External Magnet Compensation for Flow Meter

Abstract

A Coriolis flowmeter (5) is provided, the Coriolis flowmeter (5) comprising flow conduits (103A, 103B) having a driver (104) and pick-off sensors (105, 105') connected thereto. Meter electronics (20) is configured to drive the driver (104) to vibrate the flow conduits (103A, 103B) and receive signals from the pick-off sensors (105, 105'). The meter electronics (20) obtains the voltages of both pick-off sensors (105, 105') and determines PO RATIO and determines whether PO RATIO is within a predetermined PO LIMIT range. If PO RATIO is outside the predetermined PO LIMIT range, the presence of an external magnetic field is indicated, where the meter electronics (20) accesses the correlation between the PO ratio and the flow shift and, if the presence of an external magnetic field is detected, uses the correlation between the PO ratio and the flow shift to calculate a corrected flow rate with the error induced by the external magnetic field corrected.

Description

Technical Field

[0001] The embodiments described below relate to vibration sensors, and more particularly, to the detection and compensation of external magnetic fields thereof.

Background Art

[0002] Vibration sensors such as vibratory density meters and Coriolis flow meters are generally known and are used to measure mass flow rate and other information regarding the material flowing through the conduit in the flow meter. Exemplary Coriolis flow meters are disclosed in U.S. Patent No. 4,109,524, U.S. Patent No. 4,491,025, and U.S. Patent No. 31,450. These flow meters have a meter assembly having one or more conduits in a straight or curved configuration. Each conduit configuration in a Coriolis mass flow meter has a series of natural vibration modes that can be, for example, simple bending, torsion, or combined type. Each conduit can be driven to vibrate in a preferred mode. When there is no flow through the flow meter, the driving force applied to the conduit vibrates all points along the conduit in the same phase or with a small "zero offset" that is the time delay measured at zero flow.

[0003] When the material begins to flow through the conduit, due to the Coriolis force, each point along the conduit has a different phase. For example, the phase at the inlet end of the flow meter lags behind the phase at the central driver position, while the phase at the outlet advances relative to the phase at the central driver position. Pickoffs on the conduit generate a sine wave signal representing the movement of the conduit. The signal output from the pickoff is processed to determine the time delay between the pickoffs, referred to as ΔT. The time delay between two or more pickoffs is proportional to the mass flow rate of the material flowing through the conduit.

[0004] The meter electronics connected to the driver generate a drive signal for operating the driver and also determine the mass flow rate and / or other characteristics of the process material from the signals received from the pickoff. The driver can comprise one of many well-known configurations, but magnets and opposing drive coils have had great success in the flowmeter industry. An alternating current is passed through the drive coil to vibrate the conduit at a desired conduit amplitude and frequency. It is also known in the art to provide the pickoff as a magnet and coil configuration very similar to the driver device.

[0005] When the flow tube vibrates, the pickoff bobbin wire passes through the magnetic field of the magnet to generate a voltage. The main factor for generating such a voltage is the radial magnetic field. If the magnetic field is disturbed or changed during the operation of the meter, it will affect the output of the meter. One way to disturb the magnetic field of the pickoff is to place another magnet in proximity to the pickoff magnet loop. By placing an external magnet near the pickoff of the Coriolis meter, depending on the pole orientation of the external magnet on the meter or the position of the external magnet with respect to the inlet or outlet pickoff and / or the driver, the flow measurement value may change to indicate a higher or lower flow rate. When the magnet is removed, the sensor voltage and phase shift return to normal. This ability to manipulate the flow rate can be disadvantageous to those who are unaware in a flowmeter measurement transaction and has thus been used for that purpose. What is needed is an apparatus and method that compensates for the external magnetic field of the flowmeter such that a corrected flow rate value is reported and the error induced by the external magnetic field is removed. SUMMARY OF THE INVENTION

[0006] A Coriolis flowmeter according to one embodiment is provided. The Coriolis flowmeter includes a flow conduit, a driver and a pickoff sensor connected to the flow conduit, and meter electronics configured to drive the driver to vibrate the flow conduit and receive signals from the pickoff sensor. The meter electronics acquire the voltages of both pickoff sensors and PO RATIOconfigured to determine. The meter electronics also RATIO to determine whether it is within a predetermined PO LIMIT configured to determine whether it is within a predetermined PO RATIO configured to indicate the presence of an external magnetic field when it is outside a predetermined PO LIMIT and further configured to access the correlation between the PO ratio and the flow shift. When the presence of an external magnetic field is detected, the meter electronics uses the correlation between the PO ratio and the flow shift to calculate a compensated flow [Number] where the compensated flow includes the flow with the error induced by the external magnetic field corrected.

[0007] A method of operating a Coriolis flow meter according to an embodiment is provided. The method includes flowing a fluid material through a flow conduit of the flow meter and driving a driver connected to the flow conduit to vibrate the flow conduit in a first bending mode. A signal from a pick-off sensor connected to the flow conduit is received. The voltage of the pick-off sensor is obtained to determine the PO RATIO to determine the PO RATIO is determined whether it is within a predetermined PO LIMIT and the presence of an external magnetic field is indicated when the PO RATIO is outside a predetermined PO LIMIT The correlation between the PO ratio and the flow shift is accessed. When the presence of an external magnetic field is detected, the correlation between the PO ratio and the flow shift is used to calculate a compensated flow [Number] where the compensated flow includes the flow with the error induced by the external magnetic field corrected.

[0008] [Aspect] According to one aspect, a Coriolis flow meter includes a flow conduit, a driver and a pick-off sensor connected to the flow conduit, and meter electronics configured to drive the driver to vibrate the flow conduit and receive a signal from the pick-off sensor. The meter electronics is configured to obtain the voltages of both pick-off sensors and determine PO RATIO . The meter electronics is also configured to determine whether PO RATIO is within a predetermined PO LIMIT . The meter electronics is configured to indicate the presence of an external magnetic field when PO RATIO is outside the predetermined PO LIMIT , and is further configured to access the correlation between the PO ratio and the flow shift. When the presence of an external magnetic field is detected, the meter electronics uses the correlation between the PO ratio and the flow shift to calculate a compensated flow

Number

[0009] Preferably, the correlation between the PO ratio and the flow shift is calculated by the meter electronics.

[0010] Preferably, the correlation between the PO ratio and the flow shift is predetermined and stored in the meter electronics.

[0011] Preferably,

Number

Number

[0012] Preferably, Comp Mag is such that Comp Mag =(m*PO ratioCalculated using an equation composed of +b), where m and b include a gradient constant and an intercept constant, respectively.

[0013] Preferably, Comp Mag The equation of includes one of a linear form and a non - linear form, both including any number of coefficients, and this equation includes relating the PO ratio to ΔT and includes a correlation between the PO ratio and the flow shift.

[0014] Preferably, the correlation between the PO ratio and the flow shift includes at least one of density compensation and temperature compensation.

[0015] According to one aspect, a method of operating a Coriolis flowmeter includes flowing a fluid material through a flow conduit of the flowmeter and driving a driver connected to the flow conduit to vibrate the flow conduit in a first bending mode. A signal from a pick - off sensor connected to the flow conduit is received. The voltage of the pick - off sensor is obtained to determine PO RATIO is obtained. Whether PO RATIO is within a predetermined PO LIMIT is determined, and the presence of an external magnetic field is indicated when PO RATIO is outside a predetermined PO LIMIT The correlation between the PO ratio and the flow shift is accessed. When the presence of an external magnetic field is detected, the correlation between the PO ratio and the flow shift is used to calculate a compensated flow

Number

[0016] Preferably, the method includes calculating the correlation between the PO ratio and the flow shift using meter electronics.

[0017] Preferably, the method includes storing a pre - determined correlation between the PO ratio and the flow shift in the meter electronics.

[0018] Preferably, the method uses a meter electronic device to [Number] and [Number] calculate using an equation composed of

[0019] Preferably, the method uses a meter electronic device to calculate Comp Mag as Mag Comp = (m * PO ratio + b), where m and b include a gradient constant and an intercept constant, respectively.

[0020] Preferably, the equation for Comp Mag includes a linear or non-linear form with any number of coefficients, and this equation includes relating the PO ratio to ΔT and including the correlation between the PO ratio and the flow shift.

[0021] Preferably, the correlation between the PO ratio and the flow shift includes at least one of density compensation and temperature compensation.

Brief Description of the Drawings

[0022] It should be understood that in all the drawings, the same reference numerals represent the same elements. The drawings are not necessarily to scale.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 5C

Figure 6

Figure 7

Figure 8

Figure 9A

Figure 9B

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0023] Figures 1-9B and the following description show specific examples for teaching those skilled in the art how to make and use the best mode of embodiments of a sensor assembly, a brace bar, a driver, and a pickoff sensor. For the purpose of teaching the principles of the present invention, some of the conventional aspects are simplified or omitted. Those skilled in the art will understand the variations from these examples that fall within the scope of this specification. Those skilled in the art will understand that the features described below can be combined in various ways to form multiple variations of the embodiments. As a result, the embodiments described below are not limited to the specific examples described below, but are limited only by the claims and their equivalents.

[0024] FIG. 1 shows a flowmeter 5 according to one embodiment. The flowmeter 5 includes a sensor assembly 10 and meter electronics 20. The meter electronics 20 are connected to the sensor assembly 10 via a lead wire 100 and are configured to provide measurements of density, mass flow rate, volumetric flow rate, total mass flow rate, and temperature, or one or more of other measurements or information via a communication path 26. The flowmeter 5 can include a Coriolis mass flowmeter or other vibrating flowmeter. It will be apparent to those skilled in the art that the flowmeter 5 can include any form of flowmeter 5, regardless of the driver, pickoff sensor, number of flow conduits, or mode of operation of the vibration.

[0025] The sensor assembly 10 includes a pair of flanges 101 and 101', manifolds 102 and 102', a driver 104, pickoff sensors 105 and 105', and flow conduits 103A and 103B. The driver 104 and the pickoff sensors 105 and 105' are connected to the flow conduits 103A and 103B.

[0026] Flanges 101 and 101' are fixed to manifolds 102 and 102'. The manifolds 102 and 102' can be attached at both ends of the spacer 106 in some embodiments. The spacer 106 maintains the spacing between the manifolds 102 and 102'. When the sensor assembly 10 is inserted into a pipeline (not shown) carrying the process fluid to be measured, the process fluid enters the sensor assembly 10 through the flange 101, passes through the inlet manifold 102, where the entire amount of the process fluid is directed to enter the flow conduits 103A and 103B, flows through the flow conduits 103A and 103B, returns to the outlet manifold 102', and exits the sensor assembly 10 through the flange 101'.

[0027] The process fluid can include a liquid. The process fluid can include a gas. The process fluid can include, but is not limited to, a multiphase fluid such as a liquid containing entrained gas and / or entrained solids. The flow conduits 103A and 103B are selected to have substantially the same mass distribution, moment of inertia, and modulus of elasticity about their respective bending axes W-W and W'-W', and are appropriately attached to the inlet manifold 102 and the outlet manifold 102'. The flow conduits 103A and 103B extend outwardly from the manifolds 102 and 102' essentially in parallel.

[0028] The flow conduits 103A and 103B are each in what is called the first out-of-phase bending mode of the flowmeter 5 about their respective bending axes W and W', and are driven in opposite directions by the driver 104. The driver 104 can comprise one of many well-known configurations, such as a magnet attached to the flow conduit 103A and a counter coil attached to the flow conduit 103B. An alternating current is passed through the counter coil, causing vibration in both conduits. An appropriate drive signal is applied to the driver 104 by the meter electronics 20 via the lead wire 110. Other driver devices are contemplated and are within the scope of this specification and the claims.

[0029] The meter electronic device 20 receives sensor signals via lead wires 111 and 111', respectively. The meter electronic device 20 generates a drive signal on lead wire 110, whereby the driver 104 vibrates the flow conduits 103A and 103B. Other sensor devices are contemplated and are within the scope of this specification and the claims.

[0030] The meter electronic device 20, in particular, processes left and right velocity signals from the pickoff sensors 105 and 105' to calculate the flow rate. The communication path 26 provides input and output means that enable the meter electronic device 20 to interface with an operator or other electronic systems. The description of FIG. 1 is provided merely as an example of the operation of the flow meter and is not intended to limit the teachings of the present invention. In some embodiments, single-tube and multi-tube flow meters having one or more drivers and pickoffs are contemplated.

[0031] In one embodiment, the meter electronic device 20 is configured to vibrate the flow conduits 103A and 103B. The vibration is executed by the driver 104. The meter electronic device 20 further receives vibration signals obtained from the pickoff sensors 105 and 105'. The vibration signals include the vibration response of the flow conduits 103A and 103B. The meter electronic device 20 processes the vibration response and determines the response frequency and / or phase difference. The meter electronic device 20 processes the vibration response and determines one or more flow rate measurements, including the mass flow rate and / or density of the process fluid. Other vibration response characteristics and / or flow rate measurements are contemplated and are within the scope of this specification and the claims.

[0032] In one embodiment, the flow conduits 103A and 103B constitute a substantially omega-shaped flow conduit as shown. Alternatively, in other embodiments, the flow meter can comprise a substantially straight flow conduit, a U-shaped conduit, a delta-shaped conduit, etc. Additional flow meter shapes and / or configurations can be used and are within the scope of this specification and the claims.

[0033] Figure 2 is a block diagram of the meter electronics 20 of the flow meter 5 according to an embodiment. During operation, the flow meter 5 provides various measurable values that can be output, including mass flow rate, volumetric flow rate, measured or average values of the mass and volumetric flow rates of individual flow components, and total flow rate including, for example, both volumetric flow rate and mass flow rate.

[0034] The flow meter 5 generates a vibration response. The vibration response is received and processed by the meter electronics 20 to generate one or more fluid measurement values. These values can be monitored, recorded, stored, totaled, and / or output.

[0035] The meter electronics 20 includes an interface 201, a processing system 203 that communicates with the interface 201, and a storage system 204 that communicates with the processing system 203. Although these components are shown as separate blocks, it should be understood that the meter electronics 20 can be composed of various combinations of integrated components and / or individual components.

[0036] The interface 201 is configured to communicate with the sensor assembly 10 of the flow meter 5. The interface 201 can be configured to couple to, for example, the lead wire 100 (see FIG. 1) and exchange signals with the driver 104, the pick-off sensors 105 and 105', and a temperature sensor (not shown). The interface 201 can further be configured to communicate with external devices and the like via the communication path 26.

[0037] The processing system 203 can include any type of processing system. The processing system 203 is configured to read and execute stored routines to operate the flow meter 5. The memory system 204 can store routines including the flow meter routine 205 and the magnetic field detection routine 209. Other measurement / processing routines are contemplated and are within the scope of this specification and the claims. The memory system 204 can store measurement values, received values, operating values, and other information. In some embodiments, the memory system stores

Number

[0038] The flow meter routine 205 can generate and store a quantitative value and a flow measurement value of a fluid. These values can include substantially instantaneous measurement values, and can also include a total value or an accumulated value. For example, the flow meter routine 205 can generate measurement values of mass flow rate and store them, for example, in the mass flow rate 221 storage of the memory system 204. The flow meter routine 205 can generate, for example, measurement values of density 225 and store them in the density 225 storage. The values of mass flow rate 221 and density 225 are determined from the vibration response, as described above and as is also known in the art. The mass flow rate and other measurement values can include substantially instantaneous values, can include samples, can include average values over a certain time interval, or can include accumulated values over a certain time interval. The time interval can be selected to correspond to a time block in which specific fluid conditions, such as a fluid state of only liquid or alternatively a fluid state including liquid and entrained gas, are detected. Additionally, other mass flow rates and related quantitative values are contemplated and are within the scope of this specification and the claims.

[0039] By placing an external magnet near the pickoff of the Coriolis meter, the reading of the flow rate can be changed to indicate a higher or lower flow rate depending on the position of the poles of the external magnet or the position of the external magnet on the flow meter, inlet, or outlet.

[0040] Referring to FIG. 3, by monitoring the meter electronics 20, it can be seen that when the magnets and coils are used in the pickoff sensors 105 and 105', the external magnetic field affects the reading of the sensor assembly 10, regardless of whether it is from an electromagnetic source or a permanent magnet. It is clear that there are relatively steep and symmetric step changes.

[0041] The region indicated by bracket #1 in FIG. 3 represents that a magnet is disposed proximate to the pickoff sensor 105' that is closest to the output of the flowmeter. When the magnet is disposed there, a relatively sharp and symmetric step change in voltage is detected in the signal provided by the pickoff sensor 105' that is disposed closest to the output of the flowmeter (designated as PO in FIG. 3) OUT and shown).

[0042] The region indicated by bracket #2 in FIG. 3 represents that a magnet is disposed proximate to the pickoff sensor 105 that is closest to the input of the flowmeter. When the magnet is disposed there, a relatively sharp and symmetric step change in voltage is also detected in the signal provided by the pickoff sensor 105' that is disposed closest to the output of the flowmeter (designated as PO in FIG. 3) OUT and shown). A voltage spike is also detected in the signal provided by the pickoff sensor 105 that is closest to the input of the flowmeter (designated as PO in FIG. 3) IN and shown). The voltage spike is detected in the signal provided by the driver 104 as well.

[0043] The region indicated by bracket #3 in FIG. 3 represents that a magnet is disposed proximate to the driver 104. A detectable, relatively sharp and symmetric step change in voltage is detected in the signal provided by the driver 104.

[0044] Referring to FIG. 4, it is shown that an external magnet affects the ΔT reading of the flowmeter 5. When the driver 104 stimulates the flow conduits 103A, 103B to vibrate in opposite directions at the natural resonance frequency, the flow conduits 103A, 103B vibrate, and the voltages generated from the respective pickup sensors 105, 105' generate sine waves. This indicates the movement of one conduit relative to the other. The time delay between the two sine waves is referred to as ΔT and is directly proportional to the mass flow rate. When the phase of either of the flow conduits 103A, 103B is affected, ΔT changes. The flow causes a positive change in the phase of one pickup sensor and an equal negative change in the phase of the other pickup sensor.

[0045] The region indicated by bracket #1 in FIG. 4 represents that a magnet is disposed proximate to the pickup sensor 105' that is closest to the output of the flowmeter. When the magnet is disposed there, a relatively steep and symmetric stepwise decrease in ΔT is detected.

[0046] The region indicated by bracket #2 in FIG. 4 represents that a magnet is disposed proximate to the pickup sensor 105 that is closest to the input of the flowmeter. When the magnet is disposed there, a relatively steep and symmetric stepwise increase in ΔT is detected.

[0047] The region indicated by bracket #3 in FIG. 4 represents that a magnet is disposed proximate to the driver 104. When the magnet is disposed there, a relatively steep and symmetric stepwise decrease in ΔT is detected.

[0048] FIGS. 5A - 5C show how the magnetic field in the vicinity of the transducer changes in the presence of another magnet. FIG. 5A shows the magnetic field (dashed line) of the pickup assembly when no magnet is present. FIG. 5B shows the magnetic field when an external magnet is present and the S pole of the magnet is directed towards the pickup assembly, and FIG. 5C shows the magnetic field when an external magnet is present and the N pole of the magnet is directed towards the pickup assembly. As shown in FIG. 4, when the magnetic field is disturbed or changed during the operation of the measuring device, the output of the meter is affected.

[0049] In one embodiment, an approach for detecting magnetic tampering is to monitor the pickoff voltage. In one embodiment, the voltage difference between pickoff sensors 105 and 105' is measured. In one embodiment, the voltage ratio between pickoff sensors 105 and 105' is measured.

[0050] In the following description, the pickoff ratio is described. However, it is considered that the pickoff difference can be used in the same way. Pickoff sensors 105 and 105' are also referred to as LPO (left pickoff) and RPO (right pickoff), respectively.

[0051] FIG. 6 is a flowchart showing a method for determining magnetic tampering. In some embodiments, as shown in step 602, PO ZERO is determined. PO ZERO refers to the average value obtained during the zero adjustment process. PO ZERO = RPO ZERO / LPO ZERO (1) Here, RPO ZERO = the average value obtained during the zero adjustment process of RPO LPO ZERO = the average value obtained during the zero adjustment process of LPO is. The zero adjustment process is usually performed when there is no flow through the flow meter, and the driving force applied to the conduit vibrates all points along the conduit with a small "zero offset" that is the time delay measured at the same phase or zero flow. This process makes it possible to calibrate the flow meter so that the flow rate is not measured in the no-flow state.

[0052] In some embodiments, as shown in step 604, PO RATIO , which is the pickoff voltage ratio obtained while the fluid is flowing and the meter is operating, is measured. PO RATIO = RPO / LPO (2) RPO = Voltage value acquired during the meter operation of RPO LPO = Voltage value acquired during the meter operation of LPO

[0053] In some embodiments, as shown in step 606, PO LIMIT is set. PO LIMIT is the pick-off ratio limit, which is the deviation of PO RATIO from PO ZERO that is allowed before tampering. Since there are many types of flowmeter configurations, operating settings, installation variables, flow variables, and process variables, as will be understood by those skilled in the art, PO LIMIT varies from application to application.

[0054] In step 608, PO RATIO is compared with PO LIMIT . If PO RATIO is within PO LIMIT , the flowmeter is determined to be operating within the "normal" operating range. However, if PO RATIO is outside of PO LIMIT , a flag indicating the possibility of magnetic tampering is generated.

[0055] This approach may provide a flag indicating tampering under certain flow conditions, despite the fact that there was no tampering. In some embodiments, additional logic is added, including monitoring additional meter outputs, to limit the number of "false flags". These outputs can include one or more of mass flow, density, and drive gain.

[0056] A flowchart showing additional checks for reducing incorrect flags is shown in FIG. 7. In this embodiment, several system states can be returned, namely "normal", "flag", and "transition". The normal state means that all pilot variables and pick-off ratios are within their confidence intervals. The flag state means that all pilot variables are within their confidence intervals, but the pick-off ratio is outside its confidence interval. The transition state means that at least one pilot variable is outside its confidence interval. Each of these system states is simply stored as a numerical code and can be read back as such, for example via Modbus communication. The numerical code may be converted to text for human readability and may be displayed on a display.

[0057] In step 702, a plurality of zero variables are collected. The zero variables can include RPO and LPO signals, flow tube frequencies, drive gains, fluid densities, attenuation coefficients, and other flowmeter variables known in the art.

[0058] In step 704, the pick-off voltage ratio PO RATIO acquired while the fluid is flowing and the flow meter is operating is calculated according to Equation (1). In step 706, the zero variables collected over time, including the pick-off voltage ratio, are averaged and / or the standard deviation is calculated. The average and standard deviation of each variable are stored in the storage system 204 using an appropriate data structure such as an array.

[0059] Steps 702-706 are repeated under zero process or zero adjustment conditions. This helps to create a baseline for all collected variables that can be set for comparison purposes during process conditions. These values may be set at the factory during manufacturing and calibration, or may be set / reset in the field (i.e., after installation) under zero adjustment conditions.

[0060] In step 708, the flowmeter is operated under process conditions and operating variables are collected. The operating variables are from the same set of variables as those collected during zero process, but instead are collected under process conditions. The operating variables can include RPO and LPO signals, flow tube frequency, drive gain, fluid density, attenuation coefficient, and other flowmeter variables known in the art. These operating variables are collected over time, averaged and / or a standard deviation is calculated. The PO during operation RATIO is also calculated. Using an appropriate data structure such as an array, the average and standard deviation of the RPO signal and LPO signal, and the PO RATIO are stored in the storage system 204.

[0061] In step 710, some of the operating variables are compared to zero variables. In particular, the flow tube frequency, drive gain, fluid density, and / or attenuation coefficient are compared and it is determined whether all of the compared values are within a confidence interval.

[0062] The confidence interval can be determined empirically based on aiming for a desired result, as will be understood by those skilled in the art. In one embodiment, the confidence interval (CI) for a particular variable of interest (Vi) has the following formula. CI = 2 * StdDev Vi + deadband * Avg Vi (3) where StdDev Vi = standard deviation of the variable of interest deadband = coefficient to buffer observable response Avg Vi = measured average of the variable of interest is. The deadband is determined empirically to adjust the sensitivity of the system.

[0063] If any of these variables is outside its respective confidence interval, the "transition" flag state is made active. However, if all of the variables are within their respective confidence intervals, PO RATIO is compared in step 712. In particular, in step 712, the operation PO RATIO is compared with the zero PO RATIO previously determined in steps 702-704. If the operation PO RATIO is within its confidence interval, a "normal" state is returned. However, if the operation PO RATIO is outside its confidence interval, a "flag" state indicating the possibility of a magnetic tampering event is returned.

[0064] Note that if the zero value is not stored, the flowchart of FIG. 7 may start at step 708. In this case, a reference value is substituted for the comparison instead of the zero value. The reference value is an estimated value stored in memory that approximates the ideal zero value. These values vary based on details of the flow meter such as shape, size, construction material, transducer placement and type. In one embodiment, one or more zero variables can be replaced with reference values.

[0065] Returning to step 712, the following is an example of how this flowchart can be implemented in one embodiment. The pseudocode is provided merely as an aid for clarity and should not be construed as a limitation.

[0066] The first step can be to check for density changes using the density ratio. ρ’ r =(ρ m / ρ zero ) (4) Here, ρ m = measured density ρ’ r = average density ratio ρ zero = density reference value Once the density ratio is established, the following example of logic can be applied. ρ’r <=(1 - ρ l ) in the case of Check status = "Transition" Otherwise ρ' r <=(1 + ρ l ) in the case of Check status = "Transition" Otherwise Check status = "Normal" Here, ρ l = density range limit.

[0067] Another output check can be the drive gain change using the drive gain ratio. Dg r =(Dg m / Dg zero ) (5) Here, Dg m = measured drive gain Dg r = average drive gain ratio Dg zero = drive gain reference value Once the average drive gain ratio is established, the following example of logic can be applied. Dg m = 100 in the case of Check status = "Transition" Otherwise Dg r <=(1 - Dg l ) in the case of Check status = "Transition" Otherwise Dg r <=(1 + Dg l ) in the case of Check status = "Transition" Otherwise Check status = "Normal" Here, Dg l = drive gain range limit.

[0068] Finally, as shown in Equation (2), the logic of the pick-off ratio is applied. PO r <(PO ZERO - PO limitIn the case of Check state = "flag" PO r <(PO ZERO +PO limit ) case Check state = "flag" If not Check state = "normal" Here, PO limit = PO range limit.

[0069] An example of the combined logic shown using pseudocode is shown in FIG. 8. Note that the flow rate, density, and drive gain variables may or may not be present depending on some embodiments, and the order in which they are analyzed may be different. Referring to FIG. 9B, it will be apparent that applying the above flow condition logic to the PO ratio data of FIG. 9A results in significantly fewer incorrect check values ("incorrect flags") than using the pick-off ratio alone for a given PO limit.

[0070] In addition to simply detecting magnetic tampering, in some embodiments, the meter electronics 20 can perform compensation to overcome the effects of such tampering. FIG. 10 shows an example in which the PO value of a Coriolis flow meter changes from a baseline value to a new value due to the application of an external magnetic field. The dashed line represents the PO ratio and the solid line represents Δt. The amount of change in the PO ratio can be correlated with the amount of flow shift. This correlation can be used to compensate the flow signal and remove the amount of error induced in the meter. The region indicated by (1) in FIG. 10 represents that a magnet is disposed close to the pick-off sensor 105' closest to the output of the flow meter. The region indicated by (2) in FIG. 10 represents that a magnet is disposed close to the pick-off sensor 105 closest to the input of the flow meter. The region indicated by (3) in FIG. 10 represents that a magnet is disposed close to the driver 104. In any case, a significant change in the PO ratio is detectable.

[0071] In one embodiment, the correlation between the PO ratio and the flow shift is calculated by the meter electronics. In one embodiment, the correlation between the PO ratio and the flow shift is empirically predetermined and stored in the meter electronics. In some embodiments, the meter electronics 20 accesses the correlation between the PO ratio and the flow shift for use in compensation.

[0072] FIG. 11 shows an exemplary graph of the relationship of the PO ratio versus the flowmeter delta t (Δt) caused by an external magnet. The equation of the slope of the line on the graph can be used as a basis for the relationship to remove the influence of the external magnet. The equation of the slope on the graph is shown as an example only. It will be understood that other equations of the slope may be applicable to different flowmeters.

[0073] The basis of magnetic compensation arises from the fundamental equation for determining mass flow.

Number

Number

[0074] However, Equation (6) is modified to address magnetic tampering, and as a result, the corrected flow

Number

Number

[0075] In an alternative embodiment, the effects of density and temperature can also be considered. [Number] Here, c1 = density compensation c2 = temperature compensation ρ = fluid density ρ cal = density of the calibration fluid measured by the flow meter T = temperature measured by the flow meter T cal = temperature of the calibration fluid measured by the flow meter

[0076] Equation (9) shows both temperature compensation and density compensation. Those skilled in the art will understand that in some embodiments, only density or only temperature is used when calculating the compensated flow rate. The values of c1 and c2 are determined from tests at the test temperature or test density and reflect the magnitude of the compensation change for changes in temperature and / or density.

[0077] FIG. 12 shows a graph of the PO ratio (dashed line) and the uncompensated flow signal (thick solid line) and the compensated flow signal (dotted line). It can be seen that by applying the compensation method described above, the flow signal output by the meter electronics 20 can be corrected despite undesirable changes in the PO ratio.

[0078] The detailed description of the above embodiments is not an exhaustive description of all embodiments intended by the inventors to be within the scope of this description. In fact, those skilled in the art will understand that it is possible to create additional embodiments by variously combining or deleting specific elements of the above embodiments, and that such additional embodiments will fall within the scope of this description and the scope of the teachings. Also, it will be apparent to those skilled in the art that it is possible to create additional embodiments within the scope and teachings of this specification by combining the above embodiments in whole or in part.

[0079] Accordingly, while specific embodiments are described herein for purposes of illustration, various equivalent modifications are possible within the scope of this specification, as will be understood by those skilled in the art. The teachings provided herein apply not only to the embodiments described above and shown in the accompanying drawings, but also to other sensors, sensor brackets, and conduits. Accordingly, the scope of the above-described embodiments should be determined from the following claims.

Claims

1. Flow conduits (103A, 103B), A driver (104) and pick-off sensors (LPO, 105; RPO, 105') connected to the flow conduits (103A and 103B), And Meter electronics (20) configured to drive the driver (104) to vibrate the flow conduits (103A, 103B) and receive signals from the pick-off sensors (105, 105'), Comprising, The meter electronics (20) is configured to obtain the voltages of both pick-off sensors (105, 105') and determine PO ＲＡＴＩＯ is configured to determine, The meter electronics (20) is configured to determine whether the PO ＲＡＴＩＯ is within a predetermined PO ＬＩＭＩＴ is configured to determine whether it is within, The meter electronics (20) is configured to indicate the presence of an external magnetic field when the PO ＲＡＴＩＯ is outside a predetermined PO ＬＩＭＩＴ is configured to indicate the presence of an external magnetic field when it is outside, The meter electronics (20) is configured to access the correlation between the PO ratio and the flow shift, The meter electronics (20), when the presence of an external magnetic field is detected, uses the correlation between the PO ratio and the flow shift to calculate a compensated flow 【Number 15】 is configured to calculate, the compensated flow including a flow rate in which an error induced by an external magnetic field is corrected, a Coriolis flow meter (5).

2. The Coriolis flow meter (5) according to claim 1, wherein the correlation between the PO ratio and the flow shift is calculated by the meter electronics (20).

3. The Coriolis flow meter (5) according to claim 1, wherein the correlation between the PO ratio and the flow shift is predetermined and stored in the meter electronics (20).

4. 【Number 16】 is, 【No. 17】 The Coriolis flowmeter (5) according to claim 1, which is calculated using an equation composed of

5. Comp Ｍａｇ where Comp Ｍａｇ = (m * PO ｒａｔｉｏ + b), and m and b include a gradient constant and an intercept constant respectively. The Coriolis flowmeter (5) according to claim 4.

6. The equation of Comp Ｍａｇ includes one of a linear form and a non - linear form, both including any number of coefficients, the equation includes associating the PO ratio with the ΔT, and includes a correlation between the PO ratio and a flow shift. The Coriolis flowmeter (5) according to claim 4.

7. The correlation between the PO ratio and the flow shift includes at least one of density compensation and temperature compensation. The Coriolis flowmeter (5) according to claim 1.

8. A method for operating a Coriolis flowmeter, comprising: flowing a fluid material through a flow conduit of the flowmeter; driving a driver connected to the flow conduit to vibrate the flow conduit in a first bending mode; receiving a signal from a pick - off sensor connected to the flow conduit flow; obtaining the voltage of the pick - off sensor to determine PO ＲＡＴＩＯ ; determining whether the PO ＲＡＴＩＯ is within a predetermined PO ＬＩＭＩＴ , and indicating the presence of an external magnetic field when the PO ＲＡＴＩＯ is outside the predetermined PO ＬＩＭＩＴ ; accessing the correlation between the PO ratio and the flow shift and when the presence of an external magnetic field is detected, using the correlation between the PO ratio and the flow shift to obtain a compensated flow 【No. 18】 A step of calculating, wherein the compensated flow rate includes a flow rate in which an error induced by an external magnetic field is corrected A method comprising

9. The method for operating a Coriolis flowmeter according to claim 8, comprising a step of calculating a correlation between the PO ratio and the flow shift using the meter electronics

10. The method for operating a Coriolis flowmeter according to claim 8, comprising a step of storing a correlation between a predetermined PO ratio and a flow shift in the meter electronics

11. Using the meter electronics 【No. 19】 to 【No. 20】 The method for operating a Coriolis flowmeter according to claim 8, comprising a step of calculating using an equation composed of

12. Using the meter electronics to calculate Comp Ｍａｇ to Comp Ｍａｇ = (m * PO ｒａｔｉｏ + b), where m and b include a gradient constant and an intercept constant, respectively. The method for operating a Coriolis flowmeter according to claim 11

13. The equation of Comp Ｍａｇ includes a linear or non-linear form including any number of coefficients, and the equation associates the PO ratio with the ΔT and includes a correlation between the PO ratio and the flow shift. The method for operating a Coriolis flowmeter according to claim 11

14. The method for operating a Coriolis flowmeter according to claim 8, wherein the correlation between the PO ratio and the flow shift includes at least one of density compensation and temperature compensation.

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