Title of Invention	METER ELECTRONICS AND METHODS FOR DETERMINING A PHASE DIFFERENCE BETWEEN A FIRST SENSOR SIGNAL AND A SECOND SENSOR SIGNAL OF A FLOW METER
Abstract	Meter electronics (20) for processing sensor signals in a flow meter is provided according to an embodiment of the invention. The meter electronics (20) includes an interface (201) for receiving a first sensor signal and a second sensor signal and a processing system (203) in communication with the interface (201) and configured to receive the first sensor signal and the second sensor signal, generate a ninety degree phase shift from the first sensor signal, and compute a frequency from the first sensor signal and the ninety degree phase shift. The processing system (203) is further configured to generate sine and cosine signals using the frequency, and quadrate demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference.

Title of Invention

METER ELECTRONICS AND METHODS FOR DETERMINING A PHASE DIFFERENCE BETWEEN A FIRST SENSOR SIGNAL AND A SECOND SENSOR SIGNAL OF A FLOW METER

Abstract

Meter electronics (20) for processing sensor signals in a flow meter is provided according to an embodiment of the invention. The meter electronics (20) includes an interface (201) for receiving a first sensor signal and a second sensor signal and a processing system (203) in communication with the interface (201) and configured to receive the first sensor signal and the second sensor signal, generate a ninety degree phase shift from the first sensor signal, and compute a frequency from the first sensor signal and the ninety degree phase shift. The processing system (203) is further configured to generate sine and cosine signals using the frequency, and quadrate demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference.

Full Text	METER ELECTRONICS AND METH0DS FOR DETERTIMIINING A PHASE DIFFERENCE BETWEEN A FIRST SENSOR SIGNAL AND A SECOND SENSOR SIGNAL OF A FLOW ISIETER Background of the Invention 1. Field of the Invention The present invention relates to meter electronics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter. 2. Statement of the Problem It is known to use Coriolis mass flow meters to measure mass flow, density and volume flow and other information of materials through a pipeline as disclosed in U.S. Patent No. 4,491,025 issued to J.E. Smith, et al. of January 1, 1985 and Re. 31,450 to J.E, Smith of February 11, 1982. These flow meters have one or more flow tubes of different configurations. Each conduit configuration may be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial and coupled modes. In a typical Coriolis mass flovi' measurement apphcation, a conduit configuration is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. The vibrational modes of the material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flow meter from a connected pipeline on the inlet side of the flow meter. The material is then directed thi-ough the flow tube or flow tubes and exits the flow meter to a pipeline connected on the outlet side. A driver applies a force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing tlirough the flow meter, allpoints along a flow tube oscillate with an identical phase, As a material begins to flow tln'ough the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed at different points on the flow tube to p]-oduce sinusoidal signals representative of the motion of the flow tube at the different points. The phase difference between the two sensor signak is proportional to the mass flow rate of tlie material flowing tlirough the flow tube or flow tubes, In one prior art approach either a Discrete Fourier Transform (DFT) or a Fast Fourier Transform (FFT) is used to determine the phase difference between the sensor signals. The phase difference, and a vibrational fi-equency response of the flow tube assembl}^, are used to obtain the mass flow rate. hi one prior art approach, an independent reference signal is used to determine a pickoff signal frequenc}', such as by using the frequency sent to the vibrational driver system, In another prior art approach, the vibrational response fi-equency generated by a pickoff sensor can be determined by centering to that frequency in a notch niter, wherein the prior art flowmeter attempts to keep the notch of the notch filter at the pickoff sensor fi-equency. This prior art teclmique works fairly well under quiescent conditions, where the flow material in the flowmeter is uniform and where the resulting pickoff signal fi-equency is relatively stable. However, the phase measurement of the prior art suffers when the flow material is not unifomi, such as in two-phase flows where the flow material comprises a liquid and a solid or where there are air bubbles in the liquid flow material. In such situations, the prior art determined fi-equency can fluctuate rapidly. During conditions of fast and large fi-equency t-ansitions, it is possible for the pickoff signals to move outside the filter bandwidth, yielding incon-ect phase and frequency measurements. This also is a problem in empty-full-empty batcliing, where the flow meter is repeatedly operated in alternating empty and full conditions. Also, if the fi-equency of the sensor moves rapidly, a demodulation process will not be able to keep up with the actual or measured frequency, causing demodulation at an incorrect fi-equency. It should be understood that if the deten-nined frequency is incon-ect or inaccurate, then subsequentiy derived values of density, volume flow rate, etc., will also be incorrect and inaccurate. Moreover, the en-or can be compounded in subsequent flow characteristic detemiinations. In the prior art, the pickoff signals can be digitized and digitally manipulated in order to implement the notch filter. The notch filter accepts only a nan-ow band of fi-equencies. Therefore, when the target frequency is changing, the notch filter may not be able to fack the target signal for a period of time. Typically, the digital notch filter implementation takes 1-2 seconds to track to the fluctuating target signal, Due to the time required by the prior art to determine the fi-equency, the result is not only that the frequency and phase detenninations contain eiTors, but also that the eiTor measurement encompasses a time span that exceeds the time span during which the eiTor and/or two-phase flow actually occur. This is due to the relative slowness of response of a notch filter implementation. The result is that the prior art flowmeter cannot accurately, quickly, or satisfactorily track or detemiine a pickoff sensor frequency during two-phase flow of the flow material in the flovvineter. Consequently, the phase determination is likewise slow and eiTor prone, as the prior art derives the phase difference using the detemiined pickoff fi'equency. Therefore, an}^ eiror in tlie frequency detemiination is compounded in the phase determination, The result is increased en'or in the frequency deteimiination and in the phase detemiination, leading to increased error in determining the mass flow rate. In addition, because the detemiined frequency value is used to determine a density value (densit)^ is approximately equal to one over fi-equency squared), an eiTor in the frequency determination is repeated or compounded in the density determination. This is also true for a detennination of volume flow rate, where the volume flow rate is equal to mass flow rate divided by density. Because the phase difference can be derived using the determined fi-equency, an improved fi-equency determination can provide a fast and rehable phase difference detemiination. Summary of the Solution The above and other problems are solved and an advance in the art is achieved through the provision of meter electi-onics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter. Meter electi-onics for deteimiiiing a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention. The meter electi-onics comprises an interface for receiving the first sensor signal and the second sensor signal and a processing system in communication with the interface. The processing system is configured to receive the first sensor signal and the second sensor signal, generate a ninet}' degree phase shift from the first sensor signal, and compute a fi-equency from the first sensor signal and the ninety degi-ee phase shift. The processing system is further configured to generate sine and cosine signals using the frequency, and quadrature demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference, A method for detennining a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention. The method comprises receiving the first sensor signal and the second sensor signal, generating a ninet}' degree phase shift from the first sensor signal, and computing a frequency from the first sensor signal and the ninety degree phase shift. The method further comprises generating sine and cosine signals using the frequency. The method further comprises quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals in order to detemiine the phase difference. A method for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention, The method comprises receiving the first sensor signal and the second sensor signal, generating a ninety degree phase shift from the first sensor signal, and computing a frequency from the first sensor signal and the ninety degree phase shift. The method further comprises generating sine and cosine signals using the fi-equency. The method frirther comprises quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal. The method further comprises filtering the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-correlating the first demodulated signal and the second demodulated signal in order to detemiine the phase difference. Aspects of the Invention In one aspect of the meter electronics, the processing system is further configured to compute one or more of a mass flow rate, a density, or a volume flow rate using one or more of the frequency and the phase difference. hi one aspect of the meter elecfronics, the processing system is further configured to compute the ninety degree phase shift using a Hilbert transfonii. hi yet another aspect of the meter electronics, the quadrature demodulation generates a first demodulated signal and a second demodulated signal and the processing system is further configured to filter the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross- correlate the first demodulated signal and ttie second demodulated signal in order to detemiine tlie phase difference. In one aspect of the method, the method further comprises computing one or more of a mass flow rate, a density, or a volume flow rate using one or more of the fi-equency and the phase difference. In anotlier aspect of the method, the method further comprises computing the ninety degree phase shift using a Hilbert transform. In yet another aspect of the method, the quadrature demodulation generates a first demodulated signal and a second demodulated signal and the quadrature demodulation further comprises filtering the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-coiTelating the first demodulated signal and the second demodulated signal in order to deteiinine the phase difference. Description of the Drawings The same reference number represents the same element on all drawings. FIG. 1 illustrates a Coriolis flow meter in an example of the invention. FIG. 2 shows meter elecfronics according to an embodiment of the invention. FIG. 3 is a block diagi-ani of a portion of a processing system according to an embodiment of the invention. FIG. 4 shows detail of a Hilbert transform block according to an embodiment of the invention, FIG. 5 is a block diagram of a frequency portion of an analysis block according to an embodiment of the invention. FIG. 6 is a block diagram of a phase difference portion of the analysis block accordmg to an embodiment of the invention. FIG. 7 is a flowchart of a phase difference quadrature demodulation method according to an embodiment of the invention, Detailed Description of the Invention FIGS. 1-7 and the following description depict specific examples to teach those sldlled in the art how to make and use the best mode of the invention. For the puipose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall withm the scope of the invention, Those skilled in' the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. FIG. I shows a Coriolis flow meter 5 comprising a meter assembly 10 and meter electronics 20. Meter assembly 10 responds to mass flow rate and density of a process material. Meter electronics 20 is connected to meter assembly 10 via leads 100 to pro\'ide density, mass flow rate, and temperature information over path 26, as well as other information not relevant to the present invention. A Coriolis flow meter structure is described although it is apparent to those skilled in the art that the present invention could be practiced as a vibrating txibe densitometer without the additional measurement capability provided by a Coriolis mass flow meter. Meter assembly 10 includes a pair of manifolds 150 and 150', flanges 103 and 103'having flange necks 110 and 110', a pair of parallel flow tubes 130 and 130', drive mechanism 180, temperature sensor 190, and a pair of velocity sensors 170L and 170R. Flow tubes 130 and 130' have two essentially straight inlet legs 131 and 131' and outlet legs 134 and 134' which converge towards each other at flow tube mounting blocks 120 and 120'. Flow tubes 130 and 130' bend at two symmetrical locations along their length and are essentially parallel tliroughout their length. Brace bars 140 and 140' serve to define the axis W and W about which each flow tube oscillates. The side legs 131, 131' and 134, 134' of flow tubes 130 and 130' are fixedly attached to flow tube mounting blocks 120 and 120' and these blocks, in turn, are fixedly attached to manifolds 150 and 150'. This provides a continuous closed material path through Coriolis meter assembly 10. Wlien flanges 103 and 103', having holes 102 and 102' are connected, via inlet end 104 and outlet end 104' into a process line (not shown) which canies the process material that is being measured, material enters end 104 of the meter tlirough an orifice 101 in flange 103 is conducted tlirough manifold 150 to flow tube mounting block 120 having a surface 121, Within manifold 150 the material is divided and routed tlirough flow tubes 130 and 130', Upon exiting flow tubes 130 and 130', the process material is recombined in a single stream wifliin manifold 150' and is thereafter routed to exit end 104' connected by flange 103' having boh holes 102' to the process line (not shovvTi). Flow tubes 130 and 130' are selected and appropriately mounted to the flow tube mounting blocks 120 and 120' so as to have substantially the same mass distribution, moments of inertia and Young's modulus about bending axes W--W and W'--W', respectively. These bending axes go tlirough brace bars 140 and 140'. Inasmuch as the Young's modulus of the flow tubes change with temperature, and this change affects the calculation of flow and density, resistive temperature detector (RTD) 190 is mounted to flow tube 130', to continuously measure the temperature of the flow^ tube. The temperature of the flow tube and hence the voltage appearing across the RTD for a given cun-ent passing therethrough is governed by the temperature of the material passing thi'ough the flow tube. The temperature dependent voltage appearing across the RTD is used in a well ICDOMTI method by meter electronics 20 to compensate for the change in elastic modulus of flow tubes 130 and 130' due to any changes in flow tube temperature. The RTD is comiected to meter elecfronics 20 by lead 195. Both flow tubes 130 and 130' are driven by driver 180 in opposite directions about their respective bending axes W and W and at what is tenned the first out-of-phase bendmg mode of the flow meter. This drive mechanism 180 may comprise any one of many well Icnown aixangements, such as a magnet mounted to flow tube 130' and an opposing coil mounted to flow tube 130 and tln'ough which an alternating current is passed for vibrating both flow tubes. A suitable drive signal is applied by meter electronics 20, via lead 185, to drive mechanism 180. Meter electronics 20 receives the RTD temperature signal on lead 195, and the left and right velocity signals appearing on leads 165L and 165R, respectively. Meter electronics 20 produces the drive signal appearing on lead 185 to drive element ISO and vibrate tubes 130 and 130'. Meter elechonics 20 processes the left and right velocity signals and the RTD signal to compute the mass flow rate and the density of the material passing thi-ough meter assembly 10. This information, along with other information, is applied by meter electronics 20 over path 26 to utilization means 29. FIG. 2 shows meter electronics 20 according to an embodiment of the invention. The meter elech-onics 20 can include an interface 201 and a processing system 203. The meter electi-onics 20 receives first and second sensor signals 210 and 211 from the meter assembly 10, such as pickoff/velocity sensor signals. The meter electronics 20 can operate as a mass flow meter or can operate as a densitometer, including operating as a Coriolis flow meter. The meter elect'onics 20 processes the first and second sensor signals 210 and 211 in order to obtain ilovi' characteristics of the flow material flowing through the meter assemblj' 10, For example, the meter electronics 20 can determine one or more of a phase difference, a frequenc}', a time difference (At), a density, a mass flow rate, and a volume flow rate from the sensor signals, for example. In addition, other flow characteristics can be determined according to the invention. The detemiinations are discussed below. The phase difference determination and the fi-equency detei-niination are much faster and more accurate and reliable than such determinations in the prior art. This advantageously reduces the processing time required in order to compute the flow characteristics and increases the accuracy of both flow characteristics. Consequently, both the frequency and the phase difference can be determined much faster than in the prior art. The prior art frequency deteniiination methods typically take 1-2 seconds to perform. In conti-ast, the fi.-equency determination according to the invention can be perfomied in as little as 50 milliseconds (ms), Even faster frequency determination is contemplated, depending on the type and configuration of the processing S3^stem, the sampling rate of the vibrational response, the filter sizes, the decimation rates, etc. At the 50 ms frequency detemiination rate, the meter electi-onics 20 according to the invention can be about 40 times faster than the prior art. The interface 201 receives the sensor signal from one of the velocity sensors 170L and 170R via the leads 100 of FIG. 1. The interface 201 can perfoiTn any necessar}' or desired signal conditioning, such as any manner of formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning can be performed in the processing system 203. In addition, the interface 201 can enable communications between the meter electi-onics 20 and external devices. The interface 201 can be capable of any manner of electronic, optical, or wireless communication, The interface 201 in one embodiment is coupled with a digitizer 202, wherein the sensor signal comprises an analog sensor signal. The digitizer 202 samples and digitizes the analog sensor signal and produces a digital sensor signal. The digitizer 202 can also perform any needed decimation, wherein the digital sensor signal is decimated in order to reduce the amount of signal processing needed and to reduce the processing time. The decimation will be discussed in more detail below. The processing system 203 conducts operations of the meter electronics 20 and processes flow measurements from the flow meter assembly 10, The processing system 203 executes one or more processing routines and thereb}' processes the flow measurements in order to produce one or more flow characteristics. The processing system 203 can comprise a general purpose computer, a microprocessing system, a logic circuit, or some other general pmpose or customized processing device. The processing system 203 can be distributed among multiple processing devices. The processing system 203 can include any manner of integral or independent electronic storage medium, sucli as the storage system 204. The processing system 203 processes the first sensor signal 210 and the second sensor signal 211 in order to determine one or more flow characteristics. The one or more flow characteristics can include a phase difference, a frequency, a time difference (At), a mass flow rate, and/or a density' for the flow material, for example. In the embodiment shown, the processing system 203 determines the flow characteristics from the tv^'o sensor signals 210 and 211 and a single 90 degi-ee phase shift 213. The processing system 203 can detemiine at least the phase difference and the fi-equency from the two sensor signals 210 and 211 and the single 90 degi-ee phase shift 213. In addition, the processing system 203 can further determine a phase difference, a time difference (At), and/or a mass flow rate for the flow material, among other things. The storage system 204 caii store flow meter parameters and data, software routines, constant values, and variable values. In one embodiment, the storage system 204 includes routines that are executed by the proces_sing system 203. In one embodiment, the storage system 204 stores a phase shift routine 212, a phase difference routine 215, a frequency routine 216, a time difference (At) routine 217, and a flow characteristics routine 218. In one embodiment, the storage system 204 stores variables used to operate a flow meter, such as the Coriolis flow meter 5. The storage system 204 in one embodiment stores variables such as the first sensor signal 210 and the second sensor signal 211, which are received from the velocity/pickoff sensors 170L and 170R. In addition, the storage system 204 can store a 90 degree phase shift 213 that is generated in order to determine the flow characteristics. In one embodiment, the storage system 204 stores one or more flow characteristics obtained from the flow measurements. The storage system 204 in one embodiment stores flow characteristics such as a phase difference 220, a frequency 221, a time difference (At) 222, a mass flow rate 223, a density 224, and a volume flow rate The phase shift routine 212 performs a 90 deg:i-ee phase shift on an input signal, i.e., on the sensor signal 210, The phase slaift routine 212 in one embodiment implements a Hilbert ti-ansform (discussed below). The phase difference routine 215 determines a phase difference using quadrature demodulation. Additional information can also be used in order to compute the phase difference. The phase difference in one embodiment is computed from the first sensor signal 210, the second sensor signal 211, and the frequency 221. The detennined phase difference can. be stored in the phase difference 220 of the storage system 204. The phase difference, when deteimined using the dstemiined fT"equency 221, can be calculated and obtained much faster than in the prior art. This can provide a critical difference in flow meter applications having high flow rates or where multi-phase flows occur. The fi-equency routine 216 determines a frequency (such as that exhibited by either the first sensor signal 210 or the second sensor signal 211) fi-om the 90 degree phase shift 213. The detennined frequency can be stored in the frequency 221 of the storage system 204. The fi-equency, when determined fi'om the single 90 degree phase shift 213 and the sensor signal 210 or 211, can be calculated and obtained much faster than in the prior art. This can provide a critical difference in flow meter applications having high flow rates or where multi-phase flows occur. The time difference (At) routine 217 deteimiines a time difference (At) between the first sensor signal 210 and the second sensor signal 211, The time difference (At) can be stored in the time difference (At) 222 of the storage system 204, The time difference (At) comprises substantially the determined phase divided by the determined fi-equency, and is therefore used to detemiine the mass flow rate. The floM' characteristics routine 218 can detemiine one or more flow characteristics. The flow characteristics routine 218 can use the determined phase difference 220 and the determined fi-equency 221, for example, in order to accomplish these additional flow characteristics. It should be understood that additional information may be required for these determinations, such as the mass flow rate or density, for example. The flow characteristics routine 218 can detemiine a mass flow rate fi'oni the time difference (At) 222 and therefore fi-om the phase difference 220 and the fi-equsncy 221. The fomiula for determining mass flow rate is given in U.S. Patent No. 5,027,662 to Titlow et al., and is incoiporated herein by reference. The mass flow rate is related to the mass flow of flow material in the meter assembly 10. Likewise, the flow-characteristics routine 218 can also detemiine the density 224 and/or the volume flow rate 225. The determined mass flow rate, density, and volume flow rate can be stored in the mass flow rate 223, the density 224, and the volume 225 of the storage system 204, respectively. In addition, the flow characteristics can be transmitted to external devices by the meter electi'onics 20. FIG. 3 is a block diagram 300 of a portion of the processing system 203 according to an embodiment of the invention. In the figure, the blocks represent either processing circuity or processing actions.^routines. The block diagram 300 includes a stage 1 filter block 301, a stage 2 filter block 302, a Hilbert ti-ansforai block 303, and an analysis block 304. The LPO and RPO inputs comprise the left pickoff signal input and the light pickoff signal input. Either the LPO or the RPO can comprise a first sensor signal. In one embodiment, the stage 1 filter block 301 and the stage 2 filter block 302 comprise digital Finite Impulse Response (FIR) polyphase decimation filters, implemented in the processing system 203. These filters provide an optimal method for filtering and decimating one or both sensor signals, with the filtering and decimating . being perfomied at the same clii'onological tune and at the same decimation rate. Alternatively, the stage 1 filter block 301 and the stage 2 filter block 302 can comprise Infinite Impulse Response (IIR) filters or other suitable digital filters or filter processes. However, it should be understood that other filtering processes and/or filtering embodiments are contemplated and are within the scope of the description and claims. FIG. 4 shows detail of the Hilbert transfoim block 303 according to an enibodimeiit of the invention. In the embodiment shown, the Hilbert transform block 303 includes a LPO delay block 401 in parallel with a LPO filter block 402. The LPO delay block 401 introduces a sampling dela}', The LPO delay block 401 therefore selects LPO digital signal samples that are chi-onologically later in time that the LPO digital signal samples that are filtered by the LPO filter block 402. The LPO filter block 402 performs a 90 degi'ee phase shift on the inputted digital signal samples. The Hilbert fransform block 303 is a first step to providing the phase measurement. The Hilbert ti'ansform block 303 receives the filtered, decimated LPO and RPO signals and perfomis a Plilbert hansfonn. The Hilbert hansfonn produces 90 degree phase-shifted versions of the LPO signal. The output of the Hilbert transform block 303 therefore provides the new quadrature (Q) component LPO Q, along with the original, in-phase (I) signal components LPO I. The input to the Hilbert transform block 303 can be represented as: LPO^A,^^oos{cot) (1) Using the Hilbert transfomi the output becomes; LPO^nten = 4.0 sin(^0 (2) Combining the original terms with the output of the Hilbert transform yields: iPO- 4,Jcos(^0 + ?sm(a;0]- 4..^'"'"' (3) FIG. 5 is a block diagram of a frequency portion 500 of the analysis block 304 according to an embodiment of the invention. The analysis block 304 in the embodiment shown is the final stage of the frequency and delta T (At) measurements. In the embodiment shown, the frequency portion 500 determines a frequency from the in-phase (I) and quadrature (Q) components of a single sensor signal. The frequency portion 500 can operate on either the left or right pickoff signal (LPO or RPO). In the embodiment shown, the frequency portion 500 operates on the LPO signal. The frequency portion 500 in the embodiment shown includes a join block 501, a complex conjugate block 502, a sampling block.503, a complex multiplication block 504, a-filter ■ block 505, a phase angle block 506, a constant block 507, and a division block 508. The join block 501 receives both in-phase (I) and quadrature (Q) components of a sensor signal and passes thsm on. Tlie conjugate block 502 performs a complex conjugate on a sensor signal, here the LPO signal. The delay block 503 introduces a sampling delay aild tlierefore selects a digital signal sample that is clironologically older in time. This older digital signal sample is multiplied v,dth the cuiTent digital signal in the complex multiplication block 504. The complex multiplication block 504 multiplies the LPO signal and the LPO conjugate signal, implementing equation (4) below, The filter block 505 implements a digital filter, such as the FIR filter previousl}-' discussed. The filter block 505 can comprise a polyphase decimation filter that is used to remove hamionic content from the in-phase (Ij and quadrature (Q) components of the sensor signal, as well as to decimate the signal. The filter coefficients can be chosen to provide decimation of the inputted signal, such as decimation by a factor of 10, for example. The phase angle block 506 detemiines a phase angle from the in-phase (I) and quadratLire (Q) components of the LPO signal. The phase angle block 506 implements a portion of equation (5) below. The constant block 507 supplies a factor comprising a sample rate Fj divided by two pi (TI), as shov.ti in equation (6). The division block 508 performs the division operation of equation (6). The frequency processing implements the following equation: LPO,.-, X LPO,, = -V^''""' X Koe'""" = A'l.oe^'^'-^'-^ (4) The angle between two consecutive samples is therefore; (5) cot-cot _^ = tan"' siiiUot - cot_^) cos{cot - coi_^) which is the radian frequency of the left pick-off Converting to liz: r ^ icvt-cot_JxFs ,,. Here "Fs" is the rate of the Hilben transform block 303. In the example previously discussed, "Fs" is about 2 IcHz, FIG. 6 is a block diagram of a phase difference portion 600 of the analysis block 304 according to an embodiment of the invention. The phase difference portion 600 13 outputs a phase difference bet-ween the LPO input signal and the RPO input signal. The phase difference portion 600 can be included in the analysis block 304 along with the fi-equenc3' portion 500 of FIG. 5. In the figure, the blocks represent either processing circuitry or processing actions/routines. The phase difference portion 600 includes a modulation generator block 601, a join block 602, real-to-complex blocks 604 and 605, quadrature demodulation blocks 608 and 609, decimation blocks 610 and 611, a conjugate block 612, and a correlation block 614, The modulation generator block 601 generates sin and cosine terms fi-om the radian frequency value (©) that is output by the frequency portion 500. The modulation generator block 601 therefore receives a frequency reference fi'oni the fi-equency portion 500, Because the fi-equency portion 500 can be obtained much faster and more reliably than in the prior art, consequently the phase difference determination can be also obtained much faster and more reliably than in the prior art. The sin and cosine terms comprise in-pliase (I) and quadrature (Q) components of the fi-equency reference. The sin and cosine terms generated by the modulation generator block 601 are inputted into the join block 602, The join block 602 receives the in-phase (I) and quadrature (Q) components fi-om the modulation generator block 601. The join block 602 j oins the in-phase (I) and quadrature (Q) components and passes them on to the quadrature demodulation blocks 608 and 609. The real-to-complex blocks 604 and 605 generate imaginary (i.e., quadrature) components of the LPO and RPO input signals. The resulting in-phase (real) and quadrature (imaginary) components comprise sinusoids that includes both sine and cosine components. The real-to-complex blocks 604 and 605 pass the resulting in-phase (real) and quadrature (imaginar)') components of both sigi:als to the con-esponding quadrature demodulation blocks 608 and 609. The quadrature demodulation blocks 608 and 609 demodulate the LPO signal and the RPO signal using the sinusoids. The demodulation generates a first demodulated sigiial and a second demodulated signal, hi addition, this demodulation produces a zero fi-equency component and a high fi-equency component for each of the LPO and the PJO, The high fi-equency component is later removed (see belovv-'). The output of the quadrature demodulation blocks 608 and 609 are passed to the decimation blocks 610 and 611, respectively. The decimation blocks 610 and 611 can decimate the LPO and the RPO quadrature demodulation signals. For example, the decimation blocks 610 and 61 i can decimate these two signals by a factor of about 10, for example. In addition, the decimation blocks 610 and 611 can perform any desired filtering of the demodulation signals. For example, in one embodiment the decimation blocks 610 and 611 can comprise a polyphase decimation filter that is used to remove hannonic content (i.e., the high fi-equency components) fi-om the in-phase (I) and quadrature (Q) components of the sensor signal, as well as to decimate the signal. The filter coefficients can be chosen to provide decimation of the inputted signal, such as decimation by a factor of 10, for example. The decimation blocks 610 and 611 pass the demodulated RPO signal to the conjugate block 612 and pass the demodulated LPO signal to the coiTelation block 614. The conjugate block 612 performs a complex conjugate on tlie demodulated RPO signal. The conjugate block 612 passes the conjugated demodulated RPO signal to the coirelation block 614. The correlation block 614 coirelates the demodulated LPO and RPO signals. The conjugation operation followed by the coiTelation comprises a cross-coiTelation operation, The complex correlation can comprise a multiplication that produces a result shown in equations (17) and (18). As a result, the correlation block 614 produces the phase difference (or phase angle) value. The detennined phase difference can be used to deteiTiiine various flow characteristics. Because of the two separate quadrature demodulation processes shown in FIG. 6, the phase difference portion 600 can also be refeired to as a quadrature demodulation chain. FIG. 7 is a flowchart 700 of a phase difference quadrature demodulation method according to an embodiment of the invention. In step 701, the first and second sensor sigiials are received. In step 702, a 90 degi-se phase shift is generated for one of the first or second sensor signals. In step 703, a frequency (f) is determined from the 90 degi-ee phase shift and the coiresponding sensor signal. The frequency (f) can be represented as a radian frequency: The determined frequency (fj can be used to determine flow characteristics. The deteniiined frequency (f) can also be used to determine a phase difference between the first and second sensor signals, such as by using the QD chain method described above. In step 704, a reference signal (WK) is created. The reference signal (W,^) comprises a sine and cosine signal The reference S]gnals(WK) have the same frequency as the LPO and RPO signals, The radian frequency co is operated on by a modulation generator in order to recursively generate the sinusoid demodulation reference signals (Wi£), comprising: In step 705, the sensor signal XLPQ is demodulated with the reference signals W^. The demodulation comprises mixing or multiplying the sensor signal XLPO with the reference signals W^ in order to produce a demodulated LPO signal. In step 706, the sensor signal XRPO is demodulated with the reference signals W\|^. The demodulation comprises mixing or multiplying the sensor signal XRPO with the reference signals W^ in order to produce a demodulated RPO signal. As a result, the demodulated signals at the output of the quadrature demodulation blocks 608 and 609 comprise: In step 707, the demodulated signals are filtered in order to remove high frequency terms. These high frequency terms from the quadrature demodulation comprise the [exp(-j(2oDlc+ 16 embodiment, the filtering can comprise an (I, Q) decimation X 40 dual cascade of decimation filters, The output of this filtering is represented by; > In step 70S, one of the demodulated signals (such as the demodulated RPO signal in FIG. 6), is conjugated. The conjugation operation forms a negative of the imaginaiy signal. In step 709, the filter outputs are con-elated by a complex coirelation stage. The conjugation and con^elation steps of the complex con-elation operation yield: The phase difference is therefore output. The meter electronics and method for detenninmg a phase difference between a first sensor signal and a second sensor signal of a flow meter according the invention can be implemented according to any of the embodiments in order to obtain several advantages, if desired. The invention can compute a phase difference from a determined frequency and the first and second sensor signals. The invention can provide a phase difference detennination of greater accuracy' and reliability. The invention can provide a phase difference determination faster than the prior art and while consuming less processing time. We claim: 1, Meter electronics (20) for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter, comprising: an interface (201) for receiving a first sensor signal and a second sensor signal; and a processing S3'stem (203) in communication with the interface (201) and configured to receive the first sensor signal and the second sensor signal, generate a ninety degi-ephase shift looms the first sensor signal, compute a frequency from the first sensor signal and the ninety degree phase shift, generate sine and cosine signals using the Quincy, and quadrature demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference. 2, The meter electronics (20) of claim 1, with the processing system (203) being further configured to compute one or more of a mass flow rate, a density, or a volume flow rate using one or more of the piquancy and the phase difference. 3, The meter elecfonics (20) of claim 1, with the processing system (203) being further configured to compute the ninety degree phase shift using a Hilbert transform. 4, The meter electronics (20) of claim 1, wherein the quadrature demodulation generates a first demodulated signal and a second demodulated signal and with the processing system (203) being further configured to filter the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-correlate the first demodulated signal and the second demodulated signal in order to determine the phase difference. 5, A method for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter, the method comprising: generating a ninety degree phase shift food the first sensor signal; computing a frequency from the first sensor signal and the ninety devisee phase shift; generating sine and cosine signals using the frequency; and quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals in order to deteimine the phase difference. 6. The method of claim 5, further comprising computing one or more of a mass flow rate, a density, or a volume flow rate using one or more of the frequent}' and the phase difference. 7. The method of claim 5, further comprising computing the ninety degree phase shift using a Hilbert transform. 8. The method of claim 5, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal, and with the quadrature demodulating further comprising: filtering the first demodulated signal and the second demodulated signal in order to remove high fi'equency components; and cross-capitulating the first demodulated signal and the second demodulated signal in order to determine the phase difference. 9. A method for determining a phase difference between a first sensor and a second sensor signal of a flow meter, the method comprising: receiving the first sensor signal and the second sensor signal; generating a ninety degree phase shift from the first sensor signal; computing a frequency from the first sensor signal and the ninety degage phase shift; generating sine and cosine signals using the frequency; quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal; filtering the first demodulated signal and the second demodulated signal in order to remove high fi'equency components; and cross-correlating the first demodulated signal and the second demodulated signal in order to determine the phase difference, 10. The method of claim 9, further comprising computing one or more of a mass flow rate, a density, or a volume flow rate using one or more of the frequency and the phase difference, 11. The method of claim 9, further comprising computing the ninety devisee phase shift using a Hilbert inform.

Full Text

METER ELECTRONICS AND METH0DS FOR DETERTIMIINING A PHASE
DIFFERENCE BETWEEN A FIRST SENSOR SIGNAL AND A SECOND
SENSOR SIGNAL OF A FLOW ISIETER
Background of the Invention
1. Field of the Invention
The present invention relates to meter electronics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter.
2. Statement of the Problem
It is known to use Coriolis mass flow meters to measure mass flow, density and volume flow and other information of materials through a pipeline as disclosed in U.S. Patent No. 4,491,025 issued to J.E. Smith, et al. of January 1, 1985 and Re. 31,450 to J.E, Smith of February 11, 1982. These flow meters have one or more flow tubes of different configurations. Each conduit configuration may be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial and coupled modes. In a typical Coriolis mass flovi' measurement apphcation, a conduit configuration is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit.
The vibrational modes of the material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flow meter from a connected pipeline on the inlet side of the flow meter. The material is then directed thi-ough the flow tube or flow tubes and exits the flow meter to a pipeline connected on the outlet side.
A driver applies a force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing tlirough the flow meter, allpoints along a flow tube oscillate with an identical phase, As a material begins to flow tln'ough the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed at different points on the flow tube to p]-oduce sinusoidal signals representative of the motion of the flow tube at the different points. The phase difference between the

two sensor signak is proportional to the mass flow rate of tlie material flowing tlirough the flow tube or flow tubes, In one prior art approach either a Discrete Fourier Transform (DFT) or a Fast Fourier Transform (FFT) is used to determine the phase difference between the sensor signals. The phase difference, and a vibrational fi-equency response of the flow tube assembl}^, are used to obtain the mass flow rate.
hi one prior art approach, an independent reference signal is used to determine a pickoff signal frequenc}', such as by using the frequency sent to the vibrational driver system, In another prior art approach, the vibrational response fi-equency generated by a pickoff sensor can be determined by centering to that frequency in a notch niter, wherein the prior art flowmeter attempts to keep the notch of the notch filter at the pickoff sensor fi-equency. This prior art teclmique works fairly well under quiescent conditions, where the flow material in the flowmeter is uniform and where the resulting pickoff signal fi-equency is relatively stable. However, the phase measurement of the prior art suffers when the flow material is not unifomi, such as in two-phase flows where the flow material comprises a liquid and a solid or where there are air bubbles in the liquid flow material. In such situations, the prior art determined fi-equency can fluctuate rapidly. During conditions of fast and large fi-equency t-ansitions, it is possible for the pickoff signals to move outside the filter bandwidth, yielding incon-ect phase and frequency measurements. This also is a problem in empty-full-empty batcliing, where the flow meter is repeatedly operated in alternating empty and full conditions. Also, if the fi-equency of the sensor moves rapidly, a demodulation process will not be able to keep up with the actual or measured frequency, causing demodulation at an incorrect fi-equency. It should be understood that if the deten-nined frequency is incon-ect or inaccurate, then subsequentiy derived values of density, volume flow rate, etc., will also be incorrect and inaccurate. Moreover, the en-or can be compounded in subsequent flow characteristic detemiinations.
In the prior art, the pickoff signals can be digitized and digitally manipulated in order to implement the notch filter. The notch filter accepts only a nan-ow band of fi-equencies. Therefore, when the target frequency is changing, the notch filter may not be able to fack the target signal for a period of time. Typically, the digital notch filter implementation takes 1-2 seconds to track to the fluctuating target signal, Due to the time required by the prior art to determine the fi-equency, the result is not only that the

frequency and phase detenninations contain eiTors, but also that the eiTor measurement encompasses a time span that exceeds the time span during which the eiTor and/or two-phase flow actually occur. This is due to the relative slowness of response of a notch filter implementation.
The result is that the prior art flowmeter cannot accurately, quickly, or satisfactorily track or detemiine a pickoff sensor frequency during two-phase flow of the flow material in the flovvineter. Consequently, the phase determination is likewise slow and eiTor prone, as the prior art derives the phase difference using the detemiined pickoff fi'equency. Therefore, an}^ eiror in tlie frequency detemiination is compounded in the phase determination, The result is increased en'or in the frequency deteimiination and in the phase detemiination, leading to increased error in determining the mass flow rate. In addition, because the detemiined frequency value is used to determine a density value (densit)^ is approximately equal to one over fi-equency squared), an eiTor in the frequency determination is repeated or compounded in the density determination. This is also true for a detennination of volume flow rate, where the volume flow rate is equal to mass flow rate divided by density.
Because the phase difference can be derived using the determined fi-equency, an improved fi-equency determination can provide a fast and rehable phase difference detemiination. Summary of the Solution
The above and other problems are solved and an advance in the art is achieved through the provision of meter electi-onics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter.
Meter electi-onics for deteimiiiing a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention. The meter electi-onics comprises an interface for receiving the first sensor signal and the second sensor signal and a processing system in communication with the interface. The processing system is configured to receive the first sensor signal and the second sensor signal, generate a ninet}' degree phase shift from the first sensor signal, and compute a fi-equency from the first sensor signal and the ninety degi-ee phase shift. The processing system is further configured to generate sine and cosine signals using the

frequency, and quadrature demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference,
A method for detennining a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention. The method comprises receiving the first sensor signal and the second sensor signal, generating a ninet}' degree phase shift from the first sensor signal, and computing a frequency from the first sensor signal and the ninety degree phase shift. The method further comprises generating sine and cosine signals using the frequency. The method further comprises quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals in order to detemiine the phase difference.
A method for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter is provided according to an embodiment of the invention, The method comprises receiving the first sensor signal and the second sensor signal, generating a ninety degree phase shift from the first sensor signal, and computing a frequency from the first sensor signal and the ninety degree phase shift. The method further comprises generating sine and cosine signals using the fi-equency. The method frirther comprises quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal. The method further comprises filtering the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-correlating the first demodulated signal and the second demodulated signal in order to detemiine the phase difference. Aspects of the Invention
In one aspect of the meter electronics, the processing system is further configured to compute one or more of a mass flow rate, a density, or a volume flow rate using one or more of the frequency and the phase difference.
hi one aspect of the meter elecfronics, the processing system is further configured to compute the ninety degree phase shift using a Hilbert transfonii.
hi yet another aspect of the meter electronics, the quadrature demodulation generates a first demodulated signal and a second demodulated signal and the processing system is further configured to filter the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-

correlate the first demodulated signal and ttie second demodulated signal in order to detemiine tlie phase difference.
In one aspect of the method, the method further comprises computing one or more of a mass flow rate, a density, or a volume flow rate using one or more of the fi-equency and the phase difference.
In anotlier aspect of the method, the method further comprises computing the ninety degree phase shift using a Hilbert transform.
In yet another aspect of the method, the quadrature demodulation generates a first demodulated signal and a second demodulated signal and the quadrature demodulation further comprises filtering the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-coiTelating the first demodulated signal and the second demodulated signal in order to deteiinine the phase difference. Description of the Drawings
The same reference number represents the same element on all drawings.
FIG. 1 illustrates a Coriolis flow meter in an example of the invention.
FIG. 2 shows meter elecfronics according to an embodiment of the invention.
FIG. 3 is a block diagi-ani of a portion of a processing system according to an embodiment of the invention.
FIG. 4 shows detail of a Hilbert transform block according to an embodiment of the invention,
FIG. 5 is a block diagram of a frequency portion of an analysis block according to an embodiment of the invention.
FIG. 6 is a block diagram of a phase difference portion of the analysis block accordmg to an embodiment of the invention.
FIG. 7 is a flowchart of a phase difference quadrature demodulation method according to an embodiment of the invention, Detailed Description of the Invention
FIGS. 1-7 and the following description depict specific examples to teach those sldlled in the art how to make and use the best mode of the invention. For the puipose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall

withm the scope of the invention, Those skilled in' the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.
FIG. I shows a Coriolis flow meter 5 comprising a meter assembly 10 and meter electronics 20. Meter assembly 10 responds to mass flow rate and density of a process material. Meter electronics 20 is connected to meter assembly 10 via leads 100 to pro\'ide density, mass flow rate, and temperature information over path 26, as well as other information not relevant to the present invention. A Coriolis flow meter structure is described although it is apparent to those skilled in the art that the present invention could be practiced as a vibrating txibe densitometer without the additional measurement capability provided by a Coriolis mass flow meter.
Meter assembly 10 includes a pair of manifolds 150 and 150', flanges 103 and 103'having flange necks 110 and 110', a pair of parallel flow tubes 130 and 130', drive mechanism 180, temperature sensor 190, and a pair of velocity sensors 170L and 170R. Flow tubes 130 and 130' have two essentially straight inlet legs 131 and 131' and outlet legs 134 and 134' which converge towards each other at flow tube mounting blocks 120 and 120'. Flow tubes 130 and 130' bend at two symmetrical locations along their length and are essentially parallel tliroughout their length. Brace bars 140 and 140' serve to define the axis W and W about which each flow tube oscillates.
The side legs 131, 131' and 134, 134' of flow tubes 130 and 130' are fixedly attached to flow tube mounting blocks 120 and 120' and these blocks, in turn, are fixedly attached to manifolds 150 and 150'. This provides a continuous closed material path through Coriolis meter assembly 10.
Wlien flanges 103 and 103', having holes 102 and 102' are connected, via inlet end 104 and outlet end 104' into a process line (not shown) which canies the process material that is being measured, material enters end 104 of the meter tlirough an orifice 101 in flange 103 is conducted tlirough manifold 150 to flow tube mounting block 120 having a surface 121, Within manifold 150 the material is divided and routed tlirough flow tubes 130 and 130', Upon exiting flow tubes 130 and 130', the process material is recombined in a single stream wifliin manifold 150' and is thereafter routed to exit end 104' connected by flange 103' having boh holes 102' to the process line (not shovvTi).

Flow tubes 130 and 130' are selected and appropriately mounted to the flow tube mounting blocks 120 and 120' so as to have substantially the same mass distribution, moments of inertia and Young's modulus about bending axes W--W and W'--W', respectively. These bending axes go tlirough brace bars 140 and 140'. Inasmuch as the Young's modulus of the flow tubes change with temperature, and this change affects the calculation of flow and density, resistive temperature detector (RTD) 190 is mounted to flow tube 130', to continuously measure the temperature of the flow^ tube. The temperature of the flow tube and hence the voltage appearing across the RTD for a given cun-ent passing therethrough is governed by the temperature of the material passing thi'ough the flow tube. The temperature dependent voltage appearing across the RTD is used in a well ICDOMTI method by meter electronics 20 to compensate for the change in elastic modulus of flow tubes 130 and 130' due to any changes in flow tube temperature. The RTD is comiected to meter elecfronics 20 by lead 195.
Both flow tubes 130 and 130' are driven by driver 180 in opposite directions about their respective bending axes W and W and at what is tenned the first out-of-phase bendmg mode of the flow meter. This drive mechanism 180 may comprise any one of many well Icnown aixangements, such as a magnet mounted to flow tube 130' and an opposing coil mounted to flow tube 130 and tln'ough which an alternating current is passed for vibrating both flow tubes. A suitable drive signal is applied by meter electronics 20, via lead 185, to drive mechanism 180.
Meter electronics 20 receives the RTD temperature signal on lead 195, and the left and right velocity signals appearing on leads 165L and 165R, respectively. Meter electronics 20 produces the drive signal appearing on lead 185 to drive element ISO and vibrate tubes 130 and 130'. Meter elechonics 20 processes the left and right velocity signals and the RTD signal to compute the mass flow rate and the density of the material passing thi-ough meter assembly 10. This information, along with other information, is applied by meter electronics 20 over path 26 to utilization means 29.
FIG. 2 shows meter electronics 20 according to an embodiment of the invention. The meter elech-onics 20 can include an interface 201 and a processing system 203. The meter electi-onics 20 receives first and second sensor signals 210 and 211 from the meter assembly 10, such as pickoff/velocity sensor signals. The meter electronics 20 can operate as a mass flow meter or can operate as a densitometer, including operating as a

Coriolis flow meter. The meter elect'onics 20 processes the first and second sensor signals 210 and 211 in order to obtain ilovi' characteristics of the flow material flowing through the meter assemblj' 10, For example, the meter electronics 20 can determine one or more of a phase difference, a frequenc}', a time difference (At), a density, a mass flow rate, and a volume flow rate from the sensor signals, for example. In addition, other flow characteristics can be determined according to the invention. The detemiinations are discussed below.
The phase difference determination and the fi-equency detei-niination are much faster and more accurate and reliable than such determinations in the prior art. This advantageously reduces the processing time required in order to compute the flow characteristics and increases the accuracy of both flow characteristics. Consequently, both the frequency and the phase difference can be determined much faster than in the prior art.
The prior art frequency deteniiination methods typically take 1-2 seconds to perform. In conti-ast, the fi.-equency determination according to the invention can be perfomied in as little as 50 milliseconds (ms), Even faster frequency determination is contemplated, depending on the type and configuration of the processing S3^stem, the sampling rate of the vibrational response, the filter sizes, the decimation rates, etc. At the 50 ms frequency detemiination rate, the meter electi-onics 20 according to the invention can be about 40 times faster than the prior art.
The interface 201 receives the sensor signal from one of the velocity sensors 170L and 170R via the leads 100 of FIG. 1. The interface 201 can perfoiTn any necessar}' or desired signal conditioning, such as any manner of formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning can be performed in the processing system 203.
In addition, the interface 201 can enable communications between the meter electi-onics 20 and external devices. The interface 201 can be capable of any manner of electronic, optical, or wireless communication,
The interface 201 in one embodiment is coupled with a digitizer 202, wherein the sensor signal comprises an analog sensor signal. The digitizer 202 samples and digitizes the analog sensor signal and produces a digital sensor signal. The digitizer 202 can also perform any needed decimation, wherein the digital sensor signal is decimated in order

to reduce the amount of signal processing needed and to reduce the processing time. The decimation will be discussed in more detail below.
The processing system 203 conducts operations of the meter electronics 20 and processes flow measurements from the flow meter assembly 10, The processing system
203 executes one or more processing routines and thereb}' processes the flow
measurements in order to produce one or more flow characteristics.
The processing system 203 can comprise a general purpose computer, a microprocessing system, a logic circuit, or some other general pmpose or customized processing device. The processing system 203 can be distributed among multiple processing devices. The processing system 203 can include any manner of integral or independent electronic storage medium, sucli as the storage system 204.
The processing system 203 processes the first sensor signal 210 and the second sensor signal 211 in order to determine one or more flow characteristics. The one or more flow characteristics can include a phase difference, a frequency, a time difference (At), a mass flow rate, and/or a density' for the flow material, for example.
In the embodiment shown, the processing system 203 determines the flow characteristics from the tv^'o sensor signals 210 and 211 and a single 90 degi-ee phase shift 213. The processing system 203 can detemiine at least the phase difference and the fi-equency from the two sensor signals 210 and 211 and the single 90 degi-ee phase shift 213. In addition, the processing system 203 can further determine a phase difference, a time difference (At), and/or a mass flow rate for the flow material, among other things.
The storage system 204 caii store flow meter parameters and data, software routines, constant values, and variable values. In one embodiment, the storage system
204 includes routines that are executed by the proces_sing system 203. In one
embodiment, the storage system 204 stores a phase shift routine 212, a phase difference
routine 215, a frequency routine 216, a time difference (At) routine 217, and a flow
characteristics routine 218.
In one embodiment, the storage system 204 stores variables used to operate a flow meter, such as the Coriolis flow meter 5. The storage system 204 in one embodiment stores variables such as the first sensor signal 210 and the second sensor signal 211, which are received from the velocity/pickoff sensors 170L and 170R. In

addition, the storage system 204 can store a 90 degree phase shift 213 that is generated in order to determine the flow characteristics.
In one embodiment, the storage system 204 stores one or more flow characteristics obtained from the flow measurements. The storage system 204 in one embodiment stores flow characteristics such as a phase difference 220, a frequency 221, a time difference (At) 222, a mass flow rate 223, a density 224, and a volume flow rate
The phase shift routine 212 performs a 90 deg:i-ee phase shift on an input signal, i.e., on the sensor signal 210, The phase slaift routine 212 in one embodiment implements a Hilbert ti-ansform (discussed below).
The phase difference routine 215 determines a phase difference using quadrature demodulation. Additional information can also be used in order to compute the phase difference. The phase difference in one embodiment is computed from the first sensor signal 210, the second sensor signal 211, and the frequency 221. The detennined phase difference can. be stored in the phase difference 220 of the storage system 204. The phase difference, when deteimined using the dstemiined fT"equency 221, can be calculated and obtained much faster than in the prior art. This can provide a critical difference in flow meter applications having high flow rates or where multi-phase flows occur.
The fi-equency routine 216 determines a frequency (such as that exhibited by either the first sensor signal 210 or the second sensor signal 211) fi-om the 90 degree phase shift 213. The detennined frequency can be stored in the frequency 221 of the storage system 204. The fi-equency, when determined fi'om the single 90 degree phase shift 213 and the sensor signal 210 or 211, can be calculated and obtained much faster than in the prior art. This can provide a critical difference in flow meter applications having high flow rates or where multi-phase flows occur.
The time difference (At) routine 217 deteimiines a time difference (At) between the first sensor signal 210 and the second sensor signal 211, The time difference (At) can be stored in the time difference (At) 222 of the storage system 204, The time difference (At) comprises substantially the determined phase divided by the determined fi-equency, and is therefore used to detemiine the mass flow rate.

The floM' characteristics routine 218 can detemiine one or more flow characteristics. The flow characteristics routine 218 can use the determined phase difference 220 and the determined fi-equency 221, for example, in order to accomplish these additional flow characteristics. It should be understood that additional information may be required for these determinations, such as the mass flow rate or density, for example. The flow characteristics routine 218 can detemiine a mass flow rate fi'oni the time difference (At) 222 and therefore fi-om the phase difference 220 and the fi-equsncy 221. The fomiula for determining mass flow rate is given in U.S. Patent No. 5,027,662 to Titlow et al., and is incoiporated herein by reference. The mass flow rate is related to the mass flow of flow material in the meter assembly 10. Likewise, the flow-characteristics routine 218 can also detemiine the density 224 and/or the volume flow rate 225. The determined mass flow rate, density, and volume flow rate can be stored in the mass flow rate 223, the density 224, and the volume 225 of the storage system 204, respectively. In addition, the flow characteristics can be transmitted to external devices by the meter electi'onics 20.
FIG. 3 is a block diagram 300 of a portion of the processing system 203 according to an embodiment of the invention. In the figure, the blocks represent either processing circuity or processing actions.^routines. The block diagram 300 includes a stage 1 filter block 301, a stage 2 filter block 302, a Hilbert ti-ansforai block 303, and an analysis block 304. The LPO and RPO inputs comprise the left pickoff signal input and the light pickoff signal input. Either the LPO or the RPO can comprise a first sensor signal.
In one embodiment, the stage 1 filter block 301 and the stage 2 filter block 302 comprise digital Finite Impulse Response (FIR) polyphase decimation filters, implemented in the processing system 203. These filters provide an optimal method for filtering and decimating one or both sensor signals, with the filtering and decimating . being perfomied at the same clii'onological tune and at the same decimation rate. Alternatively, the stage 1 filter block 301 and the stage 2 filter block 302 can comprise Infinite Impulse Response (IIR) filters or other suitable digital filters or filter processes. However, it should be understood that other filtering processes and/or filtering embodiments are contemplated and are within the scope of the description and claims.

FIG. 4 shows detail of the Hilbert transfoim block 303 according to an enibodimeiit of the invention. In the embodiment shown, the Hilbert transform block 303 includes a LPO delay block 401 in parallel with a LPO filter block 402. The LPO delay block 401 introduces a sampling dela}', The LPO delay block 401 therefore selects LPO digital signal samples that are chi-onologically later in time that the LPO digital signal samples that are filtered by the LPO filter block 402. The LPO filter block 402 performs a 90 degi'ee phase shift on the inputted digital signal samples.
The Hilbert fransform block 303 is a first step to providing the phase measurement. The Hilbert ti'ansform block 303 receives the filtered, decimated LPO and RPO signals and perfomis a Plilbert hansfonn. The Hilbert hansfonn produces 90 degree phase-shifted versions of the LPO signal. The output of the Hilbert transform block 303 therefore provides the new quadrature (Q) component LPO Q, along with the original, in-phase (I) signal components LPO I.
The input to the Hilbert transform block 303 can be represented as:
LPO^A,^^oos{cot) (1)
Using the Hilbert transfomi the output becomes;
LPO^nten = 4.0 sin(^0 (2)
Combining the original terms with the output of the Hilbert transform yields:
iPO- 4,Jcos(^0 + ?sm(a;0]- 4..^'"'"' (3)
FIG. 5 is a block diagram of a frequency portion 500 of the analysis block 304 according to an embodiment of the invention. The analysis block 304 in the embodiment shown is the final stage of the frequency and delta T (At) measurements. In the embodiment shown, the frequency portion 500 determines a frequency from the in-phase (I) and quadrature (Q) components of a single sensor signal. The frequency portion 500 can operate on either the left or right pickoff signal (LPO or RPO). In the embodiment shown, the frequency portion 500 operates on the LPO signal. The frequency portion 500 in the embodiment shown includes a join block 501, a complex conjugate block 502, a sampling block.503, a complex multiplication block 504, a-filter ■ block 505, a phase angle block 506, a constant block 507, and a division block 508.

The join block 501 receives both in-phase (I) and quadrature (Q) components of a sensor signal and passes thsm on. Tlie conjugate block 502 performs a complex conjugate on a sensor signal, here the LPO signal. The delay block 503 introduces a sampling delay aild tlierefore selects a digital signal sample that is clironologically older in time. This older digital signal sample is multiplied v,dth the cuiTent digital signal in the complex multiplication block 504. The complex multiplication block 504 multiplies the LPO signal and the LPO conjugate signal, implementing equation (4) below, The filter block 505 implements a digital filter, such as the FIR filter previousl}-' discussed. The filter block 505 can comprise a polyphase decimation filter that is used to remove hamionic content from the in-phase (Ij and quadrature (Q) components of the sensor signal, as well as to decimate the signal. The filter coefficients can be chosen to provide decimation of the inputted signal, such as decimation by a factor of 10, for example. The phase angle block 506 detemiines a phase angle from the in-phase (I) and quadratLire (Q) components of the LPO signal. The phase angle block 506 implements a portion of equation (5) below. The constant block 507 supplies a factor comprising a sample rate Fj divided by two pi (TI), as shov.ti in equation (6). The division block 508 performs the division operation of equation (6).
The frequency processing implements the following equation:

LPO,.-, X LPO,, = -V^''""' X Koe'""" = A'l.oe^'^'-^'-^ (4)
The angle between two consecutive samples is therefore;
(5)
cot-cot _^ = tan"'
siiiUot - cot_^)
cos{cot - coi_^) which is the radian frequency of the left pick-off Converting to liz:
r ^ icvt-cot_JxFs ,,.
Here "Fs" is the rate of the Hilben transform block 303. In the example previously discussed, "Fs" is about 2 IcHz,
FIG. 6 is a block diagram of a phase difference portion 600 of the analysis block 304 according to an embodiment of the invention. The phase difference portion 600
13

outputs a phase difference bet-ween the LPO input signal and the RPO input signal. The phase difference portion 600 can be included in the analysis block 304 along with the fi-equenc3' portion 500 of FIG. 5. In the figure, the blocks represent either processing circuitry or processing actions/routines. The phase difference portion 600 includes a modulation generator block 601, a join block 602, real-to-complex blocks 604 and 605, quadrature demodulation blocks 608 and 609, decimation blocks 610 and 611, a conjugate block 612, and a correlation block 614,
The modulation generator block 601 generates sin and cosine terms fi-om the radian frequency value (©) that is output by the frequency portion 500. The modulation generator block 601 therefore receives a frequency reference fi'oni the fi-equency portion 500, Because the fi-equency portion 500 can be obtained much faster and more reliably than in the prior art, consequently the phase difference determination can be also obtained much faster and more reliably than in the prior art. The sin and cosine terms comprise in-pliase (I) and quadrature (Q) components of the fi-equency reference. The sin and cosine terms generated by the modulation generator block 601 are inputted into the join block 602,
The join block 602 receives the in-phase (I) and quadrature (Q) components fi-om the modulation generator block 601. The join block 602 j oins the in-phase (I) and quadrature (Q) components and passes them on to the quadrature demodulation blocks 608 and 609.
The real-to-complex blocks 604 and 605 generate imaginary (i.e., quadrature) components of the LPO and RPO input signals. The resulting in-phase (real) and quadrature (imaginary) components comprise sinusoids that includes both sine and cosine components. The real-to-complex blocks 604 and 605 pass the resulting in-phase (real) and quadrature (imaginar)') components of both sigi:als to the con-esponding quadrature demodulation blocks 608 and 609.
The quadrature demodulation blocks 608 and 609 demodulate the LPO signal and the RPO signal using the sinusoids. The demodulation generates a first demodulated sigiial and a second demodulated signal, hi addition, this demodulation produces a zero fi-equency component and a high fi-equency component for each of the LPO and the PJO, The high fi-equency component is later removed (see belovv-'). The

output of the quadrature demodulation blocks 608 and 609 are passed to the decimation blocks 610 and 611, respectively.
The decimation blocks 610 and 611 can decimate the LPO and the RPO quadrature demodulation signals. For example, the decimation blocks 610 and 61 i can decimate these two signals by a factor of about 10, for example. In addition, the decimation blocks 610 and 611 can perform any desired filtering of the demodulation signals. For example, in one embodiment the decimation blocks 610 and 611 can comprise a polyphase decimation filter that is used to remove hannonic content (i.e., the high fi-equency components) fi-om the in-phase (I) and quadrature (Q) components of the sensor signal, as well as to decimate the signal. The filter coefficients can be chosen to provide decimation of the inputted signal, such as decimation by a factor of 10, for example. The decimation blocks 610 and 611 pass the demodulated RPO signal to the conjugate block 612 and pass the demodulated LPO signal to the coiTelation block 614.
The conjugate block 612 performs a complex conjugate on tlie demodulated RPO signal. The conjugate block 612 passes the conjugated demodulated RPO signal to the coirelation block 614.
The correlation block 614 coirelates the demodulated LPO and RPO signals. The conjugation operation followed by the coiTelation comprises a cross-coiTelation operation, The complex correlation can comprise a multiplication that produces a result shown in equations (17) and (18). As a result, the correlation block 614 produces the phase difference (or phase angle) value. The detennined phase difference can be used to deteiTiiine various flow characteristics. Because of the two separate quadrature demodulation processes shown in FIG. 6, the phase difference portion 600 can also be refeired to as a quadrature demodulation chain.
FIG. 7 is a flowchart 700 of a phase difference quadrature demodulation method according to an embodiment of the invention. In step 701, the first and second sensor sigiials are received.
In step 702, a 90 degi-se phase shift is generated for one of the first or second sensor signals.
In step 703, a frequency (f) is determined from the 90 degi-ee phase shift and the coiresponding sensor signal. The frequency (f) can be represented as a radian frequency:

The determined frequency (fj can be used to determine flow characteristics. The deteniiined frequency (f) can also be used to determine a phase difference between the first and second sensor signals, such as by using the QD chain method described above.
In step 704, a reference signal (WK) is created. The reference signal (W,^) comprises a sine and cosine signal The reference S]gnals(WK) have the same frequency as the LPO and RPO signals, The radian frequency co is operated on by a modulation generator in order to recursively generate the sinusoid demodulation reference signals (Wi£), comprising:

In step 705, the sensor signal XLPQ is demodulated with the reference signals W^. The demodulation comprises mixing or multiplying the sensor signal XLPO with the reference signals W^ in order to produce a demodulated LPO signal.
In step 706, the sensor signal XRPO is demodulated with the reference signals W|^. The demodulation comprises mixing or multiplying the sensor signal XRPO with the reference signals W^ in order to produce a demodulated RPO signal.
As a result, the demodulated signals at the output of the quadrature demodulation blocks 608 and 609 comprise:

In step 707, the demodulated signals are filtered in order to remove high frequency terms. These high frequency terms from the quadrature demodulation comprise the [exp(-j(2oDlc+ 16

embodiment, the filtering can comprise an (I, Q) decimation X 40 dual cascade of decimation filters, The output of this filtering is represented by;

> In step 70S, one of the demodulated signals (such as the demodulated RPO signal
in FIG. 6), is conjugated. The conjugation operation forms a negative of the imaginaiy signal.
In step 709, the filter outputs are con-elated by a complex coirelation stage. The conjugation and con^elation steps of the complex con-elation operation yield:

The phase difference is therefore output.
The meter electronics and method for detenninmg a phase difference between a first sensor signal and a second sensor signal of a flow meter according the invention can be implemented according to any of the embodiments in order to obtain several advantages, if desired. The invention can compute a phase difference from a determined frequency and the first and second sensor signals. The invention can provide a phase difference detennination of greater accuracy' and reliability. The invention can provide a phase difference determination faster than the prior art and while consuming less processing time.

We claim:
1, Meter electronics (20) for determining a phase difference between a first sensor
signal and a second sensor signal of a flow meter, comprising:
an interface (201) for receiving a first sensor signal and a second sensor signal; and
a processing S3'stem (203) in communication with the interface (201) and configured to receive the first sensor signal and the second sensor signal, generate a ninety degi-ephase shift looms the first sensor signal, compute a frequency from the first sensor signal and the ninety degree phase shift, generate sine and cosine signals using the Quincy, and quadrature demodulate the first sensor signal and the second sensor signal using the sine and cosine signals in order to determine the phase difference.
2, The meter electronics (20) of claim 1, with the processing system (203) being further configured to compute one or more of a mass flow rate, a density, or a volume flow rate using one or more of the piquancy and the phase difference.
3, The meter elecfonics (20) of claim 1, with the processing system (203) being further configured to compute the ninety degree phase shift using a Hilbert transform.
4, The meter electronics (20) of claim 1, wherein the quadrature demodulation generates a first demodulated signal and a second demodulated signal and with the processing system (203) being further configured to filter the first demodulated signal and the second demodulated signal in order to remove high frequency components and cross-correlate the first demodulated signal and the second demodulated signal in order to determine the phase difference.
5, A method for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter, the method comprising:
generating a ninety degree phase shift food the first sensor signal; computing a frequency from the first sensor signal and the ninety devisee phase shift;

generating sine and cosine signals using the frequency; and quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals in order to deteimine the phase difference.
6. The method of claim 5, further comprising computing one or more of a mass flow rate, a density, or a volume flow rate using one or more of the frequent}' and the phase difference.
7. The method of claim 5, further comprising computing the ninety degree phase shift using a Hilbert transform.
8. The method of claim 5, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal, and with the quadrature demodulating further comprising:
filtering the first demodulated signal and the second demodulated signal in order to remove high fi'equency components; and
cross-capitulating the first demodulated signal and the second demodulated signal in order to determine the phase difference.
9. A method for determining a phase difference between a first sensor and a
second sensor signal of a flow meter, the method comprising:
receiving the first sensor signal and the second sensor signal;
generating a ninety degree phase shift from the first sensor signal;
computing a frequency from the first sensor signal and the ninety degage phase shift;
generating sine and cosine signals using the frequency;
quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals, with the quadrature demodulating generating a first demodulated signal and a second demodulated signal;
filtering the first demodulated signal and the second demodulated signal in order to remove high fi'equency components; and

cross-correlating the first demodulated signal and the second demodulated signal in order to determine the phase difference,
10. The method of claim 9, further comprising computing one or more of a mass flow
rate, a density, or a volume flow rate using one or more of the frequency and the phase
difference,
11. The method of claim 9, further comprising computing the ninety devisee phase shift
using a Hilbert inform.

Documents:

2450-CHENP-2008 AMENDED CLAIMS 14-11-2014.pdf

2450-CHENP-2008 AMENDED PAGES OF SPECIFICATION 14-11-2014.pdf

2450-CHENP-2008 CORRESPONDENCE OTHERS 25-02-2014.pdf

2450-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 14-11-2014.pdf

2450-CHENP-2008 FORM-3 14-11-2014.pdf

2450-chenp-2008 abstract.pdf

2450-chenp-2008 claims.pdf

2450-chenp-2008 correspondence-others.pdf

2450-chenp-2008 description (complete).pdf

2450-chenp-2008 drawings.pdf

2450-chenp-2008 form-1.pdf

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2450-chenp-2008 form-5.pdf

2450-chenp-2008 pct.pdf

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Patent Number

265049

Indian Patent Application Number

2450/CHENP/2008

PG Journal Number

06/2015

Publication Date

06-Feb-2015

Grant Date

03-Feb-2015

Date of Filing

16-May-2008

Name of Patentee

MICRO MOTION, INC.

Applicant Address

7070 WINCHESTER CIRCLE, BOULDER, COLORADO 80301, USA

Inventors:

#	Inventor's Name	Inventor's Address
1	MCANALLY, CRAIG, B.,	594 EAST 131ST WAY, THORNTON, CO 80241, USA
2	HENROT, DENIS, M.,	524 WEST CEDAR PLACE, LOUISVILLE, COLORADO 80027, USA

PCT International Classification Number

G01F1/84

PCT International Application Number

PCT/US06/40232

PCT International Filing date

2006-10-16

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/727,889	2005-10-18	U.S.A.