External magnetic detection of the flow meter

Abstract

A Coriolis flowmeter (5) is provided, which includes 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) acquires the voltages of both pick-off sensors (105, 105') and determines PO RATIO and determines whether PO RATIO is within a predetermined PO LIMIT It is configured to determine whether it is inside. PO RATIO If PO is outside the predetermined PO LIMIT the presence of an external magnetic field is indicated.

Description

Technical Field

[0001] The embodiments described below relate to a vibration sensor, and more particularly, to the detection of an external magnetic field 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 a conduit in a 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 a 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" which 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 representative of 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 electronic device connected to the driver generates a drive signal for operating the driver and also determines the mass flow rate and / or other characteristics of the process material from the signal 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.

[0005] When the flow tube vibrates, the pickoff bobbin wire generates a voltage as it passes through the magnetic field of the magnet. 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 and / or coil. 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 relative to the inlet or outlet pickoff and / or driver, the flow measurement value can 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 unaware in a flowmeter measurement transaction and has thus been used for that purpose. What is needed is an apparatus and method for detecting an external magnetic field of a flowmeter. SUMMARY OF THE INVENTION

[0006] According to one embodiment, a Coriolis flowmeter is provided that includes a flow conduit, a driver, and a pickoff sensor connected to the flow conduit. The meter electronics are configured to drive the driver to vibrate the flow conduit and receive a signal from the pickoff sensor. The meter electronics obtain the voltages of both pickoff sensors to determine PO RATIO and determine PO RATIO such that PO LIMITconfigured to determine whether it is inside. The meter electronic device is PO RATIO when outside a predetermined PO LIMIT is configured to indicate the presence of an external magnetic field.

[0007] According to one embodiment, a method of operating a Coriolis flowmeter is provided. The method 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 is received from a pickoff sensor connected to the flow conduit, the voltage of the pickoff sensor is acquired, and PO RATIO is determined. Whether PO RATIO is within a predetermined PO LIMIT is determined, and when PO RATIO is outside a predetermined PO LIMIT the presence of an external magnetic field is indicated.

[0008] [Aspect] According to one aspect, a Coriolis flowmeter includes a flow conduit, and a driver and a pickoff sensor connected to the flow conduit. The meter electronic device is configured to drive the driver to vibrate the flow conduit and receive a signal from the pickoff sensor. The meter electronic device acquires the voltages of both pickoff sensors to determine PO RATIO and is configured to determine whether PO RATIO is within a predetermined PO LIMIT The meter electronic device is such that when PO RATIO is outside a predetermined PO LIMIT it is configured to indicate the presence of an external magnetic field.

[0009] Preferably, a first process variable is collected and compared with a first confidence interval, and the meter electronic device is such that when the first process variable is within the first confidence interval and PO RATIO is outside a predetermined PO LIMIT it is configured to indicate the presence of an external magnetic field.

[0010] Preferably, a second process variable is collected and compared to a second confidence interval, and the meter electronics indicates the presence of an external magnetic field if either the first and second process variables are outside their respective confidence intervals and the PO RATIO is outside a predetermined PO LIMIT threshold.

[0011] Preferably, a third process variable is collected and compared to a third confidence interval, and the meter electronics indicates the presence of an external magnetic field if the first, second, and third process variables are outside their respective confidence intervals and the PO RATIO is outside a predetermined PO LIMIT threshold.

[0012] Preferably, the first, second, and third process variables each include one of a flow tube frequency, a drive gain, a fluid density, and an attenuation coefficient.

[0013] Preferably, the PO ZERO is collected by the meter electronics, at least one of the mean and standard deviation of the PO ZERO is determined by the meter electronics, and the meter electronics is configured to determine the PO ZERO to include an allowable deviation from the PO LIMIT threshold.

[0014] Preferably, if any of the first, second, and third process variables are outside their respective confidence intervals, the meter electronics returns a "transition" state.

[0015] Preferably, if all of the first, second, and third process variables are within their respective confidence intervals and the PO RATIO is within a predetermined PO LIMIT threshold, the meter electronics returns a "normal" state.

[0016] 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 is received from a pickoff sensor connected to the flow conduit, a voltage of the pickoff sensor is acquired, and PO RATIO is determined. PO RATIO is determined whether it is within a predetermined PO LIMIT , and if PO RATIO is outside a predetermined PO LIMIT , the presence of an external magnetic field is indicated.

[0017] Preferably, the method includes collecting a first process variable, comparing the first process variable with a first confidence interval, and indicating the presence of an external magnetic field if the first process variable is within the first confidence interval and PO RATIO is outside a predetermined PO LIMIT .

[0018] Preferably, the method includes collecting a second process variable, comparing the second process variable with a second confidence interval, and indicating the presence of an external magnetic field if both the first and second process variables are within their respective confidence intervals and PO RATIO is outside a predetermined PO LIMIT .

[0019] Preferably, the method includes collecting a third process variable, comparing the third process variable with a third confidence interval, and indicating the presence of an external magnetic field if both the first and third process variables are within their respective confidence intervals and PO RATIO is outside a predetermined PO LIMIT .

[0020] Preferably, the first, second, and third process variables each include one of a flow tube frequency, a drive gain, a fluid density, and a damping coefficient.

[0021] Preferably, the method is PO ZEROThe step of collecting, and PO ZERO The step of determining at least one of the average and standard deviation of PO ZERO PO including the tolerance deviation from PO LIMIT The step of determining PO

[0022] Preferably, the method includes the step of returning a "transition" state when any of the first, second, and third process variables is outside its respective confidence interval.

[0023] Preferably, the method includes the step of returning a "normal" state when all of the first, second, and third process variables are within their respective confidence intervals and PO RATIO Is within a predetermined PO LIMIT Including the step of returning a "normal" state when within the range.

Brief Description of the Drawings

[0024] In all the drawings, the same reference numerals represent the same elements. It should be understood that 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

DETAILED DESCRIPTION OF THE INVENTION

[0025] Figures 1-9B and the following description show specific examples for teaching those skilled in the art how to fabricate 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.

[0026] Figure 1 shows a flowmeter 5 according to an embodiment. The flowmeter 5 includes a sensor assembly 10 and meter electronics 20. The meter electronics 20 is connected to the sensor assembly 10 via a lead wire 100 and is 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 vibration operating mode.

[0027] The sensor assembly 10 includes a pair of flanges 101 and 101', manifolds 102 and 102', a driver 104, pick-off sensors 105 and 105', and flow conduits 103A and 103B. The driver 104 and the pick-off sensors 105 and 105' are connected to the flow conduits 103A and 103B.

[0028] The flanges 101 and 101' are fixed to the manifolds 102 and 102'. In some embodiments, the manifolds 102 and 102' can be attached to both ends of a spacer 106. 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'.

[0029] 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 the bending axes W-W and W'-W' respectively, and are properly 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.

[0030] Flow conduits 103A and 103B are each driven in opposite directions by driver 104 in what is called the first out-of-phase bending mode of flowmeter 5 about respective bending axes W and W'. Driver 104 can comprise one of many well-known configurations, such as a magnet attached to flow conduit 103A and a opposed coil attached to flow conduit 103B. An alternating current is passed through the opposed coil, causing vibration in both conduits. An appropriate drive signal is applied by meter electronics 20 to driver 104 via lead wire 110. Other driver devices are contemplated and are within the scope of this specification and the claims.

[0031] Meter electronics 20 receives sensor signals via lead wires 111 and 111', respectively. Meter electronics 20 generates a drive signal on lead wire 110, whereby driver 104 vibrates flow conduits 103A and 103B. Other sensor devices are contemplated and are within the scope of this specification and the claims.

[0032] Meter electronics 20 processes the left and right velocity signals from pickoff sensors 105 and 105' in particular to calculate the flow rate. Communication path 26 provides input and output means that enable meter electronics 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 a flowmeter and is not intended to limit the teachings of the present invention. In some embodiments, single-tube and multi-tube flowmeters having one or more drivers and pickoffs are contemplated.

[0033] In one embodiment, the meter electronics 20 is configured to vibrate the flow conduits 103A and 103B. The vibration is performed by the driver 104. The meter electronics 20 further receives vibration signals obtained from the pickup sensors 105 and 105'. The vibration signals include the vibration responses of the flow conduits 103A and 103B. The meter electronics 20 processes the vibration response and determines the response frequency and / or the phase difference. The meter electronics 20 processes the vibration response and determines one or more flow measurements, including the mass flow rate and / or density of the process fluid. Other vibration response characteristics and / or flow measurements are contemplated and are within the scope of this specification and the claims.

[0034] 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.

[0035] FIG. 2 is a block diagram of the meter electronics 20 of a flow meter 5 according to one embodiment. During operation, the flow meter 5 provides various measurable values that can be output, including mass flow rate, volumetric flow rate, measurements or averages 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.

[0036] 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 measurements. These values can be monitored, recorded, stored, totaled, and / or output.

[0037] The meter electronic device 20 includes an interface 201, a processing system 203 that communicates with the interface 201, and a memory system 204 that communicates with the processing system 203. Although these components are shown as separate blocks, it should be understood that the meter electronic device 20 can be composed of various combinations of integrated components and / or individual components.

[0038] The interface 201 is configured to communicate with the sensor assembly 10 of the flow meter 5. The interface 201 can be coupled to, for example, the lead wire 100 (see FIG. 1) and configured to 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.

[0039] 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 a flow meter routine 205 and a 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 the mass flow rate (m'), density (ρ), viscosity (μ), temperature (T), drive gain 306, transducer voltage 303, and any other variables known in the art. The drive gain 306 includes a relative measurement of the power consumed by the driver to keep the conduit vibrating at a desired frequency.

[0040] The flow meter routine 205 can generate and store a quantitative value of the fluid and a flow measurement value. These values can include substantially instantaneous measurement values, and can also include a total value or a cumulative value. For example, the flow meter routine 205 can generate measurement values of the mass flow rate and store them in, for example, the mass flow rate 221 storage of the memory system 204. The flow meter routine 205 can generate, for example, measurement values of the density 225 and store them in the density 225 storage. The values of the mass flow rate 221 and the 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 cumulative values over a certain time interval. The time interval can be selected to correspond to a time block in which a particular fluid condition, for example, a fluid state of only liquid, or alternatively a fluid state including liquid and entrained gas, is detected. In addition, other mass flow rates and related quantitative values are contemplated and are within the scope of this specification and the claims.

[0041] 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.

[0042] Referring to FIG. 3, by monitoring the meter electronics 20, it can be seen that when the magnets and coils are used for 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.

[0043] The region indicated by bracket #1 in FIG. 3 represents that a magnet is disposed proximate to the pick-off sensor 105' that is closest to the output of the flowmeter. When the magnet is disposed there, a relatively steep and symmetric step change in voltage is detected in the signal provided by the pick-off sensor 105' that is disposed closest to the output of the flowmeter (designated as PO in FIG. 3) OUT and shown).

[0044] The region indicated by bracket #2 in FIG. 3 represents that a magnet is disposed proximate to the pick-off sensor 105 that is closest to the input of the flowmeter. When the magnet is disposed there, a relatively steep and symmetric step change in voltage is also detected in the signal provided by the pick-off 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 pick-off sensor 105 that is closest to the input of the flowmeter (designated as PO in FIG. 3) IN and shown). The voltage spike is also detected in the signal provided by the driver 104.

[0045] The region indicated by bracket #3 in FIG. 3 represents that a magnet is disposed proximate to the driver 104. A detectable, relatively steep and symmetric step change in voltage is detected in the signal provided by the driver 104.

[0046] Referring to FIG. 4, it is shown that the external magnet affects the ΔT reading value of the flow meter 5. When the driver 104 stimulates the flow conduits 103A, 103B to vibrate in the opposite direction at the natural resonance frequency, the flow conduits 103A, 103B vibrate, and the voltages generated from each pick-off sensor 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 pick-off sensor and an equal negative change in the phase of the other pick-off sensor.

[0047] The region indicated by bracket #1 in FIG. 4 represents that a magnet is disposed in proximity to the pick-off sensor 105' that is closest to the output of the flow meter. When the magnet is disposed there, a relatively steep and symmetric stepwise decrease in ΔT is detected.

[0048] The region indicated by bracket #2 in FIG. 4 represents that a magnet is disposed in proximity to the pick-off sensor 105 that is closest to the input of the flow meter. When the magnet is disposed there, a relatively steep and symmetric stepwise increase in ΔT is detected.

[0049] The region indicated by bracket #3 in FIG. 4 represents that a magnet is disposed in proximity to the driver 104. When the magnet is disposed there, a relatively steep and symmetric stepwise decrease in ΔT is detected.

[0050] 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 pick-off 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 pick-off 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 pick-off 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.

[0051] 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.

[0052] 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.

[0053] 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 no flow is measured in the no-flow state.

[0054] 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 obtained during the meter operation of RPO LPO = Voltage value obtained during the meter operation of LPO

[0055] In some embodiments, as shown in step 606, PO LIMIT is set. PO LIMIT is the pick-off ratio limit, which is the allowable deviation of PO RATIO 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 ZERO varies for each application. LIMIT

[0056] 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 PO LIMIT , a flag indicating the possibility of magnetic tampering is generated.

[0057] This approach may provide a flag indicating tampering under certain flow conditions, despite the fact that there has been 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.

[0058] 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.

[0059] 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.

[0060] 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 memory system 204 using an appropriate data structure such as an array.

[0061] 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 the 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.

[0062] 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 in-operation PO RATIO is also calculated. Using an appropriate data structure such as an array, the average and standard deviation of the RPO and LPO signals, and the PO RATIO are stored in the storage system 204.

[0063] 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.

[0064] 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 for buffering observable responses Avg Vi = measured average of the variable of interest is. The deadband is determined empirically to adjust the sensitivity of the system.

[0065] 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 at step 712. In particular, at 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.

[0066] Note that if the zero value is not stored, the flowchart of FIG. 7 may start at step 708. In this case, instead of the zero value, a reference value is substituted for comparison. The reference value is an estimated value stored in memory that approximates the ideal zero value. These values vary based on details of the flowmeter such as shape, size, construction material, transducer placement, and type. In one embodiment, one or more zero variables can be replaced with reference values.

[0067] 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 limiting.

[0068] The first step can be to check for density changes using the density ratio. ρ’ r =(ρ m / ρ zero ) (4) where 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 ) case Check state = "Transition" Otherwise ρ' r <=(1 + ρ l ) case Check state = "Transition" Otherwise Check state = "Normal" Here, ρ l = density range limit.

[0069] 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, an example of the following logic can be applied. Dg m = 100 case Check state = "Transition" Otherwise Dg r <=(1 - Dg l ) case Check state = "Transition" Otherwise Dg r <=(1 + Dg l ) case Check state = "Transition" Otherwise Check state = "Normal" Here, Dg l = drive gain range limit.

[0070] Finally, as shown in Equation (2), the pickoff ratio logic is applied. PO r <(PO ZERO - PO limitIn the case of Check status = "Flag" PO r <(PO ZERO +PO limit ) In the case of Check status = "Flag" If not Check status = "Normal" Here, PO limit = PO range limit.

[0071] 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 exist 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.

[0072] The above detailed description of the 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 additional embodiments can be created by variously combining or deleting specific elements of the above embodiments, and that such additional embodiments fall within the scope and teachings of this description. It will also be apparent to those skilled in the art that additional embodiments can be created by combining the above embodiments in whole or in part within the scope and teachings of this specification.

[0073] Accordingly, specific embodiments are described herein for purposes of illustration, but as will be understood by those skilled in the art, various equivalent modifications are possible within the scope of this specification. The teachings provided herein can be applied 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 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 a 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) being configured to obtain the voltages of both pick-off sensors (105, 105') and determine PO ＲＡＴＩＯ and being configured to determine whether the PO is within a predetermined PO ＲＡＴＩＯ and being configured to determine whether the PO ＬＩＭＩＴ is outside the predetermined PO and the meter electronics (20) being configured to indicate the presence of an external magnetic field when the PO ＲＡＴＩＯ is outside the predetermined PO ＬＩＭＩＴ A Coriolis flowmeter (5).

2. A first process variable is collected and compared with a first confidence interval, and the meter electronics (20) being configured to indicate the presence of an external magnetic field when the first process variable is within the first confidence interval and the PO ＲＡＴＩＯ is outside a predetermined PO ＬＩＭＩＴ The Coriolis flowmeter (5) according to claim 1.

3. A second process variable is collected and compared with a second confidence interval, and the meter electronics (20) being configured to indicate the presence of an external magnetic field when both the first and second process variables are within their respective confidence intervals and the PO ＲＡＴＩＯ is outside a predetermined PO ＬＩＭＩＴ The Coriolis flowmeter (5) according to claim 2.

4. The third process variable is collected and compared with a third confidence interval, wherein the meter electronics (20) are configured to indicate the presence of an external magnetic field when the first, second, and third process variables are within their respective confidence intervals and the PO ＲＡＴＩＯ is outside a predetermined PO ＬＩＭＩＴ Coriolis flowmeter (5) according to claim 3. **Claim 5** The Coriolis flowmeter (5) according to any one of claims 2 to 4, wherein the first, second, and third process variables each include one of a flow tube frequency, a drive gain, a fluid density, and a damping coefficient. **Claim 6** PO ＺＥＲＯ is collected by the meter electronics (20), and at least one of the mean and standard deviation of the PO ＺＥＲＯ is determined by the meter electronics (20), wherein the meter electronics (20) are configured to determine the PO ＺＥＲＯ including an allowable deviation from the PO ＬＩＭＩＴ Coriolis flowmeter (5) according to claim 1. **Claim 7** The Coriolis flowmeter (5) according to any one of claims 2 to 4, wherein the meter electronics return a "transition" state when any of the first, second, and third process variables are outside their respective confidence intervals. **Claim 8** The Coriolis flowmeter (5) according to any one of claims 2 to 4, wherein the meter electronics return a "normal" state when all of the first, second, and third process variables are within their respective confidence intervals and the PO ＲＡＴＩＯ is within the predetermined PO ＬＩＭＩＴ Coriolis flowmeter (5) according to any one of claims 2 to 4. **Claim 9** A method of 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 Obtaining the voltage of the pick-off sensor and determining PO ＲＡＴＩＯ Determining step Said PO ＲＡＴＩＯ Determining whether it is within a predetermined PO ＬＩＭＩＴ Determining step And Said PO ＲＡＴＩＯ If it is outside the predetermined PO ＬＩＭＩＴ Indicating the presence of an external magnetic field Including, method.

10. Collecting a first process variable Comparing the first process variable with a first confidence interval And If the first process variable is within the first confidence interval and the PO ＲＡＴＩＯ Is outside a predetermined PO ＬＩＭＩＴ Indicating the presence of an external magnetic field Including, the method for operating a Coriolis flowmeter according to claim 9.

11. Collecting a second process variable And Comparing the second process variable with a second confidence interval Including, The meter electronics (20) is configured such that when both the first and second process variables are within their respective confidence intervals and the PO ＲＡＴＩＯ Is outside a predetermined PO ＬＩＭＩＴ Indicating the presence of an external magnetic field, the method for operating a Coriolis flowmeter according to claim 10.

12. Collecting a third process variable And Using the third process variable as a confidence interval Including, The meter electronics (20) is such that when both the first and third process variables are within their respective confidence intervals and the PO ＲＡＴＩＯis a predetermined PO ＬＩＭＩＴ The method of operating a Coriolis flowmeter according to claim 10, which is configured to indicate the presence of an external magnetic field when it is outside.

13. The method of operating a Coriolis flowmeter according to any one of claims 10 to 12, wherein the first, second, and third process variables each include one of a flow tube frequency, a drive gain, a fluid density, and an attenuation coefficient.

14. PO ＺＥＲＯ The step of collecting The PO ＺＥＲＯ The step of determining at least one of the mean and standard deviation of and The PO ＺＥＲＯ The step of determining the PO including the allowable deviation from the PO ＬＩＭＩＴ The method of operating a Coriolis flowmeter according to claim 9, including

15. The method of operating a Coriolis flowmeter according to any one of claims 10 to 12, including the step of returning a "transition" state when any of the first, second, and third process variables is outside its respective confidence interval.

16. When all of the first, second, and third process variables are within their respective confidence intervals and the PO ＲＡＴＩＯ is within the predetermined PO ＬＩＭＩＴ The method of operating a Coriolis flowmeter according to any one of claims 10 to 12, including the step of returning a "normal" state.

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