WO2004104524A2

WO2004104524A2 - Method for measuring the free volume of a tank and measuring device therefor

Info

Publication number: WO2004104524A2
Application number: PCT/IT2004/000291
Authority: WO
Inventors: Silla Martini
Original assignee: Girardello, Gianpaolo
Priority date: 2003-05-21
Filing date: 2004-05-21
Publication date: 2004-12-02
Also published as: WO2004104524A3

Abstract

A method for measuring the free volume in a tank (1a) provides for the steps of pressurising the tank to a predetermined pressure by means of the admission of a gas into the tank, and of calculating the free volume in said tank by direct or indirect measurement of the quantity of gas necessary for pressurising the tank. A measuring device (1, 100) operating according to that method is further described.

Description

Method for measuring the free volume of a tank and measuring device operating according to the method Technical field The present invention relates to a method for measuring the free volume of a tank according to the characteristics set out in the preamble of independent claim 1, and also a measuring device operating according to that method, having the characteristics listed in the preamble of independent claim 10. Background of the art

In various technical fields there is a need to know the free available volume of a tank or, conversely, the volume of the tank that is effectively occupied, for example, by a liquid contained therein.

This information is normally obtained, indirectly, by measuring the level of the liquid present in the tank. For this purpose, many measuring systems are known, based on various physical principles, such as, for example, level indicators with float, ultrasonic or magnetic means, etc., each having its own characteristics and preferred fields of application.

Such methods, however, generally prove not to be very reliable when the liquid in the tank is agitated or when the tank itself is shaken or inclined, for example in the case of the fuel tanks of boats, subjected to wave motion, or of vehicles in motion or vehicles parked on an incline. In these cases, in fact, the level of the liquid to be measured is not stable during measurement and therefore the indication provided is approximate or actually misleading.

Another limitation of these measuring systems is that in order to obtain a reliable value for the free volume of the tank by measuring the level of the liquid contained therein, it is necessary to be in possession of a precise function of correlation between these two data, which involves perfect knowledge of dimensions, shape and positioning of the tank, or the execution of appropriate experimental tests. Another drawback of these systems is that they cannot function in the absence of gravity. Description of the invention

The problem underlying the present invention is that of providing a method for measuring the free volume of a tank and a measuring device operating according to that method, structurally and functionally designed to remedy the limitations mentioned above with reference to the cited prior art.

Within the scope of this problem, it is an aim of the invention to provide a measuring device which is highly accurate and of restricted cost.

This problem is solved and the aim is achieved by the present invention by means of a method for measuring the free volume of a tank and a measuring device which are provided according to the claims which follow. Brief description of the drawings

The characteristics and advantages of the invention will become clear from the detailed description of some preferred exemplary embodiments thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which: - Figure 1 is a diagrammatic view of a first example of a device for measuring the free volume of a tank, produced according to the invention, in a first operating step,

Figure 2 is a diagrammatic view of the device of Figure 1 in a second operating step, - Figure 3 is a diagrammatic view of a second example of a device for measuring the free volume of a tank, produced according to the present invention, in a first operating step,

Figure 4 is a diagrammatic view of the device of Figure 3 in a second operating step. Best modes for carrying out the invention Referring initially to Figures 1 and 2, the reference 1 indicates as a whole a device for measuring a free volume of a tank la, produced according to the present invention.

In the preferred examples illustrated herein, the tank la is intended to contain a liquid 2 (for example fuel), which can be poured into the tank through an opening 3, reclosable in a substantially sealed manner by a cap 3a.

The device 1 is connected to the tank la and comprises pressurisation means for pressurising the tank, sensor means for measuring the pressure within the tank, control means for controlling the pressurisation means associated with the pressure sensor means, and also computing means for obtaining the measurement of the free volume in the tank la according to the method described in detail hereinafter.

In this first embodiment of the invention, the pressurisation means comprise a compressor 4, preferably of the volumetric type with pistons, the intake 5 of which is connected to the external atmosphere and the delivery of which is connected via a pipe 6 to the top of the tank la.

The sensor means for the internal pressure of the tank la comprise a digital manometer 7, positioned for example on a breather pipe 8 of the tank la interrupted before its outlet opening 9 by a solenoid valve 10.

The device 1 further comprises a control unit 11, which, besides being connected to the manometer 7 and the compressor 4, is also connected to a timer 12 associated with the compressor 4 for detecting the operating time of the latter and to a digital thermometer 13 connected via a pipe 14 to the inside of the tank la.

Power is supplied to the control unit 11 by cables 11a, or it may be provided with a battery.

According to the measuring method of the present invention, the device 1 is programmed to operate in the following terms. In response to the command for actuation of the measuring device, effected for example by pressing a push-button 15 provided on the control unit 11, the tank la is brought to atmospheric pressure by the opening of the solenoid valve 10. Alternatively, said solenoid valve may be kept normally open.

Once atmospheric pressure has been reached, suitably detected by the digital manometer 7, the control unit 11 commands the closure of the solenoid valve 10 and the actuation of the volumetric compressor 4, which proceeds to admit air through the pipe 6 to the inside of the tank la, causing its internal pressure to increase (see Figure 1). When the pressure reaches a predetermined value, the manometer 7 sends a signal to the control unit 11 which commands the shutting-off of the compressor 4. By knowing the specifics of operation of the compressor and the operating time thereof as detected by the timer 12, it is possible to calculate the quantity of air admitted into the tank in order to reach the predetermined pressure (for example, in the case of a compressor with pistons, the quantity of air will be substantially proportional to the number of cycles performed by the pistons). With this information available, it is possible to use an equation of state of the gases in order to obtain, by simple algebraic calculations, the volume in which the gas has been admitted. As a first approximation, the equation of state of ideal gases may be used, but more complex equations of state, calibrated on the specific physical parameters of the air, may provide greater accuracy of results.

Preferably, the predetermined pressure at which the admission of air into the tank la is shut off, ranges between 30 and 500 millibars gauge, even more preferably 50 relative millibars gauge. In this way, the measuring times are reduced and the effect of the variation of the pressure downstream on the calculation of the quantity of air admitted by the compressor is minimised. In order to take into due consideration also the effect of the temperature, the latter is suitably measured by the digital thermometer 13 before and after the admission of gas into the tank la. The above-mentioned calculations are carried out by a microprocessor 16, suitably programmed, included in the control unit 11, and the results of the calculations are shown on a display 17. By knowing the overall volume of the tank la, these results may of course be expressed, by difference, as the volume occupied by the liquid 2.

In the case where it may be preferred to maintain the tank la at atmospheric pressure, the breather solenoid valve 10 is opened at the end of the measuring operation (see Figure 2).

It should be noted that the measuring method described above is independent of the level of the liquid 2, as also of the overall shape of the tank. On the other hand, it lends itself to numerous advantageous applications, among which are precise measurement of the variation of the liquid 2 contained in the tank la, following, for example, a withdrawal or refilling.

The device 1 may further be programmed for carrying out successive measurements at a predetermined frequency so as to monitor the variation over time of the volume of liquid 2. The operation of the device 1 in this "continuous" control mode may be selectively operated via a push-button 18 provided on the control unit 11.

With reference to Figures 3 and 4, a measuring device indicated as a whole by 100 is shown, representing a second exemplary embodiment of the invention. Details of the device 100 analogous to the device of the preceding example are indicated in Figures 3 and 4 by the same numerical references.

The device 100 differs from the device 1 substantially in that the pressurisation means for pressurising the tank la comprise an intermediate air receiver 101 which is maintained at a constant pressure higher than the predetermined pressure to which the tank must be pressurised in order to carry out the measuring operation.

The air receiver 101 is connected to the top of the tank via a pipe 102 on which is provided a solenoid valve 103, normally closed.

The pressure and the temperature inside the air receiver 101 are monitored respectively by a pressure sensor 104, mounted on the pipe 102 upstream of the solenoid valve 103, and by a digital thermometer 105, both connected to the control unit 11. The air receiver 101 is also connected to the delivery of a compressor 4, via a pipe 106 on which is mounted a further solenoid valve 107, normally closed, and a cooling coil 108. Alternatively, the solenoid valve 107 may be substituted by a non-return valve. Analogously to the device of the preceding example, the device 100 therefore comprises pressure sensor means 7 and a digital thermometer 13, for respectively detecting the pressure and temperature inside the tank la, and a breather solenoid valve 10 for bringing the pressure of the tank to atmospheric pressure. The tank la may further be equipped with a safety valve 109.

Under normal conditions of non-operation, the solenoid valve 103 is closed, isolating the tank la from the air receiver 101, which is maintained at a preselected pressure ranging between 1 and 10 bars, for example 4. At the instant of the command for starting the measurement of the free volume of the tank la, the solenoid valve 10 is opened (if it was not already open) in order to bring back the internal pressure of the tank to atmospheric pressure, after which the pressure and internal temperature both of the air receiver 101 and of the tank la are detected.

At this point, after the breather solenoid valve 10 has been closed, the solenoid valve 103 is opened for the admission of air into the tank (see Figure 3). As in the preceding case, the admission of air proceeds until the predetermined pressure has been reached within the tank la, as detected by the pressure sensor 7, after which the solenoid valve 103 is closed again and the pressure and temperature within the air receiver and the tank are measured again.

In this case, the quantity of air admitted into the tank in order to reach the predetermined pressure is calculated from the equation of state of the gases which is applied to the initial and final states of the air receiver 101. This information is then used for calculating the free volume of the tank la, as in the preceding example.

Tests carried out by the Applicant have shown that the results obtained with the device 100 are more accurate and repeatable than those obtained with the device 1, inasmuch as the variables dependent on the volumetric compressor are eliminated.

At the end of the measuring operation, the tank is bled by means of the opening of the solenoid valve 10, and the air receiver 101 is brought back to the initial pressure by the action of the compressor 4 actuated by the control unit 11. The air emerging from the compressor is conveniently cooled by the coil 108 before entering the air receiver 101.

Provision is further made for the device 1 or 100 to be able to be programmed to transmit the data concerning the free volume (or volume occupied) to a remote control station.

The present invention therefore solves the problem mentioned above with reference to the prior art cited, offering at the same time numerous other advantages, among which are the fact of containing the overall costs and obtaining a precise and reliable measurement of the free volume of a tank in any state thereof. It should further be noted that the device of the invention also lends itself to being installed easily on existing tanks, it being sufficient to arrange a pair of connections between tank and device and if necessary to substitute the existing cap with a hermetically sealed one.

Claims

C L A I M S

1. A method for measuring the free volume in a tank (la), characterised in that it provides for the following steps: a) pressurising said tank up to a predetermined pressure by admitting a gas into the tank, and b) calculating the free volume in said tank by means of direct or indirect measurement of the quantity of gas necessary for pressurising the tank according to step a).

2. A method according to claim 1, wherein the gas is admitted into the tank by the action of a compressor (4), and said measurement of the quantity of gas admitted is obtained indirectly from the operating time of said compressor.

3. A method according to claim 2, wherein said compressor is volumetric.

4. A method according to claim 1, wherein the gas is admitted into said tank from an intermediate air receiver (101) having a pressure higher than said predetermined pressure, and said measurement of the quantity of gas is obtained indirectly from measurements of pressure and temperature carried out in said tank and in said air receiver before and after said admission of gas.

5. A method according to claim 4, wherein, at the end of said admission and of said measurement of pressure and temperature, said intermediate air receiver is brought back to the initial pressure.

6. A method according to one or more of the preceding claims, wherein said tank is normally open, is closed before said admission of gas and bled at the end thereof.

7. A method according to one or more of the preceding claims, wherein said predetermined pressure reached in said tank ranges between 30 and 500 millibars gauge.

8. A method according to one or more of claims 4 to 7, wherein the pressure maintained in said air receiver ranges between 1 and 10 bars gauge.

9. A method according to one or more of the preceding claims, wherein said free volume is calculated by using an equation of state of the gases into which are inserted the data concerning pressure, temperature and quantity of gas used for pressurising said tank.

10. A device for measuring ' the free volume of a tank (la), characterised in that it comprises pressurisation means (4, 101) for pressurising said tank by means of the admission of a gas, sensor means (7) for sensing the pressure in said tank, control means (11, 103) for the pressurisation means, arranged for shutting off the admission of gas into the tank on reaching a predetermined pressure detected by the pressure sensor means (7), and also computing means (16) for obtaining said free volume from direct or indirect measurements of the quantity of gas admitted into said tank in order to reach said predetermined pressure.

11. A device according to claim 10, wherein said pressurisation means comprise a volumetric compressor (4) directly connected to said tank.

12. A device according to claim 11, wherein said computing means comprise a timer (12) for measuring the operating time of said compressor during the admission of the gas into the tank.

13. A device according to claim 10, wherein said pressurisation means comprise an intermediate air receiver (101) connected to said tank and in which said gas is stored at a pressure higher than said predetermined pressure.

14. A device according to claim 13, wherein said control means comprise an on-off valve (103) for interrupting the connection (102) between said air receiver and said tank, said valve being slaved to the sensor means (7) for sensing the pressure within the tank.

15. A device according to claim 13 or 14, wherein sensor means are provided for sensing the pressure (104) and the temperature (105), associated with said computing means (11), for detecting the pressure and temperature of the gas in said air receiver (101).

16. A device according to one or more of claims 13 to 15, wherein a compressor (4) is provided, connected to said air receiver for maintaining said air receiver at a preset pressure.

17. A device according to one or more of claims 10 to 16, wherein sensor means (13), connected to said computing means (11), are provided for sensing the temperature in said tank.