Increasing accuracy by adding additional sensor to density measurement system

Abstract

Methods, systems, and devices for measuring density may involve performing a buoyancy measurement relative to a product in a tank and determining a first density based on the buoyancy measurement. A pressure measurement may be performed on the pressure in the tank and a second density determined based on the pressure measurement. An average density in the tank may be calculated based on the first density and the second density. The average densities measured at two or more locations in the tank may then be combined to improve the accuracy of measuring the density within the tank.

Description

Technical Field

[0001] Embodiments generally relate to density measurement devices, systems, and methods. Embodiments also relate to methods and systems for measuring density in a storage tank. Embodiments further relate to methods and systems for improving density measurement in a storage tank. Background Art

[0002] Density measurements in storage tanks can be made using the principle of buoyancy. The principle of buoyancy states that an object submerged in a fluid experiences an upward force equal to the weight of the fluid it displaces. By measuring this buoyant force, the density of the fluid can be determined.

[0003] Density measurements based on the buoyancy principle are often performed in storage tanks. The basic principle behind this method involves measuring the weight of the displaced fluid and relating it to the density of the fluid. The displacement method can be used as part of a density measurement that involves a measuring device, such as a displacer or float, that can be inserted into the fluid within the tank. The device displaces a certain volume of fluid based on the weight and buoyancy of the fluid.

[0004] Before taking measurements, the equipment needs to be calibrated. Calibration involves determining the relationship between the buoyancy experienced by the measuring device and the density of the fluid at various known densities. A reference density can be established to compare the measured density. The reference density can be a known density value or a calibration standard.

[0005] The measuring device is immersed in the fluid and the buoyancy experienced is recorded. The buoyancy is usually measured using a load cell or pressure sensor. The measured buoyancy is related to the density of the fluid using calibration data. The relationship between buoyancy and density can be established by linear regression or other mathematical models. The calculated density value can then be displayed or recorded for further analysis or control purposes.

[0006] It is important to note that accurate density measurements may also require compensation for factors such as temperature, pressure, and any impurities or contaminants in the fluid. These compensations ensure that the density reading is corrected for changes in these parameters and provides an accurate representation of the fluid's density.

[0007] In summary, density measurement in storage tanks based on the buoyancy principle provides a reliable method to determine the density of a fluid, allowing for quality control, inventory management and process optimization in a variety of industries. Density measurement based on the buoyancy principle in storage tanks is a widely used technique in a variety of industries, including oil and gas, chemical and food processing.

[0008] Current density measurement technology involves measuring the product density of the product directly in a liquid storage tank by measuring the buoyancy force on a body / displacer element that can be immersed in the liquid. This is a very direct method that does not require any sampling of the product or the use of a measurement device external to the tank.

[0009] However, various error sources can affect the measurement, such as initial errors in the known volume of the body placed in the product. In addition, the density measurement requirements for liquid storage tanks need to be increasingly accurate due to different regional and national requirements. For example, legislation in many countries requires that density measurements must be made before and / or after product transfer. Some current solutions specify an accuracy of 3Kg / m 3 Up to 5Kg / m 3 , and the new standard requires an accuracy of 0.5Kg / m 3 .

[0010] The inventors of the present invention believe that a new technology, device and / or system is needed to improve the measurement accuracy of density measurement performed in a storage tank based on the buoyancy principle. Summary of the invention

[0011] The following summary of the invention is provided to facilitate understanding of some features of the embodiments disclosed in the present invention, and is not intended to be a complete description. A comprehensive understanding of the various aspects of the embodiments disclosed herein can be obtained by taking the specification, claims, drawings and abstract as a whole.

[0012] It is therefore an aspect of an embodiment to provide an improved method, system, and apparatus for measuring density in a storage tank.

[0013] Another aspect of the embodiments is to provide a density measurement method, system and apparatus based on the principle of buoyancy and the use of one or more separate sensors that measure relevant parameters (e.g., pressure) to improve the accuracy of density measurements in storage tanks.

[0014] The above-described aspects and other objectives can now be achieved as described herein.

[0015] In an embodiment, a method for measuring density may involve: performing buoyancy measurements relative to a product in a tank and determining a first density based on the buoyancy measurements; performing pressure measurements of the pressure in the tank and determining a second density based on the pressure measurements; and calculating an average density in the tank based on the first density and the second density and combining the average densities measured at at least two locations in the tank to improve the accuracy of measuring density within the tank.

[0016] Embodiments may also involve using the average density determined at the highest level of product in the tank to calculate an offset in the buoyancy measurement.

[0017] Embodiments may further involve compensating for offset errors using an average density based on pressure measurements when the product level is at a high level for the product.

[0018] Embodiments may further involve calculating an offset in the buoyancy measurement using an average density determined at the highest level of product in the tank, and compensating for an offset error relative to the offset using an average density based on pressure measurements when the product level is at a high level for the product.

[0019] In an embodiment, buoyancy measurements may be performed by an electromechanical servo gauge.

[0020] In an embodiment, pressure measurements may be performed by a pressure sensor including a pressure transmitter.

[0021] In an embodiment, the pressure may include hydrostatic pressure.

[0022] In an embodiment, a system for measuring density may include: at least one processor; and a non-transitory computer usable medium embodying computer program code operable to communicate with the at least one processor. The computer program code may include instructions executable by the at least one processor and operable to: perform a buoyancy measurement relative to a product in a tank and determine a first density based on the buoyancy measurement; perform a pressure measurement of a pressure in the tank and determine a second density based on the pressure measurement; and calculate an average density in the tank based on the first density and the second density and combine the average densities measured at at least two locations in the tank to improve the accuracy of measuring density within the tank.

[0023] In an embodiment, the instructions are further operable to calculate the offset of the buoyancy measurement using the average density determined at the highest level of the product in the tank.

[0024] In an embodiment, the instructions are further operable to compensate for the offset error using an average density based on pressure measurements when the product level is at a high level for the product.

[0025] In an embodiment, the instructions are further operable to: calculate an offset in the buoyancy measurement using an average density determined at a highest level of product in the tank; and compensate for an offset error relative to the offset using an average density based on pressure measurements when the product level is at a high level for the product.

[0026] Embodiments of the system may further include an electromechanical servo gauge that can perform buoyancy measurements.

[0027] Embodiments of the system may also include a pressure transmitter that can perform pressure measurements.

[0028] Embodiments of the system may also include a density sensor mounted in a wall of the tank, wherein the density sensor may be used to compensate for offset errors in the density measurement.

[0029] In embodiments of the system, the pressure may include hydrostatic pressure.

[0030] In an embodiment, an apparatus for measuring density may include: an electromechanical servo meter for performing buoyancy measurements relative to a product in a tank, wherein a first density is determined based on the buoyancy measurement; and a pressure sensor for performing pressure measurements of a pressure in the tank, wherein a second density is determined based on the pressure measurement, wherein an average density in the tank is calculated based on the first density and the second density, and wherein the average density measured at at least two locations in the tank is combined to improve the accuracy of measuring the density within the tank.

[0031] In an embodiment of the apparatus, the average density determined at the highest level of product in the tank may be used to calculate the offset of the buoyancy measurement.

[0032] In an embodiment of the apparatus, an average density based on pressure measurements when the product level is at a high level for the product in the tank may be used to compensate for offset errors.

[0033] In an embodiment of the apparatus, an average density determined at the highest level of product in the tank may be used to calculate an offset in the buoyancy measurement, and an average density based on pressure measurements when the product level is at the high level of the product may be used to compensate for the offset error relative to the offset.

[0034] In embodiments of the apparatus, the pressure may include hydrostatic pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings further illustrate the embodiments and together with the detailed description serve to explain the principles of the embodiments, wherein like reference numerals refer to identical or functionally similar elements throughout the various views and are incorporated into and form a part of the specification.

[0036] Figure 1A shows a schematic diagram of an electromechanical servo gauge (ESG) adapted for use in density measurement operations according to an exemplary embodiment;

[0037] Figure 1B shows a block diagram of the ESG shown in FIG1 according to an embodiment;

[0038] Figure 2 shows a block diagram of a density measurement system including an ESG and one or more pressure sensors according to an embodiment;

[0039] Figure 3 shows a block diagram of a density measurement system including an ESG, one or more pressure sensors, and / or one or more other types of sensors (e.g., density sensors) according to an embodiment; and

[0040] Figure 4 A flow chart depicting logical operational steps of a density measurement method is shown that may be implemented in accordance with an embodiment.

[0041] The same or similar parts or elements in the drawings may be denoted by the same reference numerals. DETAILED DESCRIPTION

[0042] The specific values ​​and configurations discussed in these non-limiting examples may vary, and are cited merely to illustrate one or more embodiments, and are not intended to limit the scope thereof.

[0043] The subject matter will now be described more fully below with reference to the accompanying drawings, which form a part of the subject matter and show specific exemplary embodiments by way of example. However, the subject matter can be embodied in a variety of different forms, and therefore the subject matter covered or claimed is intended to be construed as not limited to any exemplary embodiment listed herein; the exemplary embodiments are provided for illustration only. Likewise, the subject matter intended to be claimed or covered has an appropriately broad scope. Among other things, the subject matter may be embodied as a method, device, component, or system. Thus, the embodiments may, for example, take the form of hardware, software, firmware, or a combination thereof. Therefore, the following specific embodiments are not intended to be construed as having a limiting meaning.

[0044] Throughout the specification and claims, in addition to the meanings explicitly stated, terms may have slightly different meanings suggested or implied by the context. Likewise, phrases such as "in an embodiment" or "in one embodiment" or "in an exemplary embodiment" and variations thereof as used herein may or may not necessarily refer to the same embodiment, and phrases "in another embodiment" or "in another exemplary embodiment" and variations thereof as used herein may or may not necessarily refer to different embodiments. For example, the claimed subject matter is intended to include, in whole or in part, a combination of the exemplary embodiments.

[0045] Generally speaking, the term can be understood at least in part from the usage in the context. For example, terms such as "and", "or" or "and / or" as used herein may include multiple meanings that may depend at least in part on the context in which such terms are used. Generally speaking, if "or" is used in an association list, such as A, B or C, it is intended to represent A, B and C used in an inclusive sense here, and A, B or C used in an exclusive sense here. In addition, the term "one or more" as used herein depends at least in part on the context and can be used to describe any feature, structure or characteristic in a singular sense, or can be used to describe a combination of features, structures or characteristics in a plural sense. Similarly, terms such as "one", "a kind of" or "the" also depend at least in part on the context and can be understood to convey singular usage or express plural usage. In addition, the term "at least one" can refer to "one or more". For example, "at least one widget" can refer to "one or more widgets".

[0046] Additionally, the term "based on" should be understood as not necessarily intended to convey an exclusive set of factors, but rather may depend, at least in part, on the context, allowing for the presence of additional factors that are not necessarily explicitly described again.

[0047] Figure 1A A schematic diagram of an electromechanical servo meter (ESG) 200 is shown, according to an exemplary embodiment, which is adapted for use in density measurement operations. Note that as used herein, the term "servomechanism" may also be used to refer to the ESG. According to an exemplary embodiment, the ESG 200 may include a controller 210 including a processor 215 having an associated memory 217 storing an algorithm 219 for performing density measurements involving, for example, implementing Figure 4 The steps and operations are shown as those of method 100. Processor 215 may include a microprocessor, a microcontroller, a field programmable gate array, a digital signal processor, or another processing or control device.

[0048] Force transducer 225 Figure 1A 2 is shown on a common PCB board with processor 215. Force transducer 225 can convert the torque on drum 240 into a frequency (f) which can be coupled to the input of controller 210 acting as a servo processor unit (SPU) which provides torque measurement.

[0049] The ESG 200 includes a displacer 235 that is within a tank 202 having a flange 204. The displacer 235 is suspended from a measurement wire 238 from a drum 240 that can extend through the flange 204 for generating a torque on the drum 240. Displacer shapes and displacer sizes are generally known. A servo motor (servo motor 245) with gears can be coupled via a drive shaft 249 to rotate the drum 240, thereby balancing the weight of the displacer 235 in the tank 202 with a liquid (not shown) therein. When the displacer 235 is at the top surface of the liquid, an equilibrium condition exists in which changes in the liquid level cause changes in the reaction force to move the ESG 200 out of balance. As described above, although not shown, any force sensed by the force transducer 225 acting on the drum 240 via the measurement wire 238 can be transferred to the processor side of the ESG 200 as a torque using a magnetic coupler 247.

[0050] The displacer 235 may be implemented as a mechanical body suspended on a strong thin measuring wire such as measuring wire 238, wherein the displacer material has a higher density than the liquid to be measured. The measuring wire 238 may be wound on a high accuracy machined grooved drum having a calibrated circumference. The apparent weight obtained by subtracting the weight of the displaced liquid product from the weight of the displacer 235 may be measured and then used by a computing device such as a microcontroller having a servo motor 245 for rotating the drum 240 to position the displacer 235 at different heights in the tank.

[0051] Figure 1B 1 shows a block diagram of the ESG 200 shown in FIG. 1 according to an exemplary embodiment. Figure 1B As shown, ESG200 may include three compartments: drum compartment 240a, drive compartment 225a and power compartment 222a. Drum compartment 240a may include drum 240, on which wire 238 may be wound. Drum 240 may be rotated in one direction by drive compartment 245a to lower displacer 235, and drum 240 may be rotated in another direction by drive compartment 245a to raise displacer 235. Drum 240 may include any suitable structure for raising and lowering displacer 235 via rotation.

[0052] The drive compartment 245a may include a motor 245 including a drive train 246 that imparts rotation to the drum 240 via a shaft 249. For example, the drive train 246 or shaft 249 may generate a magnetic field, and a magnetic coupler 247 may be used to transmit torque between the drive shaft 249 and the drum 240. In these embodiments, direct connection may not be required between the drum compartment 240a and other compartments 245a, 222a. However, other techniques for causing the drum 240 to rotate may be used, such as when the shaft 249 is physically connected to the drum 240. The drive train 246 includes any suitable structure for imparting rotation to the drum 240. In some embodiments, the drive train 246 may include a stepper motor that rotates the drum 240 with a specified step length, which means that the drum 240 is not freely rotated but rotates with a limited amount or "step length". Therefore, each step of the motor 245 should impart a known amount of rotation to the drum 240. In these embodiments, because the drum 240 can have a known diameter or circumference, the length of the connector (ie, wire 238) that is dispensed or collected during a single step rotation can be highly determined.

[0053] The drive compartment 245a may also include a force transducer 225 that can identify the torque caused by the weight of the displacer 235 on the drum 240. When the displacer 235 is suspended from the wire 238, the measured torque is high. When the displacer 235 is fully or partially immersed in the material in the tank, the measured torque is low. Typically, the force transducer 225 identifies the torque on the drum 240 by measuring the torque on the shaft 249.

[0054] The ESG 200 is shown as including a user interface 218 and a network interface 220 in the drive compartment 245a. The user interface 218 facilitates communication between the ESG 200 and an operator or other plant personnel. The user interface 218 may provide data from an operator to the controller 210, such as a command to initiate a level measurement, a command to raise or lower the displacer 235, or a command to enable or disable a test of the ESG 200. The user interface 218 may also allow personnel to review measurement data generated by the ESG 200. The user interface 218 may include any suitable interface for interacting with one or more users, such as a keypad or keyboard and a display.

[0055] The network interface 220 may facilitate data communication to or from the ESG 200. For example, the network interface 220 may receive a level measurement calculated by the ESG 200 and transmit the level measurement to one or more external destinations, such as the force transducer 225. The network interface 220 may include any suitable structure that supports wired or wireless communication, such as an Ethernet interface, an RF transceiver, or other wired or wireless interface.

[0056] The power supply compartment 222a includes a power supply 222 that provides operating power for the ESG 200. The power supply 222 can provide power to various components of the drive compartment 245a. Depending on the specific implementation, the power supply 222 may or may not supply power to the drum compartment 240a. The power supply 222 may include any suitable structure for providing power, such as a battery, a fuel cell, or a solar cell.

[0057] Notice, Figure 1A and Figure 1B The servomechanism or ESG 200 shown is presented herein for illustrative and exemplary purposes only and should not be considered a limiting feature of the embodiment. Other types of devices and systems may be utilized in place of the ESG 200 to achieve the same results of the embodiment. For example, the non-limiting SmartServo FlexLine 954 device may be adapted for use with the embodiment. The SmartServo FlexLine 954 device is described and illustrated in a document entitled "Installation Manual 954 SmartServo FlexLine" (Part No: 4417341 Revision 10, 2019) of Honeywell International Inc., the entire contents of which are incorporated herein by reference.

[0058] Figure 2 A block diagram of a density measurement system 302 including an ESG 200 and one or more pressure sensors 300 is shown according to an embodiment. The ESG 200 can be used to accurately measure product levels and water interface levels in a tank 202, such as a bulk storage tank for typical hydrocarbons (commonly referred to as fuels and oils) and a variety of other liquid chemicals. These products can range from very light chemicals such as so-called LPG (a mixture of propane and butane or even liquefied natural gas (LNG)) to all types of refined products such as naphtha, gasoline, diesel, jet fuel, lubricants, and all types of chemicals, both pure and mixed.

[0059] Figure 3A block diagram of a density measurement system 304 that may include an ESG 200 and one or more pressure sensors 300 and / or one or more other types of sensors 301 (e.g., density sensors) is shown according to an embodiment. The density measurement system 304 includes a tank 202. The one or more pressure sensors 300 may be used to measure, for example, the static pressure of the fluid in the tank 202. Note that in some embodiments, the pressure sensor 300 may include a pressure transducer. As described above, the sensor 301 may be implemented as another type of sensor. For example, the sensor 301 may be implemented as an external (e.g., non-buoyancy-based) density sensor that can be used to compensate for errors. In some embodiments, the use of a density sensor may result in a simpler method than using a pressure sensor, and the "process" (e.g., see Figure 4 Method 100) is even simpler.

[0060] Figure 4 A flow chart of operations that may be implemented according to an embodiment is shown, which depicts logical operational steps of a density measurement method 100. The density measurement method 100 may include the use of installed sensors (e.g., ESG 200, pressure sensor 300, other sensors 301 (e.g., density sensor), etc.), which may help improve the accuracy of measuring the density of the product in the storage tank 202. To achieve this, the accuracy of the individual densities should be improved. To do this, the average density measured from the installed sensors may be combined with the individual densities measured from the current instrument at several locations in the liquid storage tank 202.

[0061] The density measurement in the tank 202 based on the buoyancy principle discussed above has significant advantages, since it is very easy to perform measurements at different locations in the tank 202, so that a density profile can be created. In this way, a very accurate profile of the different density layers in the product can be created. However, various factors can cause offset errors that cannot be easily removed when actually implementing density measurements based on buoyancy. By combining other means for determining the density with, for example, the pressure sensor 300 (which can only determine the average density of the (partially) filled tank 202), the offset errors can be removed.

[0062] As indicated at block 102, a step or operation may be performed in which one or more buoyancy measurements are made relative to the product in tank 202. Next, as indicated at block 103, a buoyancy measurement may be performed using, for example, Figure 2 and Figure 3The pressure sensor 300 is shown taking pressure sensor measurements in the tank 202. The measurements taken by the pressure sensor 300 may generate pressure transmitter data, as shown in block 103. Thereafter, as shown in block 104, steps or operations may be performed to provide an indication that the average calculated density based on the pressure transmitter data input is more accurate for the product level than the average density data based on the buoyancy measurements taken as shown in block 102.

[0063] Once this is known, any average density calculation based on pressure transmitter data measured or determined when the product level is high can be used to compensate for the offset error. That is, the higher the product level (e.g., liquid in a tank), the more accurate the offset error calculation. Therefore, the operation shown in block 106 can involve performing an average density calculation based on the pressure transmitter data collected from the pressure sensor 300 and compensating for the offset error. In the operation shown in block 106, the average calculated density at the highest product level can be used to calculate the offset of the buoyancy measurement. Even if the product level becomes very low, the calculated offset can still be used.

[0064] Next, as shown in block 108, when the tank 202 is refilled with new product, a new offset may be calculated for diagnostic purposes. This new offset may be compared to the last calculated offset, as shown in block 110, and then used for continuous readjustment of the servo density offset value or as an automatic calibration mechanism for the density offset value of the servo mechanism 200, as shown in block 112.

[0065] In an alternative embodiment, a separate density sensor (e.g. Figure 3 The other sensor 301 shown may be mounted in the tank wall of the tank 202 at a location approximately 1 meter from the bottom of the tank 202. If the displacer 235 is at the same height as the density sensor, the density sensor may be used to compensate for offset errors in the density measurement based on the buoyancy measurement principle.

[0066] Using the method described herein, if the liquid level and pressure (e.g., hydrostatic pressure) in tank 202 are known, the volume and average density of the product in tank 202 can be calculated, provided that the shape of tank 202 and some parameters (such as, for example, local gravity, etc.) are known.

[0067] Current instruments are very good at measuring density differences at different heights in the tank 202. However, they are less effective at determining absolute density. Combining the measured average density as described above with individual densities at several locations in the tank 202 can improve the accuracy of determining the individual densities.

[0068] Although the operation of method is shown and described in a particular order herein, the order of these operations can be changed so that some operations can be performed in reverse order, or some operations can be performed at least in part simultaneously with other operations. In another embodiment, the instructions or sub-operations of different operations can be realized in an intermittent and / or alternating manner.

[0069] At least some of the operations of the methods described herein may be implemented using software instructions stored on a computer usable storage medium for execution by a computer. As an example, an embodiment of a computer program product includes a computer usable storage medium for storing a computer readable program.

[0070] A computer usable or computer readable storage medium may be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or device or apparatus). Examples of non-transitory computer usable and computer readable storage media include semiconductor or solid-state memory, magnetic tape, removable computer disk, random access memory (RAM), read-only memory (ROM), rigid disk, and optical disk. Current examples of optical disks include compact disk with read-only memory (CD-ROM), compact disk with read / write (CD-R / W), digital video disk (DVD), flash memory, etc.

[0071] Alternatively, the embodiments of the present invention may be implemented in hardware or in a specific implementation comprising hardware elements and software elements. In an embodiment that does utilize software, the software may include firmware, resident software, microcode, etc.

[0072] In some alternative implementations, the functions indicated in the blocks may not occur in the order indicated in the drawings. For example, two blocks shown in succession may actually be executed simultaneously, or the blocks may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that the blocks of the block diagrams and / or flow charts and combinations of blocks in the block diagrams and / or flow charts may be implemented by a dedicated hardware-based system that performs the specified functions or actions or executes a combination of dedicated hardware and computer instructions.

[0073] Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is defined by the appended claims and their equivalents.

[0074] It will be appreciated that the variations disclosed above and other features and functions or their alternatives may be advantageously combined into many other different systems or applications. It will also be appreciated that various currently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art, which are also intended to be covered by the following claims.

Claims

1. A method for measuring density, the method comprising: performing a buoyancy measurement relative to a product in the tank and determining a first density based on the buoyancy measurement; performing a pressure measurement of the pressure in the tank and determining a second density based on the pressure measurement; and An average density in the tank is calculated based on the first density and the second density and the average density measured at at least two locations in the tank is combined to improve the accuracy of measuring density within the tank.

2. The method according to claim 1, further comprising: An offset in the buoyancy measurement is calculated using the average density determined at the highest level of the product in the tank.

3. The method according to claim 1, further comprising: The average density based on the pressure measurement when the product level is at a high level for the product is used to compensate for offset errors.

4. The method according to claim 1, further comprising: calculating an offset of the buoyancy measurement using the average density determined at a maximum level of the product in the tank; as well as The average density based on the pressure measurement when the product level is at a high level for the product is used to compensate for an offset error relative to the offset.

5. The method of claim 1, wherein the buoyancy measurement is performed by an electromechanical servo gauge.

6. The method of claim 1, wherein the pressure measurement is performed by a pressure sensor comprising a pressure transmitter. The method of claim 1 , wherein the pressure comprises hydrostatic pressure.

8. A system for measuring density, the system comprising: at least one processor; and a non-transitory computer usable medium embodying computer program code operable to communicate with the at least one processor, the computer program code comprising instructions executable by the at least one processor and operable to: performing a buoyancy measurement relative to a product in the tank and determining a first density based on the buoyancy measurement; performing a pressure measurement of the pressure in the tank and determining a second density based on the pressure measurement; and An average density in the tank is calculated based on the first density and the second density and the average density measured at at least two locations in the tank is combined to improve the accuracy of measuring density within the tank.

9. A device for measuring density, the device comprising: an electromechanical servo meter for performing a buoyancy measurement relative to a product in the tank, wherein the first density is determined based on the buoyancy measurement; and A pressure sensor for performing a pressure measurement of the pressure in the tank, wherein a second density is determined based on the pressure measurement, wherein an average density in the tank is calculated based on the first density and the second density, and wherein the average density measured at at least two locations in the tank is combined to improve the accuracy of measuring the density within the tank.

10. Apparatus according to claim 9, wherein the average density determined at the highest level of the product in the tank is used to calculate an offset in the buoyancy measurement.

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