail by means of preferred embodiments serving as an example, by the aid of the drawings enclosed, wherein Figure 1 is the schematical arrangement of the flow meter according to the invention, Figure 2 is the schematical arrangement of another embodiment of the flow meter according to the invention, Figure 3 is showing a further version, Figure 4 is the front view of a diaphragm provided with slots, Figure 5 is the front view of another diaphragm provided with an U-shaped slot, Figure 6 is the sectional view of the flow meter measuring the fuel consumption, and Figure 7 is showing the circuit arrangement of the measuring-sensing electronics belonging to the embodiment according to Figure 4.

As it becomes obvious from the schematical arrangement according to Figure 1, the pipeline 1 of the flow meter according to the invention contains a resilient diaphragm 3 clamped into the measuring orfices 2; a reduction element 5 is fitted into the aperture 4 of the diaphragm 3. The reduction element 5 is fixed on the holder 6, while the resilient diaphragm 3 is supported by the spring 7, displacement thereof is sensed by the sensors 8 arranged on one or both sides of the diaphragm 3.

In Figure 1 the direction of the volumetric flow Xv is indicated with an arrow. After having reached the resilient diaphragm 3, the flowing medium behaves in the same manner as with traditional measuring orfices. Streamlines become concentrated at the aperture 4 of the resilient diaphragm 3 and after the aperture a whirl will be formed. As a consequence, before the resilient diaphragm the higher pressure p1, thereafter the lower pressure p2 prevail. Under the influence of the differential pressure p1 - p2 = Ap the resilient diaphragm and consequently the aperture 4 are displaced down-stream.As down-stream the reduction element 5 is narrowed in its cross-section, then, if the aperture 4 is displaced to an extent X down-stream, free cross-section A of the aperture 4 will be increased. It goes without saying that this reacts upon the differential pressure too.

The correlation ensuring the linear operation of the free cross-section A in accordance with the displacement X can be easily calculated by the analysis of the measuring orfice. It is well known that according to the basic correlation relating to the measuring orfices

wherein eisa corrective factor p stands for the density of the liquid A indicates the free cross-section of the aperture.

Between the differential pressure Ap and the volumetric flow Pv there is a quadratic correlation, accordingly it does not yield an advantageous mode of evaluation. For this reason it seems to be advantageous to alter the free cross-section A in such a way that a linear correlation could be obtained between the differential pressure Ap and the volumetric flow v. In this case the correlation ought to be

Now, if this value A is substituted into the former equation, a linear correlation between differential pressure and volumetric flow will be obtained. This can be performed by using the equations A = f(Ap) and X = f2(Ap).

In our case (having a circular aperture and a conical reduction element) that means that A = C2 , i.e. the case according to Figure 1 the outside of the reduction element 5 can be realized with a slightly concave surface compared to a straight cone. In practice this means a concave toroidal surface.

In this way a linear correlation can be obtained between the displacement X of the aperture 4 and the medium flow v; X = C3 XV wherein C3 is a constant comprising the characteristics of the resilient diaphragm 3 as well as that of the spring 7.

In Figure 2 an embodiment is shown wherein the reduction element 5 is a disc arranged perpendicularly to the direction of flow. In this case the aperture 4 of the resilient diaphragm 3 is formed as a pipe section with a narrowing cross-section down-stream. Essentially, the operation corresponds to that of the embodiment according to Figure 1.

The reduction element 5 of the embodiment according to Figure 3 is not arranged in the aperture 4 of the resilient diaphragm 3 but in the vicinity thereof, as a closing plate of the pipeline 1.

The flowing liquid arrives at the casing 9 of the flow meter through the radial bores 10 and flows through the annular gap between the reduction element 5 and the resilient diaphragm 3. The size of said gap is changing in dependence of the flow, as a consequence of the displacement of the resilient diaphragm.

In this embodiment the displacement of the resilient diaphragm is not absolutely linear, however, linearity is well approximated.

The flow meter according to the invention may also have a diaphragm with an aperture which is a slot. In given cases more than one slot may be applied. Figures 4 and 5 show diaphragms having such slots. In Figure 4 a number of slots 4 are arranged on the diaphragm 3 along central spiral lines. The diaphragm 3 in Figure 5 has a single aperture 4 made as an U-slot.

As the diaphragm deforms due to the flow of a medium, the cross-section of the slot or slots also changes as a function of the flow.

In this way, the connection between the amount of the flowing medium and the displacement of the diaphragm may be defined by the arrangement of the slots.

As the characteristics of a diaphragm provided with slots is gentler than that of a diaphragm with other apertures, the the flow meters having diaphragms with slots may be applied first of all in pipelines of small diameters. In this way applying diaphragms of big surfaces or of very small thickness may be avoided.

Figure 6 shows the sectional view of a practical embodiment of the flow meter according to the invention, i.e. a metering device measuring the fuel consumption of a car. The consumption meter is connected to the pipeline 1 via the inlet stud 11. The resilient diaphragm 3 and the reduction element 5 are arranged in the i casing 9 consisting of the halves 9a and 9b.

The reduction element 5 is fixed in the outlet stud 12 in the half 9b by means of the holder 6. The tuning screw 13 is screwed into the holder 6, the reduction element 5 is connected thereto via a shaft 14. The flow meter can be adjusted, tuned by means of the tuning screw 13.

The whole apparatus is arranged in the case 15, the case 15 also contains the measuring electronics 16.

Measuring signal is led by the cable 17 from the measuring electronics 16.

For electronic position detection of the diaphragm 3 an inductive system is used, wherein the object to be sensed exerts an influence - depending of the position and changing therewith - on an alternating magnetic field around an inductor and this reacts upon the current in the inductor or voltage. In order to obtain proper linearity two facing and interconnected coils are used as sensors 8. Accordingly, the object to be sensed between the sensors 8 the diaphragm 3 - must have magnetic properties. In case of a high-frequency magnetic field it seems to be sufficient if the object to be sensed is electrically conductive, the inducing eddy currents are quasi replacing any a high magnetic permeability.

In the embodiment shown in Figure 6 flat coils are used which enclose the diaphragms 3. Metal diaphragms do not require further components; however, with a rubber diaphragm a metal (e.g. aluminium) i sensing disc is to be used.

The block diagram of a possible version of the sensing electronics is shown in Figure 7. The voltage generator 18 generates a sinusoidal voltage with a stabilized amplitude for the sensors 8. The voltage of the division point 19 of the sensors 8 - alternating proportionally with the displacement of the diaphragm 3 - is converted by the rectifier 20 into the D.C. voltage Ucut, which can be considered already as an output signal.

The flow meter requires further signal conversion: amplifying, filtering, cut-off of zeroing voltage etc.

Optionally the flow meter can be connected to an electronic evaluating unit by the aid of which consumption can be read in 1/h or 1/100 km on a calibrated scale.

The flow meter based on the principle of the invention eliminates disturbing effect of the volumetric flow of gas - or steam bubbles; in case of a gas volume of 20 to 30 % measuring can be considered still as ideal, that means that average value of output is essentially proportional with the liquid volume. Even under pulsating conditions the flow meter follows well the changes and it is suitable for measuring small medium flows, as state of equilibrium of the resilient diaphragm is ensured by the equilibrium of relatively large forces. As a consequence, hysteresis can be neglected and a stable setting can be achieved.

Although in the examples some types of the flow meter have been disclosed to those skilled in the art it will be quite obvious that basic principle of the solution according to the invention enables the designing of any type of flow meter. These flow meters show all the advantageous features of earlier types: their operation is reliable, small and quick changes are followed, accordingly they are well suitable for measuring pulsating flows.

Claims

1. A flow meter comprising a measuring orifice arranged in the path of the flowing medium perpendicularly to the direction of flow, the measuring orifice being formed in a resilient diaphragm as a displaceable aperture, and sensing means for detecting the displacement of said resilient diaphragm.

2. Flow meter as claimed in claim 1, wherein the sensing means is connected to measuring electronics.

3. Flow meter as claimed in claim 1 or 2, wherein the measuring orifice is provided with a reductor or throttle.

4. Flow meter as claimed in claim 3, wherein the reductor is a stationary element arranged in the aperture ofthe resilient diaphragm.

5. Flow meter as claimed in claim 4, wherein the reduction element has a cross-section which narrows in a downstream direction in such a manner that there is a linear correlation between the displacement (X) of the aperture of the resilient diaphragm and the volumetric flow of the medium (4v) X= COv wherein C is a constant depending on the characteristics of the displacement of the resilient diaphragm and the shape of the reduction element.

6. Flow meter as claimed in claim 4, wherein the reduction element is formed by a plate lying perpendicularly to the direction of flow.

7. Flow meter as claimed in claim 6, wherein the aperture of the resilient diaphragm is formed as a pipe section with a cross-section that narrows in a downstream direction in such a manner that between the displacement (X) of the aperture of the resilient diaphragm and the volumetric flow of the medium (+v) there is a linear correlation X = wherein C is a constant depending on the characteristics of the displacement of the resilient diaphragm and the shape of the reduction element.

8. Flow meter as claimed in any preceding claim, wherein the aperture of the diaphragm consists of one or more slots.

9. Flow meter as claimed in any preceding claim, wherein the resilient diaphragm is supported by a spring.

10. Flow meter as claimed in claim 3 or in any claim depending therefrom, wherein there is a tuning element for adjusting the position of the reductor in the direction of flow.

11. Flow meter as claimed in any preceding claim, wherein evaluating electronic circuitry is provided for evaluating the obtained measurement results.

12. A flow meter substantially as herein described with reference to and as shown in any of Figures 1 to 6, in combination with Figure 7.