FR3104708A1 - ANALOGUE TYPE LIQUID LEVEL SENSOR - Google Patents

Abstract

Device for continuously detecting the level of a liquid present in a tank comprising a float (51) capable of being in contact with the said liquid in operation, a magnet (53) and a support (7) for a plurality of magnetoresistives (70) arranged adjacently along the support, characterized in that it comprises a rod (5) whose distal end (50) is connected to said float (51), said magnet (53) being fixed on the rod close to its proximal end (52), as well as means for guiding the rod, thanks to which the latter can slide in a longitudinal direction, and in that the said support (7) is fixed in the device for s extend along this same longitudinal direction, facing at least part of the travel of the magnet, such that in operation, the magnetic field created by said magnet is capable of being detected by said elements, which continuously generate a signal representative of the level d u liquid in the tank. Figure for abstract: Fig. 1

Description

ANALOG TYPE LIQUID LEVEL SENSOR

The invention relates to the technical field of liquid level sensors.

Many sensors are already known and used in industry.

They can be of the TOR (all or nothing) type, these sensors being calibrated with respect to a determined critical threshold and opening or closing an electrical circuit when this threshold is reached.

They can also be of the analog type and then continuously supply a signal representative of the liquid level.

The interest of such analog sensors is to be able to follow the evolution of the liquid level and to decide on preventive or corrective actions before a critical threshold is reached.

Many analog sensors have already been proposed.

Mention may in particular be made of a membrane sensor, for example that marketed by the company Rosemount or even a sensor having the shape of a rod in which a succession of magneto-resistive elements is provided and which is surrounded by a float comprising magnets, such as that described in document EP3499196.

These sensors are reliable and widely used.

However, their use in severe environments such as a nuclear environment proves difficult, if not impossible.

Indeed, in an oil tank associated with a pump of a nuclear reactor, the liquid has a temperature between -20°C and 85°C, or even 110°C, with a pressure of the order of 30 bars . The sensors used in this environment must meet resistance requirements not only to service conditions but also to so-called accidental conditions (earthquakes and irradiation mainly).

The known sensors of the "rods with float" type which would be placed directly in this tank are not tested and qualified for such temperature and pressure conditions with a long lifespan (of the order of 40 years), nor for accidental conditions.

Furthermore, it has been envisaged to install membrane sensors in a tank associated with a pump of the primary circuit of a nuclear reactor. However, this installation requires drilling the tank in several additional places to allow the connection of the sensor. Insofar as these holes increase the risk of leaks, an additional fairing is necessary around the connection zones, which complicates the installation of these sensors.

The object of the invention is therefore to overcome these drawbacks by proposing a level sensor providing continuous reliable and precise measurements and whose installation is simple, this sensor being able, moreover, to withstand extreme conditions of temperature and pressure.

Thus, the invention relates to a device for continuously detecting the level of a liquid present in a tank comprising a float capable of being in contact with the liquid in operation, a magnet and a support for a plurality of magneto-magnetic elements. resistors arranged adjacently along said support,
characterized in that it comprises a rod, a distal end of which is connected to said float, said magnet being fixed to the rod near its proximal end, as well as means for guiding the rod, thanks to which the latter can slide according to a longitudinal direction, and in that said support is fixed in the device to extend along this same longitudinal direction, facing at least part of the travel of the magnet, so that in operation, the magnetic field generated by said magnet is capable of being detected by said magneto-resistive elements, which continuously generate a signal representative of the level of the liquid in the reservoir.

The device according to the invention may also comprise one of the following characteristics, considered alone or in combination with others:

the magnetoresistive elements are equidistant from each other.

Magneto-resistive elements are reed switches.

The magnetoresistive elements and said support are coated in a layer of resin.

The device comprises a converter and a power supply unit which are fixed on the support.

The converter and the power supply unit are embedded in the resin layer.

The device also comprises a guide tube placed in a longitudinal direction in the device, in which the rod is slidably mounted.

The support is fixed on the guide tube.

The device comprises at least one threshold sensor, capable of generating an alarm.

Said at least one threshold sensor is fixed on the guide tube

The magnet is annular.

The device comprises a housing with a bottom comprising an opening for the passage of the rod, the rod being mounted to slide in the housing in a longitudinal direction, between a low position where the distance between the bottom of the housing and the float is maximum and a high position where the distance between the bottom of the housing and the float is minimal

The device comprises a base arranged under the bottom of the housing and allowing the fixing of the housing on the fluid reservoir.

The invention also relates to an assembly comprising a device as characterized above and a reservoir containing a liquid whose level is capable of being detected in operation by said device, the latter being fixed to said reservoir in such a way that said support is located outside said tank while said float is located inside said tank.

Preferably, when the device comprises a case, the assembly comprises a base arranged under the bottom of the case and allowing the case to be fixed to the fluid reservoir.

The invention will be better understood and other aims, advantages and characteristics thereof will appear more clearly on reading the description which follows and which is made with regard to the appended drawings in which:

Figure 1 is a schematic sectional view illustrating the level detection device according to the invention placed on a tank.

FIG. 2 is a perspective view partially illustrating the detection device according to the invention.

Figure 3 illustrates detail A of figure 1.

FIG. 4 is a partially cut perspective view illustrating an operating state of the detection device according to the invention.

FIG. 5 is a partially cut perspective view illustrating an operating state, different from FIG. 4, of the detection device according to the invention.

FIG. 6 is a schematic view illustrating the magnetic field generated by the magnet of the device and the support of the magnetoresistive elements.

FIG. 7 illustrates a particular use of the device according to the invention.

The elements common to the various figures will be designated by the same references.

Figure 1 illustrates a detection device according to the invention 1, fixed to a tank 2 (partially shown), via a base 3.

The level of the liquid in the tank is denoted by L. The float 51 is placed on the surface of the liquid, its movement being identical to that of the level of the liquid.

The device 1 comprises a housing 4 with a bottom 40 placed on the base 3.

This bottom 40 is pierced with an opening 41, which coincides with an opening 30 provided in the base 3.

As seen in particular in Figure 2, the base 3 has the shape of a disc and the opening 30 is located substantially in the center of the base 3.

The device 1 also comprises a rod 5 on which is fixed, at its distal end 50, the float 51 and, near its proximal end 52, a magnet 53.

“Located close to its proximal end” is understood to mean that the magnet is located at a distance of between 3 mm and 15 mm from the proximal end 52 of the rod 5.

As shown in Figures 1 and 3, the magnet 53 is an annular magnet which has a central recess 530 for the passage of the rod 50.

It should be emphasized in this respect that the device 1 comprises a single magnet which is preferably annular in shape to increase the precision of the detection device.

In the example illustrated in the figures, the rod 5 is mounted to slide inside a guide tube 6.

This tube 6, of cylindrical shape in FIG. 3, is closed by a wall at its distal end 60 and it is open at its proximal end 61. The opening 62 of the tube coincides with the openings 41 and 30, respectively of the bottom of the housing 40 and base 3. Of course, the diameter of the magnet is smaller than the internal diameter of tube 6. It can come into contact with the internal wall of tube 6.

The device also comprises a support 7 for a plurality of magneto-resistive elements 70 arranged adjacently along this support 7.

Preferably, each of these elements 70 is a switch of the REED type (in English terminology, also called reed switch). In known manner, such a switch consists of two blades of magnetic material sealed inside a glass tube containing an inert gas. The blades are arranged with a slight overlap at the level of the contacts inside the glass tube and are spaced from each other by a few hundredths of a millimeter.

When such a switch is placed in a magnetic field, in particular produced by a magnet, the two blades are magnetized by influence and attract each other until they come into contact, which causes the switch to close. Furthermore, the removal of the magnetic field causes the separation of the blades and therefore the opening of the switch.

These elements are connected on the one hand to a converter which makes it possible to supply a signal indicating which switch is closed under the influence of a magnetic field and on the other hand to a power supply unit.

In the example illustrated in Figure 2, the support 7 is fixed on the guide tube 6, so as to extend longitudinally, that is to say along the axis of revolution of the tube 6. Thus, the rod 5 is able to slide in tube 6, support 7 being parallel to the movement of rod 5.

The invention is however not limited to this embodiment. In the absence of a guide tube, the support 7 will be fixed in the casing so as to always extend longitudinally.

The distance between rod 5 and support 7 is preferably between 10.1 mm and 10.3 mm.

In a variant embodiment illustrated in FIG. 1, device 1 can also comprise two threshold detectors (all or nothing sensors) 81 and 82.

These are conventional magnetic detectors, marketed in particular by the company Celduc.

These two sensors 81 and 82 are fixed on the tube 6 in particular via flanges 83, 84.

The invention is however not limited to this embodiment. Thus, in the absence of a guide tube, other means would be provided to fix the two sensors 81 and 82 close to the rod 5.

The support 7 preferably has the shape of a thin, narrow and elongated plate, the width of this plate being greater than the length of the magneto-resistive elements that it supports and in particular that of the REED switches.

As illustrated in Figure 3, when REED switches are used, these are arranged so as to extend transversely with respect to the longitudinal direction in which the support 7 extends.

The support is fixed in the case so as to extend parallel to the travel of the rod and the magnet in the case or at least a part of the travel of the magnet in the case, that is i.e. outside the tank. Thus, the magnetic field created by the magnet is likely to be detected in operation by one of the elements, the converter continuously generating a signal representative of the level of the liquid in the tank.

For this, a calibration of the magnetoresistive elements is necessary and the position of the support in relation to the stroke of the magnet is determined accordingly.

Furthermore, the support 7 is arranged perpendicular to the plane defined by the magnet 53 and perpendicular to the tangent to the circle defined by the magnet in this plane.

Figure 6 illustrates ring magnet 53 and the magnetic field it generates. Switch 70a will be closed under the influence of this magnetic field, while the other switches will remain closed.

Preferably, the magneto-resistive elements fixed on the support 7 are coated in a layer of resin. In addition, these elements can be fixed to the support by means of a strip (not shown).

Preferably, this converter and this power supply unit are also fixed on the support 7 and they are advantageously coated in the same layer of resin as the elements 70. They can also be fixed on the strip when the latter is provided.

Figure 2 illustrates the device 1, in the absence of the entire housing 4. Of course, in industrial use, this housing 4 will be provided. However, it is not necessary for the operation of the detection device according to the invention.

In practice, it is sufficient for the device to comprise guide means for the rod. These can be of very different constructions, for example a simple opening in an element, such as the bottom 40 or the base 3 and/or a guide tube such as the tube 6.

The operation of the detection device according to the invention will now be described with reference to Figures 4 and 5.

In both cases, the device 1 according to the invention has been fixed to the liquid reservoir 31, via the base 3, so that the distal end 50 of the rod 5, with the float 51 is placed inside the tank 31, while the housing 4 is located outside the tank 31. Figures 4 and 5 show that the base 3 is located between the bottom 40 of the housing and the upper part 32 of the tank 31.

These two figures show that the device according to the invention can be mounted on the tank instead of a device already present and mounted in a similar manner, in particular by means of a base. This considerably simplifies its installation since no new drilling is particularly necessary.

Thus, only part of the rod 5, comprising its distal end and the float, is likely to be present in the reservoir 31, the rest of the rod 5 being present in the guide tube 6. The latter, like the support 7 and the sensors 81 and 82 are in the housing 4 and therefore remain outside the reservoir 31.

This arrangement therefore makes it possible to subject the support 7 and the magnetoresistive elements 70 as well as the sensors 81 and 82 to temperature and pressure conditions which are those of the ambient. They are therefore protected from the temperature and pressure conditions which exist inside the tank 31 and which can be very severe, in particular in a nuclear environment since the pressure can then reach 30 bars and the temperature can be between -20° C and 110°C.

Figure 4 illustrates a relatively high position of the float 51 in the tank 31, a significant part of the rod 5 is therefore present inside the guide tube 6.

In this position, the magnetic field created by the magnet 53 causes the closing of one of the REED switches 70 located on the side of the support 7 farthest from the base 3, the closing of this switch generating via the converter a signal indicating the height of the fluid in the tank, thanks to a prior calibration. The output of the converter is designated by the reference 71 in figures 4 and 5.

In the example illustrated, this signal leads to the display of a measurement on a screen 9, here a height of 85% of the maximum displacement provided.

FIG. 5 illustrates another situation in which the level of the fluid in the reservoir is lower than that illustrated in FIG. 4, the part of the rod 5 which is present in the reservoir is thus greater.

In this position, the magnetic field of the magnet 53 carried by the rod causes the closing of another switch located closer to the base. This closing is detected by the converter which transforms it into a signal indicating the level of the fluid in the reservoir 31, which results in a display on the screen 9. The measured height of the fluid is here 10% of the maximum possible displacement.

FIG. 7 illustrates a particular use of the device according to the invention in which, to a tank 9, is connected at least one tank 90 via two conduits 91 and 92, the conduit 91 opening into the lower part of the reservoir and of the tank and the conduit 92 opening into the upper part of the tank and of the tank. Device 1 is fixed to tank 90 via base 3.

With such an arrangement, it is possible to monitor the level of the liquid contained in the tank 9, via the device 1 fixed to the tank 90. In practice, two tanks can be provided.

Thus, the structure of the device according to the invention makes it possible to protect all the sensitive elements from temperature and pressure conditions which would be liable to degrade them. They are also protected from any contact with the fluid present in the tank.

It is also worth pointing out that this device is designed to be extremely robust and to be virtually maintenance-free.

Indeed, the operation of this device does not require any software first. There is therefore no risk associated with a software malfunction or any need for software maintenance.

Furthermore, the support 7 and the magneto-resistive elements that it supports are calibrated before mounting the support 7 in the case 4, so that the activation of one of these elements, in particular the closing of a switch in the example illustrated, generates a resistance measurement signal to which corresponds a level of fluid in the reservoir. Thus, once the support 7 is placed in a suitable position with respect to the rod, in the housing 4, no further action is necessary.

Finally, the fact that all the components are coated in a resin layer resistant to the conditions of use further reinforces their reliability and robustness.

It is thus estimated that, for the device according to the invention, the mean time between failures or mean time between failures (MTBF (mean time between failures) in English terminology), is 50 years at a temperature of 80° C.

The device according to the invention makes it possible to provide signals with an accuracy of +/- 2.5 mm corresponding to the distance between two switches or, in general, between two magnetoresistive elements.

As indicated above, the detection device according to the invention also preferably comprises all-or-nothing level detectors. Preferably, they are bistable detectors.

Thus, the sensor 82 will detect the low position of the rod 5 and therefore of the liquid in the tank, in which the distance between the bottom 40 of the housing and the float 51 is maximum.

This sensor 82 will be activated thanks to the magnetic field generated by the magnet 53 and this activation will advantageously trigger an alarm.

Likewise, the sensor 83 will make it possible to detect the high position of the rod and therefore of the liquid in the reservoir, in which the distance between the bottom 40 of the casing and the float 51 is minimal.

Again, sensor 83 will be activated by the magnetic field created by magnet 53 and this activation will preferably be associated with an alarm.

The presence of these two sensors 81 and 82 makes it possible to combine continuous detection of the level of the liquid in the tank 31 with a safety function, the high and low positions of the rod corresponding to levels of the liquid in the tank which can be prove to be dangerous for the overall operation of the installation.

As goes without saying and as results from the foregoing, the present invention is not limited to the embodiments more particularly described. On the contrary, it embraces all the variants and in particular those where the magnetoresistive elements consist of Hall effect sensors or magnetoresistance sensors, where the base is omitted and where the magnet has another shape, for example a square or rectangular shape, as long as it generates a precise and sufficiently powerful magnetic field.

Claims (14)

Device for continuously detecting the level of a liquid present in a tank comprising a float (51) capable of being in contact with the said liquid in operation, a magnet (53) and a support (7) for a plurality of magneto-resistive (70) arranged adjacently along the support, characterized in that it comprises a rod (5) whose distal end (50) is connected to said float (51), said magnet (53) being fixed on the rod close to its proximal end (52), as well as means for guiding the rod, thanks to which the latter can slide in a longitudinal direction, and in that the said support (7) is fixed in the device for s extend along this same longitudinal direction, opposite at least part of the magnet's stroke, so that in operation, the magnetic field created by said magnet is capable of being detected by said elements, which continuously generate a signal representative of the level of the liquid in the tank. Device according to Claim 1, characterized in that the magneto-resistive elements (70) are equidistant from each other. Device according to Claim 1 or 2, characterized in that the magneto-resistive elements (70) are switches of the REED type. Device according to any one of Claims 1 to 3, characterized in that the magneto-resistive elements and the said support are coated in a layer of resin. Device according to any one of Claims 1 to 4, characterized in that it comprises a converter and a supply unit which are fixed to the support. Device according to Claim 5, characterized in that the converter and the supply unit are coated in a layer of resin. Device according to any one of Claims 1 to 6, characterized in that it also comprises a guide tube (6) placed in a longitudinal direction in the device, in which the rod (5) is mounted to slide. Device according to Claim 7, characterized in that the support (7) is fixed to the guide tube (6). Device according to any one of Claims 1 to 8, characterized in that it comprises at least one threshold sensor (81, 82), capable of generating an alarm. Device according to Claim 9, characterized in that the said at least one threshold sensor (81, 82) is fixed to the guide tube (6). Device according to any one of Claims 1 to 10, characterized in that the said magnet (43) is annular. Device according to any one of Claims 1 to 11, characterized in that it comprises a casing (4) with a bottom (40) comprising an opening (41) for the passage of the rod (5), the rod being mounted sliding in the housing in a longitudinal direction, between a low position where the distance between the bottom of the housing and the float is maximum and a high position where the distance between the bottom of the housing and the float is minimum. Assembly comprising a device according to one of claims 1 to 12 and a reservoir (31) containing a liquid whose level is capable of being detected in operation by said device, the latter being fixed to said reservoir in such a way that said support (70) is located outside said tank while said float (51) is located inside said tank. Assembly according to Claim 13 in that it depends on Claim 12, comprising a base (3) arranged under the bottom (40) of the casing (4) and allowing the casing to be fixed to the fluid reservoir.