A METHOD OF DETERMINING DENSITY OF A FLUID

BACKGROUND

[0001] The invention relates generally to a method for determining density of a fluid  and more specifically  to method of determining density and/or a value of one or more density dependent property of the fluid and/or a value of one or more parameter influenced by density of the fluid using an ultrasonic density measurement system.

[0002] In industrial process control  it is often required to determine at least one parameter attributed to fluids along flow paths  for example in pipes. The parameters may include density of the fluid or density dependent parameter of the fluid. There are a number of known ultrasonic density measurement systems  which are used for detection of density of the fluid or density dependent parameters of the fluid.

[0003] One such ultrasonic density measurement system used for detection of parameters associated with the fluids includes a sensor rod. In such an ultrasonic density measurement system  the sensor rod is partially inserted into the fluid whose property needs to be measured. Wave energy is guided along the sensor rod held partially in contact with the fluid. The parameter of the fluid surrounding the sensor rod influences the wave characteristics  specifically the time of flight of the wave mode. In other words  the interaction of the wave energy along the sensor rod with the fluid results in lowering a velocity of propagation of the wave energy along the sensor rod  so that a change in flight time of the wave  as compared to a reference time with the sensor rod in air or vacuum  provides an indication of a parameter of the fluid in contact with the sensor rod. In particular circumstances  where at least one of the fluid composition  container geometry and sensor characteristics are known  a measurement of flight time of the wave energy guided along the sensor rod may provide an indication of a parameter of the fluid.

[0004] It has however been observed that an accuracy of measurement of density and therefore the density dependent parameters of the fluid of such ultrasonic density measurement system are not satisfactory and needs improvement. As a result  there is a continued need for an improved method for determining density and/or density dependent parameters of the fluid that addresses at least one of these and other shortcomings.

BRIEF DESCRIPTION

[0005] In accordance with one embodiment of the invention  a method for determining density of a fluid is disclosed. The method comprises receiving parameters comprising temperature of the fluid and bulk modulus of the fluid. The method further comprises receiving time of flight of an ultrasonic wave in the fluid as provided by an ultrasonic density measurement system. Based on the above parameters i.e. temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid  the method comprises the step of calculating a value of density with an accuracy that corresponds to an error range of less than about 0.5%. The method additionally comprises the step of providing the value of density as calculated.

[0006] In accordance with another embodiment of the invention  a device for determining density of a fluid is disclosed. The device comprises a processor receiving parameters comprising temperature of the fluid and bulk modulus of the fluid. The processor further receives time of flight of an ultrasonic wave in the fluid as provided by an ultrasonic density measurement system. Based on the above parameters i.e. temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid  the processor calculates a value of density with an accuracy that corresponds to an error range of less than about 0.5% and outputs the same.

[0007] In accordance with yet another embodiment of the invention  a system for determining density of a fluid is disclosed. The system comprises an ultrasonic sensor configured for partial immersion in the fluid. The system further comprises an excitation device configured to excite an ultrasonic wave in the ultrasonic sensor. The ultrasonic wave propagates along at least a portion of the ultrasonic sensor and interacts with the fluid surrounding the same. The interaction of the ultrasonic wave propagating through the ultrasonic sensor with the surrounding fluid affects the propagation of the ultrasonic wave in a manner dependent on the at least one parameter of the surrounding fluid. The system further comprises a detection device for detecting the ultrasonic wave in the ultrasonic sensor. The system further comprises a temperature sensor for sensing a temperature of the fluid and a device for providing data indicative of bulk modulus of the fluid. The system further comprises a processor configured to calculate and provide a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid.

DRAWINGS

[0008] These and other features  aspects  and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings  wherein:

[0009] FIG. 1 is a block diagram of a sensing system including a sensor assembly for sensing density of a fluid flowing through a conduit in accordance with an exemplary embodiment of the present invention;

[0010] FIG. 2 is a flow chart of a method for determining density of the fluid including a step of receiving time of flight of an ultrasonic wave in the fluid in accordance with an exemplary embodiment of the present invention;

[0011] FIG. 3 is an elaborate flow chart of the method of receiving time of flight of the ultrasonic wave in the fluid in accordance with an exemplary embodiment of the present invention; and

[0012] FIG. 4 is a block diagram of a device for sensing at least one parameter of a fluid flowing through a conduit in accordance with an exemplary embodiment of the present invention.

[0013] It may be noted that  to the extent possible  like reference numerals have been used to represent like elements in the drawings. Further  skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example  the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the present invention. Furthermore  the one or more elements may have been represented in the drawings by conventional symbols  and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

[0014] While the invention is susceptible to various modifications and alternative forms  specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood  however that it is not intended to limit the invention to the particular forms disclosed  but on the contrary  the invention is to cover all modifications  equivalents  and alternative falling within the spirit and the scope of the invention as defined by the appended claims.

[0015] The parts of the device have been represented where appropriate by conventional symbols in the drawings  showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

[0016] The terms "comprises"  "comprising"  or any other variations thereof  are intended to cover a non-exclusive inclusion  such that one or more devices or sub-systems or elements or structures proceeded by "comprises... a" does not  without more constraints  preclude the existence of other devices or other sub-systems or other elements or other structures or additional devices or additional sub-systems or additional elements or additional structures.

[0017] Referring to FIG. 1  a block diagram of an exemplary sensing system 10 for sensing at least one parameter of a fluid 12 flowing through a conduit 14 is illustrated. In the illustrated embodiment and subsequent embodiments  the conduit may be a vertical arrangement or a horizontal arrangement. It should be noted that even though a conduit is disclosed  the sensing system 10 is applicable to any device containing a fluid for sensing at least one parameter attributed to the fluid in both static (for example  as may be contained in a tank) and flowing conditions. The system 10 includes a processor 16 configured to calculate and provide a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid. The system 10 may include an ultrasonic sensor 18 and an excitation device 20. The ultrasonic sensor 18 may be configured for partial immersion in the fluid 12 and the excitation device 20 is configured to excite an ultrasonic wave in the ultrasonic sensor 18. The ultrasonic wave propagates along at least a portion of the ultrasonic sensor 18 and interacts with the fluid 12 surrounding the same. The interaction of the ultrasonic wave propagating through the ultrasonic sensor 18 with the surrounding fluid 12 affects the propagation of the ultrasonic wave in a manner dependent on the at least one parameter of the surrounding fluid 12. The depth of immersion of the ultrasonic sensor 18 in the fluid 12 may be varied. The system 10 may further include a detection device 22 for detecting the ultrasonic wave in the ultrasonic sensor 18. The system 10 may include a temperature sensor 24 for sensing a temperature of the fluid 12. The system may additionally include a device 26 for providing data indicative of bulk modulus of the fluid 12. The system 10 may further include a device 28 for providing parameters relating to viscosity of the fluid. The system may further include an output device 30 for presenting outputs to user. The system 10 may further include a pressure-sensing device 32 for providing pressure of the fluid.

[0018] The system 10 described above may be implemented in many ways. By way of a non-limiting example  the temperature sensor 24 may form part of ultrasonic sensor 18. In another non-limiting example  the temperature sensor 24 may form part of the device 26 providing data indicative of bulk modulus of the fluid or the device 28 providing parameters relating to viscosity of the fluid. The device 26 providing data indicative of bulk modulus of the fluid may provide the bulk modulus of the fluid as a measured quantity or alternatively as a calculate-able quantity. By way of a non-limiting example  the device 26 may provide the speed of sound in the fluid  from which the bulk modulus of the fluid may be calculated. In this example  the device 26 may take the form of a speed of sound detector. By way of another non-limiting example  the device 26 may provide the pressure of the fluid  from which the bulk modulus of the fluid may be calculated. In this example  the device 26 may take the form of a pressure sensor. Computation of the bulk modulus may be performed by way of a non-limiting example  by the processor 16. By way of another non-limiting example  the excitation device 20 may also function as the detection device 22. By way of another non-limiting example  the ultrasonic sensor 18  the excitation device 20 and the detection device 22 may be packaged together so as to be operable in various configurations such as  but not limited to a through transmission configuration  a pulse echo configuration  etc. By way of another non-limiting example  the processor 16 and the output device 30 may be integrated together.

[0019] Referring to FIG. 2  a flow chart of an exemplary method 50 for determining density of the fluid is illustrated. The method includes receiving 52  by the processor 16  parameters including temperature of the fluid and bulk modulus of the fluid. The method further includes receiving 54  by the processor 16  time of flight of an ultrasonic wave in the fluid as provided by an ultrasonic density measurement system. The method then continues to calculating 56  by the processor 16  a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid and providing 58  by the processor 16  the value of density as calculated to an output device 30.

[0020] The method 50 may additionally include receiving 60  by the processor 16  parameters relating to viscosity of the fluid  in which case  the step of calculating 56 the value of density may be based on temperature of fluid  bulk modulus of fluid  viscosity of the fluid and time of flight of ultrasonic wave in the fluid.

[0021] The method described above is not intended to be restricted to any particular method for receiving the above mentioned parameters i.e. temperature of the fluid  the bulk modulus of the fluid  the viscosity of the fluid or the time of flight of ultrasonic wave in the fluid. Each of the aforesaid parameter may be received by the processor as a directly measured quantity requiring no further data transformation or may be obtained as a data indicative of the said parameter  which upon further data transformation or data processing by the processor may yield one or more of the aforesaid parameters.

[0022] By way of a non-limiting example  the bulk modulus of the fluid may be received as a measured quantity from any of the conventional bulk modulus measuring devices. By way of another non-limiting example  speed of sound in the fluid may be received as an input and the bulk modulus of the fluid may be obtained a derived parameter. By way of yet another non-limiting example  temperature and pressure of the fluid may be received as measured quantities along with a characteristic of the fluid other than density of the fluid  known a priori and the bulk modulus of the fluid may be obtained a derived parameter by the processor. By way of a non-limiting example  the characteristic of the fluid other than density of the fluid  known a priori include bulk modulus  speed of sound  viscosity  coefficient of thermal expansion  specific heat  phase diagram  temperature  molecular weight  heat of fusion  vapor pressure  heat of vaporization  calorific value  etc.

[0023] By way of a non-limiting example  the step of calculating 56 the value of density of the fluid includes considering an interaction between the parameters i.e. the temperature of the fluid  the bulk modulus of the fluid and the time of flight of the ultrasonic wave in the fluid. More particularly  the interaction between the parameters may be of ‘Nth’ order  wherein N is equal to or greater than 1.

[0024] By way of a non-limiting example  the step of calculating 56 the value of density of the fluid may be performed by considering the parameters i.e. the temperature of the fluid  the bulk modulus of the fluid and the time of flight of the ultrasonic wave in the fluid and by adopting relation (1) as provided herein below:
… (1)
wherein:
? is the density of the fluid;
a0  a1  a2 and a3 are constants;
T is the temperature of the fluid;
TOF is the time of flight of the ultrasonic wave in the fluid; and
is a parameter indicative of the bulk modulus of the fluid  particularly  is speed of sound in the fluid and is provided by relation (2) as provided herein below:
…(2)
wherein in relation (2)  k’ is a constant.

[0025] Relation (1) is based on a first order interaction between the temperature of the fluid and the time of flight of the ultrasonic wave in the fluid.

[0026] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid may be performed with additional accuracy by considering the parameters i.e. the temperature of the fluid  the bulk modulus of the fluid  the viscosity of the fluid and the time of flight of the ultrasonic wave in the fluid and by adopting relation (3) as provided herein below:
…(3)
wherein:
a4 is constant; v is viscosity of the fluid; and remaining terms are as indicated above.

[0027] Relation (3) is once again based on a first order interaction between the temperature of the fluid and the time of flight of the ultrasonic wave in the fluid.

[0028] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid may be performed with further accuracy by considering the additional interactions between the parameters i.e. the temperature of the fluid  the bulk modulus of the fluid  the viscosity of the fluid and the time of flight of the ultrasonic wave in the fluid and by adopting relation (4) as provided herein below:
…(4)
wherein:
each of a5  a6  a7  a8 and a9 are constants; and the remaining terms are as indicated above.

[0029] The values for the constants a0  a1  a2  a3  a4  a5  a6  a7  a8 and a9 may be arrived by statistical methods. By way of a non-limiting example  the values for the constants may be arrived at by performing least square method  or by regression analysis or any other suitable method.

[0030] Relation (4) considers first order interactions between (a) temperature of the fluid and time of flight of the ultrasonic wave in the fluid  (b) temperature of the fluid and viscosity of the fluid  (c) temperature of the fluid and the parameter indicative of the bulk modulus of the fluid (i.e. )  (d) viscosity of the fluid and time of flight of the ultrasonic wave in the fluid  (e) viscosity of the fluid and the parameter indicative of the bulk modulus of the fluid (i.e. ) and (f) time of flight of the ultrasonic wave in the fluid and the parameter indicative of the bulk modulus of the fluid (i.e. ).

[0031] It may be noted that any reference to any of the parameters herein  including but limited to time of flight of ultrasonic wave in the fluid  temperature of the fluid  bulk modulus of the fluid  speed of sound in the fluid  viscosity of the fluid  pressure of the fluid  etc. is intended to cover a transformation of such parameter. By way of example  the transformation may include without limitation  identity transformation  square root transformation  inverse transformation  square transformation  polynomial transformations  rational function transformations  logarithmic transformations  trigonometric transformations  exponential transformations  or new transformation resulting out of compositions of a plurality of these transformations. By way a non-limiting example  the time of flight of the ultrasonic wave may be transformed in terms of length L of the sensor rod at the operating temperature and group velocity of the guided wave VGW in the sensor rod by using relation (5) as provided herein below:
TOF = L/VGW …(5)

[0032] It may be further possible to represent in relation (5) the group velocity of the guided wave VGW in the sensor rod by relation (6) as provided herein below:
VGW = Vo + m.? + n. + p.v …(6)
wherein:
Vo  m  n and p are constants; and the remaining terms are as indicated above.

[0033] It may be further possible to represent in relation (5) the group velocity of the guided wave VGW in the sensor rod by relation (7) as provided herein below:
VGW = Vo + m.? + n.BM + p.v …(7)
wherein:
BM is the bulk modulus of the fluid and the remaining terms as indicated above.

[0034] It may be alternatively possible to represent in relation (5) the velocity of the guided wave VGW in the sensor rod by relation (8) as provided herein below:
VGW = Vo + ?(m + n’ )+ p.v …(8)
wherein:
n’ is a constant and the remaining terms as defined by in relation (6).

[0035] It may be further possible to represent the length L of the sensor rod at the operating temperature by relation (9):
…(9)
wherein:
T1 is operating temperature;
T0 is standard temperature  which may be 25oC;
Lo is length of the sensor rod under standard temperature; and
k is a constant.

[0036] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid (?) may be performed in an alternative manner by adopting relation (10) as provided herein below:
…(10)
wherein the terms used in relation (10) are as defined above.

[0037] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid (?) may be performed in an alternative manner by adopting relation (11) as provided herein below:
…(11)
wherein the terms used in relation (11) are as defined above.

[0038] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid (?) may be performed in an alternative manner by adopting relation (12) as provided herein below:
…(12)
wherein the terms used in relation (12) are as defined above.

[0039] By way of another non-limiting example  the step of calculating 56 the value of density of the fluid (?) may be performed in an alternative manner by adopting relation (13) as provided herein below as a first order approximation:

…(13)
wherein the terms used in relation (13) are as defined above.

[0040] The method 50 may further include calculating 62  based on the value of density  a value of one or more density dependent property of the fluid or a value of one or more parameter influenced by density of the fluid. By way of non-limiting example  the density dependent property of the fluid or parameter influenced by density of the fluid includes fluid composition  fluid velocity  fluid level  absolute density  density profile  absolute temperature  temperature profile  absolute viscosity  viscosity profile  absolute flow velocity  flow velocity profile  fluid phase  absolute fluid phase fraction  fluid phase fraction profile  calorific value  or combinations thereof. By way of another limiting example  the method 50 may be adopted for sensing at least one parameter of a single-phase fluid  or a two-phase fluid mixture  or a multi-phase fluid mixture. By way of a non-limiting example  if the value of one or more density dependent property of the fluid or the value of one or more parameter influenced by density of the fluid is being calculated  the method 50 may further include providing 64  by the processor 16  the values thus calculated to an output device 30. By way of a non-limiting example  based on the value of density (which may represent the density at the operating conditions)  the processor 16 may obtain the density of the fluid at standard room temperature and pressure. The processor may obtain the density of the fluid at standard room temperature based on known PVT models.

[0041] By way of a non-limiting example  illustrated in FIG. 3  the step of receiving 54 time of flight of an ultrasonic wave in the fluid may in turn include exciting 66 an ultrasonic wave in an ultrasonic sensor partially immersed in the fluid so as to propagate the ultrasonic wave that interacts with the fluid along at least a portion of the ultrasonic sensor. The method 54 then continues to detecting 68 the ultrasonic wave from the ultrasonic sensor. Based on the detected ultrasonic wave  a time of flight of the ultrasonic wave in the fluid is determined 70.

[0042] Referring to FIG. 4  a block diagram of an exemplary device 100 for sensing at least one parameter of a fluid 12 flowing through a conduit 14 is illustrated. The device may include a processor 102. The processor 102 may be in the form of a central processing unit  a graphics-processing unit  or both. The processor 102 may be a component in a variety of systems. For example  the processor 102 may be part of a standard personal computer or a workstation. The processor 102 may be one or more general processors  digital signal processors  application specific integrated circuits  field programmable gate arrays  servers  networks  digital circuits  analog circuits  combinations thereof  or other now known or later developed devices for analyzing and processing data. The processor 102 may implement a software program  such as code (i.e.  programmed). The processor 102 may include instructions hardwired into it which may include various devices  components  circuits  gates  circuit boards  and the like that are operable  directed  or otherwise controlled during the performance of the processor 102.

[0043] The device 100 may include memory 104  such as a memory that may communicate via a bus 106. The memory 104 may be a main memory  a static memory  or a dynamic memory. The memory 104 may include  but is not limited to computer readable storage media such as various types of volatile and non-volatile storage media  including but not limited to random access memory  read-only memory  programmable read-only memory  electrically programmable read-only memory  electrically erasable read-only memory  flash memory  magnetic tape or disk  optical media and the like. In one example  the memory 104 includes a cache or random access memory for the processor 102. In alternative examples  the memory 104 is separate from the processor 102  such as a cache memory of a processor  the system memory  or other memory. The memory 104 may be an external storage device or database for storing data. Examples include a hard drive  compact disc ("CD")  digital video disc ("DVD")  memory card  memory stick  floppy disc  universal serial bus ("USB") memory device  or any other device operative to store data. The memory 104 is operable to store instructions 108 executable by the processor 102. The functions  acts or tasks illustrated in the figures or described may be performed by the programmed processor 102 executing the instructions 108 stored in the memory 104. The functions  acts or tasks are independent of the particular type of instructions set  storage media  processor or processing strategy and may be performed by software  hardware  integrated circuits  firm-ware  micro-code and the like  operating alone or in combination. Likewise  processing strategies may include multiprocessing  multitasking  parallel processing and the like.

[0044] As shown  the device 100 may further include an output unit 110  such as but not limited to a liquid crystal display  an organic light emitting diode  a flat panel display  a solid state display  a cathode ray tube  a projector  a printer or other now known or later developed display device for outputting value of the density as calculated by the processor 102. The output unit 110 may act as an interface for the user to see the functioning of the processor 102  or specifically as an interface with the instructions 108 stored in the memory 104 or in a drive unit 112. The drive unit 112 may include a computer-readable medium 114 in which one or more sets of instructions 108  e.g. software  may be embedded. Further  the instructions 108 may embody one or more of the methods or logic as described. In a particular example  the instructions 108 may reside completely  or at least partially  within the memory 104 or within the processor 102 during execution. The memory 104 and the processor 102 also may include computer-readable media 114 as discussed above.

[0045] Additionally  the device 100 may include an input device 116 configured to allow a user to interact with any of the components of device 100. The input device 116 may be a number pad  a keyboard  or a cursor control device  such as a mouse  or a joystick  touch screen display  remote control or any other device operative to interact with the device 100.

[0046] The device 100 may further include communication port or interface 118. The communication port or interface 118 may be a part of the processor 102 or may be a separate component. The communication port 118 may be created in software or may be a physical connection in hardware. The communication port 118 may be configured to connect with the detection device 22 for detecting the ultrasonic wave  the temperature sensor 24  the device 26 for providing data indicative of bulk modulus of the fluid  the device 28 for providing parameters relating to viscosity of the fluid  or any other components  or combinations thereof. The connection with the aforesaid devices / components may be a physical connection  such as a wired connection or may be established wirelessly. The wireless connection may be a cellular telephone network  an 802.11  802.16  802.20  802.1Q or WiMax network.

[0047] In order that those skilled in the art may better understand how the invention may be practiced  the following example is given by way of illustration and not by way of limitation.

Example 1
[0048] A reference fluid whose density profile (i.e. variation in density with respect to temperature) is accurately known is taken in a sensing system for the purposes of ascertaining working of the invention. An ultrasonic wave is excited in an ultrasonic sensor that is partially immersed in the fluid so as to propagate the ultrasonic wave that interacts with the fluid along at least a portion of the ultrasonic sensor. In response to excitation  the ultrasonic wave from the ultrasonic sensor is detected. Based on the detected ultrasonic wave  a time of flight of the ultrasonic wave in the fluid is determined. Temperature of the fluid and parameter indicative of bulk modulus of the fluid is detected. All of the above parameters i.e. time of flight of the ultrasonic wave  temperature of the fluid and parameter indicative of bulk modulus of the fluid i.e. speed of sound in the fluid are received by a processor and the processor calculates a value of density of the fluid by adopting the following relationship:

wherein:
? is the density of the fluid;
a0  a1  a2 and a3 are constants;
T is the temperature of the fluid;
TOF is the time of flight of the ultrasonic wave in the fluid; and
is speed of sound in the fluid.

[0049] Following the data analysis mentioned above and by way of a non-limiting example  by regression analysis  we may arrive at the values of the constants. The values of the constants a0  a1  a2 and a3 arrived by regression analysis are 696.0060  0.0002  36.7257e3 and –1037 respectively.

[0050] If the fluid exhibits a density of 864.1 Kg/m3 at a temperature 67.9oC  time of flight of the ultrasonic wave and the speed of sound in the fluid maintained 67.9oC are measured. The measured values of TOF and are 176.9 µs and 1402 m/s respectively. Substituting the aforesaid values of temperature  time of flight  speed of sound and constants a0  a1  a2 and a3 in the aforesaid relationship  the density of the fluid is calculated as:

[0051] Error percentage in the calculated value of density is arrived at by comparing the calculated value of density with the density of the fluid (as known a-priori i.e. 864.1 Kg/m3).
Error Percentage = {(864.1-864.07) * 100}/ 864.1= 0.003472% (rounded off to sixth decimal place)

[0052] It may be observed that the error percentage (rounded off to sixth decimal place) in the present instance is 0.003472%  which is well below the error range of less than about 0.5%.

[0053] While the invention is susceptible to various modifications and alternative forms  specific embodiment thereof has been shown by way of example in the drawings and described above. It should be understood  however that embodiments described above are not intended to limit the invention to the particular forms disclosed  but on the contrary  the invention is to cover all modifications  equivalents  and alternative falling within the spirit and the scope of the invention as defined by the appended claims.

WE CLAIM:

1. A method of determining density of a fluid  said method comprising:
receiving parameters comprising temperature of the fluid and bulk modulus of the fluid via a processor;
receiving time of flight of an ultrasonic wave in the fluid as provided by an ultrasonic density measurement system;
calculating a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid; and
providing the value of density as calculated to an output device.

2. The method of claim 1  wherein the bulk modulus of the fluid is a measured quantity.

3. The method of claim 1  wherein the bulk modulus of the fluid is a processed parameter determined based on speed of sound in the fluid.

4. The method of claim 1  wherein the bulk modulus of the fluid is determined based on temperature and pressure as measured and a characteristic of the fluid other than density of the fluid  known a priori  which comprises bulk modulus  speed of sound  viscosity  coefficient of thermal expansion  specific heat  phase diagram  temperature  molecular weight  heat of fusion  vapor pressure  heat of vaporization and calorific value.

5. The method of claim 1  wherein calculating a value of density comprises considering an interaction between temperature of the fluid and the time of flight of the ultrasonic wave in the fluid.

6. The method of claim 1  further comprising receiving parameters relating to viscosity of the fluid via the processor.

7. The method of claim 6  further comprising calculating  by the processor  a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid  viscosity of the fluid and time of flight of ultrasonic wave in the fluid.

8. The method of claim 7  wherein calculating a value of density comprises considering an interaction between temperature of the fluid  bulk modulus of the fluid  viscosity of the fluid and the time of flight of the ultrasonic wave in the fluid.

9. The method of claim 1  further comprising calculating  by the processor  based on the value of density  a value of one or more density dependent property of the fluid or a value of one or more parameter influenced by density of the fluid.

10. The method of claim 9  wherein the density dependent property of the fluid or parameter influenced by density of the fluid comprises fluid composition  fluid velocity  fluid level  absolute density  density profile  absolute temperature  temperature profile  absolute viscosity  viscosity profile  absolute flow velocity  flow velocity profile  fluid phase  absolute fluid phase fraction  fluid phase fraction profile  calorific value or combinations thereof.

11. The method of claim 1  comprising sensing at least one parameter of a single-phase fluid  or a two-phase fluid mixture  or a multi-phase fluid mixture.

12. The method of claim 1  further comprising exciting an ultrasonic wave in an ultrasonic sensor partially immersed in the fluid so as to propagate the ultrasonic wave that interacts with the fluid along at least a portion of the ultrasonic sensor so as to affect propagation of the ultrasonic wave in a manner dependent on the at least one parameter of the fluid and detecting the ultrasonic wave from the ultrasonic sensor.

13. The method of claim 1  wherein the parameters relating to time of flight of ultrasonic wave in the fluid  temperature of the fluid  bulk modulus of the fluid  speed of sound in the fluid  viscosity of the fluid  pressure of the fluid comprise a transformation of the parameters.

14. The method of claim 13  wherein the transformation comprises identity transformation  square root transformation  inverse transformation  square transformation  polynomial transformations  rational function transformations  logarithmic transformations  trigonometric transformations  exponential transformations or new transformation resulting out of compositions of a plurality of transformations.

15. The method of claim 5  wherein the interaction between the parameters is of ‘Nth’ order  wherein N is equal to or greater than 1.

16. The method of claim 8  wherein the interaction between the parameters is of ‘Nth’ order  wherein N is equal to or greater than 1.

17. A device for determining density of a fluid  the device comprising:

an ultrasonic density measurement system configured to receive time of flight of an ultrasonic wave in the fluid; and
a processor configured to:
receive parameters comprising temperature of the fluid and bulk modulus of the fluid;
calculate a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on the temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid; and
provide the value of density as calculated.

18. The device of claim 17  wherein the processor is further configured to receive parameters relating to viscosity of the fluid and calculate a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid  viscosity of the fluid and time of flight of ultrasonic wave in the fluid.

19. The device of claim 17  wherein the processor is further configured to calculate  based on the value of density  a value of one or more density dependent property of the fluid or a value of one or more parameter influenced by density of the fluid  wherein the density dependent property of the fluid or parameter influenced by density of the fluid comprises fluid composition  fluid velocity  fluid level  absolute density  density profile  absolute temperature  temperature profile  absolute viscosity  viscosity profile  absolute flow velocity  flow velocity profile  fluid phase  absolute fluid phase fraction  fluid phase fraction profile  calorific value  or combinations thereof.

20. A system for determining density of a fluid  the system comprising:
an ultrasonic sensor configured for partial immersion in the fluid;
an excitation device configured to excite an ultrasonic wave in the ultrasonic sensor so as to propagate the ultrasonic wave that interacts with the fluid along at least a portion of the ultrasonic sensor so as to affect propagation of the ultrasonic wave in a manner dependent on the at least one parameter of the fluid;
a detection device for detecting the ultrasonic wave in the ultrasonic sensor;
a temperature sensor for sensing a temperature of the fluid;
a device providing data indicative of bulk modulus of the fluid; and
a processor configured to calculate and provide a value of density with an accuracy that corresponds to an error range of less than about 0.5% based on temperature of fluid  bulk modulus of fluid and time of flight of ultrasonic wave in the fluid.

21. The system of claim 20  wherein the device providing data indicative of bulk modulus of the fluid is configured to provide the bulk modulus of the fluid as a measured quantity.

22. The system of claim 20  wherein the device providing data indicative of bulk modulus of the fluid is configured to provide speed of sound in the fluid and the processor is configured to calculate the bulk modulus of the fluid there from.

23. The system of claim 20  wherein the device providing data indicative of bulk modulus of the fluid is configured to provide pressure as a measured quantity and the processor is configured to calculate the bulk modulus of the fluid based on temperature of the fluid  pressure of the fluid and a characteristic of the fluid other than density of the fluid  wherein the characteristic of the fluid other than density of the fluid comprises bulk modulus  speed of sound  viscosity  coefficient of thermal expansion  specific heat  phase diagram  temperature  molecular weight  heat of fusion  vapor pressure  heat of vaporization and calorific value.