GB2118714A

GB2118714A - Volume-measuring device

Info

Publication number: GB2118714A
Application number: GB08307068A
Authority: GB
Inventors: Bernard Andre Mouchet
Original assignee: Jaeger
Current assignee: Jaeger
Priority date: 1982-03-15
Filing date: 1983-03-15
Publication date: 1983-11-02
Also published as: ES520912A0; ES8405939A1; DE3309016A1; GB8307068D0; FR2523298A1

Abstract

A device for measuring the volume of a liquid in a tank comprises level detecting equipment 1 movable along a vertical path, which equipment moves within a tube 30 communicating with the liquid by way of a nozzle at the lower end of the tube. An electric motor controls movement of the equipment 1 to bring it to the air-liquid interface, and a position-coding member 14, 15 is provided for an electrical representation of the position of the movable equipment 1 for deducing the volume measurement. <IMAGE>

Description

SPECIFICATION Volume measuring device The invention relates to the measurement of the level, or rather of the volume, of a liquid such as fuel or lubricant, present in a tank or sump.

Level measuring devices are known comprising level detecting equipment, with a float, movable along a vertical or inclined path (but not a horizontal one), and processing and measuring means, for example a rheostat connected by its slider to the float to determine a level indication depending on the position of said equipment.

Various factors, including the required volume of float, the contact pressure of the rheostat slider and the mass production of this, limit the precision to a few percent (in the case of a rheostat of the type with thick layers).

In accordance with the present invention, there is provided a device for measuring the volume of a liquid present in a tank or sump, said device comprising a level detecting equipment movable along a non-horizontal path, and processing and measuring means to determine a level indication depending on the position of said equipment, said equipment being movable inside a tube which is in communication, at a lower portion, by a nozzle with the tank, the movement of the equipment being operated by an electric motor, the processing means comprising a controlled displacement generator acting on the motor to bring the movable equipment into position for detecting the liquid-gas interface, and a position coding number being provided which is arranged to define an electrical representation of the position of the movable equipment in such a manner that the processing and measuring means deduces from it a precise value of the volume of liquid.

In one embodiment, the movable equipment may comprise a light emitter, a light receiver and sensitive means mounted in the optical path between these and adapted to modify the transmission of light between them, at least when the liquid-gas interface is reached.

More particularly, the sensitive means may advantageously be a prism, the refractive index of which is selected to create a total reflection in air and a refraction in liquid.

For its part, in a first preferred type of the device, the position coder may comprise a strip of metal with segments which are alternately opaque and translucent, mounted length-wise in the tube and placed in such a manner that its segments are interposed in the optical path between the light transducer and receiver.

The configuration, for example the distribution of the different translucent segments may advantageously be selected to take into consideration the shape of the tank.

In a first embodiment which is particularly preferred, the optical path from the light transmitter to the receiver involves the total reflection of the prism in air; the controlled displacement generator acts on the motor to cause the movable equipment to move down from a high abutment position in the tank at least until the liquid-gas interface is reached; and the processing and measuring means charge a register with the total number of translucent segments before the descent of the movable equipment, then deduct the number of translucent segments detected up to the meeting with the liquid-gas interface, the precise value of the volume being defined by the difference between the total capacity of the tank and the volume of the empty portion corresponding to the number of translucent segments detected.

Provision will normally be made for the controlled displacement generator to operate the motor in an upward movement, at the end of a time delay following on the arrival of the movable equipment at the liquid-gas interface, to restore the movable equipment to the high stop.

Nevertheless, it is also possible to envisage that the controlled displacement generator continues the descent of the movable equipment as far as a lower stop in the tank, then causes this equipment to rise again to the high stop.

In a second particular embodiment of the first type, at present considered less advantageous, the optical path from the light transmitter to the receiver involves refraction in the liquid; the controlled displacement generator acts on the motor to cause the movable equipment to move down from a high stop in the tank to a low stop, while counting the number of translucent segments encountered during the immersion of the movable equipment in the liquid, this number defining directly the precise value of the volume of liquid.

It will often be very useful for the measuring means to comprise a store adapted to associate with each value of the number of translucent segments recorded, a corresponding precise value of the volume, taking into consideration the shape of the tank. Nevertheless, a non-linear graduation may also be used with an analogue display.

According to another aspect of the invention, which combines successfully with the various modes of embodiment, the controlled displacement generator determines the arrival of the movable equipment at the high or low stop by monitoring the current of the motor, which avoids additional electrical connections to the tank.

Finally, in connection with the first preferred type of device, provision is made, in principle, that the processing and measuring means repeat the controlled displacement and volume measurement cycle at a selected rate.

In a second type of device, the position coder is selected with absolute coding to indicate the volume directly in any position of the movable equipment; the controlled displacement generator is adapted to control the movable equipment so that it remains at the level of the liquid-gas interface, by delivering orders for the rise or descent of the movable equipment, which orders are applied to the motor through a control linearization stage.

in a particular form of embodiment, a float defining a clear detection line in the air is provided in the tube; and the movable equipment cooperates with this clear line to detect the liquidgas interface.

Finally, the level detecting means may, in a modification consist of two superimposed thermistors, or of an electrical contact established when the movable equipment reaches the float.

This electrical contact may be direct (mechanical contact) or indirect: the float carries a magnet and the movable equipment a switch with a flexible blade ("reed" relay) or a Hall effect probe sensitive to the magnetic field.

Other characteristics and advantages of the invention will be apparent on reading the following detailed description, and in the accompanying drawings in which: Figure 1 illustrates the basic diagram of a first form of embodiment of the invention; Figure 2 illustrates a first level detecting arrangement which can be used; Figure 3 is a more detailed view showing the practical embodiment of the level detecting arrangement of Figure 2; Figure 4 is an operating flow chart of the processing and measuring means using the level detector of Figure 3; Figure 4A is a detail of the advantageous embodiment of the processing and measuring means; Figure 5 illustrates a modification of the flow chart of Figure 4; Figure 6 illustrates another form of embodiment of the device according to the invention; Figure 7 illustrates the level detecting arrangement corresponding to Figure 6;; Figure 8 illustrates the operating flow chart of the processing and measuring means for the structures of Figures 6 and 7; Figures 9A and 9B illustrate a second type of embodiment of the invention in which the level detector is controlled so as to remain at the level of the liquid; Figure 10 illustrates another modified embodiment of the structure of Figures 9A and 9B; Figure 11 illustrates the flow chart of the control of the device of Figures 9 or 10; Figure 1 2A illustrates, in the form of a basic diagram, a linearization servo-control which can be used to control the level; and Figure 1 2B illustrates the eiectronic basic diagram of a particular embodiment of such a control.

In the Figures, the reference numeral 3 designates a tank illustrated in partial section, and the reference numeral 2 illustrates the liquid which it contains, which will be assumed to be fuel.

In the proposed device, a tube is provided, designated in general by 30, which is immersed vertically or in a manner inclined to the horizontal, inside the tank, to cover this practically from top to bottom. This tube is generally closed at its end by a wall 31 but leaving a nozzle which permits the communication of said tube with the tank 3.

This arrangement enables, a priori, the fluctuations in level of the liquid inside the tube 30 to be reduced in relation to what they are in the tank 3, bearing in mind the fact that a fuel tank is intended to be carried by a vehicle and that the fuel level fluctuates extremely depending on the movements of the vehicle.

According to the invention, provided inside the tube 30 is a drive for the movable equipment which enables this to be displaced from top to bottom over the whole length of the tube. In the forms of embodiment illustrated, this drive consists of an endless screw 42 cooperating with a nut of the movable equipment 1. Of course, the drive of the movable equipment may be effected in another manner, for example by means of a chain, a rope or a belt, one strand of which is rigidly connected to the movable equipment and the other strand of which is reversed at the end of its travel, in such a manner that the movement can be operated by a motor situated, for example, at the top of the tank.

In the present case, the motor 41 drives the endless screw 42 directly. As Figure 1 shows, in a first form of embodiment, the movement is effected from a high stop position 1 A, from which the movable equipment moves down until it reaches the level of the liquid at 1 B, after which it rises again.

Figure 1 likewise shows a processing and measuring means generally marked 5, and comprising a controlled displacement generator portion marked 56 and an actual processing and measuring portion, marked 50. The block 5 may appropriately be connected to the motor 41 and to the detector elements carried by the movable equipment. It is considered as being within the scope of one skilled in the art to form an electrical connection between the movable equipment 1 and the fixed portion of the tank, whatever the position of the movable equipment.

Figure 2 illustrates the principle of a particular embodiment of the level detecting means incorporated in the movable equipment.

This Figure shows the light transmitting member 11, such as an electroluminescent diode which produces a beam of light 1 OA directed towards a prism 12 with total double reflection.

The prism has a cross-section in the form of an isosceles right-angled triangle with broken corners. The beam 1 0A is directed perpendicular to the hypotenuse of the right-angled triangle and therefore strikes one of the two sides of the right angle. The refractive index of the prism 1 2 is marked N 1. In air, the beam 1 OA is reflected at right angles at 1 OB to strike the other side of the right angle of the isosceles right-angled triangle after which it returns to 1 OC in a direction parallel to 1 0A but in the opposite direction. The beam then strikes a member forming a relative position coder used in this first form of embodiment and designated as a whole by 13.As Figures 2 and 3 show, this member is a strip of metal consisting of segments which are alternately opaque (1 5) and translucent (14), the strip of metal being mounted lengthwise in the tube 30 and therefore situated in such a manner that these segments 14 and 1 5 are interposed in the optical path between the light transmitter and the receiver. Therefore, to the extent that the beam 1 OC is at the level of a translucent, preferably transparent, segment 14, this beam will strike a light receiving member 19 such as a phototransistor or a photodiode.

In this form of embodiment, it will be seen that it is sufficient to take the connections of the transmitter 11 and of the light receiver 19 back to the block 5, to permit the level measurement.

It was assumed previously that the prism 12 was in the air. When this is in the liquid, here fuel, the refractive index N2 of which is close to the refractive index N1 of the prism, a refraction occurs in the liquid when the beam 1 OA strikes the first side of the right-angle of the isosceles right-angled triangle and consequently the greater part of the beam is dispersed in the liquid, which gives a signal of practically zero at the level of the receiver 1 9. Figure 3 shows better the endless screw 42 which drives the movable equipment 1, this consisting of a part in the general shape of a U, one of the arms of which supports the elements 11 and 19, and the other of which supports the prism 12. Interposed between the two arms is the strip of metal 13, equipped with alternate translucent or transparent 14 and opaque 1 5 zones.

Reference will now be made to Figure 4 which illustrates the operating flow chart of the processing and measuring means 5.

The first stage of this flow chart is the departure 100. After that, the stage 101 consists in charging a numerical register with a maximum number of pulses, corresponding to the maximum number of translucent zones which the movable equipment could meet if it travelled from the top to the bottom of the tank.

The following stage 102 consists in verifying that the motor is against the high stop, then in controlling the downward movement of this.

The verification of the fact that the motor is against the high stop is not explained here but it could be effected as will be seen further on, by urging the motor in the rising direction and by monitoring the current which it consumes in relation to a threshold value equal, for example, to 1 ampere, the motor here being assumed to be a direct-current motor. Therefore, starting from the stage 102, the movable equipment moves down from its upper position 1A in Figure 1.

The block 5 then monitors the appearance of a pulse corresponding to the fact that the light receiver 1 9 will receive light passing through a translucent zone. When such a pulse is detected at 103, the stage 107 consists in deducting a pulse in the register already mentioned.

So long as a pulse is not detected, the output of the test stage 103 consists in passing to a fresh test 104 where the appearance of a "time signal" of milliseconds is awaited, produced inside the block 5 by a suitable clock. When such a "time signal" has appeared, the stage 105 consists in incrementing a time delay which is initially assumed to be zero. After that, the stage 106 consists in monitoring the fact that this time delay has reached the value of 100 milliseconds (for example). So long as the time delay of 100 milliseconds is not reached, there is a return to the stage 103 which consists in looking to see if a pulse has been detected.

It will be noted, moreover, that the stage for deducting the pulse which may have been detected at 107 is followed by a stage 108 consisting in resetting the time delay to zero and again by a return just upstream of the pulse test stage 103.

The operation at this level is as follows: if a pulse is not detected, the time delay is started. So long as the pulse is not detected, the time delay is caused to run, the threshold value of 100 milliseconds being assumed to correspond roughly to the time taken by the movable equipment to pass from one translucent zone to the next, bearing in mind the nominal speed of the motor.

If a fresh pulse arrives before the end of the time delay, this pulse is deducted from the register and the time delay is reset to zero.

In the opposite case, it is assumed that the movable equipment has reached the level of the liquid.

Under these conditions, the output will be effected by the yes branch of the test stage 106 and the following stage 110 consists in controlling the motor in the upward direction, after which the stage 11 stores the value present in the pulse register.

After that, the test stage 1 12 is examined to see if the motor current is greater than 1 ampere.

As soon as this condition is met, the stage 1 13 controls the stopping of the motor, the movable equipment having then returned to the upper position 1 A.

After that, the stage 114 consists in displaying and/or transmitting the volume indication according to the contents of the register.

It is advisable to specify more precisely this operation which is capable of various modifications.

In a first case, the configuration or the distribution of the translucent segments of the strip of metal is adapted depending on the shape of the tank, in such a manner that a predetermined number of translucent segments represents a given volume increment. This is very advantageous because it avoids a subsequent processing to obtain the precise value of the volume, but in return assumes that a particular strip of metal is made for each tank shape.

Another variant is illustrated in Figure 4A. It consists in applying the number of pulses finally stored in the register at the stage 111 to a conversion read-only store or ROM which directly deduces from it the volume to be displayed. In this case, the strip of metal may be made commonplace, only the read-only store 54 having to ensure the transformation of the number of pulses into a volume value corresponding precisely to the tank in question.

The operation of the apparatus is naturally based on the following observation which the expert will easily understand: it is possible to make a precise value of the volume correspond to each value of the number of pulses stored, and to do so whatever the shape of the tank in crosssection.

With the arrangement which has just been described, an indication of the volume of fuel is obtained which is much more precise than that which could be obtained by the prior art, while using very simple means. The value of the volume thus obtained may be the subject of direct display either in analogue form with the well-known graduated dials, or in numerical form with the numerical dispiays which are now incorporated in the dashboard of vehicles. In a modification, a numerical output of the volume information may be effected equally advantageously to go to a computer on board. Computers on board are frequently used nowadays particularly to measure the instantaneous and/or average fuel consumption of the vehicles.The measurements effected up to now suffer from imprecisions which result essentially from the fact that these measurements of fuel consumption are effected starting from an incremental measurement of the fuel flow called for. The incremental measurement apparatuses (for example one pulse for 10 millilitres) suffer, because they are massproduced, from an imprecision which accumulates in proportion to their counting of pulses. This imprecision is expressed by a sort of deflection which may taint the consumption measurements with errors which are not negligible. The device of the present invention, by proposing a measurement of the volume of fuel which comes from another origin, and which for its part is both precise and "integrated", therefore enables the value of the consumption to be corrected at the level of the computer on board.

Returning now to Figure 4, the last stage 114 is normally followed by a stage 1 15 consisting in a wait equal for example to 2 mn after which all the operations are recommenced to obtain a fresh measurement of the volume which will be displayed in turn, and so on.

A modification of the flow chart of Figure 4 is illustrated in Figure 5.

In this modification, instead of stopping the movement of the movable equipment when this reaches the liquid-gas interface, this movement is continued to the bottom of the tank, to rise again until the movable equipment is against the high stop. The advantage of a certain simplification in the flow chart results. On the other hand, since the movable equipment has plunged completely and for a longer time into the liquid, it will take it longer to dry out, it being noted that traces of residual fuel on the prism 1 2 may disturb the operation.

In detail, the flow chart of Figure 5 comprises, after the departure 200, stages 201 to 203 and 207 which are identical to those of Figure 4, marked 101 to 103 and 107 (in principle the numerical differences 200 indicate identical stages).

It will be seen therefore that these stages merely deduct the pulses in proportion to the downward movement of the movable equipment 1 in the air. The time delay is not explained in the flow chart because it may then be effected at the level of the equipment, only supplying a decision yes or no with regard to the detection of a pulse at the end of the normal time which separates two detections of translucent zones, bearing in mind the nominal speed of the motor.

When no pulse is detected any longer, the contents of the register are stored at 211 and the volume is displayed at 214 and/or it is transmitted to a computer on board, depending on the contents of the register, as before.

After that, the test 220 detects if the motor current exceeds 1 ampere which represents the low stop. If so, the stage 221 controls the motor for rising again. After that, the stage 222 tests if the motor current exceeds 1 ampere which represents the fact that the movable equipment is against the high stop, in which case the motor is stopped at 223. Finally, the wait of 2 mn which produces a fresh progress of the same flow chart.

Another form of embodiment of the invention will now be described with reference to the Figures 6 to 8, which form of embodiment is fairly similar to the first but in which the detection of the pulses and the measurement are effected when the movable equipment is in the liquid. The same elements as in Figure 1 will be found again in Figure 6 but it will now be seen that the movable equipment will pass systematically from a position 1A against the high stop, or at least above the level of the liquid, to a position 1 C against the low stop at the bottom of the tank, and vice versa.

The elements of Figure 2 are found again in Figure 7 with numerical references increased by 10 to take into account the fact that the arrangement of the level detection is different. As a matter of fact, the prism 22 may be of the simple total reflection type with an angle of 45 0.

The light transmitter 21 sends its radiation perpendicuiar to one of the sides of this angle of 450, in return for which, when the prism 22 is in the air, this radiation is reflected at 20B to be lost in the tank. On the other hand, if the prism 22 is in the liquid, the refractive index N2 of which is assumed to be very close to the index N 1 of the prism 22, the beam originating from the motor 21 will pass through the second side of the angle of 450 to follow a path 20A which will guide it towards the strip of metal 23 consisting as before of translucent or transparent zones 24 alternating with opaque zones 25. Finally, the light receiver 29 is provided at the other side of the strip of metal.

Figure 8 now illustrates the corresponding flow chart. After the departure stage 300, the stage 301 consists in resetting the pulse register to zero, then the stage 302 consists in verifying that the motor is against the high stop, then in controlling it in the descending mode.

The test 303 monitors whether a pulse is detected. So long as the movable equipment is in the air, no pulse is detected and the level of this test 303 is retained. As soon as a pulse is detected, the stage 304 increases the pulse register by one unit. Then a test 305 examines whether the motor current is higher than 1 ampere which represents the arrival against the low stop 1 C. If this condition is not verified, there is a return to just upstream of the test 303. If it is verified, the stop is reached and the stage 306 consists in storing the contents of the register.

After that, the stage 307 consists in controlling the motor for the rising movement and it is followed by a test 308 which examines whether the motor current is higher than 1 ampere. If so, the high stop has been reached and the stage 309 stops the motor. After that, the stage 310 displays and/or transmits the volume according to the contents of the register in the same manner as before with regard to the mode of display and/or of transmission.

As for the determination of the volume, it will be noted that in principle it is just the same as before, apart from one constant.

As a matter of fact, in the previous forms of embodiment, the number of pulses stored related to the volume of air and it was necessary to cause the difference between the total volume of the tank and this volume of air to correspond to it. In the form of embodiment now considered, the volume of the liquid is obtained directly, in principle.

It will be noted, however, that obtaining precisely the volume of the liquid assumes that the movable equipment moves down as close as possible to the bottom of the tank. Bearing in mind the fact that the bottom of the tube has to be interposed and that it is necessary to provide a stop, this form of embodiment may be of less interest in certain cases, particularly those where it is necessary to provide a very flat tank and where it is not possible to form a recess so as to be able to lower the tube 30 lower than normal bottom of the tank.

Finally, to finish with the flow chart of Figure 8, the stage 311 controls a repeat of all the operations after a waiting time equal to 2 nm for example.

Preferably, a measurement is likewise effected during the return of the movable equipment, that is to say during the upward movement of the detector, and a comparison is made between the two values obtained during the downward movement and during the upward movement.

When the results differ by an amount greater than a predetermined threshold, such as one unit, for example, the results are erased and a fresh measurement cycle is carried out.

This system enables the counting errors to be eliminated.

Another type of embodiment of the invention will now be described with reference to Figures 9 et seq. in which, instead of moving the movable equipment systematically down from a stop position to the level of the liquid or conversely from the level of the liquid to a position against the low stop, the movable equipment is controlled so that it remains at the level of the liquid.

In general, this second type of embodiment assumes that the position coder is of the type with absolute coding so that it can indicate directly the position of the movable equipment at any moment, so as to deduce the volume therefrom.

Figure 9A again shows the tube housing the movable equipment 1, this being movable by an endless screw 42 or any other means, under the control of a geared motor 41.

In this Figure, the geared motor 41 likewise receives on its shaft a toothed wheel 62 which meshes with an intermediate pinion 63 to control, at 64, a potentiometric position coder 61, which may advantageously be of the multi-revolution type, and having an output S1, the sensitivity of which is 340 ohms/litre for example, and an output S2, the sensitivity of which is 5 ohms/litre for example.

The movable equipment may here advantageously be one or the other of those already described with reference to Figures 2 or 6.

Nevertheless Figure 9A illustrates a level detecting means of another type, consisting of two thermistors T, and T2 superimposed vertically with a slight spacing inside the tube 30 and naturally mounted rigidly connected to the movable equipment 1 as Figure 9B likewise shows being a view in section at the level of the thermistor T1.

The basic flow chart is then very simple. As Figure 11 shows, it consists simply of a departure 400, after which, for example, the movable equipment is caused to move systematically down from its high stop. Then the test 401 examines whether it is level with the surface, for example by comparing the current called for by the thermistor T, with that called for by the thermistor T2. It is known that a thermistor will call for a different current according to whether it is in heat exchange with the air or with the fuel. If this test 401 determines that the level of the liquid has been reached, the rise of the motor is controlled at 402 and there is a return to just upstream of 401. Conversely, if the thermistor T2 is not level with the surface, there is a passage to the stage 403 which controls the motor for downward movement, then there is a return to 401.It will be understood immediately that the movable equipment will be subject to movements of very small amplitude, at each side of the liquidgas interface in the tank.

The two outputs S1 and S2 of the coder 61 will then supply the corresponding level value directly to the processing and measuring unit 5, from which this will be able to derive a precise indication of volume by the same means as before.

Figure 1 2A shows how the signal 402 for upward movement and the signal 403 for downward movement are applied to the servocontrol block 56 of the motor incorporated in the block 5, and this block 56 in turn controls a direct-current motor 41 through a linearization circuit 57.

Figure 1 2B shows a suitable type of control in more detail. A reference voltage is applied through a resistor 470 to the thermistor T1. It is likewise applied, through an adjustable resistor 471, to the thermistor T2. And a differential amplifier 472 compares the voltage U1 at the terminals of the thermistor T, with the voltage U2 at the terminals of the thermistor T2. The output of the amplifier 472 is applied to one of the control terminals of the motor 41.

The other control terminal of the motor receives the output of another differential amplifier 473. One input of the amplifier 473 is connected to the intermediate point of a fixed voltage divider 474 and 475 which receives the reference voltage. The other input is likewise applied to a voltage divider receiving the same reference voltage, with two resistors 476 and 477, the latter, situated at the earth side, being adjustable.

The thermistors T, and T2 are assumed to be practically identical; it will be seen that the installation will be sensitive to all the small variations detected by these two thermistors and will therefore naturally be displaced very slightly in such a manner as to maintain the difference detected by the two thermistors at its maximum value, which presupposes that one is in the liquid and the other in the gas above this liquid.

Of course, it is likewise possible to use a movable equipment equipped with a level detecting member with a beam of light as in Figures 2 or 6. In this case, the strip of metal 13 may be dispensed with, and the course of the signal received by the light receiver 1 9 may simply be monitored, about an average value which represents the case where about half of the height of the prism is immersed in the liquid while the other half is in the air.

Still within the framework of the use of an opto-electronic level detecting member, the variant of Figure 10 has the interest that the level detector does not have to be immersed in the liquid at all.

In this modification, the absolute position coder 60 is represented mounted directly on the shaft of the motor 41 it being noted that the arrangement of Figure 9A can naturally also be used.

The movable equipment is illustrated at 1, inside the tube 30. Likewise seen inside the tube 30 is a float 70, pierced axially to allow the passage of the endless screw 42 and equipped laterally with an edge 71 which is reflecting. This edge is adapted in such a manner as to define a clear reflecting line to be detected by the light transmitter-receiver assembly. In this case, naturally neither the prism 1 2 nor the strip of metal 13 is needed. And the movable equipment will simply cooperate with this clear line, about which it will position itself, in such a manner that the light receiving member 1 9 receives about half the signal which it would receive in the case of total reflection.

A person skilled in the art may easily imagine other modifications of the invention, for example in which the float 70 is equipped with a horizontal and conducting metallic plate while the movable equipment 1 is equipped with two electric contacts which are connected to one another at the moment when this movable equipment reaches the float. Here the contacts are mechanical. Such mechanical contacts cooperating with a conductor could naturally be replaced by variants in which the electrical contact is realized indirectly. As previously indicated, a magnet may thus be mounted on the float 70 and the movable equipment 1 be equipped with a switch with a flexible blade ("reed" relay), or again with an element sensitive to the proximity of a magnetic field, such as a Hall effect probe.

Claims

1. A device for measuring the volume of a liquid present in a tank or sump, said device comprising a level detecting equipment movable along a non-horizontal path, and processing and measuring means to determine a level indication depending on the position of said equipment, said equipment being movable inside a tube which is in communication, at a lower portion, by a nozzle with the tank, the movement of the equipment being operated by an electric motor, the processing means comprising a controlled displacement generator acting on the motor to bring the movable equipment into position for detecting the liquid-gas interface, and a position coding member being provided which is arranged to define an electrical representation of the position of the movable equipment in such a manner that the processing and measuring means deduces from it a precise value of the volume of liquid.

2. A measuring device as claimed in claim 1 in which the movable equipment comprises a light transmitter, a light receiver and a sensitive means mounted in the optical path between these and adapted to modify the transmission of light between them at least when the liquid-gas interface is reached.

3. A measuring device as claimed in claim 2, in which the sensitive means comprise a prism the refractive index of which is selected to create a total reflection in air and a refraction in the liquid.

4. A measuring device as claimed in claim 2 or 3, in which the position coder comprises a strip metal with segments which are alternately opaque and translucent which strip of metal is mounted lengthwise in the tube and placed in such a manner that its segments are interposed in the optical path between the light transmitter and the light receiver.

5. A measuring device as claimed in claim 4, in which the configuration or the distribution of the different translucent segments is selected taking into consideration the shape of the tank.

6. A measuring device as claimed in claim 4 or 5, in which the optical path from the light transmitter to the light receiver involves the total reflection of the prism in air, and the controlled displacement generator acts on the motor to cause the movable equipment to move down from a position against a high stop in the tank, at least until the liquid-gas interface is reached, and the processing and measuring means charges a register with the total number of translucent segments before the downward movement of the movable equipment, then deducts the number of translucent segments detected up to meeting with the liquid-gas interface, the precise value of the volume being defined by the difference between the total capacity of the tank and the volume of the empty portion corresponding to the number of translucent segments detected.

7. A measuring device as claimed in claim 6, in which the controlled displacement generator operates the motor in the sense of upward movement, at the end of a time delay following on the arrival of the movable equipment at the liquidgas interface, to return the movable equipment to the high stop.

8. A measuring device as claimed in claim 6, in which the controlled displacement generator continues the downward movement of the movable equipment as far as a low stop in the tank, then causes this equipment to rise again to the high stop.

9. A measuring device as claimed in claim 4 or 5, in which the optical path from the light transmitter to the light receiver involves refraction in the liquid and the controlled displacement generator acts on the motor to cause the movable equipment to move down from a high stop in the tank to a low stop, while counting the number of translucent segments encountered during the immersion of the movable equipment in the liquid, this number defining directly the precise value of the volume of liquid.

10. A measuring device as claimed in any one of claims 6 to 9 in which the measuring means comprise a store arranged to associate, with each value of the number of translucent segments recorded, a precise corresponding value of the volume, taking into consideration the shape of the tank.

11. A measuring device as claimed in any one of claims 6 to 9, in which a measurement is likewise effected during the upward movement of the movable equipment and the information supplied by the position coding member during the downward movement and during the upward movement is compared in such a manner that this is only taken into account if the difference is less than a predetermined value, and in which in the opposite case, the information supplied is erased and the measurement cycle repeated.

12. A measuring device as claimed in any one of claims 6 to 11 in which the processing and measuring means repeats the cycle of controlled displacement and of measurement of the volume at a selected rate.

1 3. A measuring device as claimed in any one of claims 1 to 12, in which the controlled displacement generator determines the arrival of the movable equipment at the high or low stop by monitoring the current of the motor, which avoids additional electrical connections to the tank.

14. A measuring device as claimed in any one of claims 1 to 13, in which the position coder is selected with absolute coding to indicate directly the volume in any position of the movable equipment and the controlled displacement generator is arranged to control the movable equipment so that it remains at the level of the liquid-gas interface, by supplying orders for the upward movement or downward movement of the movable equipment, which orders are applied to the motor through a linearization stage of the control.

1 5. A measuring device as claimed in claim 14, in which provided in the tube is a float defining a clear detection line in air, and the movable equipment co-operates with this clear line to detect the liquid-gas interface.

1 6. A measuring device as claimed in any one of claims 1 to 1 5, in which the precise value of the volume of liquid is transmitted to an onboard computer, which enables incremental measurements of fuel consumption to be checked.

1 7. A device for measuring the volume of a liquid in a tank, substantially as herein described with reference to Figures 1-4, 6-8, 9 or 10 of the accompanying drawings.