FR2717575A1 - Liquid level measuring device - Google Patents

Abstract

The level measuring device (1) is contained in the liquid reservoir (2) and provides a readout of level. The indication is magnetic (10), by corresponding angular position, rotating around an axis. A Hall effect sensor produces an electrical signal, as a function of the angular magnetic position. This electrical signal may be transmitted, or converted to a display, of level indication. The reservoir may be enclosed, with a magnetic boss (5) in its top, with the magnet internally adjacent, influencing the Hall sensor outside, by its magnetic field. A float (6) on the liquid surface may have a fixed spindle (7), joined to the magnet by gearing (8,9), converting level to angular rotation.

Description

The present invention relates to a device for measuring the level of a

  liquid contained in a tank. It relates more particularly to such a device in which the liquid level corresponds to an angular position of magnetic means, rotatable around it

of an axis.

  Measuring devices of this type are known, particularly for level reading in pressurized tanks, such as those containing liquefied gases and / or petroleum gases, such as butane, propane. In these devices, a float on the surface of the liquid is connected by a float arm to a fixed angle gear. This bevel gear is itself connected by a transmission shaft to a magnet rotatable parallel to a wall of the tank. At this place, the

  wall consists of a boss of non-magnetic material.

  On its outer face, the reservoir carries a reading device formed of an outer magnet, rotatable about a pivot located in the same axis as the inner magnet, and associated with an indicator needle whose position can be read. on a graduated dial. In other embodiments, the magnet is associated with a graduated dial rotating with it and whose orientation is marked

compared to a fixed index.

  The level of the liquid in the tank determines the inclination of the float axis and, through the bevel gear and the transmission axis, the position

  angle of the inner magnet and the outer magnet.

  The position of the indicator needle in relation to the dial

  graduated therefore indicates the level of the liquid in the tank.

  These devices are commonly used to measure the fill level of liquefied gas tanks

  under pressure, and have so far satisfied.

  However, they imply a direct reading, whereas it appeared necessary to be able to know remotely the filling level of the tanks and, possibly, to be able to control or to control various processes to

from the value of this level.

  There are different level measuring devices or probes providing information in the form of an electrical signal. However, the use of these different devices requires communication between the inside of the tank and the outside, which presents problems difficult to solve in the case of

  tanks of liquefied gas under pressure.

  The equipment of existing tanks with such

  devices is an additional constraint.

  The object of the invention is to propose a device

  able to solve these different problems.

  It is therefore an object of the invention to provide a device for measuring the level of a liquid contained in a tank that does not require a material passage to the tank.

through a wall.

  It is another object of the invention to provide such a device which provides an electrical measurement signal.

  representing the filling level of the tank.

  It is another object of the invention to provide a level measuring device that allows the modernization of the existing installations, described above, for measuring the level of the liquefied gas tanks.

  under pressure without having to empty said tanks.

  For this purpose, the invention relates to a device for measuring the level of a liquid contained in a reservoir comprising means for matching said level to an angular position of means.

  magnetic, mobile in rotation about an axis.

  According to the invention, this device comprises at least one Hall effect sensor providing an electrical measurement signal, a function of the angular position of the magnetic means, and means of acquisition and

  visualization of the liquid level from the electrical measurement signal.

  According to different preferred embodiments, the device of the invention comprises the following characteristics, possibly taken in all their technically possible combinations: the Hall effect sensor or sensors are placed parallel to a plane perpendicular to the axis of rotation of the means; magnetic; it comprises a plurality of Hall effect sensors, angularly out of phase with each other about the axis of rotation of the magnetic means; it comprises two Hall effect sensors, approximately phase-shifted by 90 relative to one another; it comprises three Hall effect sensors, approximately phase-shifted relative to one another; it is intended for a tank closed by walls and comprises a non-magnetic boss inserted in one of the walls of the tank and the magnetic field is produced by an internal magnet placed inside the tank in the vicinity of the non-magnetic boss, and the sensors Hall effect are placed in the vicinity of the non-magnetic boss outside the tank; - An outer magnet, rotatable, is placed between the non-magnetic boss and Hall effect sensors and the outer magnet has an angular position determined by the angular position of the inner magnet; - It comprises a float on the surface of the liquid, connected by a float arm to a fixed angle transmission, itself connected to the magnetic means by a transmission axis; the position of the float, a function of the level of the liquid, determines the orientation of the float axis and, through the bevel gear and the transmission axis, the orientation of the magnetic means; the acquisition and display means are placed at a distance from the Hall effect sensors, and transmission means send the measurement signals supplied by the Hall effect sensors to said acquisition or display means; - the liquid contained in the tank is a gas of

  Liquefied Petroleum (G.P.L.), or a Liquefied Chemical Gas.

  The invention will be described in detail with reference to the accompanying drawings, in which: - Figure 1 is a schematic vertical sectional representation of the elements of the measuring device connected to the reservoir; - Figure 2 is a schematic representation in partial vertical section of the device; - Figure 3 is a schematic representation in partial vertical section of the device equipped with local display means; - Figure 4 is a partial schematic representation top view of the device in a first embodiment; FIG. 5 is a schematic representation of the signals produced by the Hall effect sensors of the device of FIG. 4; - Figure 6 is a partial schematic representation of the device in a second embodiment; FIG. 7 is a schematic representation of the signals produced by the Hall effect sensors of the device of FIG. 6; FIG. 8 is a schematic example seen from above of the implantation of a measuring device in a third embodiment with four Hall effect sensors; FIG. 9 is a schematic example seen from above of the implantation of a measuring device in a

fourth embodiment.

  A liquid 1 is contained in a tank 2, represented here by its upper wall, approximately horizontal 3. The level of this liquid is represented by

  line 4 separating the gaseous phase from the liquid phase.

  The measuring device comprises a non-magnetic boss 5 sealingly attached to the wall 3; A float 6 is connected by a float arm 7 to a fixed angle transmission 8. A transmission axis 9 carries, at its upper part, in the vicinity of the non-magnetic boss 5,

  magnetic means 10 producing a magnetic field.

  Thus, the position of the level of the liquid 4 determines that of the float 6 and hence the angle made by the float axis 7 with the horizontal. This angle determines the angular position of the transmission axis on itself and

  thus, that of the magnetic means 10.

  On the outside of the tank, Hall effect sensors 12-1, 12-2 are positioned on the non-magnetic boss 5 in

look at magnetic means 10.

  The magnetic means 10 advantageously comprise two permanent magnets 210, 310 carried by an arm 410

  mobile in rotation about the axis 9.

  The sensors are covered with a housing 15 fixed on

the non-magnetic boss 5.

  In order to provide level information on the tank 2 itself, the device, as shown in FIG. 3, advantageously comprises means for

local visualization.

  In this case, external magnetic means 110 are used to provide on-site visualization using a needle 13 or a rotating dial whose position

  is located relative to an index 113.

  The external magnetic means 110 have a structure

  analogous to that of the magnetic means 10.

  Hall effect sensors are then placed between the nonmagnetic boss 5 and the magnetic means 110.

  In the rest of the description, for all modes

  embodiment, the similar elements will bear the same reference in the various Figures, Hall effect sensors will be generally designated by the reference 12 and

  individually by references 12-1, 12-2, etc.

  The signals produced by these sensors are referenced

  respectively by 19-1, 19-2, etc.

  Each Hall effect sensor 12 is powered from a source 16 and provides an electrical signal to the processing unit 17, a function of the magnetic field it receives, that is to say in practice the angular position. at

magnetic means 10.

  The processing unit 17 supplies a signal representative of the angular position to magnetic means 10 and thus, from the level of the liquid contained in the reservoir to the operating means and / or

visualization 18.

  These operating and display means 18 may be placed at a distance from the processing unit 17 with which they are connected, either by a wire connection, or possibly by an immaterial connection,

such as radio, infrared ....

  The operating or viewing means 18 may be extremely varied in nature, they may correspond either to a simple dial or display screen, or may be used to control control devices, alert, etc .... They can still be used to perform statistical analysis by exploiting the filling level by

relation to time, etc.

  The signal supplied by each of the Hall effect sensors 12 as a function of the orientation angle has magnetic means is a sinusoidal curve 19. The curve associated with each of the sensors 12-1 is out of phase with that provided by another 12-2 sensor according to the angle formed by the axis of one of the sensors

12-1 with the axis of the other 12-2.

  As shown in Figures 2 to 5 corresponding to a first embodiment, the implementation of two Hall effect sensors perpendicular to each other gives rise to signals 19-1, 19-2 sinusoidal based the orientation of the magnetic means 10, out of phase 90

relative to each other.

  In this case, the processing unit 17 can exploit the ratio of these two signals corresponding to the tangent

  angle to provide the value of the desired level.

  In the second embodiment, shown in FIGS. 6 and 7, where three Hall effect sensors are angularly offset from each other by 60, the three provided sinusoidal signals 19-1, 19-2, 19-3 are

  2r / 3 out of phase with each other.

  In this case, since the angle a represents the position of the magnetic means at a given level, the theoretical sum of these three signals is zero: sin a + sin (a + 2 f / 3) + sin (a + 4 z / 3 ) = 0 For ease of understanding, the three signals provided by Hall sensors 19-1, 19-2, 19-3

  will be called U1, U2, U3 respectively.

  At a desired position of the magnetic means, the processing unit 17 therefore measures the voltages U1, U2, U3 which can be decomposed as follows: U1 = K. sin a1 U2 = K. sin (a2 + 2 f / 3) U3 = K. sin (a3 + 4 T / 3) Practically, the values a1, a2, a3 correspond to a E, E representing the intrinsic tolerances of the Hall effect sensors and the processing electronics,

  As well as their positioning tolerances, the coefficient K represents the absolute and maximum value of the signal arbitrarily chosen at 1 volt to facilitate understanding of the following.

  To access the value of a, it is first of all necessary to define the quadrant in which is a: sin a1 = Ul Two possible cases: 1) if sin a1 2 0, two cases arise: a) if U2 S U3 - quadrant n 1 to 2 0 and a S 90, where a = a1 b) if U2> U3 - quadrant n 2 a> 90 and a S 180, of o a = I - a1 2) if sin a1 <0, two cases arise again: a) if U2 2 U3 - quadrant n 3 a> 180 and a <270, of o a = r + a1 b) if U2 <U3 - quadrant n 4 a> 2700 and a <3600, from o a = 2r - a1 Then, a can be extracted from the following three relations: U1 = sin aa1 sin 1 = U1 U2 = (sin a2.cos 2n / 3) + (sin 2v / 3 .cos a2) the cos of 27/3 = - 0.5 and the sin of 2e / 3 = 0.866 U2 = - 0.5 sin a2 + 0.866 cos a2 Moreover, a1 being different from a2 than of the value

E, we consider a1 = a2.

- U1 U2 + U1 / 2

U2 - + 0.866 cos a2 - cos a2 =

2 0.866

  similarly U3 = (sin a3.cos 4v / 3) + (sin 4v / 3.cos a3) U3 = - 0,5 sin a3 - 0,866 cos a3 - U1 - U3 + U1 / U3 = - 0,866 cos a3 - cos a3 =

2 0.866

  The processing unit 17 calculates the arithmetic mean of a <a> as follows: i = 3 i = 3 <a> = 1 E ai 3 i = 1 <a> representing the position of the magnetic means and therefore by the same, the position of the float and by

therefore, the level of liquid.

  In the third embodiment shown in FIGS. 3 and 9, the sensors 12-1, 12-2, 12-3, 12-4 are shifted relative to one another by an angle of

r / 5 = 36.

  Whatever the embodiment, the operation in differential measurement of the signals emitted by the sensors relative to each other makes it possible to overcome the uncertainties of the embodiment, as well as variations in the climatic conditions and, as a result, to improve

the accuracy of the measurement.

  In the embodiments of FIGS. 8 and 9, elements 20, 21 of magnetic flux-conducting material, respectively, are used to channel the magnetic flux emitted by the magnetic means 10 towards the

Hall effect sensors.

  In the first case (FIG. 8), this element 20 is in the form of a set of contiguous fingers in the vicinity of the center of rotation of the magnetic means 10 and carrying

  each a Hall effect sensor at its other end.

  In the second case (Figure 9), this element 21 has the

  shape of a ring carrying Hall effect sensors.

  The reference signs inserted after the technical characteristics mentioned in the

  claims, have the sole purpose of facilitating the

  understanding of these, and in no way limit

the scope.

Claims (10)

  A device for measuring the level of a liquid (1) contained in a reservoir (2) having means for matching said level to an angular position of magnetic means (10) rotatable about an axis, characterized in that it comprises at least one Hall effect sensor providing an electrical measurement signal, a function of the angular position of the magnetic means and means for acquiring or displaying the level of the   liquid (1) from the electrical measuring signal.   2. Measuring device according to claim 1, characterized in that the Hall effect sensor or sensors are placed parallel to a plane perpendicular to the axis of rotation of the magnetic means.   3. Measuring device according to claim 2, characterized in that it comprises a plurality of Hall effect sensors, angularly out of phase with each other   around the axis of rotation of the magnetic means.   4. Measuring device according to claim 3, characterized in that it comprises two Hall effect sensors, approximately phase-shifted by 900 with respect to each other. 5. Measuring device according to claim 3, characterized in that it comprises three Hall effect sensors, approximately phase-shifted relative to each other. 6. Measuring device according to any one of claims 1 to 5 for a tank (2) closed by walls, characterized in that it comprises a non-magnetic boss (5) inserted into a wall (3) of the reservoir ( 2), that the magnetic field is produced by an inner magnet placed inside the tank in the vicinity of the nonmagnetic boss (5), and that the Hall effect sensors are placed in the vicinity of the non-magnetic boss (5) to the outside of the tank.   7. Measuring device according to claim 6, characterized in that a rotating external magnet is placed between the non-magnetic boss (5) and the Hall effect sensors, said external magnet having an angular position determined by the position angular of the inner magnet. 8. Measuring device according to any one of   Claims 1 to 7, characterized in that it comprises a   float (6) on the surface of the liquid (1), connected by a float axis (7) to a fixed angle gear (8), itself connected to the magnetic field transmitter (10) by an axis transmission (9); the position of the float (6), a function of the liquid level (1), determining the orientation of the float axis (7) and via the angle gear (8) and the transmission axis (9), the orientation of magnetic means.   9. Measuring device according to any one of   Claims 1 to 8, characterized in that the means   acquisition or display are placed at a distance from the Hall effect sensors, and that transmission means send the measurement signals supplied by the Hall effect sensors to said acquisition means or of visualization.   10. Measuring device according to any one of   Claims 1 to 9, characterized in that the liquid (1)   is a Liquefied Petroleum Gas (G.P.L.).