FR2844594A1 - Universal liquid volume measuring gauge uses probe detecting pressure under liquid to determine depth and hence volume of liquid stored - Google Patents

Abstract

The measuring system includes two pressure probes (40,10), one of which is submerged in the liquid (10). A processor determines the difference in pressure between the two values, to determine the volume of liquid held within the container. The liquid measuring system includes two probes (40,10) measuring the pressure firstly of the atmosphere (40), and secondly at a depth submerged in the liquid (10). These probes are supplied with power (70) and their signals applied to a processor (80). The processor determines the difference in pressure between the two values, in order to calculate the depth of the liquid as a function of this pressure difference. From this figure, the processor then derives a value for the volume of liquid held within the container. The output signal from the processor may be applied to a display (60), and to a radio communication module (90) linked to an aerial (100) in order to alert the user.

Description

UNIVERSAL DEVICE FOR MEASURING A VOLUME OF LIQUID IN A TANK

  The invention relates to a universal device for

  measurement of a volume of liquid contained in a tank.

  The invention can in particular be used in tanks containing hydrocarbons such as gas oils, fuel oils, lubricants, etc. For measuring the volume of a tank containing a hydrocarbon, a commonly used device comprises a string provided with a ballast light enough to float on the liquid contained in the tank. The device also includes a measuring system capable of tensioning the string and measuring the length of the remaining string. The volume of liquid is then obtained from the measured length and the section of the tank. A disadvantage of such a device is that the string wears and breaks easily, the device must therefore be changed regularly. Furthermore, the measurement is relatively unreliable and it is difficult to obtain

  a measurement with an accuracy of less than 10 or 20%.

  Another known method for measuring the volume in a tank consists in emitting an ultrasonic signal from the top of the tank and in detecting the time taken for the signal to return to the source after reflection on the liquid. The height of the liquid in the tank is in this case inversely proportional to the time

  measured between the transmitted signal and the reflected signal.

  This method gives results of greater

  precision. However, a measuring device using this principle is quite expensive, due to the high cost of an ultrasound source.

  Given the drawbacks of the known devices for measuring the volume in a tank, a first object of the invention is to propose a more reliable, simpler and / or less expensive measuring device than existing measuring devices. Another object of the invention is to propose a

  measuring device that can send information remotely, or be remotely controlled, and allowing automated management of the content of the tank with which it is associated.

  To achieve these objectives, the invention provides a device for measuring the volume of a liquid, for example a hydrocarbon, in a tank, comprising: - a control unit for activating a means for measuring a pressure relative to the bottom of the tank, and to calculate a height of liquid as a function of the relative pressure then calculate the volume of liquid in the tank as a function of the height, and - a communication means for communicating the

  volume of liquid obtained from a user.

  The measuring means preferably comprises an absolute pressure measuring probe immersed in the liquid at the bottom of the tank, and a second pressure measuring probe above the surface of the liquid, generally

  the atmospheric pressure above the tank.

  Thus, according to the invention, the height of liquid in the tank is obtained by measuring the pressure relative to the bottom of the tank. Such a pressure measurement 30 is reliable and moreover, a probe capable of measuring such a pressure is very inexpensive compared to a source of ultrasound. The invention also relates to a method of measuring a volume of a liquid, for example a hydrocarbon, in a tank, comprising: - a step of measuring a pressure relative to the bottom of the tank, - a step of calculating a height of liquid as a function of the relative pressure then calculation of the volume of liquid in the tank as a function of the height and of the density of the liquid, and - an information step for communicating the

  volume of liquid obtained from a user.

  Finally, the subject of the invention is also a system for managing and monitoring the contents of tanks containing liquids, for example of the hydrocarbon type, comprising: - several measuring devices as described above, each measuring device being associated to a tank, and - a control device comprising a communication means associated with the communication means of each measuring device, to receive from one or more of the 20 measuring devices an indication of a volume measured at a preset time, and / or, optionally, - send a signal to activate one of the measuring devices and receive from said device an indication of a measured volume. The invention will be better understood and others

  characteristics and advantages will appear on reading the description which follows, of an example of implementation of a volume measurement device according to the invention. The description is to be read in relation to

  attached drawings in which: - Figure 1 is a block diagram of a measuring device according to the invention, and - Figure 2 is a block diagram of a system using several measuring devices according to the invention. The device of FIG. 1 makes it possible to measure the volume of liquid remaining in a tank, for example a tank containing a hydrocarbon product, generally comprising a vent for venting to the open air. The product may be more or less viscous (for example a

fuel or lubricant).

  The device of FIG. 1 comprises a submerged probe 10, a control member such as a button 20 or 10 a clock 120, an atmospheric probe 40, a memory, a display device 60, a power source 70

and a control unit 80.

  The energy source 70 is preferably an autonomous energy source such as a rechargeable battery or accumulator. The energy source 70 could also be a connection socket to a public energy distribution network. On instruction from the control unit 80, the source 70 supplies the submerged probe 10 and the atmospheric probe 40 with energy. The source 70 20 also supplies the control unit 80 continuously, including in standby mode, when the probes 10,

are not powered.

  The submerged probe 10 is an absolute pressure measurement probe. The probe is placed at the bottom of the tank 25 for which it is desired to determine the volume of liquid remaining,

  and preferably far enough from the edges of the tank. The probe 10 is a conventional probe, preferably an absolute pressure probe of high precision, which has been made waterproof and having explosion-proof characteristics, to avoid risks of explosion.

  The probe 40 is a pressure measurement probe

  absolute conventional, used here to measure an atmospheric pressure P0. When receiving energy from the source 70, the probe 40 transmits to the control unit 80 a measurement of the atmospheric pressure.

  The memory 50 is a non-volatile memory, and preferably an electrically modifiable memory, for example an EEPROM type memory. The memory 50 contains in particular values of one or more parameters characteristic of the liquid contained in the

  instrumented tank, and in particular the value of the density of the liquid. The memory preferably also contains values of parameters characteristic of the tank and more precisely of its geometric shape, as will be seen more clearly below.

  The display 60 is a conventional LED display, for example displaying 4 digits. It is used to display information relating to the volume of liquid contained in a given tank. The information can be the volume of the liquid in the tank or the free volume

  in the tank, expressed in a unit such as a liter or a gallon. The display is directly controlled by the unit 80 which transmits to it information to be displayed.

  The display may include a timer device, used to limit the duration of the display of information. This limits the

  energy consumption of the volume measuring device.

  When not requested by a user or by the clock, the device of FIG. 1 is in a standby mode, in which only the control unit is partially supplied with energy by the source 70 and is waiting for a command signal. In standby mode, the other elements of the measuring device, in particular the probes 10, 40, are not supplied with energy. We

  thus limits the overall consumption of the device.

  When a user wishes to obtain information on the content of the tank instrumented by the device in FIG. 1, he can press the push button 20 to signal to the control unit 80 that he wishes information. The control unit 80 transmits

  a start signal to the power source, which in turn supplies energy to the probes 10, 40.

  When supplied with energy, the submerged probe 10 provides the unit 80 with a measurement of the absolute pressure P at the bottom of the tank and the probe 40 provides the unit 80 with a measurement of the atmospheric pressure Po. L unit 80 will read from the memory of the parameters characteristic of the liquid and of the tank then calculates the volume of liquid in the tank as a function of these parameters and of the relative pressure P - P0 at the bottom of the tank. Unit 80 finally transmits the result

on display 60.

  According to one embodiment, the unit 80 calculates the height H of liquid in the tank from the relative pressure P - Po and the density d of the liquid in the tank. The height is given by the relation: H = CTE * d * (P-Po), or CTE is a constant Unit 80 then calculates the volume of liquid in the tank according to the geometry of the tank and the calculated height H V = f (H) If the tank has a constant section over its entire height, in this case the tank parameter used is the constant value S of this section: the volume is calculated by multiplying the height measured by the section

  S. If the tank has a variable section with the height H and if the volume of the tank can be defined by a simple mathematical function f, in this case the parameters of the tank used are used are the parameters 30 necessary for the definition of the function f.

  In some cases, however, it is not possible to define the volume of the tank in a simple manner according to its height. This is particularly the case for tanks made by blowing plastics in a mold which may have a particular shape for

  adapt for example to a particular environment.

  In the case where the volume of the tank as a function of the height cannot be defined by a simple mathematical relation, the volume can be defined by a table with two columns, indicating the value of the volume for 5 different heights in the tank. The table can for example be obtained during a calibration phase of the measuring device. Values not recorded in the table will be obtained for example by interpolation or extrapolation. Different improvements to the described measuring device can be envisaged, alone or together, depending on the application which is envisaged for the measuring device. All the improvements envisaged have essentially the advantage of facilitating the remote operation of the measuring device of the invention, and of facilitating the management of the contents of the tank. A first possible improvement is the addition

  an external communication means, to allow the control unit 80 to communicate with external management or piloting devices.

  When a volume measurement is made, the result of the measurement can then be transmitted by the control unit on a modulated radio signal to an appropriate receiving device. The transmission of the result can be envisaged before, during, after or in place of the display. The measuring device of the invention is in this case associated with a remote centralizing device comprising means for

appropriate reception.

  In one example, the external communication means comprises a radio frequency module 90 and an antenna 100 35 shown in dotted lines in FIG. 1. The radio module is capable of modulating digital signals or

  analog over radio signals.

  In another example, the means of communication comprises a modem capable of transmitting or receiving digital or analog information on a power distribution network by carrier currents, or else on

a wired telephone network.

  In another example, the means of communication comprises a device for connection to a dedicated link, such as a two-wire link, an Ethernet link, a link called an RS232 link, etc. A second group of possible improvements concerns the addition of protection or alert devices to facilitate the management of the content of the instrumented tank or to ensure the maintenance of the measurement device. The measurement device can thus be improved by the addition of a programmable clock 120, capable of activating the control device 80 at predefined regular time intervals (for example every four hours), in place of the 'user. In this case, the result of the measurement of the volume remaining in the tank will preferably be transmitted to an external receiving device 25 via the communication means at these same intervals. It can also be provided that, before activating the power source 70 to carry out a measurement, the control device checks the electrical charge of the source 70. If the charge is less than a predefined low level, an alert is issued. transmitted on the display 60

  or by means of external communication.

  It can also be provided that, if the volume of liquid measured is less than a predefined minimum level 35 and / or if one of the probes 10, 40 signals a malfunction, the control device transmits a corresponding alert on the display 60 or

by means of external communication.

  FIG. 2 is an example of a system for monitoring the contents of three tanks Ai, Bi, Cl. The system comprises three measuring devices as described above. The submerged probe 10 of each measuring device is immersed in the bottom of the tank with which the measuring device is associated. The other 10 elements of each measuring device are grouped in corresponding boxes A2, B2, C2, fixed for example on a wall of the corresponding tank. The shape of the tanks is arbitrary, two tanks can have different shapes. For each tank, a table containing 15 volume values according to different heights

  liquid is stored in the memory 50 of the associated measuring device. Finally, each measurement device is equipped with a radiofrequency transmitter (integrated in the corresponding box) and an incorporated antenna A3, 20 B3, C3.

  The system also includes a reception or control device D comprising a radio frequency reception unit and an associated internal antenna

or external.

  In one example, the device D simply receives signals representative of the volume of liquid in the tank associated with the measuring device emitting the

  signals, at predefined times.

  In another example, the device D can also send a control signal to activate the measuring device of one of the tanks and receive in return a

  signal corresponding to the volume measured.

  This can be achieved for example by the action of a user on a selection button provided for this purpose on the control device D. The user thus immediately has information on the content of a

  tank, without the need to move to the tank.

  The transmission of the measurement signal can also be carried out automatically at predefined times, the production of the control signals preferably being managed in this case by software means provided for this purpose in the measurement device, which moreover can provide an alert. to the receiving device D. Such an alert could for example be activated 10 when the volume of liquid in a tank has reached a minimum level, or during a failure of an immersed probe or during a power supply failure of the control device of one of the measuring devices. The reception device D may also display a light and / or sound signal in the event of detection of an absence of reception of signal from one of the measurement devices, for any reason whatsoever, in particular for failure to food, significant for example of

  depletion of a battery pack.

  Instead of having a wired connection 110 established directly from the measurement device, as shown in FIG. 1, it is also possible to use a radio frequency connection between the measurement device and a reception device, the latter then being directly supplied by a power source 75 and

  comprising, as illustrated in FIG. 2, means 115 for internal connection to a dedicated wired link, such as a two-wire link, ethernet, RS232, etc. connecting the receiver device D to remote control, display or management means, not shown.

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Claims (12)

  1. Device for measuring the volume of a liquid, for example a hydrocarbon, in a tank, comprising: - a control unit (80) for activating a means for measuring (10, 40) of a relative pressure (P- P0) at the bottom 5 of the tank, to calculate a height (H) of liquid as a function of the relative pressure then calculate the volume of liquid in the tank as a function of the height (H), and - a means of communication (60 , 90, 110) for   communicate the volume of liquid obtained to a user.   2. Device according to claim 1, in which the measuring means comprises a probe (10) for measuring absolute pressure immersed in the liquid at the bottom of the tank, and a probe (40) for measuring an atmospheric pressure (P0) , the measuring means providing a relative pressure representative of the pressure exerted   by the liquid on the bottom of the tank.   3. Device according to one of the preceding claims, in which the communication means   comprises a display (60) and / or a radio frequency module and a radio frequency antenna (90, 100), and / or a modem capable of transmitting or receiving signals by carrier currents and / or a means of connection to a dedicated wired link (110).   4. Device according to one of claims   above, also comprising a memory (50) for storing parameters characteristic of the liquid 30 and / or parameters characteristic of the tank, in particular a parameter relating to the density of the liquid and one or more parameters relating to the volume of the tank in depending on the height.   5. Device according to one of claims   previous, also comprising a clock (120) for activating the control unit (80) at one or more predefined times. 6. Method for measuring a volume of a liquid, for example a hydrocarbon, in a tank, comprising: - a step of measuring a relative pressure (P-P0) at the bottom of the tank, - a step calculating a height (H) of liquid as a function of the relative pressure then calculating the volume of liquid in the tank as a function of the height (H), and - an information step to communicate the   volume of liquid obtained from a user.   7. The method of claim 6, wherein the height of the liquid in the tank is obtained by multiplying the relative pressure measured by a density of the liquid.   8. The method of claim 6 or 7, wherein the volume of liquid is obtained by multiplying the height of the liquid by a section of the tank, the   said section being a function of the height of liquid.   9. Method according to one of claims 6 to 8,   in which the variations in the volume of the tank as a function of the height of liquid are defined by a table with two columns indicating a value of the volume for   different values of the liquid height.   10. Method according to one of claims 6 to 9, 35 wherein the measurement step, the calculation step and   the communication step are repeated, at the request of a   user or at predefined times.   11. Management system for monitoring the contents of 5 tanks containing liquids, for example of the hydrocarbon type, comprising: - several measuring devices (A2, A3; B2, B3   C2, C3) according to one of claims 1 to 5, each   measuring device being associated with a tank (Ai, BI, 10 CI), and - a receiving or piloting device (D) comprising a communication means associated with the communication means (90, 100) of each measuring device, to - receive from one or more of the measuring devices an indication of a volume measured at a predefined or determined time by a user, or, optionally, send a signal to activate one of the 20 measuring devices and receive from said device a indication of a measured volume.   12. Surveillance management system according to claim 11, in which the reception device 25 includes means (115) for connection to a dedicated wired link connecting the receiver device (D) to   remote control, display or management means.