KR100260961B1 - Flow meter having a fluidic oscillator - Google Patents

Abstract

The two-dimensional fluid jet oscillating transversely with respect to the plane of symmetry P is sweeped on the lower part of the cavity part 24, and the flow velocity is lowered by the electronic means 42 and 44 under the cavity part 24. And tapping at a point P ₃ located on the intersecting axis between the planes of symmetry and pressure at two points P ₁ , P ₂ located symmetrically on each axial plane of the plane of symmetry. A fluid oscillator flowmeter is disclosed that is determined from a signal corresponding to a differential pressure resulting from a difference between differential pressures.

Description

Flowmeter with Fluid Oscillator

The present invention relates to a fluidic oscillator in which the flow rate of the fluid or gaseous emulsion can be measured.

U.S. Patent No. 4,244,230 describes a fluid oscillator flow meter that is symmetric about a plane of symmetry. The flow meter has an inlet in the form of a nozzle for supplying a two-dimensional fluid jet into the chamber. Inside the chamber, an obstacle has a front cavity located in the jet path. The oscillation of the jets traverses the plane of symmetry of the flow meter and involves the formation of a cavity that constitutes two vortices with one vortex on both sides of the jet.

Two pressure tappings located on each side of the plane of symmetry are connected to one or more pressure sensors in a manner that allows the cavity to measure the oscillation frequency of the jet. FIG. 1 schematically shows the electrical signal provided by a pressure sensor which measures the pressure difference between two pressure tapping points as a function of time t.

Each extreme has a double peak. The lowest point of the trough located between the two peaks corresponds to the collision point of the eruption passing through the maximum exit point.

Thus, considering the jet sweeping the cavity spaced from the plane of symmetry after passing through the pressure tapping region, the jet continues to head towards the maximum breakaway point.

After reaching the maximum, the pressure measured at the pressure tapping point decreases.

When the maximum breakaway point (lower bone between peaks) is reached, the jet returns towards the symmetry plane as it approaches pressure tapping (the second peak corresponds to passage of the jet through the position of pressure tapping), and then Pass towards pressure tapping opposite to

If the appropriate selection threshold is exceeded, the signal S is transformed into a square wave by a suitable electronic system. Each square wave corresponds to the volume of fluid passing through the flow meter. Thus, the flow rate can be determined by counting the square wave.

The accuracy of such measurements is half of the oscillation cycle.

Thus, if fluid flow is interrupted at the moment the oscillation is stopped, the exact location of the jet impact point at the bottom of the cavity is not known, resulting in uncertainty in the measurement.

One object of the present invention is to improve the accuracy of a flow meter of the type described above by at least twice, and to do this without increasing the oscillation frequency of the jets in the cavity.

To this end, the present invention proposes to place at least one pressure tapping at a point located on the intersecting axis between the symmetry plane and the bottom of the cavity, in addition to the symmetry pressure tapping on each side of the symmetry plane. The differential pressure measurement is made between (a) the pressure difference between pressure tapping symmetrically located on each side of the plane of symmetry and (b) the pressure present in the pressure tapping region located on the cross axis. The square wave formed from the signal corresponding to the differential pressure is generated at a frequency (at least twice the frequency) than the frequency in the prior art, each square wave being a smaller unit of flow amount to improve the accuracy of the measurement.

Pressure tapping symmetrical with respect to the plane of symmetry is preferably located substantially at the maximum breakout point position of the impact point of the ejection inside the cavity within the flow rate range.

The features of the present invention are shown by way of example and with reference to the accompanying drawings, which are not intended to be limiting.

1 schematically shows the signal measured by a prior art flow meter, as described above.

2 shows a device according to the invention which constitutes the schematic drawing obtained from above.

3 is a schematic perspective view of an obstacle forming part of the flow meter according to the invention.

4 schematically shows the signal output by the measurement of the differential pressure as well as the square wave of the countable flow amount.

Referring to FIG. 2, one embodiment of the device according to the invention is described, which may equally be used for liquids or gases. The flow meter includes a fluid inlet 10, one end of which is connected to the inlet conduit 12 for the fluid and the other end of which is connected to the oscillation chamber 14.

The fluid inlet 10 includes a parallelepiped fixation chamber 16 that allows transition from a circular cross-section jet inherent in the conduit 12 to a jet of a square or rectangular cross-section. The stationary chamber is finished with a converging section 18 with an inlet orifice 20. The rectangular inlet orifice follows the principle of two-dimensionality, which is well known to those skilled in the art, by supplying the oscillation chamber 14 with two-dimensional jets oscillating transversely with respect to the plane of symmetry P of the flowmeter.

The obstacle 22 is located in the oscillation chamber. The cavity part 24 is formed in the front part of the obstacle 22 which opposes the said inlet orifice 20. The fluid jet introduced into the oscillation chamber is sweeped on the wall of the cavity 24 during the oscillation process.

The fluid flow is left by chambers 26 and 28 formed between the wall of the obstacle 22 and the wall of the oscillation chamber 14. The flow is directed to an outlet orifice 30 which is connected to the drain conduit 32 by the chamber.

The measurement of the flow rate is achieved by detecting the jet sweeping the lower part of the cavity 24 during the oscillation process. The oscillation frequency of the jet is proportional to the flow rate.

According to the invention, in order to measure the flow rate, the device shown in FIG. 2 comprises three pressure tappings P ₁ , P ₂ , P ₃ . As can be seen in FIG. 3, which is a perspective view of the obstruction 22, these pressure tappings are formed by chambers passing through the obstruction 22, each pressure tapping being for example a cavity 24 at one end. ) Open at one of the three points (P ₁ , P ₂ , P ₃ ) inherent at) and at each of the three points located on top of the obstacle at the other end.

The pressure tappings P ₁ , P ₂ are located symmetrically on each side of each of the planes of symmetry P, for example reaching halfway of the obstacle. The pressure tapping (P ₁ , P ₂ ) is advantageously located in the region of the maximum departure point of the jet when oscillation in the cavity.

It is known that these maximum breakaway points vary slightly with fluid flow rate. Only the position of one pressure tapping exactly matches the maximum breakout point for a given flow rate. Referring to FIG. 1, the difference between the position of the breakaway point and the position of the pressure tapping is that if the spray passes over the range of pressure tapping as the spray moves away from the plane of symmetry during the oscillation process, the spray will pass through the pressure tapping. This results in a groove between the two pressure peaks that are detected. This result is not faced if the oscillation amplitude is not sufficient to pass through the range of pressure tapping positions as the jet moves away from the plane of symmetry. Thus, within the measurement range, the pressure tapping (P) in such a way that the grooves, which can form as a signal between two peaks corresponding to the continuous passage of the pressure tapping by the jet, is not wide enough or deep enough to disturb the measurement. ₁ , P ₂ ) is located.

Referring to FIG. 2, it is shown that the pressure tappings P ₁ , P ₂ are connected to each other by a connecting piece 36 in a T-shape.

The pressure tapping P ₃ is for example located at the part leading up to half the path of the obstacle on the intersecting axis between the plane of symmetry P and the lower part of the cavity 24.

The outlet conduit of the channel 38 and the connecting piece 36 connected to the pressure tapping P ₃ is, for example, a pressure sensor 40 or some other form of silicon and in the form of a thermal effect. It is connected to the flow and pressure sensor of. An example pressure sensor of type Validyne DP 103 sold by Validyne Engineering Corporation may be used.

In a variant embodiment, each pressure tapping can be connected to an independent pressure sensor with the proper processing of the signals provided by these sensors, for which desired results can be obtained.

The pressure sensor 40 varies the pressure difference between the pressure at point P ₃ taken as a reference value and the differential pressure between points P ₁ and P ₂ directly obtained at the outlet of the T-shaped connecting piece 36. It provides an output signal (S) corresponding to. 4 shows, by way of example, the signal S obtained schematically as a function of time t. For the sake of simplicity, no trough is shown, which may be formed at the peak value of the pulse and corresponds to the case of a jet passing through the position of the symmetrical pressure tapping during the oscillation process.

Assuming that the pressure fluctuations in the region of point P ₃ are greater than the pressure fluctuations that can occur in the region of P ₁ or P ₂ , the head loss is pressure tapping P ₃ to at least partially compensate for the consequences of these pressure fluctuations. It can be introduced in the area of. In the example shown in FIG. 3, the headloss is provided by a porous plug 39 located in the channel 38.

The introduction of this head loss makes it possible to prevent asymmetry in the signal 5 which leads to the risk of losing the measuring frequency.

The output of the pressure cell 40 is connected to the input of the electronic system 42 to transform the signal S into a series of square waves (which form a signal C) that occur when passing a preselected threshold. .

The resulting square wave appears at a frequency corresponding to twice the frequency of the square wave measured in the prior art. In this way, each square wave corresponds to a volume of fluid that passes through the flowmeter (about twice as large) as the square wave of the preceding surprise. The coefficient of the square wave is proportional to the flow rate since it corresponds to the volume of fluid that has passed through the flowmeter during the counting time.

Since the counted unit capacity per square wave is small compared to the prior art, the accuracy of the measurement is correspondingly increased.

Claims (3)

In the two-dimensional fluid jet type oil flow meter having a jet oscillating on both sides of the symmetric plane P in the transverse direction, the oscillation chamber 14, the jet during the oscillation process, is formed on the wall of the cavity 24. Means for providing a signal (S) corresponding to an obstacle (22) located in the oscillation chamber, the differential pressure, having a cavity (24) located at the front end of the fluid ejection path in a sweeping manner. 40, and means 42, 44 for determining the fluid flow rate from the differential pressure measurement, wherein the differential pressure is a point located on the intersecting axis between the lower part of the cavity 24 and the plane of symmetry P. From the tapping pressure at P ₃ ) and the differential pressure resulting from tapping pressure at two points P ₁ , P ₂ symmetrically located on two sides of the symmetry plane P Fluid oscillator flowmeter, characterized in that. 2. The maximum deviation of the fluid jet from the cavity 24 inherent in the flow rate range according to claim 1, wherein two points P ₁ , P ₂ located symmetrically on two respective sides of the plane of symmetry P. A fluid oscillator flowmeter, characterized in that it is substantially positioned at the location of the point. 2. A fluid oscillator flow meter according to claim 1, wherein the head loss (39) is introduced into a pressure tapping region located on the intersecting axis between the bottom of the cavity (24) and the plane of symmetry (P).