HK1125169B - Meter electronics and methods for verification diagnostics for a flow meter - Google Patents

Description

Meter electronics and methods for verification diagnostics of a flow meter

Technical Field

The invention relates to meter electronics and methods for verification diagnostics of a flow meter.

Background

Statement of problem

Vibrating conduit sensors, such as Coriolis (Coriolis) mass flowmeters or vibrating tube densitometers, generally operate by detecting motion of a vibrating conduit containing a flow material. Properties associated with the material in the conduit, such as mass flow, density, etc., may be determined by processing measurement signals received from motion transducers associated with the conduit. The stiffness and damping characteristics generally affect the vibration modes of the vibrating material filled system through the combined mass of the contained conduit and the material contained therein.

The conduit of the vibratory flowmeter can include one or more flow tubes. The flow tube is forced to vibrate at a resonant frequency, in which case the resonant frequency of the tube is proportional to the density of the fluid in the flow tube. Sensors positioned on the inlet and outlet portions of the tube measure the relative vibrations between the ends of the tube. During flow, the vibrating tube and the flow mass couple together due to coriolis forces, causing a phase shift in the vibration between the ends of the tube. The phase shift is directly proportional to the mass flow.

A typical coriolis mass flowmeter includes one or more conduits that are connected internally in a pipeline or other transport system and transport material, such as fluid, mud, etc., in the system. Each conduit may be considered to have 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 points spaced along the conduit. Excitation is typically provided by an actuator, for example an electromechanical device such as a voice coil type driver, which interferes with the conduit in a periodic fashion. The mass flow rate can be determined by measuring the time delay or phase difference between the movements at the transducer positions. Two such sensors (or pick-off sensors) are typically employed to measure the vibrational response of the flow conduit or conduits, and are typically positioned at locations upstream and downstream of the actuator. The two pickoff sensors are connected to the electronic device by a cable. The device receives signals from two pickoff sensors and processes the signals to obtain a mass flow measurement.

The phase difference between the two sensor signals relates to the mass flow rate of the material flowing through the flow tube or flow tubes. The mass Flow of the material is proportional to the time delay between the two sensor signals and thus the mass Flow can be determined by multiplying the time delay by a Flow Calibration Factor (FCF), in this case the time delay includes the phase difference divided by the frequency. FCF reflects the material and cross-sectional properties of the flow tube. In the prior art, the FCF is determined by a calibration step prior to installation of the flow meter into a pipeline or other conduit. In the calibration step, fluid is passed through the flow tube at a given flow rate, and a characteristic between the phase difference and the flow rate is calculated.

One advantage of coriolis flowmeters is that the accuracy of the measured mass flow is not affected by wear of the moving parts of the flowmeter. The flow rate is determined by multiplying the phase difference between two points of the flow tube by a flow rate calibration factor. The only input is the sinusoidal signal from the sensor, representing the oscillation at two points on the flow tube. Phase differences are calculated from these sinusoidal signals. There are no moving parts in the vibrating flow tube. Thus, the measurement of the phase difference and the flow calibration factor is not affected by wear of the moving parts in the flow.

FCF may relate to the stiffness characteristics of the flow meter device. If the stiffness characteristics of the flow meter device change, then the FCF also changes. The changes thus affect the accuracy of the flow measurement produced by the flow meter. Changes in the material and changes in the cross-sectional properties of the flow tube can be caused, for example, by corrosion or erosion. It is therefore highly desirable to be able to detect and/or quantify any change to the stiffness of the flow meter device, thereby maintaining a high level of accuracy of the flow meter.

Disclosure of Invention

In accordance with an embodiment of the present invention, meter electronics for a flow meter is provided. The meter electronics includes an interface for receiving a vibrational response from the flow meter and a processing system in communication with the interface. The vibrational response comprises a response to vibration of the flow meter at the fundamental resonant frequency. The processing system is arranged to receive the vibrational response from the interface, determine the frequency (ω) of the vibrational response₀) Determining the response voltage (V) and drive current (I) of the vibrational response, measuring the attenuation characteristic (ζ) of the flow meter, and deriving the frequency (ω) from the measured attenuation characteristic (ζ)₀) The response voltage (V), the drive current (I) and the damping characteristic (ζ) determine a stiffness parameter (K).

In accordance with an embodiment of the present invention, there is provided a method for determiningA method of determining a stiffness parameter (K) of a flowmeter. The method includes receiving a vibrational response from the flow meter. The vibrational response comprises a response to vibration of the flow meter at the fundamental resonant frequency. The method further includes determining a frequency (ω) of the vibrational response₀) Determining a response voltage (V) and a drive current (I) of the vibrational response, and measuring a damping characteristic (ζ) of the flow meter. The method further comprises deriving the frequency (ω) from the frequency (ω)₀) The response voltage (V), the drive current (I) and the damping characteristic (ζ) determine a stiffness parameter (K).

In accordance with an embodiment of the present invention, a method for determining a stiffness change (Δ K) of a flow meter is provided. The method includes receiving a vibrational response from the flow meter. The vibrational response comprises a response to vibration of the flow meter at the fundamental resonant frequency. The method further includes determining a frequency (ω) of the vibrational response₀) Determining a response voltage (V) and a drive current (I) of the vibrational response, and measuring a damping characteristic (ζ) of the flow meter. The method further comprises deriving the frequency (ω) from the frequency (ω)₀) The response voltage (V), the drive current (I) and the damping characteristic (ζ) determine a stiffness parameter (K). The method further comprises at a second time t₂Receives a second vibrational response from the flow meter, generates a second stiffness characteristic (K) from the second vibrational response₂) Comparing the second stiffness characteristics (K)₂) With a stiffness parameter (K) and, if the second stiffness characteristic (K) is not present₂) And the stiffness parameter (K) is different by more than a predetermined tolerance, a stiffness change (Δ K) is detected.

In accordance with an embodiment of the present invention, meter electronics for a flow meter is provided. The meter electronics includes an interface for receiving three or more vibrational responses from the flow meter. The three or more vibrational responses include a fundamental frequency response and two or more non-fundamental frequency responses. The meter electronics further includes a processing system in communication with the interface, and the processing system is arranged to receive three or more vibrational responses from the interface, generate a pole-residue frequency response function from the three or more vibrational responses, and determine at least one stiffness parameter (K) from the pole-residue frequency response function.

In accordance with an embodiment of the present invention, a method for determining a stiffness change (Δ K) of a flow meter is provided. The method includes receiving three or more vibrational responses, the three or more vibrational responses including a fundamental frequency response and two or more non-fundamental frequency responses. The method further includes generating a pole-residue frequency response function from the three or more vibrational responses, and determining at least one stiffness parameter (K) from the pole-residue frequency response function.

In accordance with an embodiment of the present invention, a method for determining a stiffness parameter (K) of a flow meter is provided. The method includes receiving three or more vibrational responses, the three or more vibrational responses including a fundamental frequency response and two or more non-fundamental frequency responses. The method further includes generating a pole-residue frequency response function from the three or more vibrational responses and determining at least one stiffness parameter (K) from the pole-residue frequency response function. The method further comprises at a second time t₂Receives a second set of three or more vibrational responses from the flow meter, generates a second stiffness characteristic (K) from the second set of three or more vibrational responses₂) Comparing the second stiffness characteristics (K)₂) With a stiffness parameter (K) and, if the second stiffness characteristic (K) is not present₂) If the difference from the stiffness parameter (K) is greater than a predetermined tolerance, a stiffness change (Δ K) is detected.

Various aspects of the invention

In one aspect of the meter electronics, measuring the decay characteristic (ζ) further comprises allowing the vibrational response of the flow meter to decay down to a predetermined vibrational target.

In another aspect of the meter electronics, the processing system is further arranged to measure the damping characteristic (ζ) by removing excitation of the flow meter and allowing a vibrational response of the flow meter to damp down to a predetermined vibrational target while measuring the damping characteristic.

In another aspect of the meter electronics, the stiffness parameter (K) includes K ═ BL_PO*BL_DR*ω₀)/2ζV。

In one aspect of the method, measuring the damping characteristic (ζ) further comprises allowing the vibrational response of the flow meter to damp down to a predetermined vibrational target.

In another aspect of the method, measuring the damping characteristic (ζ) further includes removing excitation of the flow meter, and allowing a vibrational response of the flow meter to damp down to a predetermined vibrational target while measuring the damping characteristic.

In another aspect of the method, the stiffness parameter (K) comprises K ═ BL_PO*BL_DR*ω₀)/2ζV。

In another aspect of the method, a second stiffness characteristic (K) is generated from the second vibrational response₂) Includes generating a second stiffness characteristic (K) from a second frequency, a second response voltage, a second drive current, and a second damping characteristic₂)。

In another aspect of the method, the method further comprises if the second stiffness parameter (K)₂) And the stiffness parameter (K) is different by more than a predetermined stiffness tolerance, a stiffness change (Δ K) is detected.

In another aspect of the method, the method further comprises starting from K₂And K to quantify the stiffness change (Δ K).

In an embodiment of the meter electronics, the processing system is further arranged to determine the damping parameter (C) from the pole-residue frequency response function.

In another embodiment of the meter electronics, the processing system is further arranged to determine the quality parameter (M) from a pole-residue frequency response function.

In another embodiment of the meter electronics, the processing system is further arranged to calculate a pole (λ), a left residue (R), from the pole-residue frequency response function_L) And the right residue (R)_R)。

In another embodiment of the meter electronics, the three or more vibrational responses include at least one tone (tone) above the fundamental frequency response and at least one tone below the fundamental frequency response.

In another embodiment of the meter electronics, the three or more vibrational responses comprise at least two tones above the fundamental frequency response and at least two tones below the fundamental frequency response.

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a first order pole-residue frequency response function.

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a first order pole-residue frequency response function comprising

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a first order pole-residue frequency response function comprising

And wherein M is 1/2jR ω according to the equation_d，K＝(ω_n)²M and C ═ 2 ζ ω_nM determines a stiffness parameter (K), a damping parameter (C) and a mass parameter (M).

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a second order pole-residue frequency response function.

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a second order pole-residue frequency response function comprising

In another embodiment of the meter electronics, the pole-residue frequency response function comprises a second order pole-residue frequency response function comprising

And in which is based on

Determining a stiffness parameter (K) according to M ═ K/(ω)_n)²Determining a quality parameter (M) and in accordance withA damping parameter (C) is determined.

In an embodiment of the method, said determining comprises further determining a damping parameter (C) from the pole-residue frequency response function.

In another embodiment of the method, said determining comprises further determining a quality parameter (M) from the pole-residue frequency response function.

In another embodiment of the method, the determining further comprises calculating a pole (λ), a left residue (R) from a pole-residue frequency response function_L) And the right disabilityNumber (R)_R)。

In another embodiment of the method, the three or more vibrational responses include at least one tone above the fundamental frequency response and at least one tone below the fundamental frequency response.

In another embodiment of the method, the three or more vibrational responses comprise at least two tones above the fundamental frequency response and at least two tones below the fundamental frequency response.

In another embodiment of the method, the pole-residue frequency response function comprises a first order pole-residue frequency response function.

In another embodiment of the method, the pole-residue frequency response function comprises a first order pole-residue frequency response function comprising

In another embodiment of the method, the pole-residue frequency response function comprises a first order pole-residue frequency response function comprising

And wherein M is 1/2jR ω according to the equation_d，K＝(ω_n)²M and C ═ 2 ζ ω_nM determines a stiffness parameter (K), a damping parameter (C) and a mass parameter (M).

In another embodiment of the method, the pole-residue frequency response function comprises a second order pole-residue frequency response function.

In another embodiment of the method, the pole-residue frequency response function comprises a second order pole-residue frequency response function comprising

In another embodiment of the method, the pole-residue frequency response function comprises a second order pole-residue frequency response function comprising

And in which is based on

Determining a stiffness parameter (K) according to M ═ K/(ω)_n)²Determining a quality parameter (M) and in accordance withA damping parameter (C) is determined.

In another embodiment of the method, the method further comprises if the second stiffness characteristic (K) is₂) A stiffness variation (Δ K) is detected if the stiffness parameter (K) differs by more than a predetermined stiffness tolerance.

In another embodiment of the method, the method further comprises selecting K from K and K₂To quantify the stiffness change (Δ K).

Drawings

Like reference numerals refer to like elements throughout the several views.

FIG. 1 shows a flow meter including a meter assembly and meter electronics;

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

FIG. 3 is a flow chart of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention;

FIG. 4 is a flow chart of a method for determining a change in stiffness (Δ K) of a flow meter according to an embodiment of the invention

FIG. 5 shows meter electronics in accordance with another embodiment of the present invention;

FIG. 6 is a flow chart of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention;

FIG. 7 illustrates an implementation of the pole (λ) and residue (R) solution in accordance with an embodiment of the invention;

FIG. 8 is a block diagram illustrating the calculation of M, C and K system parameters in accordance with an embodiment of the present invention;

FIG. 9 illustrates an overall FRF-based stiffness estimation system in accordance with embodiments of the invention;

FIG. 10 is a flow chart of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention;

FIG. 11 shows an implementation of the solution of M, C and K to the second order pole-residue response from equation (29) in accordance with an embodiment of the present invention;

FIG. 12 illustrates an overall FRF-based stiffness estimation system in accordance with an embodiment of the present invention.

Detailed Description

Fig. 1-12 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. As a result, 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 that includes a meter assembly 10 and meter electronics 20. The meter assembly 10 responds to the mass flow and density of the process material. The meter electronics 20 is connected to the meter assembly 10 via leads 100 to provide density, mass flow, and temperature information, as well as other information not relevant to the present invention, via path 26. A coriolis flowmeter structure is described, however, it will be apparent to those skilled in the art that the present invention may be practiced with a vibrating tube densitometer without the additional measurement capability provided by a coriolis mass flowmeter.

The 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', 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 (leg)131 and 131' and outlet legs 134 and 134 'that converge toward each other at the flow tube blocks 120 and 120'. Flow tubes 130 and 130' are bent at two symmetrical locations along their length and are substantially parallel throughout their entire length. Diagonal braces 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 attached to the flow tube mounting blocks 120 and 120 ', and these blocks are in turn fixedly attached to the manifolds 150 and 150 '. This provides a continuous closed material path through coriolis meter assembly 10.

When flanges 103 and 103 ' having holes 102, 102 ' are connected, via inlet end 104 and outlet end 104 ', into a process line (not shown) that carries the process material being measured, through hole 101 in flange 103, the material enters end 104 of the flow meter, is directed through manifold 150 to flow tube mounting block 120 having surface 121. Inside the manifold 150, the material is divided and routed (route) through the flow tubes 130 and 130'. Based on the current flow tubes 130 and 130 ', the process material is recombined in a single flow in the manifold 150 ' and thereafter routed to the outlet end 104 ' which is connected to the production line (not shown) through a flange 103 ' having bolt holes 102 '.

Flow tubes 130 and 130 ' are selected and suitably 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 diagonal draw bars 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 dominated by the temperature of the material passing through the flow tube. The temperature dependent voltage developed across the RTD is used in a known method by the meter electronics 20 to compensate for changes in the elastic modulus of the flow tubes 130 and 130' due to any changes in the flow tube temperature. The RTD is connected to the 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 in a first out of phase bending mode, referred to as 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 the two flow tubes. An appropriate drive signal is applied by the meter electronics 20 to the drive mechanism 180 via lead 185.

The 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. The meter electronics 20 generates a drive signal that appears on lead 185 to drive element 180 and vibrate tubes 130 and 130'. The meter electronics 20 processes the left and right velocity signals and the RTD signal to calculate mass flow and density through the meter assembly 10. This information is applied to the utilization device 29 on path 26 by the meter electronics 20 together with other information.

Fig. 2 shows meter electronics 20 according to an embodiment of the invention. The meter electronics 20 may include an interface 201 and a processing system 203. The meter electronics 20 receives a vibrational response 210, such as from the meter assembly 10. The meter electronics 20 processes the vibrational response 210 to obtain flow characteristics of the fluid flowing through the meter assembly 10. Further, in meter electronics 20 according to the present invention, vibrational response 210 is also processed to determine a stiffness parameter (K) of meter assembly 10. Further, the meter electronics 20 may process two or more such vibrational responses over time to detect a change in stiffness (Δ K) in the meter assembly 10. The stiffness determination may be made under flow or no-flow conditions. The no-flow determination may provide the advantage of a reduced noise level in the resulting vibrational response.

As previously discussed, the Flow Calibration Factor (FCF) reflects the material properties and cross-sectional properties of the flow tube. The mass flow rate of the flow material flowing through the flow meter is determined by multiplying the measured time delay (or phase difference/frequency) by the FCF. The FCF may relate to a stiffness characteristic of the meter assembly. If the stiffness characteristics of the meter assembly change, the FCF also changes. Changes in the stiffness of the flow meter will therefore affect the accuracy of the flow measurement produced by the flow meter.

The present invention is significant because it allows the meter electronics 20 to perform stiffness determinations in the field without performing actual flow calibration tests. It allows stiffness determination without calibration of the test stand or other specific equipment or specific fluid. This is desirable because performing flow calibration in the field is expensive, difficult and time consuming. However, better and easier calibration checks are desirable because the stiffness of the meter assembly 10 may change over time. Such changes may be due to factors such as corrosion of the flow tube, erosion of the flow tube, and damage to the meter assembly 10.

The present invention can be expressed using a mathematical model. With open-loop, the second order drive model can represent the vibrational response of the flow meter, including:

where f is the force applied to the system, M is the mass of the system, C is the damping characteristic, and K is the stiffness characteristic of the system. The term K includes K ═ M (ω)₀)²And term C includes C ═ M2 ζ ω₀Where ζ includes a delay characteristic, and ω₀＝2πf₀Wherein f is₀Is the natural/resonant frequency of the meter assembly 10 in Hz. In addition, x is the physical displacement distance of the vibration,is the velocity of the flow tube displacement and x is the acceleration. This is commonly referred to as the MCK model. The formula can be rearranged to the following form:

equation (2) can be further processed into a transfer function form. Using a force up shift term in the form of a transfer function, comprising:

well-known magnetic equations can be used to simplify equation (3). Two applicable equations are:

and

f＝BL_DR*I (5)

sensor voltage V of equation (4)_BMFEqual to the pick-up sensitivity factor BL (at the pick-up sensor 170L or 170R)_POMultiplied by the pick-up speed of the motionFor each pickup sensor, the pickup sensitivity factor BL is typically known or measured_PO. The driver 180 through equation (5) yieldsThe resulting force (f) is equal to the driver sensitivity factor BL_DRMultiplied by the drive current (I) supplied to the driver 180. The driver sensitivity factor BL of the driver 180 is generally known or measured_DR. Factor BL_POAnd BL_DRAre a function of temperature and can be corrected by temperature measurements.

By substituting magnetic equations (4) and (5) into the transfer function of equation (3), the result is:

if the meter assembly 10 is driven open-loop at resonance, i.e., at the resonance/natural frequency ω₀Where (where ω is₀＝2πf₀) Then equation (6) can be rewritten as:

by replacing the stiffness, equation (7) is simplified to:

here, the stiffness parameter (K) can be separated, so that:

as a result, by measuring/quantifying the attenuation characteristic (ζ) as well as the drive voltage (V) and the drive current (I), the stiffness parameter (K) can be determined. The response voltage (V) from the pick-up can be determined from the vibration response and the drive current (I). The step of determining the stiffness parameter (K) is discussed in more detail below in conjunction with fig. 3.

In use, the stiffness parameter (K) may be tracked over time. For example, statistical techniques may be used to determine any change over time (i.e., stiffness parameter (K)). Statistical changes in the stiffness parameter (K) may indicate that the FCT has changed for a particular flow meter.

The invention provides a stiffness parameter (K) independent of a stored or retrieved calibration density value. This is in contrast to the prior art, where known flow materials are used in factory calibration operations in order to obtain density standards that can be used for all future calibration operations. The present invention provides a stiffness parameter (K) that is derived solely from the vibrational response of the flow meter. The present invention provides a stiffness detection/calibration method that does not require a factory calibration step.

Via lead 100 of fig. 1, interface 201 receives vibrational response 210 from one of velocity sensors 170L and 170R. The interface 201 may perform any necessary or desired signal conditions such as formatting, amplifying, buffering, etc. in any manner. Alternatively, some or all of the signal conditions may be performed in the processing system 203. Further, the interface 201 may allow communication between the meter electronics 20 and external devices. The interface 201 is capable of any one of electrical, optical, or wireless communication.

In one embodiment, interface 201 is coupled to a digitizer (not shown), wherein the sensor signal comprises an analog sensor signal. The digitizer samples and digitizes the analog vibrational response and generates a digital vibrational response 210.

The processing system 203 manages the operation of the meter electronics 20 and processes flow measurements from the meter assembly 10. The processing system 203 executes one or more processing routines and processes the flow measurements accordingly, thereby generating one or more flow characteristics.

The processing system 203 may comprise a general purpose computer, a micro-processing system, a logic circuit, or some other general purpose or customized 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 memory system 204 may store flow meter parameters and data, software programs, constants, and variables. In one embodiment, the memory system 204 includes a program executed by the processing system 203, such as a stiffness program 230 that determines a stiffness parameter (K) of the flow meter 5.

In one embodiment stiffness routine 230 may arrange processing system 203 to receive vibrational responses from the flow meterThe vibrational response includes a response to vibration of the flow meter at the fundamental resonant frequency, and a frequency (ω) of the vibrational response is determined₀) Determining the response voltage (V) and drive current (I) of the vibrational response, measuring the attenuation characteristic (ζ) of the flow meter, and deriving the frequency (ω) from the measured attenuation characteristic (ζ)₀) In response to the voltage (V), the drive current (I) and the decay characteristic (ζ) determine the stiffness parameter (K) (see fig. 3 and related discussion).

In one embodiment, stiffness program 230 may arrange processing system 203 to receive the vibrational response, determine the frequency, determine the response voltage (V) and drive current (I), measure the decay characteristic (ζ), and determine the stiffness parameter (K). In this embodiment stiffness program 230 further arranges for processing system 203 to at a second time t₂Receives a vibrational response from the flow meter, repeats the determining and measuring steps for a second vibrational response, and generates a second stiffness characteristic (K)₂) Comparing the second stiffness characteristics (K)₂) With a stiffness parameter (K) and if the second stiffness characteristic (K) is₂) If the difference from the stiffness parameter (K) is greater than the tolerance 224, then the stiffness change (Δ K) is detected (see fig. 4 and related discussion).

In one embodiment, the memory system 204 stores variables used to operate the flow meter 5. The storage system 204 in one embodiment stores variables, such as vibration responses 210, which may be received from the speed/pickup sensors 170L and 170R, for example.

In one embodiment, the storage system 204 stores constants, coefficients, and working variables. For example, the storage system 204 may store the determined stiffness characteristic 220 and a second stiffness characteristic 221 generated at a subsequent point in time. The memory system 204 may store operating values such as the frequency 212 of the vibrational response 210, the voltage 213 of the vibrational response 210, and the drive current 214 of the vibrational response 210. The storage system 204 may further store the vibration target 226 and the measured attenuation characteristics 215 of the flow meter 5. Further, the storage system 204 may store constants, thresholds, or ranges, such as the tolerance 224. In addition, the storage system 204 may store data, such as stiffness changes 228, accumulated over a period of time.

FIG. 3 is a flow chart 300 of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention. In step 301, a vibrational response is received from a flow meter. The vibrational response is a response of the flow meter to vibration at the fundamental resonant frequency. The vibration may be continuous or intermittent. The flow material may flow through the meter assembly 10 or may be stable.

In step 302, the frequency of the vibrational response is determined. From the vibration response, the frequency ω can be determined by any method, procedure or hardware₀。

In step 303, the voltage (V or V) of the vibrational response is determined_BMF) And a drive current (I). The voltage and drive current can be obtained from the vibration response that is not processed or adjusted.

In step 304, the damping characteristics of the flow meter are measured. The damping characteristics are measured by allowing the vibrational response of the flow meter to damp down to the vibrational target while simultaneously measuring the damping characteristics. This attenuation can be performed in several ways. The drive signal amplitude may be reduced, the driver 180 may actually perform the braking of the meter assembly 10 (in a suitable flow meter), or the driver 180 may simply be boosted until the target is reached. In one embodiment, the vibration target comprises a reduced level in the drive setpoint. For example, if the drive set point is currently at 3.4mV/Hz, then for the damping measurement, the drive set point may be reduced to a lower value, such as 2.5 mV/Hz. In this manner, the meter electronics 20 may simply slide the meter assembly 10 until the vibrational response substantially matches the new drive target.

In step 305, a stiffness parameter (K) is determined from the frequency, voltage, drive current and attenuation characteristics (ζ). The stiffness parameter (K) can be determined according to equation (9) above. In addition to determining and tracking the stiffness (K), the method also determines and tracks the damping parameter (C) and the mass parameter (M).

The method 300 may be performed iteratively, periodically, or randomly. The method may be performed at a predetermined landmark (landmark), such as at a predetermined hour of operation, when the flow material changes, etc.

FIG. 4 is a flow chart 400 of a method for determining a change in stiffness (Δ K) of a flow meter according to an embodiment of the invention. In step 401, a vibrational response is received from the flow meter, as previously discussed.

In step 402, the frequency of the vibrational response is determined, as previously discussed.

In step 403, the voltage and drive current of the vibrational response are determined, as previously discussed.

In step 404, the attenuation characteristic (ζ) of the flow meter is measured, as previously discussed.

In step 405, a stiffness parameter (K) is determined from the frequency, voltage, drive current and attenuation characteristics (ζ), as previously discussed.

In step 406, at a second time t₂A second vibrational response is received. At time t₂A second vibrational response is generated from the vibration of the meter assembly 10.

In step 407, a second stiffness characteristic K is generated from the second vibrational response₂. For example, the second stiffness characteristic K may be generated using steps 401 to 405₂。

In step 408, the second stiffness characteristic K₂And comparing with the rigidity parameter (K). The comparison includes a comparison of stiffness characteristics obtained at different times in order to detect a stiffness change (Δ K).

In step 409, K is determined₂And any stiffness change between K (Δ K). The stiffness change determination may employ any manner of statistical or mathematical method for determining a significant change in stiffness. This stiffness change (Δ K) may be stored for future use and/or transmitted to a remote location. In addition, this stiffness change (Δ K) may trigger an alarm condition in the meter electronics 20. The stiffness change (Δ K) in one embodiment is first compared to a tolerance 224. If the stiffness change (Δ K) exceeds tolerance 224, an error is determinedThe situation is. In addition to determining and tracking the stiffness (K), the method also determines and tracks the damping parameter (C) and the mass parameter (M).

The method 400 may be performed iteratively, periodically, or randomly. The method may be performed at a predetermined landmark, such as at a predetermined hour of operation, when the flow material changes, and so forth.

Fig. 5 shows meter electronics 20 according to another embodiment of the invention. The meter electronics 20 in this embodiment may include an interface 201, a processing system 203, and a storage system 204, as previously discussed. The meter electronics 20 receives three or more vibrational responses 505, such as from the meter assembly 10. The meter electronics 20 processes the three or more vibrational responses 505 to obtain flow characteristics of the flow material flowing through the meter assembly 10. Further, the three or more vibrational responses 505 may also be processed to determine a stiffness parameter (K) of the meter assembly 10. The meter electronics 20 may further determine a damping parameter (C) and a mass parameter (M) from the three or more vibrational responses 505. These meter assembly parameters may be used to detect changes in the meter assembly 10, as previously discussed.

The storage system 204 may store processing programs, such as a stiffness program 506. The storage system 204 may store received data, such as the vibrational response 505. The memory system 204 may store preprogrammed or user input values such as stiffness tolerance 516, damping tolerance 517, and mass tolerance 518. The storage system 204 may store working values such as a pole (λ)508 and a residue (R) 509. The storage system 204 may store the determined final values, such as stiffness (K)510, damping (C)511, and mass (M) 512. The memory system 204 may store comparison values generated and operated over a period of time, such as a second stiffness (K)₂)521, second mass (M)₂)522, stiffness change (Δ K)530, damping change (Δ C)531, and mass change (Δ M) 532. The stiffness change (Δ K)530 may include a change in a stiffness parameter (K) of the meter assembly 10 as measured over time. The stiffness change (Δ K)530 may be used to detect and determine physical changes in the meter assembly 10 over time, such as corrosion and erosion effects.Further, the mass parameter (M)512 of the meter assembly 10 may be measured and tracked over time and stored in the mass change (Δ M)532, and the damping parameter (C)511 may be measured over time and stored in the damping change (Δ C) 531. The mass change (Δ M)532 may indicate the increased presence of flow material in the meter assembly 10, and the damping change (Δ C)531 may indicate changes in the flow tube, including material degradation, erosion and corrosion, cracking, and the like.

In operation, the meter electronics 20 receives three or more vibrational responses 505 and processes the vibrational responses 505 using the stiffness program 506. In one embodiment, the three or more vibrational responses 505 include five vibrational responses 505, as will be discussed below. The meter electronics 20 determines a pole (λ)508 and a residue (R)509 from the vibrational response 505. The pole (λ)508 and the residue (R)509 may include a first order pole and residue, or may include a second order pole and residue. The meter electronics 20 determines a stiffness parameter (K)510, a damping parameter (C)511, and a mass parameter (M)512 from the pole (λ)508 and the residue (R) 509. The meter electronics 20 may further determine a second stiffness (K)₂)520, a stiffness change (Δ K)530 may be determined from the stiffness parameter (K)510 and the second stiffness (K)₂) The stiffness change (Δ K)530 may be determined 520 and the stiffness change (Δ K)530 may be compared to the stiffness tolerance 516. If the stiffness change (Δ K)530 exceeds the stiffness tolerance 516, the meter electronics 20 can initiate any manner of error logging and/or error handling routine. Likewise, the meter electronics 20 may further track the damping and mass parameters over time, and may determine and record a second damping (C)₂)521 and a second mass (M)₂) And the resulting damping change (Δ C)531 and mass change (Δ M) 532. Damping change (Δ C)531 and mass change (Δ M)532 may likewise be compared to damping tolerance 517 and mass tolerance 518.

The invention can be described using a mathematical model. With open-loop, the second order drive model can represent the vibrational response of the flow meter, including:

where f is the force applied to the system, M is the mass parameter of the system, C is the damping parameter, and K is the stiffness parameter. The term K includes K ═ M (ω)₀)2, and term C includes C ═ M2 ζ ω₀Wherein ω is₀＝2πf₀And f is and₀is the resonant frequency of the meter assembly 10 in Hz. The term ζ includes the damping characteristic measurement obtained from the vibration response, as previously discussed. In addition, x is the physical displacement distance of the vibration,is the velocity of the flow tube displacement, andis the acceleration. This is commonly referred to as the MCK model. The formula can be rearranged into the following form:

equation (11) can be further processed into a transfer function form while ignoring the initial conditions. The results were:

further processing may transform equation (12) into a first order pole-residue frequency response function form, including:

where λ is the pole, R is the residue, term (j) comprises the square root of-1, and ω is the circular excitation frequency (in radians per second).

The system parameters include a natural/resonant frequency (ω) defined by the poles_n) Damping natural frequency (ω)_d) And a decay characteristic (ζ).

ω_n＝|λ| (14)

ω_d＝imag(λ) (15)

From the poles and residuals, a stiffness parameter (K), a damping parameter (C) and a mass parameter (M) of the system can be obtained.

C＝2ζω_nM (19)

Thus, the stiffness parameter (K), the damping parameter (C) and the mass parameter (M) can be calculated from good estimates of the pole (λ) and the residue (R).

The poles and residuals can be estimated from the measured frequency response function. The pole (λ) and residue (R) can be estimated using some form of direct or iterative computation.

The response near the drive frequency is composed primarily of the first term of equation (13), with the complex conjugate term sharing only a small, approximately constant "remainder" of the response. As a result, equation (13) can be simplified to:

in equation (20), the term H (ω) is the measured Frequency Response Function (FRF), which is obtained from the three or more vibrational responses. In this derivation, H consists of the displacement output divided by the force input. However, in the typical case of voice coil pick-up for a coriolis flow meter, the measured FRF (i.e., the FRF)Term) is based on velocity divided by force. Thus, equation (20) can be transformed into the following form:

equation (21) can be further rearranged into a form that is easily solved for the pole (λ) and the residue (R).

Equation (22) forms an over-determined system of equations. The solution equation (22) may be calculated to derive the velocity/force FRFThe pole (λ) and the residue (R) are determined. The terms H, R and λ are complex numbers.

In one embodiment, forced frequency (forcing frequency) ω is 5 tones. The 5 tones in this embodiment include the drive frequency and 2 tones above the drive frequency and 2 tones below the drive frequency. These tones may be separated from the fundamental frequency by 0.5-2 Hz. However, the forced frequency ω can include more tones or fewer tones, such as 1 tone above and below the drive frequency. However, a good compromise between the accuracy of the 5-tone impact result and the processing time required to obtain this result.

Note that in the preferred FRF measurement, two FRFs are measured for a particular drive frequency and vibration response. One FRF measurement is obtained from the driver to Right Pick (RPO) and one FRF measurement is obtained from the driver to Left Pick (LPO). This approach is referred to as single input, multiple output (SIMO). In a distinguishing novel feature of the present invention, the SIMO technique is used to better estimate the pole (λ) and residue (R). Previously, two FRFs were used to give two separate pole (λ) and residue (R) estimates, respectively. It can be appreciated that the two FRFs share a common pole (λ), but separate residuals (R)_L) And (R)_R) The two measurements can be advantageously combined in order to obtain a more robust pole and residue determination.

Equation (23) may be solved in any number of ways. In one embodiment, the equations are solved by a recursive least squares method. In another embodiment, the equations are solved by a pseudo-inverse technique. In another embodiment, since all measurements are available at the same time, standard Q-R decomposition techniques may be used. This Q-R decomposition technique is discussed in Modern Control Theory (Modern Control Theory) (William Brogan, copyright 1991, Prentice Hall, pp.222-224, 168-172).

In use, the stiffness parameter (K) as well as the damping parameter (C) and the mass parameter (M) may be tracked over time. For example, statistical techniques may be used to determine any change in the stiffness parameter (K) over time (i.e., stiffness change (Δ K)). The statistical change in the stiffness parameter (K) may indicate that the FCF for a particular flow meter has changed.

The invention provides a stiffness parameter (K) independent of a stored or retrieved calibration density value. This is in contrast to the prior art, where known flow materials are utilized in factory calibration operations in order to obtain density standards that can be used for all future calibration operations. The present invention provides a stiffness parameter (K) derived solely from the vibrational response of the flow meter. The present invention provides a stiffness detection/calibration method that does not require a factory calibration step.

FIG. 6 is a flow chart 600 of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention. In step 601, three or more vibrational responses are accepted. The three or more vibrational responses may be received from a flow meter. The three or more vibrational responses may include a fundamental frequency response and two or more non-fundamental frequency responses. In one embodiment, one tone is received that exceeds the fundamental frequency response and one tone is received that is below the fundamental frequency response. In another embodiment, two or more tones are received that exceed the fundamental frequency response and two or more tones are received that are below the fundamental frequency response.

In one embodiment, the tones are spaced substantially equidistant above and below the fundamental frequency response. Alternatively, the tones are not equally spaced.

In step 602, a first order pole-residue frequency response is generated from the three or more vibrational responses. The first order pole-residue frequency response has the form given in equation (23).

In step 603, a quality parameter (M) is determined from the first order pole-residue frequency response. The mass parameter (M) is determined by determining a first order pole (λ) and a first order residue (R) of the vibrational response. Then, the natural frequency ω is determined from the first order pole (λ) and the first order residue (R)_nDamping natural frequency omega_dAnd a decay characteristic (ζ). Subsequently, the natural frequency ω is damped_dThe residue (R) and imaginary term (j) are inserted into equation (17) to obtain the quality parameter (M).

In step 604, a stiffness parameter (K) is determined from the solution of equation (18). The solution uses the natural frequency omega_nAnd the mass parameter (M) determined from step 603 is inserted into equation (18) to obtain the stiffness parameter (K).

In step 605, a damping parameter (C) is determined from the solution of equation (19). The solution uses the attenuation characteristic (ζ), the natural frequency ω_nAnd the determined quality parameter (M).

FIG. 7 illustrates an implementation of the pole (λ) and residue (R) solution in accordance with an embodiment of the invention. This embodiment follows equation (23). The FRF input is on the left side of the figure. These FRF inputs are in this embodiment five frequencies (four test signal frequencies and a drive frequency) at which the FRF coefficients are calculated. The FRF _ L and FRF _ R inputs are the driver pickup complex FRF coefficients calculated at those frequencies, corresponding to equation (23)Andthese FRF coefficients enter the B input of QR solver block 701. The a matrix for the QR solver block 701 is formed on a term-by-term basis from FRF coefficients divided by j ω, and includes 1 and 0 columns so as to conform to equation (23). The matrix is redefined to the appropriate [10 x 3 ]]Complex dimension and enters the a input of QR solver block 701. The x-vector output of QR solver block 701 includes left and right residuals R_LAnd R_RAnd a pole lambda. For processing, these outputs are passed out of the QR block 701 to generate system parameters.

FIG. 8 is a block diagram illustrating the calculation of M, C and K system parameters according to an embodiment of the present invention. This embodiment determines the M, C and K system parameters from the pole and residue estimates of each of equations (14-16) and equations (17-19). These residuals are purely imaginary to the true standard modal model. However, due to noise in the measurement data and due to model fitting numerical accuracy issues, there will often be some real part. Thus, the absolute value of the residue is used, which has a similar effect of dividing j for each equation (17). The mass and stiffness are calculated using the poles and residuals of each equation (17-18). It is noted that there are "left" and "right" masses and stiffnesses, i.e., the mass stiffness calculated from the FRFs of the LPO/driver and the RPO/driver. Due to the asymmetry of the coils and magnets and the structure itself, from right to left, the mass and stiffness estimates may differ. The change in differential or differential ratio represents a non-uniform change in mass or stiffness and can be used to give additional diagnostic information about the integrity of the flow or change in FCF.

Two other outputs from the system parameter calculation are the damping coefficient, Z (zeta) or zeta, and the natural frequency ω_n. This embodiment gives a more certain or better estimated global parameter set.

ω_nThe evaluation of (a) results in a good quality check for the closed-loop drive system. If the drive is actually operating at resonance, the drive frequency will be within a few millihertz (agreeto) for the natural frequency estimation. If the difference is greater than a few millihertz, an alarm flag may be set indicating that the drive system is not working properly or that the current stiffness estimate is suspect.

FIG. 9 illustrates an overall FRF-based stiffness estimation system in accordance with embodiments of the invention. There are seven different inputs to the stiffness estimation subsystem, represented by pentagons as signal sources (five on the top left and two on the far right). The "Rawdrive" and "RawPOs" inputs are raw readings of the pickup voltage and drive current. These signals are down-sampled to 2kHz, for example by decimation (decimation), and then fed into the FRF coefficient estimation subsystem. The "CmdmA" input is the command current drawn from the output of the corresponding digital drive system. The "StiffnessEnable" estimate is a logical input, allowing the digital drive system to control when the FCF check algorithm is valid. The "freq" input is the drive frequency, as estimated by the digital drive system. It is the input to the test signal generator subsystem and the stiffness calculation subsystem.

The FRF stiffness calculation block 902 outputs system parameter estimates M and K left and right as well as ζ and FreqEst. These are the main diagnostic outputs used in the FCF check. The figure also shows a frequency differential alarm block 903 and a frequency differential error block 904 that implement the drive quality check discussed above by comparing the drive frequency to the estimated natural frequency.

Measuring FRF typically requires current measurement, requiring an additional analog-to-digital (a/D) converter. However, this embodiment utilizes a calibrated command current, avoiding the need for an additional A/D converter. The CL input selection block 906 and the CL output correction block 907 perform a calibration algorithm. This calibration step utilizes a "test signal FRF" block 901 to calculate the frequency response function of the actual (RawDrive) current versus the command current (CmdmA) at one state of the control logic. During FCF check logic states, the FRF between the original POs and the command current is calculated and corrected by raw data for the command current FRF coefficient to give the FRFs for further processing.

The FRF stiffness estimation algorithm outputs a "test signal" output at the left of the center of the graph. The test signal output includes stimuli at four test frequencies that are added to the drive commands immediately prior to output. These test signals are added to the digital drive signal when FCF verification is enabled.

The logic is such that: when the FCF check is off, the digital drive signal just passes through a switch or other means, in this case an interpolation filter, to up-sample the digital drive signal from its base rate (typically 4kHz) to a suitable output rate (typically 8 kHz). When FCF verification is enabled, a test signal up-sampled from 2 to 4kHz is added to the digital drive signal. The drive signal is then composed of the closed loop drive frequency signal and 4 test tones, which are then all passed through an upsampling filter.

The FCF check program is desirably transparent to the drive system. In one embodiment, the test signal is removed from the pick-up to ensure good frequency and amplitude estimation for the closed loop drive. This is done with a set of notch filters tuned to the exact frequency of the test signal.

In another embodiment, the pole-residue approach may employ a second order pole-residue frequency response function, thereby achieving better results. The second order pole-residue method provides a more realistic fit to real numbers than the first order pole-residue method. The trade-off is greater numerical complexity and increased processing time.

The MCK embodiment of the stiffness estimation starts with a simple second order system model, as shown in equation (24) below. Due to the pick-up of the meter measurement speed, not the position, the equation is differentiated and then estimated at a specific frequency ω.

Since the goal is to solve for M, C and K from measurements of drive current (or force) and pickup voltage (or velocity), conveniently, equation (24) is rewritten to separate the unknowns. This yields equation (25).

At this point, the equation can be split into real and imaginary parts.

Is unfoldedEquation (26) can be rewritten as:

the second equation is now a simple, algebraic algorithm. To further simplify the first part of the equation, the measured resonant drive frequency is used. Due to the fact thatIt is thus possible to establish:

as long as ω ≠ ω_n. Returning M from the solution for K,three solutions for M, C and K are given in equation (29).

Note that given a resonant frequency ω_nA specific frequency ω₁The driver at (a) picks up the FRF enough to solve the equation and determine the parameters M, C and K. This is particularly useful; when FRFs are obtained at multiple frequencies, the least squares fit to the data is simply the average of the individual estimates for each coefficient. This is more than the pseudo-inverse that would typically have to be performedSimple and good processing mode. However, it should be noted that ω ≠ ω_nThe limitation of (1) excludes the use of resonant drive FRF in solving for K or M. This is not particularly surprising since the height of the peak at resonance is determined only by damping. However, one potential drawback of this approach is: the parameters estimated from the left and right pickup data must not depend on each other. This is in contrast to the pole-residue approach, where some advantage is gained by limiting the left and right pickups to estimate the same pole, regardless of their difference in amplitude.

FIG. 10 is a flow chart 1000 of a method for determining a stiffness parameter (K) of a flow meter according to an embodiment of the invention. In step 1001, three or more vibrational responses are received, as previously discussed.

In step 1002, a second order pole-residue frequency response is generated from the three or more vibrational responses. The second order pole-residue frequency response has the form given in equation (24).

In step 1003, a stiffness parameter (K) is determined from the solution of equation (29). The solution uses the natural frequency omega_nThe imaginary part of one or more frequency tones ω, FRF (i.e. the imaginary part of the frequency tone or tones ω, FRF)The imaginary part of) and the amplitude of the FRF (i.e., the FRF amplitude)Absolute value of).

In step 1004, a quality parameter (M) is determined from the second order pole-residue frequency response. Determining a mass parameter (M) from the solution of equation (29) and using the stiffness parameter (K) and the natural frequency ω_nThe quality parameter (M) is obtained.

In step 1005, a damping parameter (C) is determined from the second order pole-residue frequency response. Determining a damping parameter (C) from the solution of equation (29) and using the real part of the one or more frequency tones ω, FRF (i.e., the real part of the frequency tones ωReal part of) and the amplitude of the FRF (i.e., the FRF)Absolute value) to obtain the damping parameter (C).

FIG. 11 shows an implementation of the solution from equation (29) for M, C, and K for the second order pole-residue response in accordance with an embodiment of the invention. The input appears as an elliptical input port at the left of the figure. These are the measured drive frequencies ω _ drive, which are used in equation (29) as ω_nFive frequencies at which the FRF coefficients are calculated (four test signal frequencies and drive frequency, denoted by ω test), and drivers calculated at those frequencies pick up the complex FRF coefficients ((r) ("FRF coefficientsOr Hdot). The drive frequency FRF is discarded (discard) by the selector block because it cannot be used in the M and K solutions as described previously. The K solution is calculated as:

which is the equivalent of the solution given in equation (29). The solution for C is the same form as the derived solution in equation (29), and M is calculated directly from the solution for K. Note that an averaging operation is applied to each coefficient estimate. The result of this averaging in the solution method is a least squares fit to the input data. Finally, given the M, C and K estimates, the decay characteristic (ζ or Z) is calculated as:

the attenuation characteristic (ζ) is considered to be a more useful parameter than the damping parameter C. Therefore, the mass M, the stiffness K, and the attenuation characteristic (ζ) are the outputs of the measurement.

FIG. 12 illustrates an overall FRF-based stiffness estimation system in accordance with an embodiment of the present invention. There are six different inputs to the system, represented by pentagons as signal sources (three above the left and three below the right). The "Rawdrive" and "RawPOs" inputs are raw readings from the pick-up and drive currents. These are down-sampled to 2kHz by a Decimator (Decimator) block 1201 and then fed into the FRF coefficient estimation subsystem. The "DriveDemod" inputs are the sine and cosine signals at the drive frequency obtained from the digital drive system. These signals are combined with the sinusoids generated at the test frequency and fed into the FRF coefficient estimation subsystem as a basis for demodulation. The "StiffnessEnable" estimate is a logical input that allows the digital drive system to control when the stiffness estimation algorithm is active. The "freq" input is the drive frequency, as estimated by the digital drive system. Which is an input to the test signal generation block 1204 and the stiffness calculation block 1206. The "Temp" input is the temperature reading from the flow meter that is input into the temperature correction block 1207. The FRF stiffness estimation algorithm outputs the system parameter estimates, as well as the "test signal" output at the far left of the graph. The test signal output includes stimuli at four test frequencies that are added to the driver commands.

These inputs and outputs form the interface ensemble (bulk) to the digital drive. The test signal is added to the drive command immediately before the output to the driver device. In order for this FCF check program to be transparent to the drive system, the test signal must be removed from the pick-up. This may be done in one embodiment with a set of notch filters tuned to the exact frequency of the test signal.

The test signal FRF block 1208 of fig. 11 performs demodulation. The pick-up and drive signals are demodulated at each of five input frequencies (four resulting test signal frequencies and a drive frequency). After complex demodulation using sine and cosine basis, the real and imaginary parts of each signal are decimated down to lower frequencies and low pass filtered to 0.4 Hz. These signals must be uncontaminated in this region because any spectral components in the 0.4Hz of the test signal will not be suppressed and will appear as output. The complex coefficients for the pick-up and drive currents at each frequency are then used to estimate the FRF at that frequency. The power spectrum is averaged over multiple samples and a lower rate FRF estimate is output.

The meter electronics and methods according to the present invention may be employed according to any of the embodiments, thereby providing several advantages, if desired. The invention provides a stiffness parameter (K) that is substantially related to the stiffness of a flow tube of a flow meter. The present invention provides a stiffness parameter (K) that does not depend on a stored or retrieved calibration value for generation. The present invention provides a stiffness parameter (K) derived solely from the vibrational response of the flow meter. Likewise, the invention provides a mass parameter (M) and a damping parameter (C) from the vibrational response.

The present invention provides a stiffness detection/calibration method that does not require a factory calibration step. The present invention may perform the stiffness/FCF calibration method in the field. The present invention can perform the stiffness/FCF calibration method at any time. The present invention can perform a stiffness/FCF calibration method that does not require calibration of the test ring and/or known flow materials. The present invention can implement a stiffness/FCF calibration method that determines changes in stiffness of a flow meter over time.

Claims (11)

1. Meter electronics (20) for a flow meter (5), the meter electronics (20) including an interface (201) for receiving a vibrational response from the flow meter (5), the vibrational response including a response to vibration of the flow meter (5) at a fundamental resonant frequency; and a processing system (203) in communication with the interface (201), the meter electronics (20) further comprising:

the processing system (203) is arranged to receive the vibrational response from the interface (201), determine a frequency ω of the vibrational response₀Determining the response voltage V and drive current I of the vibrational response, measuring the flow meter (5)) And from frequency ω, and₀in response to the voltage V, the drive current I and the damping characteristic ζ determine a stiffness parameter K, which includes K ═ BL (I × BL)_P0*BL_DR*ω₀) V,/2 ζ, wherein BL_P0Pickup sensitivity factor for pickup sensors used for measuring vibrational response, BL_DRIs a driver sensitivity factor for a driver used to measure the attenuation characteristic ζ of the flow meter (5).

2. The meter electronics (20) of claim 1, with measuring the decay characteristic ζ further comprising allowing a vibrational response of the flow meter (5) to decay down to a predetermined vibrational target.

3. The meter electronics (20) of claim 1, with the processing system (203) further arranged to measure the damping characteristic ζ by removing excitation of the flow meter (5) and allowing a vibrational response of the flow meter (5) to damp down to a predetermined vibrational target while measuring the damping characteristic.

4. A method for determining a stiffness parameter K of a flow meter includes receiving a vibrational response from the flow meter, the vibrational response comprising a response to vibration of the flow meter at a fundamental resonant frequency, and determining a frequency ω of the vibrational response₀The method further comprises:

determining a response voltage V and a driving current I of the vibration response;

measuring a decay characteristic ζ of the flow meter; and

from frequency omega₀In response to the voltage V, the drive current I and the damping characteristic ζ determine a stiffness parameter K, which includes K ═ BL (I × BL)_P0*BL_DR*ω₀) V,/2 ζ, wherein BL_P0Pickup sensitivity factor for pickup sensors used for measuring vibrational response, BL_DRIs the driver sensitivity factor of the driver used to measure the attenuation characteristic ζ of the flow meter.

5. The method of claim 4, measuring the decay characteristic ζ further comprises allowing the vibrational response of the flow meter to decay down to a predetermined vibrational target.

6. The method of claim 4, measuring the decay characteristic ζ further comprising:

removing excitation of the flowmeter; and

the damping characteristics are measured while allowing the vibrational response of the flow meter to damp down to a predetermined vibrational target.

7. A method for determining a stiffness change Δ K of a flow meter, the method comprising receiving a vibrational response from the flow meter, the vibrational response comprising a response to vibration of the flow meter at a fundamental resonant frequency, and determining a frequency ω of the vibrational response, the method further comprising:

determining a response voltage V and a driving current I of the vibration response;

measuring a decay characteristic ζ of the flow meter;

from frequency omega₀In response to the voltage V, the drive current I and the damping characteristic ζ determine a stiffness parameter K, which includes K ═ BL (I × BL)_P0*BL_DR*ω₀) V,/2 ζ, wherein BL_P0Pickup sensitivity factor for pickup sensors used for measuring vibrational response, BL_DRA driver sensitivity factor for a driver used to measure a decay characteristic ζ of the flow meter;

at a second time t₂Receiving a second vibrational response from the flow meter;

generating a second stiffness characteristic K from a second vibrational response₂；

Comparing the second stiffness characteristics K₂And a stiffness parameter K; and

if the second stiffness characteristic K₂And the stiffness parameter K is different by more than a predetermined tolerance, the stiffness change deltak is detected.

8. The method of claim 7, further comprising quantifying a stiffness change Δ K from the comparison.

9. The method of claim 7, measuring the decay characteristic ζ further comprises allowing a vibrational response of the flow meter (5) to decay down to a predetermined vibrational target.

10. The method of claim 7, measuring the decay characteristic ζ further comprising:

removing excitation of the flowmeter; and

the damping characteristics are measured while allowing the vibrational response of the flow meter to damp down to a predetermined vibrational target.

11. The method of claim 7, producing a second stiffness characteristic K from the second vibrational response₂Includes generating a second stiffness characteristic K from a second frequency, a second response voltage, a second drive current, and a second damping characteristic₂。