FR2985566A1 - LIQUID LEVEL SENSOR WITH FREE FLOAT - Google Patents

Abstract

The device for measuring a level of liquid in a tank comprising a float able to float on the surface of said liquid, said float being housed inside a main tube for translational guidance of said float under the hydrostatic thrust exerted by the fluid, the device further comprising a plurality of housings each comprising at least one probe attached within said housing to a predetermined depth.

Description

The field of the invention is that of the level sensors of a liquid stored in a tank such as a pond or swimming pool. More particularly, the invention relates to large size sensors and is particularly applicable to tanks to be highly reliable such as tanks used in nuclear facilities, including pools for receiving fuel assemblies. STATE OF THE ART Currently, there are different types of level sensors of large sizes of a liquid stored in a basin. Among these systems, there are electromagnetic sensors such as those described in patent document US2005109105. This latter document describes a system for measuring the level of a liquid in a tank using a float comprising a magnet floating in the tank. The patent document EP 0397338 also describes an electromagnetic liquid level sensor comprising a floating magnet which slides in a tube. A sensor is arranged around the magnet.

There are also optical type sensors such as those described in US patent document 6173609. This discloses a system for measuring the level of a liquid using an optical sensor, including a waveguide. The waveguide may consist of a plurality of fibers having different lengths.

There are also hybrid sensors of the electromagnetic and optical type, such as those described in the patent application WO2004076987. The latter document describes a liquid level sensor having a magnetic float that slides in a tube and an optical sensor element around the float. The sensor element has variable reflection characteristics as a result of the action of a magnetic field.

Generally, a magnetic sensor makes it possible to act on electrical circuits at the surface of the liquid in order to measure the level thereof. US 5552774 typically discloses a standard method of determining the level of a liquid in a tank with a magnetic float that opens or closes an electrical circuit in response to a change in fluid level. Nevertheless, these solutions have many disadvantages. In particular, systems for measuring the level of a liquid such as pool water intended to receive the nuclear fuel assemblies must be operational under all conditions. In this case, the measuring systems must be able to withstand earthquakes and therefore the probes used must not be too large. Current solutions often present a problem in the realization of the probes which must be large and which present a game too important for an antiseismic dimensioning.

In addition, none of these systems allows easy maintenance. Thus, one of the major drawbacks of large devices comes from the fact that the architecture of the structures does not allow easy maintenance. In the event of an accident or breakdown, the maintenance of a sensor / probe must be simplified to its maximum.

SUMMARY OF THE INVENTION The invention solves the aforementioned drawbacks.

The invention relates to a device for measuring a level of liquid in a tank. Advantageously, the device comprises a float able to float on the surface of said liquid, said float being housed inside a main tube for translational guidance of said float under the hydrostatic thrust exerted by the fluid. The device further comprises a plurality of probes disposed near the main tube, each probe being capable of measuring the position of the float on a portion of the depth of the basin, said probe being maintained at a predetermined depth. Advantageously, all the measuring portions covering the maximum stroke of the float in the main tube under the effect of the hydrostatic thrust. Advantageously, the measuring device comprises a plurality of housings, each housing each comprising at least one probe, the probes being held inside said housing. This solution makes it possible to carry out specific maintenance operations on each of the probes without generating a total interruption of operation of the measuring device. Indeed, each housing includes a probe that can be replaced or repaired without impact on the probes of other dwellings. The housings are preferably tubes juxtaposed to the main tube, called secondary tubes. Structurally the shape of a tube facilitates the installation and removal of a probe during maintenance operations. Advantageously, two secondary tubes taken in pairs each have an end located substantially at the same height and have different lengths extending in the depth of the basin so that the probes are placed at the bottom of each secondary tube. As a result, two secondary tubes taken in pairs have different lengths so that the probes are capable of measuring the position of the float on different portions of the depth of the reservoir. Thus, this solution makes it possible to limit the size of the probes. Advantageously, each measurement portion is less than 2m. In addition, the measurement probes are arranged in secondary tubes surrounding the main tube. Each of the secondary tubes comprises a probe which is disposed at a specific height and different from at least one other probe of another secondary tube. This characteristic makes it possible to limit the size of the probes and to avoid providing a large ceiling height. It therefore facilitates maintenance operations. It also makes it possible to control the level of the water over the entire stroke of the float since the probes are arranged at different depths. In addition, if a component is damaged, a localized maintenance operation can be performed without interrupting the operation of the device or the service completely. In a preferred embodiment, the measurement probes are all identical to one another and are arranged at different depths, thus making it possible to limit the number of spare part references. The invention proposes to use a floating magnet, which is a float, and which slides in a main tube. The use of a magnetic field has the advantage of being independent of the levels of irradiation or temperature that can damage electronic components. Advantageously, in this case, the float comprises means for generating a magnetic field and the probes comprise electromagnetic relays activated when they are under the action of the magnetic field of the float. Advantageously, the electromagnetic relays are deactivated outside the magnetic field of the float. The secondary tubes are preferably arranged to exceed the maximum height to be measured of the liquid of the basin to avoid the use of connector (s) waterproof (s). The tubes then form a sealed cavity. In addition to the main features that have just been mentioned in the preceding paragraph, the measuring device according to the invention may have one or more additional characteristics below, taken individually or in any technically feasible combination: Advantageously, a variant of FIG. The embodiment comprises secondary tubes of substantially the same size and holding means disposed within each tube to hold the probes at different depths. Advantageously, each secondary tube comprises a single probe. The secondary tubes can be located around the main tube and form a spiral. Advantageously, each probe comprises a full-length electrical circuit formed of an alternation of resistors and relays, the measurement of the level of the liquid being effected by a measurement of current. BRIEF DESCRIPTION OF THE FIGURES Other characteristics and advantages of the invention will emerge clearly from the description given below, purely by way of indication and in no way limiting, of embodiments referring to various figures in which: FIG. 1 represents a view from above of the device of the invention; Figure 2 shows a front view of the device of the invention; Figure 3 shows a secondary tube of the invention comprising a probe; Figure 4 shows a probe of the invention comprising a plurality of electromagnetic relays; FIG. 5 represents a first alternative embodiment of the device of the invention; FIG. 6 illustrates a second alternative embodiment of the device of the invention.

DESCRIPTION Figure 1 shows a top view of the device 1 of the invention. The device 1 comprises a main tube 2 and secondary tubes 3 which are arranged around the main tube 1. According to the embodiments, the secondary tubes may wholly or partially surround the main tube. A plurality of secondary tubes 3 surrounding the main tube 2 in a circular arc would be suitable for certain applications of the invention.

Figure 2 shows a front view of the device of the invention. The main tube 2 is surrounded by secondary tubes, labeled 31, 32, 33, 34, 35 in Figure 2, of different lengths. The secondary tubes 31, 32, 33, 34, 35 correspond to the tubes 3 of FIG. 1. A float 4 is guided in the main tube 2. The float can travel the total length of the main tube 2. The main tube 2 is provided with opening means and possibly filtering means for equalizing the level of the liquid inside the main tube 2 with that of the basin. The water levels are symbolized by the two horizontal lines 5 and 6 corresponding to two different configurations depending on the filling of the basin. The float 4 may be of ovoid shape as shown in Figure 2. It may also have any other form of eligible float. The float 4 allows to align with the level 5, 6 of water of a pool while being maintained in a position of which two degrees of freedom are fixed. The only guided translation in the tube is allowed.

In one embodiment the float comprises means for generating an electromagnetic field such as a magnet in its simplest embodiment to implement. Each secondary tube 31, 32, 33, 34, 35 comprises a probe s whose height is smaller than the height of the secondary tube associated therewith. During installation or maintenance, each probe can slide in translation in each secondary tube so as to be withdrawn or positioned inside. When a probe is introduced into a secondary tube, means make it possible to fix the probe at a certain predefined height. For example, in the embodiment of Figure 2, the probes inserted into the secondary tubes can be naturally retained by the bottom of each secondary tube. Each probe is positioned at a different depth since the tubes are of different lengths. Alternatively, each secondary tube may comprise means for holding a probe. Typically, Figures 5 and 6 show examples of alternatives detailed in the following description. The device of the invention makes it possible to use as many secondary tubes as probes. This solution makes it possible to have a single probe for a secondary tube and simplifies the maintenance of the devices for measuring the water level of a pool. This advantage is particularly important in the event of an accident, that is to say when the liquid level control measures are necessary and / or when maintenance operations must be undertaken to replace defective probes. The probes can be easily removed from the secondary tubes 30 from the top of the emerging tube. Indeed, a preferred configuration of the invention allows to arrange the tubes so that they exceed the maximum water level of a pool. It is not necessary that a ceiling height is provided to remove a probe several meters in length. FIG. 3 represents a probe 40 in a secondary tube 33. s The probe 40 is retained by the bottom 42 of the secondary tube 43. The probes can be connected to an external calculator making it possible to record the measurements of the probes via wires. 41. In FIG. 4, each probe 40 comprises, for example, a series of series-connected relays 51, 52, 53, 54, 55 and 56 which change state when they are in the magnetic field of the float. . One embodiment relates to probes that include electromagnetic relays arranged in series and spaced a fixed distance apart. For example, the electromagnetic relays may be disposed between resistors of a series of resistors connected in series and arranged on a printed circuit designed in full length. When the magnetic field of a magnet is close to an electromagnetic relay, it activates or deactivates a metal element that opens or closes the printed electrical circuit. As a result, the circuit formed of the series of resistors mounted on a circuit opens or closes as a function of the presence of the magnetic field. The metal parts react to the presence of the magnetic field and make it possible to define an equivalent total resistance of the circuit thus modified by the presence of the magnetic cham. A metal strip can be used to short circuit the mounting or open it or metal resistors can be used. The resistors may be, for example, embedded in ceramic. An entirely mechanical assembly would be equivalent in the device of the invention. The magnet in the latter case actuates metal parts such as switches or slats which are attracted by the presence of the magnet. The advantage of using resistors forming an electrical circuit is that the liquid level can be directly read and interpreted by an equivalent intensity or output resistance measurement or a voltmeter. A calculator makes it possible to convert an electrical data item into a physical quantity, in particular a level of a liquid in a pool. The relays arranged in series in the probe form a natural graduation of the secondary tube at the probe. The magnetic field of the float activates the relay with respect to the water level at which it is located and determines an equivalent resistance of the circuit of the probe of one of the secondary tubes. When the relays are spaced apart for example by 1 cm, the device of the invention makes it possible to obtain the level of the liquid of the basin with a suitable precision for large basins. The probes are arranged in the secondary tubes at different depths so that a basin of great depth, for example of the order of 20 meters deep, can be graduated over its entire depth. The probes, which are of limited size, for example, 1 meter long, are arranged in secondary tubes surrounding the main tube. The secondary tubes can be chosen and arranged so that they form a spiral around the main tube. In the example of Figure 2, the secondary tubes comprise different depths. The probes, which are arranged at the bottom of each secondary tube, can graduate the entire height of a basin. An advantage of this solution is that it is not necessary to have large probes that impose a high ceiling height. Thus, the probes of limited dimensions are easier to handle and to get out of the secondary tubes during maintenance operations, especially when the basin is full. In addition, this configuration also avoids an arrangement of several probes in each tube also penalizing maintenance operations. These latter operations must provide some flexibility in some applications, especially when the basins are nuclear plant wastewater ponds. s The spiral arrangement allows the magnetic field of the float to always be present next to an electromagnetic relay. Figure 2 shows the float 4 also in a configuration where it is immersed in the main tube at a level 6 corresponding to the level of the liquid of the basin. Figure 5 shows an alternative embodiment in which shims 43 are used to retain the probes at a certain depth. When these wedges are used, they are positioned at different depths of the secondary tubes. FIG. 6 represents another variant embodiment, in which the means for holding the probes at a fixed height of the tube are a shim 43 positioned at the bottom of the secondary tube. The alternative embodiments of FIGS. 5 and 6 make it possible to produce the device of the invention with a series of substantially identical secondary tubes. The tubes are distributed around the main tube forming a barrel. This embodiment may therefore have an advantage in its design since the secondary tubes do not need to be machined. An advantage of the device of the invention is that it makes it possible to maintain high temperatures of around 200 ° C., in particular by limiting the maximum number of electronic parts and by making maximum use of metal parts. In particular, the temperatures of 100 ° C do not damage the device of the invention. In particular, the device can be used in particular in case of accident when temperatures are no longer controlled. Another advantage of the device of the invention results from the resistance to irradiation of high levels. This behavior is enabled by the use of metal materials and the limitation of the on-board electronics in the sensor of the invention. The invention makes it possible to maintain high levels of radioactivity above 50 kilo Gray and up to 1 million Gray. Finally, another advantage results from the limited dimensions of the sensors, and therefore probes, the length of which is limited. The limitation of the dimensions of the probes makes it possible to make them hold important elastic deformations in particular in the event of violent shocks or earthquakes. The probes can be from 50 cm to 3 m in the so-called "nominal" configurations of the device of the invention. Beyond the game can become important and can cause a limitation in the measurement records. An advantage of the device of the invention is that it is waterproof vis-à-vis the water basin. The upper part of the tubes is emerged and the water can not seep inside the tubes. In addition to sealing the system, the advantage is twofold given the simplicity of removing the probes from the tubes in the event of replacement. Depending on the basin configurations, the relays of the probes can be arranged every centimeter or every two centimeters, for example. Probes with different graduations can be used. In particular, the invention may comprise probes comprising relays arranged every centimeter and probes whose relays are arranged every 5 cm. This system makes it possible to offer a device comprising precision probes and level estimation probes. In addition, this device makes it possible to provide a redundancy of level readings which makes it possible to guarantee the measurement of the level with a predefined margin of error. According to an alternative embodiment an optical transmitter / detector could replace the magnet and the electromagnetic relays. Some modifications of the device should then be realized. In particular, the optical transmitter in the float must emit over its entire circumference or at least opposite a circular arc on which secondary tubes are positioned vertically. The optical sensors must be able to receive the signals emitted in any configuration. This requirement requires the use of materials allowing the non-filtering of the light signals emitted by the optical transmitter. An exemplary embodiment allows the use of a measuring device of the invention comprising a main tube of about twenty meters. The secondary tubes form a spiral around the main tube. The height of the secondary tubes range from 1m50-2m to 20m. The diameter of the secondary tubes is 10 to 15 cm. The probes are of fixed size, about 1m to 1.5m in length, and all identical to each other. Each probe comprises electromagnetic relays arranged every centimeter and distributed in the length of the probe. Each probe comprises on average 100 to 150 relays. There is ideally between 6 and 20 secondary tubes around a main tube. The probes forming the sensors are thus distributed so as to graduate the entire depth of the basin of about twenty meters. The sensors are arranged in the secondary tubes so as to occupy a portion of approximately 1m to 1m50 from a depth of the basin. The first secondary tube, i.e. the smaller one, is substantially of the same length as the probe, or even a little larger to constitute the emergent part of the device when the basin is at its maximum level. The device of the invention is particularly suitable for large basins, especially having a great depth. However, the device of the invention is also suitable for smaller basins in which the accuracy of the measurement can be increased. In one embodiment, the probes are molded in their housing. In another embodiment, the probes comprise a waterproof shell. In an exemplary embodiment, the main tube comprises fastening means for fixing the sealed shells of the probes along the main tube at different depths. The hull may possibly replace each secondary tube to the extent that a probe can be extracted from the basin and be dissociated simply from the main tube. For example, a system using a mechanism similar to or similar to door hinges may be employed. The sealed shells of the probes are then embedded along the main tube in a slide connection having a stop at a given depth. The removal of the hull is effected simply by performing the reverse movement to the surface of the liquid. The stops are then located at different depths on the circumference of the main tube. In a particular embodiment, the main tube comprises one or more rails for making the slide connection along the main tube.

Claims (13)

REVENDICATIONS1. Device (1) for measuring a liquid level in CLAIMS1. Device for measuring (1) a level of liquid in a tank comprising a float (4) able to float on the surface of said liquid, said float being housed inside a main tube (2) for guiding in translation of said float (4) under the hydrostatic thrust exerted by the fluid, the device (1) further comprising a plurality to of probes (40) disposed near the main tube (2), each probe (40) being capable of measuring the position of the float (4) on a portion of the depth of the basin, said probe (40) being maintained at a predetermined depth, the set of measurement portions covering the maximum stroke of the float in the main tube (2) under the effect of the hydrostatic thrust. 2. Device for measuring a liquid level according to claim 1, characterized in that it comprises a plurality of housings (3), each housing (3) each comprising at least one probe (40), the probes being held within said housing (3). 3. Device for measuring a liquid level according to claim 2, characterized in that the housings (3) are tubes (30, 31, 32, 33, 34, 35) juxtaposed to the main tube (2), called secondary tubes. 4. A device for measuring a liquid level according to claim 3, characterized in that two secondary tubes taken in pairs each have an end located substantially at the same height and have different lengths extending in the depth of basin so that the probes (40) are placed at the bottom of each secondary tube. 5. Device for measuring a liquid level according to claim 3, characterized in that the secondary tubes are substantially of the same size and that holding means disposed inside each tube to maintain the probes at different depths . 6. Device for measuring a liquid level according to any one of claims 2 to 5, characterized in that each secondary tube comprises a single probe (40). 7. Device for measuring a liquid level according to any one of claims 2 to 6, characterized in that the secondary tubes are located around the main tube (2) and form a spiral. 8. Device for measuring a liquid level according to any one of claims 2 to 7, characterized in that the secondary tubes 20 exceed the maximum level of the liquid so as to form a sealed cavity. 9. Liquid level measuring device according to any one of claims 1 to 8, characterized in that each probe (40) is identical. 10. Device for measuring a liquid level according to any one of claims 1 to 9, characterized in that the float (4) comprises means for generating a magnetic field and that the probes (40) comprise electromagnetic relays activated when they are under the action of the magnetic field of the float (4). 11. Device for measuring a liquid level according to claim 10, characterized in that the electromagnetic relays are deactivated outside the magnetic field of the float (4). 5 12.Device for measuring a liquid level according to any one of claims 10 to 11, characterized in that each probe comprises a full-length electrical circuit formed of an alternation of resistors and relays, the measurement of the level of the liquid taking place by measuring the current. 13.Device for measuring a liquid level according to any one of the preceding claims, characterized in that each measuring portion is less than 2m.