FR2946138A1 - METHOD AND DEVICE FOR RAPID MEASUREMENT OF PRESSURE OR VOLUME VARIATION IN A RESERVOIR - Google Patents

Abstract

Method and device for measuring a variation of pressure or volume in a reservoir (10) containing a liquid and connected by a passage (18) to a measuring column (20) partially filled with liquid, lighting means ( 24) and image pickup means (22) for detecting the first peaks of the liquid level oscillations in the column (20) caused by a change in pressure or volume in the reservoir (10).

Description

METHOD AND DEVICE FOR RAPID MEASUREMENT OF PRESSURE OR VOLUME VARIATION IN A RESERVOIR

The invention relates to a method and a device for rapid measurement of a variation of pressure or volume in a reservoir containing a liquid. When a reservoir containing a liquid is connected according to the principle of communicating vessels to a column containing liquid and that the volume of the liquid contained in the reservoir is varied, for example by increasing the pressure in the reservoir, the variations the height of the liquid in the column corresponds to the variations in the volume of the liquid contained in the reservoir, with a ratio of proportionality equal to the ratio of the horizontal sections of the reservoir and the column.

When the variation of the volume of liquid in the reservoir is rapid, oscillations of the liquid level in the column occur. It is necessary to wait until the end of these oscillations, which represents a relatively important loss of time, before being able to make an accurate measurement of the height of liquid in the column, from which one can deduce information such as the variation of volume or pressure in the tank. The present invention is intended to provide a simple and satisfactory solution to this problem, allowing a quick and accurate measurement of pressure or volume variations in a tank of the aforementioned type. To this end, it proposes a method for measuring a pressure or volume variation in a reservoir containing a liquid and connected by a liquid passage to a column containing a liquid, characterized in that it consists, following a variation of pressure or volume in the reservoir causing oscillations of the liquid level in the column, detecting at least the first peak of the oscillations of the liquid level in the column and deducing therefrom, compared to measurements of calibration, the variation of the pressure or the volume of liquid in the tank. When the variations in volume in the reservoir occur under substantially identical and reproducible conditions, for example by admission of a volume of gas under pressure into a closed reservoir, the determination of the first peak of oscillation of the liquid level in the column is sufficient to accurately determine the volume of gas admitted to the tank, with a prior calibration consisting of the admission of known volumes of known pressure gas into the tank and measurement of the corresponding liquid heights in the column after stabilization. The measurement of the first peak of oscillation of the liquid level in the column can be carried out rapidly, in a few tens of milliseconds, depending on the experimental conditions. Optionally, to refine the measurement, the invention provides for detecting at least the first two peaks of oscillation of the liquid level in the column and to deduce the variation of pressure or volume of liquid in the reservoir.

This detection of the first two peaks of oscillation of the liquid level in the column substantially improves the accuracy of the variation of pressure or volume in the tank. Moreover, when these measurements must be carried out repeatedly at a high rate, it is necessary after the measurement to open the tank to evacuate the previously admitted gas, let back into the tank a certain amount of the liquid contained in the column, which can be translate by oscillations of the level of liquid in the tank, and wait for the end of these oscillations before admitting pressurized gas again in the tank for a new measurement.

To accelerate this process, the method according to the invention also consists in opening the tank or in exhausting it and closing at least once the passage of liquid between the tank and the column after the measurement when the liquid levels in the tank and in the column are substantially identical. It is thus possible to achieve a high measurement rate, since the level of liquid in the reservoir is stabilized by avoiding these oscillations. The invention also proposes a device for carrying out this method, this device comprising a liquid reservoir, a measuring column, a liquid passage connecting the reservoir to the column and means for measuring the level of liquid in the column. , characterized in that it also comprises means for opening and closing the liquid passage and means for controlling these opening and closing means as a function of the liquid level in the column.

In a first embodiment, these opening and closing means comprise at least one solenoid valve operating in all or nothing. In an alternative embodiment, these opening and closing means comprise two solenoid valves mounted in parallel and in opposite directions. In another variant embodiment, the opening and closing means comprise a chamber filled with liquid and connected by conduits to the reservoir and to the column, a valve movable in the chamber between an open position and a closed position. the outlet of one of the ducts in the chamber, and electromagnetic means for moving the valve between these two positions. According to another characteristic of the invention, the column is transparent and the means for detecting the level of liquid in the column comprise column illumination means, for example in backscattered light, and image pickup means, such as a CCD camera or the like, placed on either side of the column.

In a variant, the liquid level detection means in the column comprise an ultrasonic sensor immersed in the column and oriented towards the free surface of the liquid in the column. In another variant, these means for detecting the level of liquid in the column may comprise photoelectric or capacitive sensors, for measurements made in all or nothing. The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the accompanying drawings, in which: FIG. schematically a measuring device according to the invention; - Figure 2 shows schematically an alternative embodiment of this device; FIG. 3 is a graph showing oscillations as a function of time of the liquid level in a column of a device according to the invention; - Figures 4, 5 and 6 show schematically other embodiments of the device according to the invention.

Referring first to Figure 1 wherein the reference 10 designates a closed reservoir comprising in the upper part an inlet 12 of a pressurized gas and an exhaust valve 14. The reservoir is partially filled with a liquid 16 and its lower part is connected by a conduit 18 to a vertical column 20 partially filled with a liquid, advantageously the same as that contained in the reservoir 10 and the conduit 18. Initially, the reservoir 10 being at atmospheric pressure and the With the upper end of the column 20 open, the liquid levels in the reservoir 10 and the column 20 are identical.

Means are provided for detecting changes in the height of the liquid level in the column 20, these means comprising for example a CCD camera or the like 22 and lighting means 24, for example backscattering, the camera 22 and the means of lighting 24 being placed facing each other and on either side of the column 20, so that the variations of the liquid level in the column 20 are in the field of the camera 22. The conduit 18 is equipped with a solenoid valve 26 which, in the position shown, allows a liquid communication between the reservoir 10 and the column 20. This solenoid valve 26 is controlled by means 28 for processing the information, for example the type PC or the like, an input receives the output signals from the camera 22. This device is used as follows: the tank 12 being at atmospheric pressure, the liquid levels in this tank and in the column 20 are ide Ntiques. With the exhaust valve 14 closed, a certain amount of pressurized gas is admitted into 12 in the tank 10, which will have the effect of lowering the level of the liquid 16 in the tank of the line shown in dashed lines until at the level shown in full line, and conversely to raise the liquid level in the column 20. If the admission of the gas into the tank 10 is rapid, there are oscillations of the liquid level in the column 20 represented by schematically by the graph of Figure 3. These oscillations amortized more or less quickly and stabilize after a certain time at a value N. The difference between this value N and the initial level of liquid in the column 20 allows to determine the volume of gas admitted into the tank 10. However, the duration of damping oscillations of the liquid level in the column 20 may take a certain time, for example 10 or 15 sec waves. To accelerate the measurements, the invention provides for detecting the level of the first oscillation peak P1 and for deducing the volume of gas admitted into the tank 10, by comparison of the measurement with previously determined calibration values, by example by admission of known volumes of gas at known pressure in the tank 10 and measuring levels corresponding to the first peak P1. The measurement is then carried out in a few tens of milliseconds.

It is possible, to improve the accuracy on the determination of the volume of gas admitted into the tank 10, also to measure the level corresponding to the second oscillation peak P2 and possibly the level corresponding to the third peak P3, if there is enough of time and, as previously, deduce the desired value N by comparison with previously recorded calibration values. If this type of measurement has to be repeated at a relatively high rate, the procedure is as follows: after acquisition of the levels corresponding to peak P1 (or peaks P1 and P2 or peaks P1, P2 and P3), the valve is opened 14, the liquid level is allowed to rise in the tank 10 approximately to its initial level, corresponding to the initial level in the column 20, then the solenoid valve 26 is controlled to close the communication between the tank 16 and the tank. column. This avoids the oscillations of the level of liquid in the tank 10 which would normally accompany the return of the liquid in the tank to the opening of the exhaust valve 14. It can if necessary reopen the solenoid valve 26 and close, one or several times, to stabilize the fluid level. A solenoid valve 26 having a short total response time, for example less than 50 ms, is preferably used.

FIG. 2 diagrammatically shows an alternative embodiment of the liquid level detection means in the column 20, these means comprising an ultrasonic sensor 30 which is mounted in a chamber 32 filled with liquid at the base of the column 20 and which is oriented towards the free surface of the liquid in the column 20. The ultrasonic sensor 30 serves both as transmitter and receiver, and captures the echoes corresponding to the reflection of an ultrasonic beam on the free surface of the liquid in column 20, the propagation time of the ultrasound in the liquid making it possible to determine the height of the liquid in the column 20. In the variant embodiment of FIG. 4, there is the same device, but equipped with level detection means of liquid in the column 20 which operate in all or nothing, that is to say that only allow to determine if a liquid is present or not in the column 20 at the height where they are p laced. For this purpose, for example, a capacitive sensor 34 or photoelectric means comprising a transmitter 36 and a receiver 38 placed on either side of the column 20 may be used, the reception of a signal by the receiver 38 being possible only in the form of a sensor. no liquid in column 20 at the receiver. Optionally, in this variant embodiment and in the previous embodiments, it is possible to provide a float 40 of an appropriate type on the free surface of the liquid in the column 20, to facilitate detection. FIG. 5 diagrammatically represents an embodiment variant in which, to improve the speed of a transfer of liquid in one direction and in the other between the reservoir 10 and the column 20, the electrovalve 26 previously used has been replaced by two solenoid valves 42 mounted in parallel and in opposite directions. It has been found that the commercially available solenoid valves generally have a preferred direction of passage and that the passage of the liquid in the opposite direction results in a greater pressure drop. The two solenoid valves 42 connected in parallel and in opposite directions thus make it possible to accelerate the transfer of the liquid from the tank 10 to the column 20 for one and the column 20 to the tank 10 for the other.

It is also possible to replace these solenoid valves by a device such as that shown in FIG. 6 which is designed to cause a minimal loss of pressure in the liquid when it is opened. This device comprises a small chamber 44, part of which is connected by a conduit 46 to the reservoir 10 and another part of which is connected by a conduit 48 to the column 20, this conduit 48 possibly also being the lower part of the column 20. A spherical shutter 50 is movable in displacement inside the chamber 44 between a closed position of the outlet of the duct 46, shown in dashed lines, and an open position shown in solid lines. This shutter 50 is displaceable between these two positions by means of an electromagnetic actuator 52, connected to the shutter 50 by a cylindrical rod 54 guided in translation in bearings 56 mounted in an extension of the chamber 44, the rod 54 being by elsewhere associated with seals 58 to prevent leakage of liquid along this rod. In the chamber 44, the free space surrounding the spherical shutter 50 is at least equal to the section of the conduits 46 and 48. Thus, as soon as the shutter 50 is in the open position, the liquid passage can effector between the ducts 46 and 48 with minimal pressure drop.

Claims (10)

REVENDICATIONS1. A method of measuring a pressure or volume change in a liquid-containing reservoir (10) (16) and connected by a liquid passage (18) to a liquid-containing column (20), characterized in that consists, as a result of a change in pressure or volume in the reservoir causing oscillations of the liquid level in the column (20), to detect at least the first peak (P1) of the oscillations of the liquid level in the column and deducing therefrom, in comparison with calibration measurements, the variation of the pressure or the volume of liquid in the reservoir (10). 2. Method according to claim 1, characterized in that it consists in detecting at least the first two peaks (P1, P2) of oscillation of the liquid level in the column to deduce the variation of pressure or volume of liquid. in the tank (10). 3. Method according to claim 1 or 2, characterized in that it then consists in opening the reservoir (10) or in the exhaust and closing at least once the passage of liquid (18) between the reservoir and the column after the measurement when the liquid levels in the reservoir and in the column are substantially identical. 4. Device for carrying out the method according to one of the preceding claims, comprising a liquid reservoir (10), a measuring column (20), a liquid passage (18) connecting the reservoir to the column, and means for measuring the liquid level in the column (20), characterized in that it also comprises means (26, 42) for opening and closing the liquid passage (18) and means (28) for controlling of these opening and closing means as a function of the liquid level in the column (20). 5. Device according to claim 4, characterized in that the opening and closing means comprise at least one solenoid valve (26) operating in all or nothing. 6. Device according to claim 5, characterized in that the opening and closing means comprise two solenoid valves (42) mounted in parallel and in the opposite direction. 7. Device according to claim 4, characterized in that the opening and closing means comprise a chamber (44) filled with liquid and connected by conduits (46, 48) to the reservoir (10) and to the column (20). ), a valve (50) movable in the chamber between an open position and a closed position of the outlet of one of the ducts in the chamber, and electromagnetic means (52) for moving the valve between these two positions. 8. Device according to one of claims 4 to 7, characterized in that the column (20) is transparent and the liquid level detection means in the column comprises means (24) for illuminating the column and the image pickup means (22), such as a CCD camera or the like, placed on either side of the column (20). 9. Device according to one of claims 4 to 7, characterized in that the means for detecting the liquid level in the column comprises an ultrasonic sensor (30) immersed in the column and oriented towards the free surface of the liquid in the column. 10. Device according to one of claims 4 to 7, characterized in that the means for detecting the liquid level in the column comprise photoelectric sensors (36, 38) or capacitive (34).