HK1125998A

HK1125998A - Meter electronics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter

Info

Publication number: HK1125998A
Application number: HK09103664.0A
Authority: HK
Inventors: Craig B. Mcanally; Denis M. Henrot
Original assignee: Micro Motion, Inc.
Priority date: 2005-10-18
Filing date: 2006-10-16
Publication date: 2009-08-21

Description

Meter electronics and methods for determining a phase difference between a first sensor signal and a second sensor signal of a flow meter

Technical Field

The 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.

Background

It is known to measure mass flow, density and volumetric flow and other information of materials flowing through pipelines using coriolis mass flowmeters, as disclosed in U.S. patent No.4,491,025 issued to j.e.smith et al at 1 st 1 1985 and re.31,450 issued to j.e.smith at 11 nd 2 st 1982. These flow meters have one or more flow tubes of different configurations. Each conduit structure 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 flow measurement application, a conduit structure is excited in one or more vibration modes as material flows through the conduit, and motion of the conduit is measured at spaced points along the conduit.

The vibration mode of the material filled system may be determined in part by the combined mass of the flow tube and the material in the flow tube. Material flows into the flow meter from the associated conduit on the inlet side of the flow meter. The material is then guided through a flow tube or flow tubes and out of the flow meter to a connected pipe on the outlet side.

The driver applies pressure to the flow tube. This pressure causes the flow tube to vibrate. When no material flows through the flowmeter, all points along the flow tube vibrate with the same phase. As material begins to flow through 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 arranged at different points on the flow tube to produce sinusoidal signals representative of the motion of the flow tube at the different points. The phase difference between the two sensor signals is proportional to the mass flow rate of material flowing through the flow tube or flow tubes. In prior art methods, 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 the oscillation frequency response of the flow tube arrangement are used to obtain the mass flow rate.

In prior art methods, a separate reference signal is used to determine the pickup signal frequency, such as by using the frequency sent to the vibration driver system. In another prior art approach, the vibrational response frequency produced by the pickoff sensors can be determined by focusing on the frequency in the notch filter, where the prior art flow meter attempts to maintain the notch of the notch filter at the pickoff sensor frequency. This prior art works reasonably well under quiescent conditions where the flow material in the meter is uniform and the resulting pick-up signal frequency is relatively stable. However, the phase measurement of the prior art is impaired when the flow material is not uniform, such as in a two-phase flow where the flow material comprises a liquid and a solid or where there are bubbles in the liquid flow material. In this case, the frequency determined by the prior art may fluctuate rapidly. During conditions of fast and large frequency transitions, it is possible for the pickup signal to move outside the filter bandwidth, resulting in inaccurate phase and frequency measurements. This is also a problem in empty-full-empty batching, where the flow meter is operated repeatedly under alternating empty and full conditions. Furthermore, if the frequency of the sensor is moving rapidly, the demodulation process will not be able to keep up with the actual or measured frequency, causing demodulation at an incorrect frequency. It should be appreciated that if the determined frequency is incorrect or inaccurate, the resulting density values, volume flow values, etc. will also be incorrect or inaccurate. Furthermore, errors are compounded in subsequent flow characteristic determinations.

In the prior art, the pick-up signal may be digitized and digitally processed to perform notch filtering. The notch filter receives only narrow band frequencies. Therefore, when the target frequency changes, the notch filter cannot track the target signal for a period of time. Typically, digital notch filtering implementations take 1-2 seconds to track a fluctuating target signal. Due to the time required by the prior art for determining frequency, the result is: not only does the frequency and phase determination contain errors, but the error measurement includes a time interval that exceeds the time interval during which the error and/or two-phase flow actually occurs. This is due to the relatively slow response performed by the notch filtering.

The result is that prior art flow meters cannot accurately, quickly, or satisfactorily track or determine the pickoff sensor frequency during two-phase flow of the flow material in the flow meter. Thus, when the prior art drives the phase difference with the determined pick-up frequency, the phase determination is also slow and prone to errors. Therefore, errors in frequency determination are compounded in phase determination. The result is increased error in the frequency determination and in the phase determination, resulting in increased error in the determination of mass flow. Furthermore, since the determined frequency values are used to determine density values (density is approximately equal to one divided by the squared frequency), errors in the frequency determination are repeated or compounded in the density determination. This is also true for the determination of the volumetric flow rate when the volumetric flow rate is equal to the mass flow rate divided by the density.

Since the determined frequency can be used to generate the phase difference, an improved frequency determination may provide a fast and reliable phase difference determination.

Disclosure of Invention

The above and other problems are solved and an improvement over the prior art is achieved by providing meter electronics and a method of determining a phase difference between a first sensor signal and a second sensor signal of a flow meter.

Embodiments in accordance with the present invention provide meter electronics that determine a phase difference between a first sensor signal and a second sensor signal of a flow meter. The meter electronics includes 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 90 degree phase shift from the first sensor signal, and calculate a frequency from the first sensor signal and the 90 degree 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 to determine the phase difference.

A method of 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 includes receiving the first sensor signal and the second sensor signal, generating a 90 degree phase shift from the first sensor signal, and calculating a frequency from the first sensor signal and the 90 degree phase shift. The method further includes generating sine and cosine signals using the frequency. The method further includes quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals to determine the phase difference.

A method of 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 includes receiving the first sensor signal and the second sensor signal, generating a 90 degree phase shift from the first sensor signal, and calculating a frequency from the first sensor signal and the 90 degree phase shift. The method further includes generating sine and cosine signals using the frequency. The method further includes quadrature demodulating the first sensor signal and the second sensor signal using the sine and cosine signals, and the quadrature demodulating produces a first demodulated signal and a second demodulated signal. The method further includes filtering the first and second demodulated signals to remove high frequency components and cross-correlating the first and second demodulated signals to determine the phase difference.

In one aspect of the meter electronics, the processing system is further configured to calculate one or more of a mass flow, a density, or a volumetric flow using one or more of the frequency and the phase difference.

In one aspect of the meter electronics, the processing system is further configured to calculate the 90 degree phase shift using a hilbert transform.

In another aspect of the meter electronics, the quadrature demodulation produces 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 to remove high frequency components and to cross-correlate the first demodulated signal and the second demodulated signal to determine the phase difference.

In one aspect of the method, the method further comprises calculating one or more of a mass flow, a density, or a volume flow using one or more of the frequency and the phase difference.

In another aspect of the method, the method further comprises calculating the 90 degree phase shift using a Hilbert transform.

In yet another aspect of the method, the quadrature demodulation produces a first demodulated signal and a second demodulated signal, and the quadrature demodulation further includes filtering the first demodulated signal and the second demodulated signal to remove high frequency components and cross-correlating the first demodulated signal and the second demodulated signal to determine the phase difference.

Drawings

Like reference symbols in the various drawings indicate like elements.

Fig. 1 depicts a coriolis flow meter in one example of the invention.

FIG. 2 shows meter electronics in accordance with an embodiment of the invention.

FIG. 3 is a block diagram of a portion of a processing system according to an embodiment of the present invention.

Fig. 4 shows details of a hilbert transform block according to an embodiment of the present invention.

FIG. 5 is a block diagram of a frequency portion of an analysis block in accordance with an embodiment of the present invention.

FIG. 6 is a block diagram of a phase difference portion of an analysis block in accordance with an embodiment of the present invention.

Fig. 7 is a flowchart of a phase difference quadrature demodulation method according to an embodiment of the present invention.

Detailed Description

Fig. 1-7 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose 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 within 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. Accordingly, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

Fig. 1 shows a coriolis flow meter 5 comprising a flow meter device 10 and meter electronics 20. The flow meter device 10 is responsive to the mass flow and density of the process material. Meter electronics 20 is connected to meter assembly 10 via leads 100 to provide density, mass flow, and temperature information, among other information not relevant to the present invention, over path 26. Although a coriolis flowmeter structure is described herein, it will be apparent to those skilled in the art that the present invention can be implemented as a vibrating tube densitometer without the additional measurement capability provided by a coriolis mass flowmeter.

The flow meter device 10 includes a pair of manifolds 150 and 150 ', flanges 103 and 103' with flange necks 110 and 110 ', a pair of parallel flow tubes 130 and 130', a drive mechanism 180, a temperature sensor 190, and a pair of speed sensors 170L and 170R. The flow tubes 130 and 130 'have two substantially straight inlet legs 131 and 131' and outlet legs 134 and 134 'which converge towards each other at the flow tube fitting blocks 120 and 120'. The flow tubes 130 and 130' are bent at two symmetrical locations along their length and are substantially parallel throughout their length. Brace bars 140 and 140 'are used to define axes W and W' about which each flow tube vibrates.

The side legs 131, 131 ' and 134, 134 ' of the flow tubes 130 and 130 ' are fixedly connected to the flow tube mounting blocks 120 and 120 ', and these blocks are in turn fixedly connected to the manifolds 150 and 150 '. This provides a continuous closed material path through coriolis flowmeter apparatus 10.

When flanges 103 and 103 ' with holes 102, 102 ' are connected via inlet end 104 and outlet end 104 ' to a process line (not shown) that carries the process material to be tested, the material enters the end 104 of the meter through hole 101 in flange 103, is directed through manifold 150 to flow tube mounting block 120 with surface 121. Within manifold 150, the material is split and routed through flow tubes 130 and 130'. After exiting the flow tubes 130 and 130 ', the process material is recombined into a single stream in the manifold 150' and routed thereafter out the outlet end 104 ', which outlet end 104' is connected to the production line (not shown) by a flange 103 'having bolt holes 102'.

Flow tubes 130 and 130 ' are selected and properly assembled to flow tube assembly blocks 120 and 120 ' to have substantially the same mass distribution, moment of inertia and young's modulus about bending axes W-W and W ' -W ', respectively. These bending axes pass through the struts 140 and 140'. Since the young's modulus of the flow tube changes with temperature and this change affects the flow and density calculations, a Resistance Temperature Detector (RTD)190 is fitted to the flow tube 130' to continuously measure the temperature of the flow tube. The temperature of the flow tube, and thus the voltage developed across the RTD for a given current passing therethrough, is controlled by the temperature of the material passing through the flow tube. The temperature dependent voltage developed across the RTD is used by meter electronics 20 in a well known manner to compensate for changes in the modulus of elasticity of flow tubes 130 and 130' due to any changes in flow tube temperature. The RTD is connected to meter electronics 20 by lead 195.

The two flow tubes 130 and 130 ' are driven by the driver 180 in opposite directions about their respective bending axes W-W and W ' -W ', and are referred to as the first out of phase bending mode of the flow meter. The drive mechanism 180 may comprise any one of a number of well known arrangements, such as a magnet mounted to the flow tube 130' and an opposing coil mounted to the flow tube 130 and through which an alternating current is passed in order to vibrate both flow tubes. Appropriate drive signals are applied by meter electronics 20 to drive mechanism 180 via lead 185.

Meter electronics 20 receives the RTD temperature signal on lead 195 and the left and right velocity signals appear on leads 165L and 165R, respectively. Meter electronics 20 generates drive signals that appear on leads 185 to drive element 180 and vibrate tubes 130 and 130'. Meter electronics 20 processes the left and right velocity signals and the RTD signals to calculate the mass flow and density through meter assembly 10. This information, along with other information, is applied by meter electronics 20 to application 29 via path 26.

Fig. 2 shows meter electronics 20 in accordance with an embodiment of the invention. The meter electronics 20 can include an interface 201 and a processing system 203. The meter electronics 20 receives first and second sensor signals 210 and 211, such as pick-off/speed sensor signals, from the flow meter assembly 10. The meter electronics 20 can operate as a mass flow meter or can operate as a density meter, including operating as a coriolis flow meter. The meter electronics 20 processes the first and second sensor signals 210 and 211 to obtain a flow characteristic of the flow material flowing through the flow meter assembly 10. For example, meter electronics 20 can determine one or more of phase difference, frequency, time difference (Δ t), density, mass flow rate, and volume flow rate of the sensor signals, for example. In addition, other flow characteristics may be determined in accordance with the present invention. This determination will be discussed below.

The phase difference determination and the frequency determination are much faster and more accurate and reliable than these determinations in the prior art. This advantageously reduces the processing time required to calculate the flow characteristic and this improves the accuracy of both flow characteristics. Thus, the frequency and phase difference can be determined more quickly than in the prior art.

The prior art frequency determination method typically takes 1-2 seconds to complete. In contrast, frequency determination in accordance with the present invention may be accomplished in as little as 50 milliseconds (ms). Even faster frequency determination is contemplated, depending on the type and configuration of the processing system, the sampling rate of the vibrational response, filter size, decimation rate, and the like. At a 50ms frequency determination rate, meter electronics 20 in accordance with the present invention may be approximately 40 times faster than the prior art.

Via the lead 100 of fig. 1, the interface 201 receives a sensor signal from one of the speed sensors 170L and 170R. The interface 201 may perform any needed or desired signal conditioning, such as any manner of formatting, amplifying, buffering, etc. Alternatively, some or all of the signal conditioning may be performed in the processing system 203.

Further, interface 201 may allow communication between meter electronics 20 and external devices. The interface 201 is capable of any manner of electrical, optical, or wireless communication.

The interface 201 in one embodiment is coupled to a digitizer 202, wherein the sensor signal is comprised of an analog sensor signal. Digitizer 202 samples and digitizes the analog sensor signal and generates a digital sensor signal. Digitizer 202 may also perform any required decimation, wherein the digital sensor signal is decimated in order to reduce the amount of signal processing required and reduce processing time. The decimation operation will be discussed in more detail below.

Processing system 203 manages the operation of meter electronics 20 and processes flow measurements from flow meter device 10. The processing system 203 executes one or more processing routines and processes the flow measurements accordingly to generate one or more flow characteristics.

The processing system 203 may be comprised of a general purpose computer, a micro-processing system, a logic circuit, or some other general purpose or custom processing device. The processing system 203 may be distributed among a plurality of processing devices. The processing system 203 may include any manner of integral or independent electronic storage media, such as storage system 204.

The processing system 203 processes the first sensor signal 210 and the second sensor signal 211 to determine one or more flow characteristics. The one or more flow characteristics may include, for example, phase difference, frequency, time difference (Δ t), mass flow rate, and/or density for the flowing material.

In the illustrated embodiment, the processing system 203 determines the flow characteristic from the two sensor signals 210 and 211 and the single 90 degree phase shift 213. The processing system 203 can determine at least the phase difference and the frequency from the two sensor signals 210 and 211 and the single 90 degree phase shift 213. Additionally, the processing system 203 may further determine the phase difference, time difference (Δ t), and/or mass flow rate of the flowing material, among other values.

The storage system 204 may store flow meter parameters and data, software programs, constants, and variables. In one embodiment, the storage system 204 includes programs executed by the processing system 203. In one embodiment, the memory system 204 stores a phase shift routine 212, a phase difference routine 215, a frequency routine 216, a time difference (Δ t) routine 217, and a flow characteristic routine 218.

In one embodiment, the memory system 204 stores variables used to operate a flow meter, such as coriolis flow meter 5. The storage system 204 in one embodiment stores variables, such as a first sensor signal 210 and a second sensor signal 211, that are received from the speed/pickup sensors 170L and 170R. Further, the storage system 204 may store the 90 degree phase shift 213 generated to determine the flow characteristic.

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 phase difference 220, frequency 221, time difference (Δ t)222, mass flow 223, density 224, and volume flow 225.

The phase shift routine 212 performs a 90 degree phase shift on the input signal, i.e., on the sensor signal 210. The phase shift routine 212 in one embodiment performs a hilbert transform (discussed below).

Using quadrature demodulation, the phase difference routine 215 determines the phase difference. Additional information may also be used to calculate the phase difference. In one embodiment, the phase difference is calculated from the first sensor signal 210, the second sensor signal 211, and the frequency 221. The determined phase difference may be stored in the phase difference 220 of the storage system 204. When the determination is made using the determined frequency 221, the phase difference can be calculated and obtained more quickly than in the prior art. This can provide a critical difference in flow meter applications with high flow rates or where multi-phase flow occurs.

The frequency routine 216 determines the frequency (as indicated by the first sensor signal 210 or the second sensor signal 211) based on the 90 degree phase shift 213. The determined frequency may be stored in the frequency 221 of the storage system 204. When determined from a single 90 degree phase shift 213 and the sensor signal 210 or 211, the frequency can be calculated and obtained more quickly than in the prior art. This can provide a critical difference in flow meter applications with high flow rates or where multi-phase flow occurs.

The time difference (Δ t) routine 217 determines the time difference (Δ t) between the first sensor signal 210 and the second sensor signal 211. The time difference (Δ t) may be stored in the time difference (Δ t)222 of the storage system 204. The time difference (Δ t) substantially comprises the determined phase divided by the determined frequency and is thus used for determining the mass flow.

The flow characteristics program 218 may determine one or more flow characteristics. The flow characteristic routine 218 may utilize the determined phase difference 220 and the determined frequency 221, for example, to achieve these additional flow characteristics. It should be appreciated that additional information may be required for these determinations, such as mass flow or density. The flow characteristic routine 218 can determine the mass flow rate from the time difference (Δ t)222 and thus from the phase difference 220 and the frequency 221. The formula for determining mass flow is given in U.S. patent No.5,027,662 to Titlow et al, and incorporated herein by reference. The mass flow rate relates to the mass flow of the flow material in the flow meter device 10. Likewise, the flow characteristics routine 218 may also determine the density 224 and/or the volumetric flow rate 225. The determined mass flow, density, and volume flow may be stored in mass flow 223, density 224, and volume 225, respectively, of storage system 204. In addition, the flow characteristics can be communicated to an external device by meter electronics 20.

FIG. 3 is a block diagram 300 of a portion of the processing system 203 according to an embodiment of the present invention. In the figure, a block represents a processing circuit or a processing action/program. The block diagram 300 comprises a filter block 301 of order 1, a filter block 302 of order 2, a hilbert transform block 303 and an analysis block 304. The LPO and RPO inputs include a left pickoff signal input and a right pickoff signal input. The LPO or RPO may include a first sensor signal.

In one embodiment, the order 1 filter block 301 and the order 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, the filtering and decimation being performed at the same time in time and at the same decimation rate. Alternatively, the order 1 filter block 301 and the order 2 filter block 302 may comprise Infinite Impulse Response (IIR) filters or other suitable digital filters or filtering 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 a hilbert transform block 303 according to an embodiment of the present invention. In the illustrated embodiment, the hilbert transform block 303 comprises an LPO delay block 401 in parallel with an LPO filter block 402. The LPO delay block 401 introduces a sampling delay. The LPO delay block 401 thus selects LPO digital signal samples that are later in time-sequence time than the LPO digital signal samples filtered by the LPO filter block 402. The LPO filter block 402 performs a 90 degree phase shift on the input digital signal samples.

The hilbert transform block 303 is the first step to provide a phase measurement. The hilbert transform block 303 receives the filtered, decimated LPO and RPO signals and performs a hilbert transform. The hilbert transform produces a 90 degree phase shifted version of the LPO signal. The output of the hilbert transform block 303 thus provides, along with the original, in-phase signal (I) component LPO I, a new quadrature (Q) component LPO Q.

The input to the hilbert transform block 303 may be represented as:

LPO＝A_lpocos(ωt) (1)

with the hilbert transform, the output becomes:

LP_OHllberl＝A_lposin(ωt) (2)

combining the original term with the output of the hilbert transform yields:

LPO＝A_lpo[cos(ωt)+isin(ωt)]＝A_lpoe^j(ωt) (3)

fig. 5 is a block diagram of a frequency portion 500 of the analysis block 304 in accordance with an embodiment of the present invention. The analysis block 304 in the illustrated embodiment is the last stage of the frequency and delta T (Δ T) measurements. In the illustrated embodiment, the frequency portion 500 determines the frequency from the in-phase (I) and quadrature (Q) components of a single sensor signal. The frequency section 500 may operate on either the left or right pickoff signals (LPO or RPO). In the illustrated embodiment, the frequency portion 500 includes a combining 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 combining block 501 receives the in-phase (I) and quadrature (Q) components of the sensor signal and passes them on. The conjugation block 502 performs complex conjugation on the sensor signal, here the LPO signal. Delay block 503 introduces a sample delay and thus selects digital signal samples that are chronologically older in time. The older digital signal samples are multiplied by the current digital signal in a complex multiplication block 504. The complex multiplication block 504 multiplies the LPO signal and the LPO conjugate signal to implement the following equation (4). The filter block 505 performs digital filtering, such as FIR filtering as discussed above. The filter block 505 may include polyphase decimation filters for removing harmonic content from the in-phase (I) and quadrature (Q) components of the sensor signal, as well as decimating the signal. The filter coefficients may be selected to provide decimation of the input signal, such as by a factor of 10, for example. The phase angle block 506 determines the phase angle from the in-phase (I) and quadrature (Q) components of the LPO signal. The phase angle block 506 performs a portion of equation (5) below. The constant block 507 provides a factor comprising the sampling rate F divided by two pi (π)_sAs shown in equation (6). The division block 508 performs the division operation of equation (6).

The frequency processing implements the following equation:

the angle between two consecutive samples is thus:

which is the angular frequency picked up to the left. Conversion to Hz:

where "Fs" is the rate of the hilbert transform block 303. In the previously discussed example, "Fs" is about 2 kHz.

Fig. 6 is a block diagram of a phase difference portion 600 of analysis block 304 in accordance with an embodiment of the present invention. The phase difference section 600 outputs a phase difference between the LPO input signal and the RPO input signal. The phase difference portion 600 may be included in the analysis block 304 along with the frequency portion 500 in fig. 5. In the drawings, a block represents a processing circuit or a processing operation/program. The phase difference part 600 includes a modulation generator block 601, a combining block 602, real-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 sine and cosine terms according to the angular frequency value (ω) output from the frequency part 500. The modulation generator block 601 thus receives a frequency reference from the frequency part 500. Since the frequency part 500 can be obtained more quickly and more reliably than in the prior art, the phase difference determination can also be obtained more quickly and more reliably than in the prior art. The sine and cosine terms comprise in-phase (I) and quadrature (Q) components of the frequency reference. The sine and cosine terms generated by the modulation generator block 601 are input to a combining block 602.

The combining block 602 receives in-phase (I) and quadrature (Q) components from the modulation generator block 601. The combining block 602 combines the in-phase (I) and quadrature (Q) components and passes them to quadrature demodulation blocks 608 and 609.

The real-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 a sinusoid containing sine and cosine components. The real-complex blocks 604 and 605 pass the resulting in-phase (real) and quadrature (imaginary) components of the two signals to respective quadrature demodulation blocks 608 and 609.

The quadrature demodulation blocks 608 and 609 demodulate the LPO signal and the RPO signal using sinusoids. The demodulation operation produces a first demodulated signal and a second demodulated signal. In addition, the demodulation produces zero-frequency components and high-frequency components of each of the LPO and RPO signals. The high frequency components are removed in subsequent operations (see below). The outputs of the quadrature demodulation blocks 608 and 609 are passed to decimation blocks 610 and 611, respectively.

The decimation blocks 610 and 611 may decimate the LPO and RPO quadrature demodulated signals. For example, decimation blocks 610 and 611 may decimate the two signals by a factor of, for example, about 10. Furthermore, decimation blocks 610 and 611 may perform any desired filtering of the demodulated signal. For example, in one embodiment, decimation blocks 610 and 611 may include polyphase decimation filters that remove harmonic components (i.e., high frequency components) from the in-phase (I) and quadrature (Q) components of the sensor signal and decimate the signal. The filter coefficients may be selected to provide decimation of the input signal, for example by a factor of 10. The decimation blocks 610 and 611 pass the demodulated RPO signal to a conjugate block 612 and the demodulated LPO signal to a correlation block 614.

The conjugation block 612 performs complex conjugation on the demodulated RPO signal. The conjugate block 612 passes the conjugated demodulated RPO signal to a correlation block 614.

The correlation block 614 correlates the demodulated LPO and RPO signals. The correlation operation after the conjugate operation constitutes a cross-correlation operation. The complex correlation may include a multiplication that produces the results shown in equations (17) and (18). Thus, correlation block 614 generates a phase difference (or phase angle) value. The determined phase difference may be used to determine various flow characteristics. The phase difference portion 600 can also be considered a quadrature demodulation chain due to the two independent quadrature demodulation processes shown in fig. 6.

Fig. 7 is a flowchart 700 of a phase difference quadrature demodulation method according to an embodiment of the present invention. In step 701, first and second sensor signals are received.

At step 702, a 90 degree phase shift is imparted to one of the first and second sensor signals.

In step 703, a frequency (f) is determined from the 90 degree phase shift and the corresponding sensor signal. This frequency (f) can be expressed as an angular frequency:

ω＝2πf (7)

the determined frequency (f) may be used to determine the flow characteristic. The determined frequency (f) may also be used to determine the phase difference between the first and second sensor signals, for example by using the QD chain method described above.

In step 704, a reference signal (W) is generated_K). Reference signal (W)_K) Including sine and cosine signals. Reference signal (W)_K) Having the same frequency as the LPO and RPO signals. The angular frequency omega is operated by a modulation generator to recursively generate a sinusoidal demodulation reference signal (W)_K) The method comprises the following steps:

W_k＝exp(-jωk) (8)

and the LPO and RPO input signals include:

x_LPO(k)＝Acos(ωk+φ_LPO) (9)

x_RPO(k)＝Acos(ωk+φ_RPO) (10)

in step 705, a reference signal W is used_KDemodulating sensor signal x_LPO. The demodulation operation includes using a reference signal W_KFor sensor signal x_LPOMixing or multiplying to produce a demodulated LPO signal.

In step 706, a reference signal W is used_KDemodulating sensor signal x_RPO. The demodulation operation includes using a reference signal W_KFor sensor signal x_RPOMixing or multiplying to produce a demodulated RPO signal.

As a result, the demodulated signals output at the orthogonal demodulation blocks 608 and 609 include:

z_LPO(k)＝W_kx_LPO(k) (11)

z_RPO(k)＝W_kx_RPO(k) (12)

it can be rewritten as:

in step 707, the demodulated signal is filtered to remove high frequency terms. These high frequency terms from quadrature demodulation include [ exp (-j (2 ω k + Φ) in equations (13) and (14) above_LPO/RPO))]An item. A low pass filter operation may be used to remove the high frequency terms. In one embodiment, the filtering may include an (I, Q) decimating X40 double cascaded decimation filter. The output of this filtering can be expressed as:

at step 708, one of the demodulated signals (e.g., the demodulated RPO signal in fig. 6) is conjugated. The conjugation operation forms the negative of the imaginary signal.

In step 709, the filter output is correlated by a complex correlation stage. The correlation steps of the conjugate operation and the complex correlation operation yield:

q(k)＝z_LPO(k)z_RPO(k) (17)

where the second z term represents the complex conjugate from step 708. The correlation/multiplication output includes, in accordance with equation (16):

thus, the phase angle includes:

φ(k)＝arg(q(k))＝φ_LPO-φ_RPO (19)

and further outputs the phase difference.

Flowmeter electronics and methods of determining a phase difference between a first sensor signal and a second sensor signal of a flowmeter according to the present invention can be implemented in accordance with any of the embodiments to achieve desired advantages. The invention may calculate the phase difference based on the determined frequency and the first and second sensor signals. The present invention may provide phase difference determination with greater accuracy and reliability. The invention may provide a more rapid phase difference determination than the prior art while taking less processing time.

Claims

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 system (203) in communication with the interface (201) thereof and for receiving the first and second sensor signals, producing a 90 degree phase shift from the first sensor signal, calculating a frequency from the first sensor signal and the 90 degree phase shift, producing sine and cosine signals using the frequency, and quadrature demodulating the first and second sensor signals using the sine and cosine signals to determine the phase difference.

2. The meter electronics (20) of claim 1, with the processing system (203) being further to calculate one or more of a mass flow, a density, or a volumetric flow using one or more of the frequency and the phase difference.

3. The meter electronics (20) of claim 1, with the processing system (203) being further configured to calculate the 90 degree phase shift using a hilbert transform.

4. The meter electronics (20) of claim 1, with the quadrature demodulation producing a first demodulated signal and a second demodulated signal, and with the processing system (203) further being configured to filter the first demodulated signal and the second demodulated signal to remove high frequency components and to cross-correlate the first demodulated signal and the second demodulated signal to determine the phase difference.

5. A method of determining a phase difference between a first sensor signal and a second sensor signal of a flow meter, the method comprising:

receiving the first sensor signal and the second sensor signal;

generating a 90 degree phase shift from the first sensor signal;

calculating a frequency from the first sensor signal and the 90 degree 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 to determine the phase difference.

6. The method of claim 5, further comprising calculating one or more of a mass flow, a density, or a volume flow using one or more of the frequency and the phase difference.

7. The method of claim 5, further comprising calculating the 90 degree phase shift using a Hilbert transform.

8. The method of claim 5, wherein the quadrature demodulation produces 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 to remove high frequency components; and

cross-correlating the first demodulated signal and the second demodulated signal to determine the phase difference.

9. A method of determining a phase difference between a first sensor signal and a second sensor signal of a flow meter, the method comprising:

receiving the first sensor signal and the second sensor signal;

generating a 90 degree phase shift from the first sensor signal;

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, and the quadrature demodulating produces a first demodulated signal and a second demodulated signal;

10. The method of claim 9, further comprising calculating 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 calculating the 90 degree phase shift using a hilbert transform.