WO2002029367A2

WO2002029367A2 - Method and apparatus for determining the volume of liquid in a reservoir

Info

Publication number: WO2002029367A2
Application number: PCT/IB2001/001807
Authority: WO
Inventors: Peter James Erasmus; Evert Philippus Vermeulen; Leslee Vernon Gouws
Original assignee: Directech International Limited
Priority date: 2000-10-02
Filing date: 2001-10-02
Publication date: 2002-04-11
Also published as: AU9018701A; WO2002029367A3; AU2001290187B2

Abstract

This invention relates to a method of determining the volume of liquid (50) in a reservoir (52), which includes the steps of feeding a pressurised gas through a flow path (26) to a low point in the reservoir (52), measuring the back pressure in the flow path (26) with pressure measuring means (16), and using the measured back pressure to calculate the depth of liquid (50) in the reservoir (52). This invention extends to an apparatus (10) for use in determining the volume of liquid (50) in a reservoir (52), and to a probe (12) suitable for use in the apparatus (10). The invention also relates to a method of detecting the presence of contaminants in a body of liquid (50).

Description

A METHOD OF AND APPARATUS FOR DETERMINING THE VOLUME OF LIQUID IN A RESERVOIR

THIS INVENTION relates to a method of and apparatus for use in determining the volume of liquid in a reservoir. It further relates to a probe suitable for use in the apparatus. This invention extends to a method of detecting the presence of contaminants in a body of liquid. It further relates to a liquid storage facility and to a measuring installation. It also relates to a computer program product.

According to one aspect of the invention there is provided a method of determining the volume of liquid in a reservoir which includes the steps of feeding a pressurised gas through a flow path to a low point in the reservoir; measuring the back pressure in the flow path with pressure measuring means; and using the measured back pressure to calculate the depth of liquid in the reservoir, and using the depth to calculate the volume of liquid.

The Inventors believe that the invention will find application particularly, though not necessarily exclusively, in the measuring of the level of a liquid fuel such as petrol, diesel, or the like, in underground storage tanks of a filling station or f industrial site or in storage tanks in aircraft, ships, and road and rail tankers, or the like. The invention will furthermore find application in the measuring of the level of a liquid, other than fuel, in storage tanks and dams.

The method may include incorporating into the calculation of the depth of liquid a factor to compensate for changes in density due to changes in temperature. Accordingly, the method may include sensing an ambient temperature in the reservoir. At least part of the flow path may be defined by a probe inserted into the liquid and the method may include feeding the gas, typically air, to the probe from a supply of gas at a predetermined pressure.

The method may include periodically correlating a zero reading of the pressure measuring means to a standard. The standard may be atmospheric pressure e.g. when the reservoir is open to atmosphere. Instead, where the reservoir is closed to atmosphere, the standard may be the pressure within the reservoir above a body of liquid in the reservoir. In this way the measured back pressure will correspond to the depth of the liquid and not be affected by changes in the pressure of gas in the reservoir above the liquid.

Measuring the back pressure in the flow path may include sensing the back pressure by use of at least one pressure sensor, and converting the pressure reading so obtained into an electrical signal.

The method may include stabilising the at least one pressure sensor. Stabilising the at least one pressure sensor may include maintaining the sensor at a predetermined temperature. Maintaining the sensor at a predetermined temperature includes mounting the sensor on a mass, typically aluminium, which is heated to a predetermined temperature.

According to another aspect of the invention there is provided apparatus for use in determining the volume ot liquid in a reservoir which includes a probe through which a flow path having an inlet end and an outlet end extends, the probe being insertable into the reservoir such that the outlet end of the flow path is adjacent to a low point of the reservoir; gas supply means for feeding gas under pressure to the inlet end of the flow path; and pressure measuring means for measuring back pressure in the gas as a result of the depth of the liquid. The apparatus may include a temperature sensor for sensing an ambient temperature in the reservoir.

The apparatus may include processing means to which the pressure measuring means is connected, the processing means being configured to calculate the depth of liquid in the reservoir. The temperature sensor may be linked to the processing means so as to permit the processing means to compensate for density variations in the liquid due to changes in its temperature. The processing means may be configured to calculate the volume of liquid in the reservoir. Instead, or in addition, the processing means may be configured to calculate the mass of liquid in the reservoir.

The apparatus may include a display connected to the processing means for displaying data such as the depth of liquid, volume of liquid, etc., calculated by the processor. The display may be positioned remote from the reservoir.

The apparatus may include monitoring means for monitoring a pressure of gas of the gas supply means. The monitoring means may include an alarm for generating an alarm signal when a pressure of the gas rises above or falls below a predetermined threshold value.

The apparatus may include calibrating means for correlating a zero reading of the pressure measuring means to a standard. The standard may be atmospheric pressure. Instead, when the reservoir is closed to atmosphere, the standard may be the pressure in a reservoir above the body of liquid contained in the reservoir. The calibrating means may include a vent for permitting the pressure measuring means to be vented to atmosphere or to the space in a reservoir above a body of liquid in a closed reservoir, as the case may be. The apparatus may include a timer which is configured to permit the pressure measuring means to be vented at predetermined intervals. The pressure measuring means may include at least one pressure sensor coupled to a transducer for converting a measured pressure into an electrical signal. The apparatus may include pressure sensor stabilising means for stabilising the at least one pressure sensor. The pressure sensor stabilising means may include a mass, typically of aluminium, on which the pressure sensor is mounted, the mass being heated to and maintained at a predetermined temperature.

The processing means may include a database defining data relating to the liquid in the reservoir. The data may relate to the relative density (specific gravity) of the liquid in the reservoir.

According to yet another aspect of the invention there is provided a probe suitable for use in the above apparatus which probe includes at least one elongate inner member through which a flow path having an inlet end and an outlet end extends; and a sleeve extending around the at least one inner member for at least part of its length.

The at least one inner member may be tubular, the inlet and outlet ends of the flow path being defined by the operatively upper and lower ends, respectively, of the at least one inner member.

The sleeve may be tubular and the at least one inner member may be positioned within the sleeve such that there is clearance between a radially outer surface of the at least one inner member and a radially inner surface of the sleeve.

A lower end of the sleeve may protrude beyond a lower end of the at least one inner member.

At least one bleed opening, e.g. in the form of a recess, may be provided in the lower end of the sleeve. Preferably, a plurality of circumferentially spaced recesses is provided in the lower end of the sleeve. The provision of the bleed opening permits liquid to enter the probe when it is inserted into a body of liquid.

The at least one inner member may be secured within the sleeve by longitudinally spaced locating members. The locating members may be in the form of springs.

In one embodiment of>the invention, the probe includes at least two, and preferably three, spaced apart elongate inner members through each of which a flow path having an inlet end and an outlet end extends, the sleeve extending with clearance around the three inner members. In this embodiment of the invention, the lower end of each inner member terminates at a position longitudinally off -set from the lower end of each of the other two inner members.

Naturally, the materials from which the probe is constructed will be selected to resist attack from the liquid within which the probe is to be inserted.

Hence, when the probe is intended for use in measuring the level of liquid fuels in reservoirs, the components of the probe will typically be formed from stainless steel.

According to yet another aspect of the invention, there is provided a method of detecting the presence of contaminants in a body of liquid, which method includes the steps of feeding a pressurised gas through a first flow path to a first point in the reservoir; feeding a pressurised gas through a second flow path to a second point in the reservoir which is at a level which is different to the level of the first point; measuring the back pressure in each flow path; and using the measured back pressures to calculate the density of the liquid between the first and second points in the reservoir.

The method may include comparing the density calculated with a reference density for the liquid. The method may include feeding a pressurised gas through a third flow path to a third point in the reservoir which is at a level which is different to that of each of the first and second points, and measuring the back pressure in the third flow path with the pressure measure means.

The method may then include comparing the calculated density of the liquid between the first and second points with the calculated density of the liquid between the third point and one o the first and second points.

According to yet another aspect of the invention, there is provided a liquid storage facility which includes a reservoir within which liquid can be contained; and at least one gas flow path having an inlet which is connectable to a pressurised supply of gas and an outlet which opens into the reservoir at a low level.

The liquid storage facility may include at least two gas flow paths, each of which has an inlet connectable to a pressurised supply of gas and an outlet, the outlets opening into the reservoir at different levels.

According to a furthe/ aspect of the invention, there is provided a data processing installation for a storage facility, which installation includes pressure measuring means for measuring a back pressure in a probe inserted into a body of liquid in a reservoir; temperature sensing means for sensing an ambient temperature in the reservoir; and processing means to which the pressure measuring means and temperature sensing means are linked, the processing means including memory means having a database defining data relating to the liquid in the reservoir.

The data may relate to the relative density (specific gravity) of the liquid in the reservoir. The processing means may be configured to receive a signal from the pressure measuring means and/or temperature sensing means and to use the measured back pressure and temperature to calculate the volume of liquid in the reservoir.

Data input means may be linked to the processing means. The data input means may include a keyboard. f

The processing means may be provided at a terminal remote from the reservoir. The data input means may-be provided at the remote terminal. Instead, the processing means may be provided on a wheeled unit.

According to yet another aspect of the invention, there is provided a computer program product, which product includes an interface module for receiving input data relating to a liquid in a reservoir; a database reading module for accessing a database defining data relating to the liquid in the reservoir; and a comparator module for comparing the input data with the database data.

The computer program product may be installed on a central processing unit of a filling station or industrial site. Instead, the computer program may be installed on a processor provided on a wheeled unit, intended for use, for example, on an airport apron, or the like.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings, Figure 1 shows a schematic view of apparatus for use in determining the volume of liquid in a reservoir in accordance with the invention;

Figure 2 shows a side view of a lower end portion of a probe forming part of the apparatus of Figure 1 ; > Figure 3 shows a schematic representation of another apparatus in accordance with the invention;

Figure 4 shows a schematic representation of still another apparatus in accordance with the invention; and Figure 5 shows a schematic view of a further apparatus in accordance with the invention.

In Figure 1 of the drawings, reference numeral 1 0 refers generally to apparatus for use in determining the volume of liquid in a reservoir in accordance with the invention.

The apparatus 10 includes a probe, generally indicated by reference numeral 1 2, gas supply means, generally indicated by reference numeral 1 4 for feeding gas, typically air, under pressure to the probe and pressure measuring means, generally indicated by reference numeral 1 6 for measuring back pressure, as described in more detail below.

The probe 1 2 is elongate and includes a tubular inner member 1 8 and a tubular sleeve 20. The inner member 1 8 has an upper end 22 and a lower end 24 which define, respectively, the inlet and outlet ends of a flow path 26 extending through the inner member 1 8. The tubular inner member 1 8 will typically have an inner diameter of about 6 mm. It will be appreciated, however, that the inner diameter of the inner member 1 8 will vary with the length of probe and the material of which the probe is manufactured.

The sleeve 20 is in the form of a tubular member of larger cross-section than the inner member 1 8 and has a vented upper end 28 and a lower end 30. The inner member 1 8 is secured in position relative to the sleeve 20 by a plurality of locating members in the form of springs 32 which serve both to retain the inner member 1 8 at a desired longitudinal position within the sleeve 20 and to maintain an annular clearance between a radially outer surface of the inner member 1 8 and a radially inner surface of the sleeve 20. The Inventors believe that the annular clearance between the radially outer surface of the inner member 1 8 and the radially inner surface of the outer member 20 will typically be about 1 0 mm.

At least one and possibly a plurality of circumferentially spaced recesses 34, of a depth of about 1 5 mm each, (one of which is shown in Figures 1 and 2) is provided in the lower end 30 of the sleeve 20. The lower end 24 of the inner member

1 8 is positioned such that it is recessed relative to the lower end 30 of the sleeve 20, i.e. the lower end portion of the sleeve 20 protrudes beyond the lower end 24 of the inner member 18. Typically, the sleeve 20 will protrude beyond the lower end 24 of the inner member 1 8 by a distance of between about 5 mm and 10 mm. However, it is to be appreciated, that the optimum distance for a particular application can be ascertained by means of routine experimentation.

The gas supply means 1 4 includes a compressor 36 which is connected to a buffer tank 38, for moderating the impact of vibrations, or the like, which may have a destabilising effect on the gas supply. The compressor 36 typically supplies t air at a pressure of between about 300 kPa and 600 kPa. An air supply tank 40 is connected to the buffer tank 38 via a pressure regulator 42. A flow line 44 leads from the air supply tank 40 and is connected to the upper end 22 of the inner member 1 8.

A flow regulator, for example, in the form of an orifice 46, is mounted in the flow line

44.

Air within the air supply tank 40 is maintained at a predetermined pressure, for example, about 30 kPa to 40 kPa. The air pressure in the buffer tank 38 from which the air supply tank 40 is supplied is maintained at a pressure which is substantially higher than that in the air supply tank 40, for example, of the order of about 300 kPa to 600 kPa. The pressure regulator 42 serves to maintain air entering the air supply tank 40 at a pressure approximately equal to the maximum back pressure which might be exerted toy a column of liquid, the depth of which is to be measured, in the flow line 44. ln use, if the air pressure in the air supply tank 40 is maintained at a pressure in excess of the maximum back pressure, amplifications of, and resulting inaccuracies in, the back pressure as measured by the pressure measuring means may arise. Similarly, where the air pressure in the air supply tank 40 is maintained at a pressure less than the maximum back pressure which might be exerted by the column of liquid to be measured, incorrect measurements of actual back pressure may result.

The orifice 46 is of a magnitude which maintains the rate of flow of air along the flow path 26 defined through the inner member 1 8 at between about 1 50 ml and 200 ml per minute. It is to be appreciated that a sufficient rate of flow of air along the flow path 26 for a particular application will depend upon the inner diameter and length of the inner member 1 8 and if necessary can be ascertained by routine experimentation.

The apparatus 10 also includes a temperature sensor (not shown) for sensing an ambient temperature.

The pressure measuring means 1 6 is connected to the flow line 44 to measure the pressure in the flow line upstream of the probe 1 2 and downstream of the orifice 46. The pressure measuring means 1 6 is connected to a processor 48 which is configured, in response to signals received from the pressure measuring means, to calculate the depth of liquid 50 in a reservoir, such as an underground storage tank 52. The temperature sensor is also linked to the processor 48, the processor 48 being configured to compensate for variations in the density of the liquid 50, and therefore in the depth of liquid 50, in response to measured changes in its temperature. The apparatus 1 0 includes a display 54 which is connected to the processor 48. If desired, the display 54 can be positioned at a location remote from the processor.

In use, the probe 1 2 is inserted through an opening 56 in the top of a f storage tank 52 until the lower end 30 of the sleeve 20 abuts against the bottom of the storage tank 52. The provision of the recess or recesses 34 ensures that liquid 50 flows into the sleeve 20 to a level corresponding to the level of liquid 50 within the tank 52. It will be appreciated that in addition to or instead of the recess 34 a bleed opening may be provided in the slέeve 20.

Air is bled from the air supply tank 40 through the orifice 46, along the flow line 44 and through the flow path 26, to be discharged from the lower end 24 of the inner member 1 8. The air discharged therefrom forms bubbles which flow upwardly in the annular space defined between the inner member 1 8 and the sleeve 20, the locating springs 32 permitting the escape of bubbles through the annular space. The air bubbles are vented into the tank 40. It will be appreciated that the sleeve 20 provides a so-called "stilling well", that is, it serves to shield the inner member 1 8 from fluctuations which may occur in the depth of the liquid 50, for example, due to swells or waves, such that the back pressure in the inner member 1 8 is indicative of an average depth of the liquid 50.

The pressure measuring means 1 6 measures the back pressure in the flow line 44 and transmits a resulting signal to the processor 48. Similarly, the temperature measuring means measures the temperature and transmits a signal in response thereto to the processor 48.

With this information, the processor calculates the depth of the liquid 50 within the storage tank 52, which information can be displayed on the display 54. If desired, by making use of a suitable algorithm, the processor can convert the depth measurement into an indication of the volume of liquid contained with the storage tank

52. Likewise, if desired, the processor can convert the depth measurement into an indication of the mass of liquid in the reservoir.

f When the apparatus 10 is intended for use in determining the volume of liquid fuel within an underground storage tank, for example, at a filling station, the display 54 will typically be positioned where it is readily visible to a manager of the filling station. He is then able to monitor the volume of fuel contained within the tank, thus facilitating stock control. Reference is now made to Figure 3 of the drawings, in which reference numeral 60 refers generally to another apparatus for use in determining the volume of liquid in a reservoir in accordance with the invention and, unless otherwise indicated, the same reference numerals used above are used to designate similar parts.

The apparatus 60 includes monitoring means, generally indicated by reference numeral 70, linked to the air supply tank 40 for monitoring a pressure of air in the air supply tank 40. The monitoring means 70 includes an alarm for generating an alarm signal when a pressure of the air in the air supply tank 40 rises above or falls below predetermined limits or threshold values, viz. the maximum back pressure which might be exerted by a column of liquid, the depth of which is to be measured. It will be appreciated, that if the pressure of gas being fed to the probe is too high, then the bubbling from the lower end 24 of the inner member 1 8 will be excessive which f means that the pressure reading at the pressure transducer will be amplified and in excess of the pressure exerted by the column of liquid, resulting in an incorrect measurement and fluctuations. If, However, the pressure of gas fed to the probe is too low, then the bubbling from the lower end 24 of the inner member 1 8 will be reduced or cease which means that the pressure reading at the pressure transducer will be reduced and not in relation to the pressure exerted by the column of liquid, resulting in an incorrect measurement of the depth of the liquid.

The apparatus 60 includes flow direction regulating means in the form of a three-way solenoid valve 62, having three ports 64, 66, 68. When the solenoid is de-energised ports 64 and 66 are connected in flow communication. When the solenoid is energised ports 64 and 68 are connected in flow communication. The apparatus 60 further includes a controller, generally indicated by reference numeral 72, linked to the monitoring means, the controller 72 in turn being linked to the valve 62 and configured to disconnect ports 64 and 68 (by a de-energising of the solenoid) in response to an alarm signal generated by the alarm of the monitoring means 70, thereby to isolate the inner member 1 8 from the pressure measuring means 1 6. The controller 72 and three-way valve 62 linked thereto, via potential-free relays, also provide calibrating means for correlating a zero reading of the pressure measuring means 1 6 to a standard. To this end, the port 66 of the valve 62 provides a vent for permitting the pressure measuring means 1 6 to be vented to atmosphere or to the air above a body of liquid in a closed reservoir, as the case may be. In this regard, where the liquid 50 in the reservoir 52 is open to atmosphere, the standard will be atmospheric pressure and the port 66 will open to atmosphere. Where the reservoir 52 is closed to atmosphere, the standard will instead be the pressure of air or gas above the body of liquid 50 in the reservoir 52 and the port 66 will open to the air or gas above the body of liquid 50 in the closed reservoir 52. The controller 72 typically includes a progammable memory (volatile RAM and non-volatile RAM) and a real-time clock and may be configured to Nent, and thereby calibrate (or "auto-zero"), the pressure measuring means 1 6 at predetermined intervals. During "venting" of the pressure measuring means, the measured pressure should correspond to the known standard value. If this is not the case, the controller 72 is configured to correct all subsequent pressure measurements by factoring in the deviation from the standard.

The pressure measuring means 1 6 includes a sensor unit comprising a series of pressure sensors coupled to transducers for converting a measured pressure into an electrical signal. The controller 72 includes the processor 48 and has sixteen analogue input channels, for receiving 4 - 20 mA analogue input signals from the pressure transducers, and three digital output channels (in a potential free format) . Each pressure sensor/transducer has a high pressure port, which is connected via the valve 62 to the inner member 1 8, and a low pressure port, which is vented to atmosphere. The electrical output of the sensors/transducers is typically fed via an amplifier (not shown) to the processor 48/controller 72. The sensor unit has nine discrete pressure measurement channels, one of which may define the monitoring means 70.

The apparatus 60 further includes pressure sensor stabilising means for stabilising the pressure sensors, that is, preventing 'sensor drift' due to changes in temperature. In one embodiment of the invention, the pressure sensor stabilising means is provided by a block of aluminium heated to a predetermined temperature and positioned in heat exchange relationship with a sensor. Naturally, however, any other suitable heat conducting material may be used. It will be appreciated that heating a sensor serves to stabilise the sensor. This arrangement also permits the use of relatively inexpensive sensors.

The controller 72/processor 48 may have a plurality of serial ports for connection to a personal computer or to the central processor 1 00 of, for example, a data processing installation of a filling station, or the like.

The Inventors believe that the apparatus 10, 60 in accordance with the invention will be sufficiently accurate to permit detection of leakage from the storage tank 52, even at a relatively low rate, enabling remedial action to be taken as soon as possible, thereby to minimise the impact on the environment as well as financial losses. In this regard the inventors believe the apparatus will have an accuracy substantially better than 0.5%.

In Figures 4 and 5 of the drawings, reference numeral 80 refers generally to still another apparatus for use in determining the volume of liquid in a reservoir in accordance with the invention and, unless otherwise indicated, similar reference numerals indicate similar parts. In the embodiment of the invention shown in Figures

4 and 5, the probe 82 includes three tubular inner members 87, 88, 89 each having t an upper end 92 and a lower end 94, which respectively define the inlet and outlet ends of a flow path 86 which extends through each inner member 87, 88, 89. A tubular sleeve 90 extends with clearance around the three inner members 87, 88, 89 with the lower end 94 of each inner member 87, 88, 89 being recessed relative to the lower end of the sleeve 90 and furthermore being longitudinally off -set from the lower end 94 of each of the other two inner members 87, 88, 89. An upper end 28 of the sleeve 90 is vented to the space above the liquid 50 in the reservoir 52.

The Inventors believe that the inner diameter of the sleeve 90 will typically be about 40 mm. It will be appreciated, however, that the inner diameter of the sleeve 90 will vary with the length of probe and the material of which the probe is manufactured. The inner diameter of the sleeve 90 will typically be sufficiently large to permit the three inner members 87, 88, 89 to be received within the sleeve 90 with a clearance of about 1 0 mm between their radially outer surfaces and the radially inner surface of the sleeve 90. The depth of the recess or recesses 34 will in turn depend upon the inner diameter of the sleeve 90.

Typically, the sleeve 90 will protrude beyond the lower end 94 of the inner member 87 by a distance of_/between about 5 mm and 10 mm. The lower end 94 of the inner member 87 typically protrudes in turn by a predetermined distance, e.g. about 400 mm, beyond the lower end 94 of the inner member 88, which in turn protrudes beyond the lower end 94 of the inner member 89 by a predetermined distance, e.g. about 400 mm. In this way the lower end 94 of each inner member 87, 88, 89 is longitudinally off-set from the lower end 94 of each of the other two inner members 87, 88, 89.

ln use, with the probe inserted into the liquid in the tank or reservoir 52, pressurised air is fed through the inner member 87 to a first point in the reservoir 52 spaced longitudinally inwardly of the end of the sleeve 90, which abuts against the bottom of the reservoir 52, by a distance of about 5 mm to 10 mm. Pressurised air is also fed through the inner member 88 to a second point in the reservoir 52 spaced longitudinally inwardly of the first point by a distance of about 400 mm. The back pressure in the flow lines 44, 45 is measured by the pressure measuring means 1 6 and the resulting signals are transmitted to the processor 48 which, given that the difference in depth of liquid at the lower ends 94 of the inner members 87, 88 is known, is configured to calculate the density of the liquid between the first and second points in the reservoir in response thereto. In one embodiment of the invention, the density calculated is then compared with a reference density for the liquid, a disparity between the calculated density and the reference density being indicative of the presence of contaminants in the liquid 52. In another embodiment of the invention (Figure 5), pressurised air is also fed through the inner member 89 to a third point in the reservoir 52 spaced longitudinally inwardly of the second point and the first point, i.e. at a level which is above the levels of the first and second points by about 400 mm and 800 mm, respectively. The back pressure in the flow line 47 is measured by the pressure measuring means 1 6 and the resulting signal is transmitted to the processor 48 which calculates the density of liquid between the second and third points and/or the first and third points in the reservoir 52. The calculated density of the liquid between the first and second points is then compared with the calculated density of the liquid between the first and third points and/or the calculated density of the liquid 50 between the second and third points, a disparity between the t calculated densities for the liquid 52 being indicative of the presence of contaminants in the liquid 52.

The Inventors believe that the apparatus 80 will accurately report the presence of contaminants, such as, for example, water, in a storage tank/reservoir 52 containing liquid fuel.

In the embodiment of the invention shown in Figure 4, the inner member 89 is used only during a calibration of the apparatus 80, after which the inner member

89 is sealed, in the embodiment of the invention shown in Figure 5 of the drawings, all three inner members 87, 88, 89 are operative in a measurement mode of the apparatus 80 (that is, when the apparatus 80 is being used to measure a depth of liquid in a reservoir 52) . '

Naturally, the components of the probe 1 2, 82 will be of a material selected to resist attack from the liquid 50 contained within the storage tank 52. In this regard, the various components of the probe 1 2, 82 will typically be formed of stainless steel. Moreover, the material from which the components of the probe 1 2, 82 is constructed will be selected to provide a probe of sufficient rigidity for its length.

The Inventors believe that the apparatus 1 0, 60, 80 in accordance with the invention will permit continuous, real time, accurate and repeatable tank level or volume measurement. A further advantage of the invention is that it ensures complete galvanic isolation between electronics and electrical components of the apparatus and the liquid fuel, in that the gas supply means 1 4 and pressure measuring means 1 6 may be remotely situated relative to the probe 1 2, 82.

The construction of the probe 1 2, 82 is such as to reduce the probability of mechanical damage. In addition, the probe reduces the air/fuel contact and interaction. ^•'

The probe 1 2, 82 will typically be dimensioned to fit directly into a standard tank "dip stick" opening, therefore, permitting the use of the apparatus 1 0, 60, 80 without any modification of the tank.

The Inventors believe that a major advantage of the apparatus 1 0, 60, 80 in accordance with the invention is that it will be producible at a price which is substantially lower than the price of other devices of which they are aware. The apparatus 10, 60, 80 permits the use of "low-cost" pressure transducers, which conventionally introduce inherent errors, because of the calibration and sensor stabilisation techniques employed in the apparatus 1 0, 60, 80 thereby reducing the overall cost of manufacture of the apparatus 10, 60, 80. In addition, installation of the apparatus is relatively simple, thereby reducing costs and installation time. In addition, maintenance costs are minimised.

Furthermore, compressed air is often readily available at a filling station, thereby permitting the apparatus 1 0, 60, 80 to use available compressed air sources and electrical power.

The apparatus 1 0, 60,80 may include a memory permitting storage of historical data which can be used in optimising stock control.

The apparatus 1 0, 60 ,80 may further include a printer to permit a hard copy of measured data to be supplied. A number of probes 12, 82 may be connected to the processor 48 permitting the liquid level in a number of tanks to be monitored.

Claims

CLAIMS:

1 ■ A method of determining the volume of liquid in a reservoir which includes the steps of feeding a pressurised gas through a flow path to a low point in the reservoir; measuring the back pressure in the flow path with pressure measuring means; and using the measured back pressure to calculate the depth of liquid in the reservoir, and using the depth to calculate the volume of liquid.

2. A method as claimed in Claim 1 , which includes incorporating into the calculation of the depth of liquid in the reservoir a factor to compensate for changes in density due to changes in temperature.

3. A method as claimed in Claim 2, which includes sensing an ambient temperature in the reservoir.

4. A method as claimed in any one of Claims 1 to 3, inclusive, in which at least part of the flow path is defined by a probe inserted into the liquid, the method including feeding the gas to the probe from a supply of gas at a predetermined pressure.

5. A method as claimed in any one of Claims 1 to 4, inclusive, which includes periodically correlating a zero reading of the pressure measuring means to a standard.

6. A method as claimed in Claim 5, in which the standard is atmospheric pressure.

7. A method as claimed in Claim 5, in which the standard is the pressure within the reservoir above a body of liquid in the reservoir.

8. A method as claimed in any one of the preceding claims, in which measuring the back pressure in the flow path includes sensing the back pressure by use of at least one pressure sensor, and converting the pressure reading so obtained into an electrical signal. ^;

9. A method as claimed in Claim 8, which includes the step of stabilising the at least one pressure sensor.

10. A method as claimed in Claim 9, in which stabilising the at least one pressure sensor includes maintaining the sensor at a predetermined temperature.

1 1 . Apparatus for use in determining the volume of liquid in a reservoir, which apparatus includes a probe through which a flow path having an inlet end and an outlet end extends, the probe being insertable into the reservoir such that the outlet end of the flow path is adjacent to a low poipt of the reservoir; gas supply means for feeding gas under pressure to the inlet end of the flow path; and pressure measuring means for measuring back pressure in the gas as a result of the depth of the liquid.

1 2. Apparatus as claimed in Claim 1 1 , which includes processing means to which the pressure measuring means is connected, the processing means being configured to calculate the depth of liquid in the reservoir.

1 3. Apparatus as claimed in Claim 1 1 or Claim 1 2, which includes a temperature sensor for sensing an ambient temperature in the reservoir.

f

14. Apparatus as claimed in Claim 1 3, in which the temperature sensor is linked to the processing means so as to permit the processor to compensate for density variations in the liquid due to changes in its temperature.

1 5. Apparatus as claimed in any one of Claims 1 2 to14, inclusive, in which the processing means is configured to calculate the volume of liquid in the reservoir.

1 6. Apparatus as claimed in any one of Claims 1 2 to 1 5, inclusive, in which the processing means is configured to calculate the mass of liquid in the reservoir.

1 7. Apparatus as claimed in any one of Claims 1 2 to 1 6, inclusive, which includes a display connected to the processing means for displaying data.

1 8. Apparatus as claimed in Claim 1 in which the display is positioned remote from the reservoir.

1 9. Apparatus as claimed in any one of Claims 1 2 to 1 8, inclusive, which includes monitoring means for monitoring a pressure of gas of the gas supply means.

20. Apparatus as claimed in Claim 1 9, in which the monitoring means includes an alarm for generating an alarm signal when a pressure of the gas rises above or falls below a predetermined threshold value.

21 . Apparatus as claimed in any one of Claims 1 2 to 20, inclusive, which includes calibrating means for correlating a zero reading of the pressure measuring means to a standard.

22. Apparatus as claimed in Claim 21 , in which the standard is atmospheric pressure.

23. Apparatus as claimecj in Claim 21 , in which the standard is the pressure in a reservoir above the body of liquid contained in the reservoir.

24. Apparatus as claimed in any one of Claims 21 to 23, inclusive, in which the calibrating means includes a vent for permitting the pressure measuring means to be vented to atmosphere or the space in a reservoir above a body of liquid in a closed reservoir.

25. Apparatus as claimed in any one of Claims 1 2 to 24, inclusive, in which the pressure measuring means includes at least one pressure sensor coupled to a transducer for converting a measured pressure into an electrical signal.

26. Apparatus as claimed in any one of Claims 1 2 to 25, inclusive, which includes pressure sensor stabilising means for stabilising the at least one pressure sensor.

27. Apparatus as claimed in any one of Claims 1 2 to 26, inclusive, in which the processing means includes a database defining data relating to the liquid in the f reservoir.

28. Apparatus as claimed in-CIaim 27, in which the data relates to the relative density of the liquid in the reservoir.

29. A probe suitable for use in the apparatus as claimed in any one of Claims 1 0 to 28, inclusive, which probe includes at least one elongate inner member through which a flow path having an inlet end and an outlet end extends; and a sleeve extending around the at least one inner member for at least part of its length.

30. A probe as claimed in' Claim 29, in which the at least one inner member is tubular, the inlet and outlet ends of the flow path being defined by the operatively upper and lower ends, respectively, of the at least one inner member.

31 . A probe as claimed in Claim 30, in which the sleeve is tubular and the at least one inner member is positioned within the sleeve such that there is clearance between a radially outer surface of the at least one inner member and a radially inner surface of the outer member.

32. A probe as claimed in Claim 31 , in which a lower end of the sleeve protrudes beyond a lower end of the at least one inner member.

33. A probe as claimed in Claim 32, in which at least one recess is provided in the lower end of the sleeve.

34. A probe as claimed in any one of Claims 31 to 33, inclusive, in which the at least one inner member is secured within the sleeve by longitudinally spaced locating members.

35. A probe as claimed in Claim 34, in which the locating members are in the form of springs.

36. A probe as claimed in any one of Claims 31 to 35, inclusive, which includes three spaced apart elongate inner members through each of which a flow path having an inlet end and an outlet end extends, the sleeve extending with clearance around the three inner members.

37. A probe as claimed in Claim 36, in which the lower end of each inner member terminates at a position longitudinally off-set from the lower end of each of the other two inner members.

38. A probe as claimed in any one of Claims 31 to 37, inclusive, which is formed from stainless steel.

39. A method of detecting the presence of contaminants in a body of liquid, which method includes the steps of feeding a pressurised gas through a first flow path to a first point in the reservoir; feeding a pressurised gas thrσugh a second flow path to a second point in the reservoir which is at a level which is different to the level of the first point; measuring the back pressure in each flow path; and using the measured back pressures to calculate the density of the liquid between the first and second points in the reservoir.

40. A method as claimed in Claim 39, which includes comparing the density calculated with a reference density for the liquid.

41 . A method as claimed in Claim 39, which includes feeding a pressurised gas through a third flow path to a third point in the reservoir which is at a level which is different to that of each of the first and second points, and measuring the back pressure in the third flow path with the pressure measure means.

42. A method as claimed in Claim 41 , which includes comparing the calculated density of the liquid between the first and second points with the calculated density of the liquid between the third point and one of the first and second points.

43. A liquid storage facility which includes a reservoir within which liquid can be contained; and at least one gas flow path having an inlet which is connectable to a pressurised supply of gas and an outlet which opens into the reservoir at a low level.

44. A liquid storage facility as claimed in Claim 43, which includes at least two gas flow paths, each of which has an inlet connectable to a pressurised supply of gas and an outlet, the outlets opening into the reservoir at different levels.

45. A measuring installation for a storage facility, which installation includes pressure measuring means for measuring a back pressure in a probe inserted into a body of liquid in a reservoir; temperature sensing means for sensing an ambient temperature in the reservoir; and processing means to which the pressure measuring means and temperature sensing means are linked, the processing means including memory means having a database defining data relating to the liquid in the reservoir.

46. A measuring installation as claimed in Claim 45, in which the data relates to the relative density of the liquid in the reservoir.

47. A measuring installation as claimed in Claim 45 or Claim 46, in which the processing means is configured to receive a signal from the pressure measuring means and/or temperature sensing means and to use the measured back pressure and temperature to calculate the volume of liquid in the reservoir.

48. A measuring installation as claimed in any one of Claims 45 to 47, inclusive, in which data input means is linked to the processing means.

49. A measuring installation as claimed in Claim 48, in which the data input means includes a keyboard.

50. A measuring installation as claimed in any one of Claims 45 to 49, inclusive, in which the processing means is provided at a terminal remote from the reservoir.

51 . A measuring installation as claimed in Claim 50, in which the data input means is provided at the remote terminal.

52. A measuring installation as claimed in any one of Claims 45 to 49, inclusive, in which the processing means is provided on a wheeled unit.

53. A computer program product, which product includes an interface module for receiving input data relating to a liquid in a reservoir; a database reading module for accessing a database defining data relating to the liquid in the reservoir; and a comparator module for comparing the input data with the database data.

54. A computer program product as claimed in Claim 53, which is installed on a central processing unit of a filling station or industrial site.

55. A computer program product as claimed in Claim 53, which is installed on a processor provided on a wheeled unit.

56. A method of determining the volume of liquid in a reservoir as claimed in

Claim 1 , substantially as herein described and illustrated.

57. Apparatus for use in determining the volume of liquid in a reservoir as claimed in Claim 10, substantially as herein described and illustrated.

58. A probe suitable for use in an apparatus for use in determining the volume of liquid in a reservoir as claimed in Claim 29, substantially as herein described and illustrated.

59. A method of detecting the presence of contaminants in a body of liquid as claimed in Claim 39, substantially as herein described and illustrated.

60. A liquid storage facility as claimed in Claim 43, substantially as herein described and illustrated.

61 . A measuring installation for a storage facility as claimed in Claim 45, substantially as herein described and illustrated.

62. A computer program product as claimed in Claim 53, substantially as herein described and illustrated.

63. A new method, a new apparatus, a new probe, a new storage facility, a new installation or a new computer program product, substantially as herein described.