Title of Invention

CORIOLIS-TYPE MASS FLOW METER / DENSIMETER

Abstract

A Coriolis mass flow/density meter for a medium flowing through a pipe, said Coriolis mass flow/ density meter comprising: at least one flow tube for conducting said medium, said flow tube having an inlet-side end and an outlet-side end; support means fixed to said inlet-side end and said outlet-side end of the flow tube such that the at least one flow tube is capable of being vibrated; vibration exciting means for vibrating said at least one flow tube to generate inlet-side bending vibrations and outlet-side bending vibrations; measuring means for detecting said inlet-side and outlet-side bending vibrations of said at least one flow tube, said measuring means delivering a first measurement signal representative of said inlet-side bending vibrations of the flow tube and a second measurement signal representative of said outlet-side bending vibrations of the flow tube; means for delivering a third measurement signal during operation from which an instantaneous Reynolds number of the flowing medium can be derived; and evaluation electronics for receiving said first, second and third measurement signals and delivering a measured value representative of mass flow rate which is derived from said first, second, and third measurement signals.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10) CORIOLIS-TYPE MASS FLOW METER/DENSIMETER ENDRESS+HAUSER FLOWTEC AG of KAGENSTRASSE 7, CH-4153 REINACH, SWITZERLAND, SWISS Company The following specification particularly describes the nature of the invention and the manner in which it is to be performed : - 1 FL 109 US Nov. 23, 1999 Coriolis Mass Flow/Density Meter FIELD OF THE INVENTION This invention relates to a Coriolis mass flow/density 5 meter for media flowing through a pipe and to a method of generating a measured value representative of mass flow rate. 10 BACKGROUND OF THE INVENTION In Coriolis mass flow/density meters for media flowing through a pipe, the measurement of the mass flow rate is based on the principle of causing a medium to flow through 15 a flow tube inserted in the pipe and vibrating during operation, whereby the medium is subjected to Coriolis forces. The latter cause inlet—side and outlet—side portions of the flow tube to vibrate out of phase with respect to each other. The magnitude of these phase 20 differences is a measure of the mass flow rate. The vibrations of the flow tube are therefore sensed by means of two vibration sensors positioned at a given distance from each other along the flow tube, and converted by these sensors into measurement signals from whose phase 25 difference the mass flow rate is derived. FL 109 US Nov. 23, 1999 U.S. Patent 4,187,721 discloses a Coriolis mass flow meter comprising: -a single U-shaped flow tube having an inlet-side end and an outlet-side end, through which flow tube a medium 5 flows during operation; -a support means fixed to an inlet-side end and an outlet-side end of the flow tube such that the flow tube is capable of being vibrated; -a vibration exciter which sets the flow tube into 10 vibration during operation; - a first measuring means positioned on the inlet-side of the flow tube for measuring the vibrations and for delivering a first measurement signal during operation; - a second measuring means positioned on the outlet-side of 15 the flow tube for measuring the vibrations and for delivering a second measurement signal during operation;and -evaluation electronics for delivering, during operation, -- a first measured value representative of mass flow rate 20 wich is derived from the first and second measurement signals. Further EP-A 849 568 (corresponding to U.S. Serial No. 08/940,644, filed September 30, 1997) discloses a Coriolis 25 mass flow meter comprising: - a single straight flow tube having an inlet-side end and an outlet-side end, through which flow tube a medium flows during operation; - a support means fixed to an inlet-side end and an outlet- 30 side end of the flow tube such that the flow tube is capable of being vibrated; FL 109 US Nov. 23, 1999 -a vibration exciter which sets the flow tube into vibration during operation; -a first measuring means positioned on the inlet-side of the flow tube for measuring the vibrations and for 5 delivering a first measurement signal during operation; - a second measuring means positioned on the outlet-side of the flow tube for measuring the vibrations and for delivering a second measurement signal during operation;and 10 -evaluation electronics for delivering, during operation, - a measured value representative of mass flow rate wich is derived from the first and second measurement signals. 15 In addition each of U.S. Patent 4,660,421 and U.S. Patent 4,733,569 discloses a Coriolis mass flow meter comprising: - a spiraled flow tube having an inlet-side end and an outlet-side end, through which flow tube a medium flows during operation; 20 - a support means fixed to an inlet-side end and an outlet-side end of the flow tube such that the flow tube is capable of being vibrated; - a vibration exciter which sets the flow tube into vibration during operation; 25 -a first measuring means positioned on the inlet-side of the flow tube for measuring the vibrations and for delivering a first measurement signal during operation; - a second measuring means positioned on the outlet-side of the flow tube for measuring the vibrations and for 30 delivering a second measurement signal during operation;and -evaluation electronics for delivering, during operation, FL 109 US Nov. 23, 1999 a measured value representative of mass flow rate wich is derived from the first and second measurement signals. 5 Furthermore each of U.S. Patent 4,491,025, U.S. Patent 4,660,421 and U.S. Patent 5,218,873 discloses a Coriolis mass flow meter with two communicating flow tubes through which a medium flows during operation. These flow tubes are interconnected by means of an inlet-side first manifold 10 having an inlet-side first end and an outlet-side second manifold having an outlet-side second end and are fixed by a support means such that the flow tube is capable of being vibrated. 15 Both U.S. Patent 4,187,721, which was referred to at the beginning, and EP-A 849 568 mention that Coriolis mass flow meters can also be used to measure the instantaneous density of the flowing medium. For the invention it is therefore assumed that the devices referred to above as 20 Coriolis mass flow meters also measure the instantaneous density of the flowing medium even though this is not always described in the individual documents, since it is self-evident. 25 In Coriolis mass flow meters and Coriolis mass flow/density meters, the ratio of the width D of the flow tube to the length L of the flow tube (D/L ratio) is of significance for the measurement accuracy. If a single flow tube is used, the width D is virtually equal to the nominal 30 diameter of the pipe. FL 109 US Nov. 23, 1999 At a D/L ratio greater than approximately 0.05, the instantaneous velocity field of the medium in the flow tube may affect the measurement accuracy so that the resulting increased measurement error may no longer be negligibly 5 small. Measurements have shown that at D/L ratios greater than 0.05, this influence of the velocity field may cause an additional error of a few per mille to one percent. However, the minimization of the D/L ratio is limited by 10 constraints placed on the design of the meter, namely, on the one hand, by the nominal pipe diameter specified in a concrete application and, on the other hand, by the fact that meters are required which are as short and compact as possible. 15 SUMMARY OF THE INVENTION It is an object of the invention to provide a Coriolis mass 20 flow/density meter which provides highly accurate measurement results independently of the instantaneous velocity field while being as compact in construction as possible. Another object is to provide a method of producing such measurement results. 25 To attain the first-mentioned object, the invention provides a Coriolis mass flow/density meter for a medium flowing through a pipe, said Coriolis mass flow/density meter comprising: 30 - at least one flow tube having an inlet-side end and an outlet-side end, through which at least one flow tube the medium flows during operation; FL 109 US Nov. 23, 1999 -a support means fixed to an inlet-side end and an outlet-side end of the flow tube such that the flow tube is capable of being vibrated; -a vibration exciter which sets the flow tube into 5 vibration during operation; - a first measuring means positioned on the inlet-side of the flow tube for measuring the vibrations and for delivering a first measurement signal during operation; - a second measuring means positioned on the outlet-side of 10 the flow tube for measuring the vibrations and for delivering a second measurement signal during operation; - a third measuring means for delivering a third measurement signal during operation wich is representative of the instantaneous Reynolds number of 15 the flowing medium; and -evaluation electronics for delivering, during operation, - a first measured value representative of mass flow rate wich is derived from the first, second, and third measurement signals, and 20 - a second measured value representative of the instantaneous density of the medium, which is derived from the first and second measurement signals. Furthermore, the invention consists in a method of 25 generating a first measured value representative of mass flow rate by means of a Coriolis mass flow/density meter for a medium flowing throug a pipe, said Coriolis mass flow/density meter comprising: - at least one flow tube having an inlet-side end and an 30 outlet-side end, through which at least one flow tube the medium flows during operation; FL 109 US Nov. 23, 1999 -a support means fixed to an inlet-side end and an outlet-side of the flow tube, such that the flow tube is capable of being vibrated; - a vibration exciter which sets the flow tube into 5 vibration during operation, said method comprising the steps of: - sensing the vibrations of the flow tube and generating a first measurement signal representative of inlet-side vibrations and a second measurement signal representative 10 of outlet-side vibrations for developing an intermediate value representative of an uncorrected mass flow rate; -generating a third measurement signal representative of an Reynolds number of the flowing medium by means of the intermediate value and by means of a fourth measurement 15 signal representative of a dynamic viscosity of the medium; and -correcting the intermediate value by means of a correction value derived from the third measurement signal. 20 In a first embodiment of the Coriolis mass flow/density meter according to the invention, the evaluation electronics provide a correction value derived from the third measurement signal. 25 In a second embodiment of the Coriolis mass flow/density meter according to the invention, the evaluation electronics provide the correction value by means of a constant correction value for laminar flow determined by 30 calibration, by means of a constant correction value for turbulent flow determined by calibration, and by means of an interpolated correction value determined according to an FL 109 US Nov. 23, 1999 interpolation function lying between the two constant correction values. In a third emobodiment of the Coriolis mass flow/density 5 meter according to the invention, the evaluation electronics comprise a table memory in which Reynolds-number-dependent digitized correction values are stored, and which provides the correction value by means of a digital memory access address formed on the basis of the 10 third measurement signal. In a fourth embodiment of the Coriolis mass flow/density meter according to the invention, the evaluation electronics provide an intermediate value derived from the 15 first and second measurement signals which is representative of an uncorrected mass flow rate. In a fifth embodiment of the Coriolis mass flow/density meter according to the invention, the evaluation 20 electronics deliver the first measured value in response to the intermediate value and the correction value. In a sixth embodiment of the Coriolis mass flow/density meter according to the invention, the Coriolis mass 25 flow/density meter comprises a fourth measuring means which measures a dynamic viscosity of the medium and delivers a fourth measurement signal representative of said dynamic viscosity. 30 In a seventh embodiment of the Coriolis mass flow/density meter according to the invention, the third measuring means delivers the third measurement signal in response to the FL 109 US Nov. 23, 1999 uncorrected intermediate value and the fourth measurement signal. In an eighth embodiment of the Coriolis mass flow/density 5 meter according to the invention, the fourth measuring means measures a kinematic viscosity of the medium and delivers a fifth measurement signal representative of said kinematic viscosity. 10 In a ninth embodiment of the Coriolis mass flow/density meter according to the invention, the fourth measuring means delivers the fourth measurement signal in response to the second measured value and the fifth measurement signal. 15 In a tenth embodiment of the Coriolis mass flow/density meter according to the invention, the vibration exciter comprises a coil which is supplied with excitation energy and from whose current and/or voltage the fourth measuring means derives the fourth measurement signal and/or the 20 fifth measurement signal. In an eleventh embodiment of the Coriolis mass flow/density meter according to the invention, the fourth measuring means derives the fourth measurement signal and/or the 25 fifth measurement signal from a pressure difference measured along the pipe. In a first embodiment of the method according to the invention, the fourth measurement signal is derived from a 30 current and/or a voltage of an excitation energy supplied to the vibration exciter. FL 109 US Nov. 23, 1999 In a second embodiment of the method according to the invention, the fourth measurement signal is derived from a pressure difference measured along the pipe. 5 One advantage of the invention is that even at a D/L ratio greater than 0.05, the Coriolis mass flow/density meter provides a mass flow value in which the effect of the instantaneous velocity field on measurement accuracy has been compensated. 10 BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more apparent from the following 15 description of embodiments when taken in conjunction with the accompanying drawings. Like parts are designated by like referenence characters throughout the figures; reference characters that were already introduced are omitted in subsequent figures for the sake of clarity. In 20 the drawings: Fig. 1 is vertical longitudinal view, partially in section, of a mass flow sensor of a Coriolis mass flow/density meter; 25 30 Fig. 2 is a schematic block diagram of subcircuits of the evaluation electronics of the Coriolis mass flow/ density meter which serve to increase measurement accuracy; Fig. 3 is a schematic block diagram of a subcircuit which serves to. derive a sufficiently accurate FL 109 US Nov. 23, 1999 mass flow value from an uncorrected mass flow value using a correction value; 4 is a schematic block diagram of a subcircuit which derives a mass flow correction value from a measured Reynolds number; 5 is a schematic block diagram of a subcircuit which produces a mass flow correction value according to an interpolation function; 6a is a schematic block diagram of a subcircuit which determines the Reynolds number from a measured dynamic viscosity of the medium; 6b is a schematic block diagram of a subcircuit which determines the Reynolds number from a measured kinematic viscosity of the medium; 7 is a schematic block diagram of a subcircuit which determines the kinematic viscosity of the medium from a measured excitation energy of the vibration exciter; 8a is a schematic block diagram of a subcircuit which derives measured values for the kinematic viscosity in laminar flow from a pressure difference measured in the direction of flow; and 8b is a schematic block diagram of a subcircuit which derives measured values for the kinematic FL 109 US Nov. 23, 1999 viscosity in turbulent flow from a pressure difference measured in the direction of flow; and Fig. 9 is a schematic block diagram of a subcircuit for 5 determining the instantaneous kinematic viscosity of the medium. DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS 10 Referring now to Fig. 1, there is shown a vertical longitudinal view, partially in section, of a mass flow sensor 1 of a Coriolis mass flow/density meter with a single straight flow tube 11, which has an inlet-side first 15 end and an outlet—side second end. The first end of the flow tube 11 is provided with a first flange 111, and the second end with a,second flange 112, so that the mass flow sensor 1 can be inserted in a pressure— 20 tight manner in a pipe through which a medium flows during operation. The mass flow sensor 1 further comprises a support means 12 with a first end plate 121 fixed to the first end of the 25 flow tube 11, a second end plate 122 fixed to the second end of the flow tube 11, and a support tube 123 inserted between the first and second end plates 121, 122. The end plates 121, 122 are connected with the flow tube 11 and the support tube 123 in a rigid and pressure—tight manner, 30 particularly in a vacuum-tight manner. The flow tube 11 is thus mounted in a lumen of the support tube 123 between the FL 109 US Nov. 23, 1999 end plates 121, 122 in a self-supporting manner, so that it can be set into vibration. The joints between the flow tube 11 and the end plates 121, 5 122 and the flanges 111, 112 and the joints between the end plates 121, 122 and the support tube 123 may be welded or soldered joints, for example; the end plates 121, 122 may also be attached to the support tube 123 by means of screws, one of which, 124, is shown in Fig. 1. It is also 10 possible to form the two end plates 121, 122 integrally with the support tube 123. Besides mass flow sensors of the type shown in Fig. 1, mass flow sensors with two straight flow tubes are commonly 15 used. Instead of straight flow tubes, however, all other forms of flow tubes described in connection with Coriolis mass flow/density meters, particularly U- or omega—shaped or 20 spiraled flow tubes, can be employed. Two or more flow tubes, preferably two, may be connected in parallel or series with respect to the flow the medium. If flow tubes are connected in parallel, the ends will be fitted with suitable manifolds for separating and combining the flowing 25 medium. The medium may be any fluid substance, particularly liquids, gases, or vapors. 30 The flow tubes are preferably made of titanium, zirconium, or high—grade steel. FL 109 US Nov. 23, 1999 Fig. 1 further shows a vibration exciter 13, which is positioned within the support means 12 between flow tube 11 and support tube 123, preferably midway between the first and second end plates 121, 122. In operation, this 5 vibration exciter 13 sets the flow tube 11 into vibration at a mechanical resonant frequency, which, in turn, is a measure of the instantaneous density of the medium. The vibration exciter 13 may be a solenoid assembly, for 10 example, which comprises a soft—magnetic core attached to the flow tube 11, a permanent magnet movable therein, and a coil attached to the support tube 123 and traversed in operation by a time—variable exciting current. The permanent magnet is moved by the action of the time— 15 variable exciting current, thus setting the flow tube 11 into vibration, with the inlet-side portion and the outlet-side portion vibrating out of phase with respect to each other as the medium passes through the flow tube 11. 20 For an example of exciter electronics for driving the vibration exciter 13, reference is made to U.S. Patent 4,801,897. In the case of straight flow tubes, the vibrations are 25 generally bending vibrations, which are comparable to the vibrations of a string. These bending vibrations may have torsional vibrations superimposed on them, see EP—A 84 9 568. Besides bending/torsional vibrations, hoop—mode vibrations are commonly excited, in which case the flow 30 tube moves peristaltically, see U.S. Patent 4,949,583. FL 109 U.S Nov. 23, 1999 In the case of U— or omega—shaped flow tubes, the vibrations are cantilever vibrations, which are comparable to those of a tuning fork, see U.S. Patent 4,187,721. 5 Within the support means 12, a first measuring means 141 and a second measuring means 142 are positioned at a given distance from each other along the flow tube 11 for measuring the vibrations. The measuring means 141, 142 are preferably located at equal distances from the middle of 10 the flow tube 11 and provide a first measurement signal xs1 and a second measurement signal xs2, which are representative of the vibrations. To that end, the measuring means 141, 142 comprise 15 vibration sensors which are preferably implemented as electrodynamic vibration sensors as in U.S. Patent 5,736,653, but may also be designed as optical vibration sensors, see U.S. Patent 4,801,897. 20 The mass flow sensor 1 is protected from environmental influences by a sensor housing 15. The latter is so designed that both the support means 12 and all electric leads connected to the mass flow sensor 1 are accommodated therein, the leads being not shown for clarity of 25 illustration. The sensor housing 15 has a necklike transition portion 16, to which an electronics housing 17 is fixed. 30 In the electronics housing 17 both the above-mentioned exciter electronics and evaluation electronics 2 as well as other circuits wich are also used for the operation of the FL 109 US Nov. 23, 1999 Coriolis mass flow/density meter are accommodated. These circuits can be, for instance, electronics for power supplying the coriolis mass flow/density meter wich are fed from an external power source, and/or communication 5 electronics for data transmission between the Coriolis mass flow/density meter and an external signal processing unit. If the vibratory behavior of the mass flow sensor 1 should be adversely affected by the electronics housing 17, the 10 latter may also be located separately from the mass flow sensor 1. Then, only an electric lead will exist between the electronics housing 17 and the mass flow sensor 1, so that the electronics housing 17 and the sensor 1 are practically vibration-isolated from each other. 15 Fig. 2 shows a block diagram of subcircuits of the evaluation electronics 2 of the Coriolis mass flow/density meter, which provide a first measured value Xm representing the mass flow rate. 20 The measurement signals xs1, xS2 are fed to a measuring circuit 21 of the evaluation electronics 2. The measuring circuit 21 may, for instance, be implemented with the evaluation electronics of a Coriolis mass flow/density 25 meter disclose in U.S. Patent 5,648,616, which derive a mass flow value using an exciter circuit as disclosed in U.S. Patent 4,801,897, for example. It is also possible to use other measuring electronis for Coriolis mass flow/density meters that are familar to those skilled in FL 109 US Nov. 23, 1999 At large D/L ratios, however, the mass flow value determined by the measuring circuit 21 is not yet accurate enough and needs to be corrected; it will therefore be referred to herein as the intermediate value X*m, from 5 which the measured value Xm is derived, which represents the mass flow rate with sufficient accuracy. The correction of the intermediate value X*m is based on the following recognition by the inventors. 10 The mass flow rate in the flow tube 11 is given by the following equation: (1) 15 where dQ/dt = mass flow rate D = inside diameter of the flow tube 11 p = instantaneous density of the medium vm = mean velocity of the medium flowing through the 20 flow tube 11. The mean velocity vm is the arithmetic mean of all velocity vectors of the flowing medium over a cross—sectional area of the flow tube 11. 25 The intermediate value X*m is given by FL 109 US Nov. 23, 1993 where Xf = measured value representative of the instantaneous frequency of the vibrations of the flow tube 11 5 Xφ = measured value representative of the instantaneous phase difference between the both measurement signals xs1, xs2 K1 = a first parameter of the Coriolis mass flow/density meter. 10 The parameter K1 is primarily dependent on the instantaneous temperature of the medium; it may also be dependent on the instantaneous density of the medium. 15 For Eq.(2) it is assumed that the properties of the medium determining the parameter Kl namely its instantaneous temperature and instantaneous density, are known, since they are also measured during the operation of Coriolis mass flow/density meters, cf. U.S. Patent 4,768,384 for the 20 temperature measurement and U.S. Patent 4,187,721 for the density measurement. For Eq.(2) it is further assumed that the Coriolis—induced phase difference between a flow tube vibration sensed on 25 the inlet side and a flow tube vibration sensed on the outlet side is proportional to the instantaneous mass flow rate. This assumption supposes that all velocity fields occurring in the flow tube 11 produce the same Corriois forces at the same instantaneous flow rate. This is true 30 with increasing accuracy as the D/L ratio decreases, since in that case all velocity fields are equal or at least very similar to each other. At great D/L ratios, particularly at 19 FL 109 US Nov. 23, 1999 ratios greater than 0.05, the correctness of that assumption decreases, resulting in an intermediate value X*m of decreasing accuracy. 5 Investigations have shown that the value of the measurement accuracy depends particularly on whether the flow of the medium is laminar or turbulent. Thus, to determine the measured value Xm, the intermediate 10 value X'm can be corrected by determining the presence of laminar flow or turbulent flow in the flow tube 11 and taking this into account in a correction value XK for the intermediate value X*m. Modifying Eq. (2) gives 15 Eq.(3) is implemented with a'second subcircuit 22 of the evaluation electronics 2, which is shown in Fig. 3 in block-diagram form. 20 The subcircuit 22 comprises a first adder 221, which forms a first sum value from the correction value XK at a first input and a value for 1 at a second input and delivers this first sum value at an output. 25 The subcircuit 22 further comprises a first multiplier 222 with a first input for the first sum value and a second input for the intermediate value X*m. The multiplier 222 provides at an output a first product value for (1+XK)-X*, which corresponds to the measured value Xm. FL 109 US Nov. 23, 1999 In the invention, the correction value XK is derived from the instantaneous Reynolds number of the medium, a quantity which describes the velocity field of the flowing medium. Accordingly, the mass flow sensor 1 includes a third 5 measuring means 143 for measuring the instantaneous Reynolds number of the medium, see Fig. 2. The measuring means 143 provides a third measurement signal xRe, which is representative of the Reynolds number, and feeds it to the evaluation electronics 2. 10 In the case of laminar flow, the values of the measurement signal xRe are smaller than in the case of turbulent flow. Thus, for each width D of the flow tube 11 and the associated nominal width of the pipe, there is an upper 15 limit value of the Reynolds number for laminar flow and a lower limit value of the Reynolds number for turbulent flow, which are not identical. These two limit values are determined during calibration. The upper limit value of the Reynolds number for laminar flow, which is determined during calibration, is represented by a second parameter K2, which is stored in the evaluation electronics 2. The lower limit value of the Reynolds number for turbulent flow, which is determined during calibration, is represented by a third parameter K3, which is stored in the evaluation electronics 2. A comparison of the measurement signal xRe to these two parameters K2, K3 shows whether laminar flow or turbulent 30 flow is present in the flow tube 11, and provides a corresponding correction value XK. This comparison is based on the following inequalities: FL 109 US Nov. 23, 1999 where XK2 = constant correction value for laminar flow, 5 determined by calibration XK3 = constant correction value for turbulent flow, determined by calibration f(xRe) = interpolation function rising monotonically from XK2 to XK3, whose shape can be adjusted, 10 see below. The result of the comparison of the measurement signal xRe to the two parameters K2, K3 according to Eq.(4) is a correction value XK = XK2, for laminar flow, a correction 15 value XK = Xk3 for turbulent flow, or an interpolated correction value XK = f(xRe) corresponding to interpolation function f (xRe) . Eq.(4) is implemented with a third subcircuit 23, whose 20 individual functional elements are shown in Fig. 4 in block-diagram form. The subcircuit 23 comprises a first comparator 231 with a reference input for the parameter K2 and with a signal 25 input for the measurement signal xRe. The comparator 231 provides a first binary value for xRe 30 first input of a second multiplier 232. A second input of FL 109 US Nov. 23, 1999 this multipier 232 receives the constant correction value for laminar flow, XK2. The subcircuit 23 further comprises a second comparator 233 5 with a reference input for the parameter K3 and with a signal input for the measurement signal xRe. The comparator 233 provides a second binary value for xRe > K3, which is 1 when the instantaneous value of the measurement signal xRe is greater than the value of the parameter K3; otherwise 10 the second binary value is 0. The second binary value is fed to a first input of a third multiplier 234. A second input of the multiplier 234 receives the constant correction value for turbulent flow 15 XK3. The subcircuit 23 further comprises a NOR gate 235 with a first input for the first binary value and with a second input for the second binary value. The NOR gate 235 20 provides a third binary value for K2 S xRe An inverter 236 following the NOR gate 235 changes the 25 third binary value into an inverted fourth binary value, which is applied to a third input of the second multiplier 232 and to a third input of the multiplier 234. The multiplier 232 thus provides a second product value, 30 which is equal to the constant correction value XK2 for laminar flow if the first and fourth binary values are 1; otherwise the second product value is 0. Analogously, the FL 109 US Nov. 23, 1999 multiplier 234 provides a third product value, which is equal to the constant correction value XK3 for turbulent flow if the second and fourth binary values are 1; otherwise the third product value is 0. 5 The interpolated correction value corresponding to interpolation function f(xRe), whose formation will be described below, is fed to a first input of a fourth multiplier 237. The third binary value is presented to a 10 second input of the multiplier 237, so that the latter provides a fourth product value, which is equal to the interpolated correction value corresponding to f(xRe) if the third binary value is 1; if the third binary value is 0, then the fourth product value is also 0. 15 The second, third, and fourth product values are fed, respectively, to first, second, and third inputs of a second adder 238, which delivers a second sum value. Since only either the second or the third or the fourth product 20 value is nonzero at any given time, the second sum value corresponds to the required correction value XK. The correction value XK can also be generated by means of a fuzzy logic provided in the subcircuit 23. To accomplish 25 this, the first comparator 231 is replaced by a first membership function for laminar flow, the second comparator 233 by a second membership function for turbulent flow, and the NOR gate 235 by a third membership function for coexisting laminar flow and turbulent flow. These 30 membership functions must be determined by calibration measurements and provide first, second, and third membership values which replace the first, second, and FL 109 US Nov. 23, 1999 third binary values, respectively, and lie in a range between 0 and 1. The inverter 236 must be replaced by a subtracter, for example, which then deducts the third membership value from the value 1. 5 For flow conditions with laminar and turbulent components, the correction value XK is interpolated according to Eq. (4) using the interpolation function f(xRe). The interpolation function f(xRe) can be expanded in the form of a power 10 series in the usual manner, e.g., with the paramter K2 as the center, so that ( Thus, the interpolation function f(xRe) can be implemented 15 with arbitrary accuracy using an approximation polynomial of degree n. The coefficients an of the interpolation function f (xRe) must be determined by calibration. If ,for example, the approximation polynomial is to be only 20 of the first degree, i.e., if n = 1, a linear relationship is obtained for the corresponding interpolation function f (xRe); ( 25 Using Eq. (4) , Fig. 5 shows a block diagram of a fourth subcircuit 24, which implements the interpolation function f(xRe) 30 according to Eq. (7) . FL 109 US Nov. 23, 1999 The subcircuit 24 comprises a first subtracter 241 with a subtrahend input for the correction value XK2, for laminar flow and with a minuend input for the correction value XK3 5 for turbulent flow, which provides a first difference value for XK2~XK3. A second subtracter 242 with a subtrahend input for the parameter K2 and a minuend input for the parameter K3 provides a second difference value for K3-K2. A third subtracter 243 with a subtrahend input for the parameter K2 10 and with a minuend input for the measurement signal xRe provides a third difference value for XRe-K2. The subcircuit 24 further includes a first divider 244 with a dividend input for the first difference value and with a 15 divisor input for the second difference value. The divider 244 delivers a first quotient value, which corresponds to the expression (XK3-XK2) / (K3-K2) . A fifth multiplier 245 with a first input for the first 20 quotient value and with a second input for the third difference value generates a fifth product value for (xRe~K2) -(XK3-XR2) / (K3-K2) , which is fed to a first input of a third adder 246. A second input of the adder 246 is supplied with the correction value XK2 for laminar flow, so 25 that the adder 246 provides a third sum value for XK2+(xRe-K2)-(XK3-XK2)/(K3-K2) . If K2 FL 109 US Nov. 23, 1999 Instead of Eq.(7), any other approximation polynomial based on Eqs.(4) and (5) can be implemented with the subcircuit 24. 5 Instead of the subcircuits 23 and 24 shown in Figs. 4 and 5, respectively, the evaluation electronics 2 may inlcude a table memory containing discrete values for the correction value KK. These are accessed via a digital memory address derived from the measurement signal xRe. This digital 10 memory address is formed by means of an analog—to—digital converter followed by an encoder. The table memory can be a programmable read-only memory, for example, an EPROM or an EEPROM. 15 For the measurement of the Reynolds number necessary according to Eq.(4), the following relations are used: where n = the dynamic viscosity of the medium 20 C, = the kinematic viscosity of the medium. Substituting the mean velocity vm according to Eq.(1) into Eq. (8) gives the Reynolds number as 25 In accordance with the invention, according to Eq.(9), either the dynamic viscosity of the medium or the kinematic viscosity is used to generate the third measurement signal xRe, and thus to determine the correction value XK, since 30 the two viscosities can be readily converted to each other FL 109 US Nov. 23, 1999 taking into account the instantaneous density p of the medium. Substituting the corresponding measurement signals into 5 Eq.(9) gives the following relation for the measurement signal xRe if the dynamic viscosity is used: xRe= K4 Xn Xm (10) Xwhere 10 xn = a fourth measurement signal, representative of the dynamic viscosity of the medium K4 = a fourth parameter, derived from the quotient 4/πD. 15 Eq.(10) is implemented in the third measuring means 143 with a fifth subcircuit 25, which is shown in block-diagram form in Fig. 6a. The subcircuit 25 comprises a second divider 251 with a 20 dividend input for the parameter K4 and with a divisor input for the measurement signal xn. The divider 251 . delivers a second quotient value for K4/xn, which is fed to a first input of a sixth multiplier 252. A second input of the multiplier 252 is supplied with the intermediate value 25 X'm. The multiplier 252 thus provides a sixth product value which corresponds to the measurement signal xRe according to Eq.(10). FL 109 US Nov. 23, 1999 The measurement signal xn, which is necessary according to Eq.(lO) to determine the measurement signal xRe, is generated by a further, fourth measuring means 144, see Fig. 2. 5 According to Eq.(8), the kinematic viscosity and the instantaneous density of the medium can be used to determine the dynamic viscosity of the medium. Using Eq. (9) gives the measurement signal xn as 10 xn=Xc-Xp (11) where xc = a fifth measurement signal, representative of the kinematic viscosity of the medium, 15 Xp = a second measured value, representative of the instantaneous density of the medium. In an embodiment of the invention based on Eq.(ll), the measuring means 144 uses the measurement signal xc, which 20 represents the kinematic viscosity of the medium, to generate the measurement signal x,,. Accordingly, the subcircuit 25, as shown in Fig. 6b in block-diagram form, comprises a seventh multiplier 253 with a first input for the measurement signal xc and with a second input for the 25 measured value Xp. The multiplier 253 delivers as a product value the measurement signal xn, which is fed to the divisor input of the second divider 251. The measured value Xn is derived, for example, from the instantaneous vibration frequency of the flow tube, see the above- 30 mentioned U.S. Patent 4,187,721. FL 109 US Nov. 23, 1999 The measures necessary to generate the measurement signal xc are explained in the following. Since the viscosity is a quantity describing the internal friction of the flowing 5 medium, the inventors have come to the conclusion that a determination of the kinematic viscosity is possible by measuring the excitation energy supplied to the vibration exciter 13. Due to the internal friction of the medium, the vibrations of the fluid-conducting flow tube 11 are 10 additionally damped as a function of the viscosity of the medium, particularly of the kinematic viscosity, as compared with the empty flow tube 11. To maintain the vibrations of the flow tube 11, the additional energy loss caused by friction must be compensated for by 15 correspondingly increased excitation energy. Therefore, in a preferred embodiment of the invention, the measurement signal xc is determined using the following relation: 20 xc=K5-(xexc-K6)2 (12) where Xexc = a sixth measurement signal representative of the excitation energy supplied to the vibration 25 exciter 13, K5, K6 = a constant fifth parameter and a constant sixth parameter, respectively. According to Eqs.(ll) and (12), the measurement signal xc 30 is dependent exclusively on defining quantities occurring during the operation of Coriolis mass flow/density meters, FL 109 US Nov. 23, 1999 namely on the measured value Xp and on the measurement signal xexc, which is representative of the excitation energy. 5 In an embodiment of the invention based on Eq.(12), the measuring means 144 comprises a sixth subcircuit 26, which is shown in Fig. 7 in block-diagram form. The subcircuit 26 comprises a fourth subtracter 261 with a 10 minuend input for the measurement signal xexc, which represents the excitation energy, and with a subtrahend input for the parameter K6. The subtracter 261 forms a fourth difference value for xexc-K6 and feeds it to a signal input of a first exponentiator 262. An exponent input is 15 supplied with the value 2, so that the exponentiator 262 changes the fourth difference value into a first power value for (xexc—K6)2. The power value is fed to a first input of an eighth multiplier 263, which multiplies it by the parameter K5 applied at a second input to form an 20 eighth product value for Ks- (xexc~K6)2, which corresponds to the measurement signal x The measurement signal xexc which represents the excitation energy, is formed by a current and/or voltage measurement 25 or by an impedance measurement at the vibration exciter. In one embodiment of the invention, a voltage—to—current converter associated with the vibration exciter 13, which is formed by a solenoid assembly, converts an exciting voltage applied to the coil into a current proportional 30 thereto, which, in turn, is converted by a subsequent root— mean-square converter into an rms value. The latter is then FL 109 US Nov. 23, 1999 the measurement signal representative of the excitation energy, xexc. Instead of measuring the excitation energy, a further 5 possibility of determining the kinematic viscosity of the medium is to measure and evaluate a pressure difference over a suitable measuring length along the pipe or along the flow tube 11. 10 In the case of predominantly laminar flow along the measuring length, the kinematic viscosity is (13) and in the case of predominantly turbulent flow, the 15 kinematic viscosity is (Δp)4 (14) where L = the measuring length 20 Ap = the pressure difference over the measuring length. Eq. (13) is based on the well-known Hagen-Poiseuille law, while Eq.(14) is determined empirically. With respect to 25 the pressure difference, both equations are monotonically rising functions which have a single point of intersection. Therefore, in a further embodiment of the invention, the measurement signal xc is determined using the following FL 109 US Nov. 23, 1999 relations, which are obtained by substituting the respective measurement signals into Eqs.(13) and (14) (15) 5 where 10 15 XΔp K8 = a measured value representative of the kinematic viscosity of the medium in the case of laminar flow, = a measured value representative of the kinematic viscosity of the medium in the case of turbulent flow, = a seventh measurement signal, represenative of the pressure difference, = a seventh parameter, derived from the quotient 2πD4/L according to Eq. (13) = an eighth parameter, derived from the quotient 0.3-4D19/L4 according to Eq. (14). According to Eq.(15), the valid value for the measurement 20 signal xC is always the smaller one of the two measured values Xc1 for laminar flow and Xc2 for turbulent flow. According to Eq.(15), the measurement signal xc is dependent on defining quantities occurring during the 25 operation of Coriolis mass flow/density meters, namely on the intermediate value X*m and on the second measured value Xp. In addition, the measurement signal xc is dependent on FL 109 US Nov. 23, 1999 a further defining quantity, namely on the measurement signal xΔp, which is representative of the pressure difference and is determined during operation. 5 In a further embodiment of the invention, to implement Eq.(15), the measuring means 144 comprises a seventh subcircuit 27 as shown in Fig. 8a, 8b and an eighth subcircuit 28 as shown in Fig. 9. 10 The subcircuit 27 serves to generate the two measured values representative of the viscosity of the medium, Xc1 and Xc2. It comprises a third divider 271 with a dividend input for the measurement signal xΔp and with a divisor input for the intermediate value X'm. The divider 271 15 provides a third quotient value for XΔP/X'm, which is fed to a first input of a ninth multiplier 272. A second input the multiplier 272 is supplied with the parameter K7, so that the multiplier 272 delivers a ninth product value for K7-XΔP/X'm, which corresponds to the measured value 20 representative of the kinematic viscosity of the medium in the case of laminar flow, Xc1. The subcircuit 27 further comprises a second exponentiator 273 with a signal input for the measurement signal xΔp and 25 with an exponent input for the value 4. The exponentiator 273 provides a second power value for (xΔp)4 and feeds it to a dividend input of a fourth divider 276. The subcircuit 27 further comprises a third exponentiator 30 274 with a signal input for the intermediate value X'm and with an exponent input for the value 7. The exponentiator FL 109 US Nov. 23, 1999 274 provides a third power value for (Xm)7. A fourth exponentiator 275 with a signal input for the measured value Xp and with an exponent input for the value 3 delivers a fourth power value for (Xp)3. 5 The third power value (Xm)7 is fed to a divisor input of the fourth divider 276, while the fourth power value (Xp)3 is presented to the first input of a tenth multiplier 277. The multiplier 277 has a second input for the parameter K8 10 and a third input for a fourth quotient value for (xAp)V(X*m)7, which is provided by the divider 276. The multiplier 277 thus delivers a tenth product value for Kr(Xp)3-(K&p)'i/(XlJ1f which corresponds to the measured value representative of the kinematic viscosity of the medium in 15 turbulent flow, X- The subcircuit 28, shown in Fig. 9, serves to implement the two inequalities according to Eq.(15). The subcircuit 28 comprises a third comparator 281 with a first input for the 20 ninth product value and with a second input for the tenth product value. The comparator 281 provides a fifth binary value for K7xAp/X'm 25 The fifth binary value is fed to a second inverter 282 and to a first input of a eleventh multiplier 283. A second input of the multiplier 283 is supplied with the ninth product value, so that the multiplier 283 delivers an 30 eleventh product value, which is equal to the ninth product FL 109 US Nov. 23, 1999 value if the fifth binary value is 1, or which is 0 if the fifth binary value is 0. The inverter 282 provides a sixth binary value, which is 5 inverted with respect to the fifth binary value and is applied to the first input of a twelfth multiplier 284. A second input of the multiplier 284 is supplied with the tenth product value, so that the multiplier 284 provides a twelfth product value, which is equal to the tenth product 10 value if the sixth binary value is 1, or which is 0 if the sixth binary value is 0. The eleventh product value is fed to a first input of a fourth adder 285, and the twelfth product value is fed to a 15 second input of the adder 285. Since only one of the two product value is nonzero at any given time, a fourth sum value provided by the adder 285 is equal to the measurement signal x. 20 Any difference between the kinematic viscosity determined according to Eq.(15) and the actual kinematic viscosity in the flow tube 11, which is due, for example, to the effect of temperature differences in the medium, can be readily compensated for by suitable temperature measurements. 25 The subcircuits 21, 22, 23, 24, 25, 26, 27, and 28 are assumed to be analog computing circuits but can also be implemented, at least in part, as digital computing circuits using discrete components or a microprocessor. FL 109 US Nov. 23, 1999 If the operation of the subcircuits 22...28, which operate virtually in parallel, is time-uncritical, like functions, such as add, subtract, multiply, divide, and exponentiate, can be combined using multiplexers and demultiplexers in 5 such a way that each of these functions is implemented in a subcircuit only once and that the individual computed values are generated by sequential application of the corresponding input values to the inputs. WE CLAIM: 1. A Coriolis mass flow/density meter for a medium flowing through a pipe, said Coriolis mass flow/ density meter comprising: at least one flow tube for conducting said medium, said flow tube having an inlet-side end and an outlet-side end; support means fixed to said inlet-side end and said outlet-side end of the flow tube such that the at least one flow tube is capable of being vibrated; vibration exciting means for vibrating said at least one flow tube to generate inlet-side bending vibrations and outlet-side bending vibrations; measuring means for detecting said inlet-side and outlet-side bending vibrations of said at least one flow tube, said measuring means delivering a first measurement signal representative of said inlet-side bending vibrations of the flow tube and a second measurement signal representative of said outlet-side bending vibrations of the flow tube; means for delivering a third measurement signal during operation from which an instantaneous Reynolds number of the flowing medium can be derived; and evaluation electronics for receiving said first, second and third measurement signals and delivering a measured value representative of mass flow rate which is derived from said first, second, and third measurement signals. 2. A Coriolis mass flow/ density meter as claimed in claim 1 wherein the evaluation electronics comprise means for deriving a correction value from the third measurement signal. 3. A Coriolis mass flow/density meter as claimed in claim 2 wherein the evaluation electronics derive the correction value from the third measurement signal using a laminar flow constant correction value determined by calibration, a turbular flow constant correction value determined by calibration, and an interpolated correction value determined according to an interpolation function lying between the laminar flow constant correction value and the turbulent flow constant correction value. 4. A Coriolis mass flow/ density meter as claimed in claim 2 wherein the evaluation electronics comprise a table memory in which Reynolds-number-dependent digitized correction values are stored, and a digital memory access address formed on the basis of the third measurement signal. 5. A Coriolis mass flow/density meter as claimed in claim 4 wherein the evaluation electronics provide an intermediate value derived from the first and second measurement signals which is representative of an uncorrected mass flow rate. 6. A Coriolis mass flow/ density meter as claimed in claim 1 wherein the evaluation electronics derive from the first and second measurement signals an intermediate value representative of an uncorrected mass flow rate. 7. A Coriolis mass flow/density meter as claimed in claim 6 wherein the evaluation electronics derive a correction value from the third measurement signal and deliver the first measured value in response to the intermediate value and the correction value. 8. A Coriolis mass flow/density meter as claimed in claim 1 wherein the Coriolis mass flow/ density meter comprises means for determining a viscosity of the medium and delivering a fourth measurement signal which is representative of said viscosity. 9. A Coriolis mass flow/ density meter as claimed in claim 8 wherein said means for delivering a third measurement signal delivers the third measurement signal in response to said uncorrected intermediate value and said fourth measurement signal. 10. A Coriolis mass flow/density meter as claimed in claim 8 wherein said means for determining a viscosity measures a kinematic viscosity of the medium and delivers a fifth measurement signal representative of said kinematic viscosity. 11. A Coriolis mass flow/ density meter as claimed in claim 10 wherein said means for determining a viscosity delivers the fourth measurement signal in response to the measured value and the fifth measurement signal. 12. A Coriolis mass flow/ density meter as claimed in claim 10 wherein said means for determining a viscosity of the medium delivers the fourth measurement signal in response to the second measured value and the fifth measurement signal. 13. A Coriolis mass flow/density meter as claimed in claim 10 wherein the vibration exciting means comprises a coil which is supplied with excitation energy from which said means for determining a viscosity derives the fourth measurement signal and/or the fifth measurement signal. 14. A Coriolis mass flow/density meter as claimed in claim 10 wherein said means for determining a viscosity derives the fourth measurement signal and/or the fifth measurement signal from a pressure difference measured along the pipe. 15. A method of generating a measured value representative of mass flow rate by means of a Coriolis mass flow/ density meter for a medium flowing through a pipe, said Coriolis mass flow/density meter comprising: at least one flow tube having an inlet-side end and an outlet-side end, wherein the medium flows through the at least one flow tube during operation; a support means fixed to said inlet-side end and said outlet-side of the at least one flow tube, such that the at least one flow tube is capable of being vibrated; a vibration exciter which sets the at least one flow tube into vibration during operation, said method comprising the steps of: sensing vibrations of the at least one flow tube and generating a first measurement signal representative of inlet-side bending vibrations and a second measurement signal representative of outlet-side bending vibrations for developing an intermediate value representative of an uncorrected mass flow rate; generating a third measurement signal representative of a Reynolds number of the flowing medium using the intermediate value and a fourth measurement signal representative of a viscosity of the medium; and correcting the intermediate value using a correction value derived from the third measurement signal. 16. A method as claimed in claim 22 wherein the fourth measurement signal is derived from a current and/or a voltage of an excitation energy suppling to the vibration exciter. 17. A method as claimed in claim 22 wherein the fourth measurement signal is derived from a pressure difference measured along the pipe. Dated this 17th day of July, 2000. HIRAL CHANDRAKANT JOSHI AGENT FOR ENDRESS+HAUSER FLOWTEC AG.

Documents:

in-pct-2000-00186-mum-cancelled pages(21-07-2003).pdf

in-pct-2000-00186-mum-claims(granted)-(21-07-2003).doc

in-pct-2000-00186-mum-claims(granted)-(21-07-2003).pdf

in-pct-2000-00186-mum-correspondence(23-08-2004).pdf

in-pct-2000-00186-mum-correspondence(ipo)-(09-11-2004).pdf

in-pct-2000-00186-mum-form 1a(21-07-2003).pdf

in-pct-2000-00186-mum-form 2(granted)-(21-07-2003).doc

in-pct-2000-00186-mum-form 2(granted)-(21-07-2003).pdf

in-pct-2000-00186-mum-form 3(21-07-2003).pdf

in-pct-2000-00186-mum-form 4(16-08-2004).pdf

in-pct-2000-00186-mum-form 5(21-07-2003).pdf

in-pct-2000-00186-mum-form-pct-isa-210(26-11-1999).pdf