External magnetic detection for flow meters

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 specifically, to its detection of an external magnetic field. [Background technology] 【0002】 Vibration sensors, such as vibrating densimeters and Coriolis flowmeters, are commonly known and used to measure mass flow rate and other information about a material flowing through a conduit in a flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Patents 4,109,524, 4,491,025, and 31,450. These flowmeters have a meter assembly having one or more conduits in a straight or curved configuration. Each conduit configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be, for example, simple bending, torsion, or coupling. Each conduit can be driven to vibrate in a preferred mode. When there is no flow through the flowmeter, the driving force applied to the conduit causes all points along the conduit to vibrate in the same phase or with a small “zero offset,” which is a time delay measured at zero flow rate. 【0003】 As material begins to flow through a conduit, the Coriolis force causes each point along the conduit to have 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 leads the phase at the central driver position. Pickoffs on the conduit generate a sinusoidal signal representing the movement of the conduit. The signals output from the pickoffs are processed to determine the time delay between the pickoffs, which is called 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 to operate the driver and also determine the mass flow rate and / or other properties of the process material from the signal received from the pickoff. While the driver can comprise one of many well-known configurations, the magnet and opposing drive coil have achieved great success in the flowmeter industry. An alternating current flows through the drive coil, causing the conduit to vibrate at a desired conduit amplitude and frequency. It is also known in the art that the pickoff may be provided as a magnet and coil configuration very similar to that of the drive unit. 【0005】 When the flow tube vibrates, the pick-off bobbin wire generates a voltage as it passes through the magnetic field of the magnet. The primary factor generating such a voltage is the radial magnetic field. If the magnetic field is disturbed or changed during the operation of the meter, the meter's output will be affected. One way to disturb the pick-off magnetic field is to place another magnet close to the pick-off magnet and / or coil. By placing an external magnet near the pick-off of a Coriolis meter, the flow measurement can be altered to indicate a higher or lower flow rate, depending on the polar orientation or position of the external magnet on the meter relative to the inlet or outlet pick-off and / or driver. When the magnet is removed, the sensor voltage and phase shift return to normal. This ability to manipulate the flow rate can be detrimental to parties unaware of it in flow meter measurement transactions, and has been used for this purpose. What is needed are devices and methods for detecting the external magnetic field of a flow meter. [Overview of the project] 【0006】 According to one embodiment, a Coriolis flow meter is provided comprising a flow conduit and a driver and a pick-off sensor connected to the flow conduit. The meter electronics are configured to drive the driver to vibrate the flow conduit and to receive signals from the pick-off sensor. The meter electronics acquire the voltages from both pick-off sensors and PO RATIO We decided on PO RATIO is the specified PO LIMITconfigured to determine whether it is inside. The meter electronics 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 pick-off sensor connected to the flow conduit, the voltage of the pick-off 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, a driver and a pick-off sensor connected to the flow conduit. The meter electronics is configured to drive the driver to vibrate the flow conduit and receive a signal from the pick-off sensor. The meter electronics acquires the voltages of both pick-off sensors to determine PO RATIO and is configured to determine whether PO RATIO is within a predetermined PO LIMIT 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 electronics is configured to indicate the presence of an external magnetic field when the first process variable is within the first confidence interval and PO RATIO is outside a predetermined PO LIMIT 【0010】 ​Preferably, a second process variable is collected and compared to a second confidence interval, and the meter electronics determines that both the first and second process variables are within their respective confidence intervals, PO RATIO is the specified PO LIMIT When located outside, it is configured to indicate the presence of an external magnetic field. 【0011】 Preferably, a third process variable is collected and compared to a third confidence interval, and the meter electronics determines that the first, second, and third process variables are within their respective confidence intervals, and PO RATIO is the specified PO LIMIT When located outside, it is configured to indicate the presence of an external magnetic field. 【0012】 Preferably, the first, second, and third process variables include one of the following: flow tube frequency, drive gain, fluid density, and damping coefficient. 【0013】 Preferably, PO ZERO This is collected by the meter electronic equipment, PO ZERO At least one of the mean and standard deviation is determined by the meter electronics, and the meter electronics is PO ZERO PO to include the allowable deviation from LIMIT It is configured to determine this. 【0014】 Preferably, the meter electronics returns a “transition” state if any of the first, second, and third process variables are outside their respective confidence intervals. 【0015】 Preferably, all of the first, second, and third process variables are within their respective confidence intervals, and PO RATIO is the specified PO LIMIT If it is present, the meter electronics will return a "normal" status. 【0016】 According to one embodiment, the method of operating a Coriolis flow meter includes the steps of flowing a fluid material through the 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 is received from a pick-off sensor connected to the flow conduit, the voltage of the pick-off sensor is obtained, and PO RATIO This is determined. PO RATIO is the specified PO LIMIT It is determined whether it is inside, PO RATIO is the specified PO LIMIT If it is located outside, it indicates the presence of an external magnetic field. 【0017】 Preferably, the method includes the steps of collecting a first process variable, comparing the first process variable with a first confidence interval, and determining if the first process variable is within the first confidence interval. RATIO is the specified PO LIMIT If located outside, the process includes the step of indicating the presence of an external magnetic field. 【0018】 Preferably, the method includes the steps of collecting a second process variable, comparing the second process variable with a second confidence interval, and determining whether both the first and second process variables are within their respective confidence intervals. RATIO is the specified PO LIMIT If located outside, the process includes the step of indicating the presence of an external magnetic field. 【0019】 Preferably, the method includes the steps of collecting a third process variable, comparing the third process variable with a third confidence interval, and determining whether both the first and third process variables are within their respective confidence intervals. RATIO is the specified PO LIMIT If located outside, the process includes the step of indicating the presence of an external magnetic field. 【0020】 Preferably, the first, second, and third process variables include one of the following: flow tube frequency, drive gain, fluid density, and damping coefficient. 【0021】 Preferably, this method is PO ZEROThe steps to collect and PO ZERO A step of determining at least one of the mean and standard deviation, and PO ZERO PO including the allowable deviation from LIMIT This includes the step of determining the following. 【0022】 Preferably, the method includes a step of returning a “transition” state if any of the first, second, and third process variables are outside their respective confidence intervals. 【0023】 Preferably, in this method, all of the first, second, and third process variables are within their respective confidence intervals, and PO RATIO is the specified PO LIMIT If present, the step includes returning a "normal" state. [Brief explanation of the drawing] 【0024】 In all drawings, the same reference number represents the same element. Please understand that the drawings are not necessarily to scale. [Figure 1] Figure 1 shows a vibration meter according to one embodiment. [Figure 2] Figure 2 shows a meter electronic device according to one embodiment. [Figure 3] Figure 3 shows the effect of a magnetic field on the pick-off voltage of a flow meter sensor according to one embodiment. [Figure 4] Figure 4 shows the effect of a magnetic field on flow rate measurement according to one embodiment. [Figure 5A] Figure 5A shows the magnetic field of a pick-off assembly in which no magnets are present. [Figure 5B] Figure 5B shows the magnetic field of the pick-off assembly when an external magnet is present and the south pole of the magnet is pointed towards the pick-off assembly. [Figure 5C] Figure 5C shows the magnetic field of the pick-off assembly when an external magnet is present and the north pole of the magnet is pointed towards the pick-off assembly. [Figure 6] Figure 6 shows a flowchart illustrating an example of an embodiment for detecting magnetic tampering. [Figure 7] Figure 7 shows a flowchart illustrating another example of an embodiment for detecting magnetic tampering. [Figure 8] Figure 8 shows a pseudocode for a magnetic tampering embodiment. [Figure 9A] Figure 9A shows a false flag detection according to an embodiment of the present invention. [Figure 9B] Figure 9B shows a false flag detection according to an embodiment of the present invention. [Modes for carrying out the invention] 【0025】 Figure 1-9B and the following description illustrate specific examples to teach those skilled in the art how best modes of the sensor assembly, brace bar, driver, and pick-off sensor embodiments can be fabricated and used. Some of the prior art embodiments have been simplified or omitted for the purpose of teaching the principles of the present invention. Those skilled in the art will understand variations from these embodiments that fall within the scope of this specification. Those skilled in the art will understand that multiple variations of the embodiments can be formed by combining the features described below in various ways. Consequently, 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 flow meter 5 according to one embodiment. The flow meter 5 comprises a sensor assembly 10 and meter electronics 20. The meter electronics 20 is connected to the sensor assembly 10 via lead wires 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 flow meter 5 may include a Coriolis mass flow meter or other oscillating flow meter. It will be apparent to those skilled in the art that the flow meter 5 may include any form of flow meter 5, regardless of the driver, pick-off sensor, number of flow conduits, or mode of vibration operation. 【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 pick-off sensors 105 and 105' are connected to the flow conduits 103A and 103B. 【0028】 Flanges 101 and 101' are fixed to manifolds 102 and 102'. In some embodiments, manifolds 102 and 102' can be attached to both ends of a spacer 106. The spacer 106 maintains the distance between 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 flange 101, passes through inlet manifold 102, where the entire amount of process fluid is guided into flow conduits 103A and 103B, flows through flow conduits 103A and 103B, returns to outlet manifold 102', and exits the sensor assembly 10 through flange 101'. 【0029】 The process fluid may include a liquid. The process fluid may include a gas. The process fluid may include, but is not limited to, a multiphase fluid such as a liquid containing encompassing gases and / or encompassing solids. Flow conduits 103A and 103B are selected to have substantially the same mass distribution, moment of inertia, and modulus of elasticity around the bending axes WW and W'-W', respectively, and are appropriately mounted to the inlet manifold 102 and the outlet manifold 102'. Flow conduits 103A and 103B extend outward essentially parallel to the manifolds 102 and 102'. 【0030】 Flow conduits 103A and 103B are driven in opposite directions by a driver 104 around their respective bending axes W and W', in what is called the first out-of-phase bending mode of the flowmeter 5. The driver 104 may comprise one of many well-known configurations, such as a magnet attached to flow conduit 103A and a counter coil attached to flow conduit 103B. An alternating current is passed through the counter coil, causing vibrations in both conduits. An appropriate drive signal is applied to the driver 104 via lead wires 110 by the meter electronics 20. Other driver devices are conceivable and are within the scope of this specification and the claims. 【0031】 The meter electronics 20 receives sensor signals on lead wires 111 and 111', respectively. The meter electronics 20 generates a drive signal on lead wire 110, which causes the driver 104 to vibrate the flow conduits 103A and 103B. Other sensor devices are also conceivable and are within the scope of this specification and the claims. 【0032】 The meter electronics 20 calculates the flow rate by processing left and right velocity signals from pick-off sensors 105 and 105', in particular. The communication path 26 provides input and output means that enable the meter electronics 20 to interface with an operator or other electronic system. The description in Figure 1 is provided merely as an example of the operation of a flow meter and is not intended to limit the teachings of the present invention. In some embodiments, single-pipe and multi-pipe flow meters having one or more drivers and pick-offs are assumed. 【0033】 In one embodiment, the meter electronics 20 is configured to vibrate flow conduits 103A and 103B. The vibration is performed by a driver 104. The meter electronics 20 further receives vibration signals obtained from pick-off sensors 105 and 105'. The vibration signals include the vibration response of flow conduits 103A and 103B. The meter electronics 20 processes the vibration response and determines the response frequency and / or phase difference. The meter electronics 20 processes the vibration response and determines one or more flow measurement values, including the mass flow rate and / or density of the process fluid. Other vibration response characteristics and / or flow measurement values ​​are conceivable and are within the scope of this specification and the claims. 【0034】 In one embodiment, the flow conduits 103A and 103B constitute substantially omega-shaped flow conduits, as shown. Alternatively, in other embodiments, the flow meter may comprise substantially straight flow conduits, U-shaped conduits, delta-shaped conduits, and the like. Additional flow meter shapes and / or configurations may be used, and these are within the scope of this specification and the claims. 【0035】 Figure 2 is a block diagram of the meter electronic equipment 20 of a flow meter 5 according to one embodiment. During operation, the flow meter 5 provides a variety of outputtable measurements, including one or more of the following: 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, which includes both volumetric and mass flow rates, for example. 【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 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 and / or individual components. 【0038】 Interface 201 is configured to communicate with the sensor assembly 10 of the flow meter 5. Interface 201 can be configured, for example, to be coupled to lead wire 100 (see Figure 1) and to exchange signals with driver 104, pick-off sensors 105 and 105', and temperature sensor (not shown). Interface 201 can also be configured to communicate with external devices, etc., via communication path 26. 【0039】 The processing system 203 may include any type of processing system. The processing system 203 is configured to read and execute stored routines in order to operate the flowmeter 5. The storage system 204 may store routines including the flowmeter routine 205 and the magnetic field detection routine 209. Other measurement / processing routines are conceivable and are within the scope of this specification and the claims. The storage system 204 may store measured values, received values, operating values, and other information. In some embodiments, the storage system stores mass flow rate (m') 221, density (ρ) 225, viscosity (μ) 223, temperature (T) 224, 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 oscillating at a desired frequency. 【0040】 The flowmeter routine 205 can generate and store quantified values ​​and flow rate measurements of a fluid. These values ​​may include substantially instantaneous measurements, and may also include sums or cumulative values. For example, the flowmeter routine 205 can generate mass flow rate measurements and store them, for example, in the mass flow rate 221 storage of the memory system 204. The flowmeter routine 205 can also generate density 225 measurements and store them, for example, in the density 225 storage. The values ​​of mass flow rate 221 and density 225 are determined from the vibration response, as previously described and as further known in the art. The mass flow rate and other measurements may include substantially instantaneous values, may include samples, may include average values ​​over a time interval, or may include cumulative values ​​over a time interval. The time interval can be selected to correspond to a time block in which specific fluid conditions, e.g., a fluid state of liquid only, or alternatively, a fluid state including liquid and contaminating gases, are detected. In addition, other mass flow rates and associated quantified values ​​are conceivable and are within the scope of this specification and the claims. 【0041】 By positioning an external magnet near the Coriolis meter's pickoff point, the flow rate reading can be altered to indicate a higher or lower flow rate depending on the position of the external magnet's poles, or the position of the external magnet on the flow meter, inlet, or outlet. 【0042】 Referring to Figure 3, monitoring the meter electronics 20 reveals that when magnets and coils are used in the pick-off sensors 105 and 105', an external magnetic field, whether from an electromagnetic source or a permanent magnet, affects the reading of the sensor assembly 10. It is clear that a relatively steep and symmetrical step change exists. 【0043】 The area indicated by bracket #1 in Figure 3 represents the placement of a magnet in close proximity to the pick-off sensor 105', which is the closest to the flow meter output. When the magnet is placed there, the signal provided by the pick-off sensor 105', which is the closest to the flow meter output (PO in Figure 3) OUT (As indicated by the text) A relatively steep and symmetrical step change in voltage is detected. 【0044】 The area indicated by bracket #2 in Figure 3 represents the placement of a magnet close to the pick-off sensor 105, which is the closest to the input of the flowmeter. When the magnet is placed there, the signal provided by the pick-off sensor 105', which is the closest to the output of the flowmeter (PO in Figure 3) OUT (as indicated) a relatively steep and symmetrical step change in voltage is also detected. The voltage spike is also provided by the pick-off sensor 105 located closest to the input of the flowmeter (PO in Figure 3). IN Voltage spikes are detected in the (displayed as) section. Voltage spikes are also detected in the signal provided by driver 104. 【0045】 In Figure 3, the region indicated by bracket #3 represents the placement of the magnet in close proximity to the driver 104. A detectable, relatively steep, and symmetrical step change in voltage is detected in the signal provided by the driver 104. 【0046】 Referring to Figure 4, it is shown that the external magnet affects the ΔT reading of the flow meter 5. When the driver 104 stimulates the flow conduits 103A and 103B to vibrate in opposite directions at their natural resonant frequencies, the flow conduits 103A and 103B vibrate, and the voltages generated from each pick-off sensor 105 and 105' produce a sine wave. This represents the movement of one conduit relative to the other. The time delay between the two sine waves is called ΔT and is directly proportional to the mass flow rate. If the phase of either flow conduit 103A or 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 Figure 4 represents the placement of a magnet in close proximity to the pick-off sensor 105', which is the closest to the flowmeter output. When the magnet is placed there, a relatively steep and symmetrical step-like decrease in ΔT is detected. 【0048】 The region indicated by bracket #2 in Figure 4 represents the placement of a magnet in close proximity to the pick-off sensor 105, which is the closest to the flowmeter input. When the magnet is placed there, a relatively steep and symmetrical step-like increase in ΔT is detected. 【0049】 The region indicated by bracket #3 in Figure 4 represents the position of the magnet in close proximity to the driver 104. When the magnet is positioned there, a relatively steep and symmetrical step-like decrease in ΔT is detected. 【0050】 Figures 5A-5C show how the magnetic field near the transducer changes in the presence of another magnet. Figure 5A shows the magnetic field of the pick-off assembly when no magnet is present (dashed line). Figure 5B shows the magnetic field when an external magnet is present with its south pole pointed towards the pick-off assembly, and Figure 5C shows the magnetic field when an external magnet is present with its north pole pointed towards the pick-off assembly. As shown in Figure 4, disturbances or changes in the magnetic field during the operation of the measuring instrument affect the meter's output. 【0051】 In one embodiment, the approach to detecting magnetic tampering is to monitor the pick-off voltage. In one embodiment, the voltage difference between pick-off sensors 105 and 105' is measured. In one embodiment, the voltage ratio between pick-off sensors 105 and 105' is measured. 【0052】 The following explanation describes the pick-off ratio. However, the pick-off difference can also be used in a similar manner. Pick-off sensors 105 and 105' are also referred to as LPO (left pick-off) and RPO (right pick-off), respectively. 【0053】 Figure 6 is a flowchart showing a method for determining magnetic tampering. In some embodiments, as shown in step 602, PO ZERO This is determined. PO ZERO This refers to the average value obtained during the zero adjustment process. PO ZERO =RPO ZERO / LPO ZERO (1) Here, RPO ZERO =Average value obtained during RPO zero adjustment process LPO ZERO =Average value obtained during LPO zero adjustment process That is the case. The zero adjustment process is typically performed when there is no flow through the flowmeter, and the driving force applied to the conduit causes all points along the conduit to vibrate with a small "zero offset," which is a time delay measured at the same phase or zero flow rate. This process allows the flowmeter to be calibrated so that no flow rate is measured in a no-flow state. 【0054】 In some embodiments, as shown in step 604, PO is the pick-off voltage ratio acquired while the fluid is flowing and the meter is operating. RATIO This is measured. PO RATIO =RPO / LPO (2) RPO = Voltage value obtained during RPO meter operation Voltage values ​​obtained during LPO=LPO meter operation 【0055】 In some embodiments, as shown in step 606, PO LIMIT This is set. PO LIMIT This is the pick-off ratio limit, which is the acceptable limit before tampering, PO RATIO PO ZERO This is a deviation from PO. There are many types of flow meter configurations, operating settings, installation variables, flow variables, and process variables, so as those skilled in the art will understand, LIMIT This varies depending on the application. 【0056】 In step 608, PO RATIO ga PO LIMIT It is compared to PO. RATIO ga PO LIMIT If it is within the range, the flow meter is determined to be operating within the "normal" operating range. However, PO RATIO ga PO LIMIT If it is outside the specified range, a flag indicating the possibility of magnetic tampering is generated. 【0057】 This approach may provide a flag indicating tampering under certain flow conditions, even if no tampering actually occurred. In some embodiments, additional logic is added, including monitoring additional meter outputs to limit the number of "false flags." These outputs may include one or more of the following: mass flow rate, density, and drive gain. 【0058】 A flowchart illustrating additional checks to reduce false flags is shown in Figure 7. In this embodiment, several system states can be returned, namely "Normal," "Flag," and "Transition," where 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 of that confidence interval. The Transition state means that at least one pilot variable is outside of its confidence interval. Each of these system states is simply stored as a numerical code and can be read back in that way, for example, via Modbus communication. The numerical code may be converted to human-readable text and displayed on a screen. 【0059】 In step 702, several zero variables are collected. These zero variables may include the RPO and LPO signals, the flow tube frequency, the drive gain, the fluid density, the damping coefficient, and other flow meter variables known in the art. 【0060】 In step 704, the fluid flow meter is used to obtain the pick-off voltage ratio PO RATIO However, this 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 their standard deviations are calculated. The mean and standard deviation of each variable are stored in the storage 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 under process conditions. These values ​​may be set at the factory during manufacturing and calibration, or they 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 may include RPO and LPO signals, flow tube frequency, drive gain, fluid density, damping coefficient, and other flowmeter variables known in the art. These operating variables are collected over time, averaged, and / or have their standard deviations calculated. RATIO The mean and standard deviation of the RPO signal and LPO signal, as well as PO, are calculated using an appropriate data structure such as an array. RATIO This is stored in the memory system 204. 【0063】 In step 710, several operating variables are compared to zero variables. In particular, the flow tube frequency, drive gain, fluid density, and / or damping coefficient are compared, and it is determined whether all of the compared values ​​fall within a confidence interval. 【0064】 Confidence intervals can be determined empirically based on targeting the desired result, as will be understood by those skilled in the art. In one embodiment, the confidence interval (CI) for a particular desired variable (Vi) has the following formula: CI = 2 * StdDev Vi +deadband*Avg Vi (3) Here, StdDev Vi = Standard deviation of the target variable deadband = coefficient that buffers the observable response Avg Vi = Actual mean of the target variable That is the case. The deadband is determined empirically to adjust the system's sensitivity. 【0065】 If any of these variables are outside their respective confidence intervals, the "transition" flag state is activated. However, if all variables are within their respective confidence intervals, then in step 712, PO RATIO These are compared. In particular, in step 712, operation PO RATIO This is the zero PO previously determined in steps 702-704. RATIO It is compared to the operation PO. RATIO If it falls within that confidence interval, the "normal" state is returned. However, the operation PO RATIO If the value is outside that confidence interval, a "flag" state is returned, indicating a possible magnetic tampering event. 【0066】 Note that if a zero value is not stored, the flowchart in Figure 7 may start at step 708. In this case, a reference value is substituted for the zero value for comparison. The reference value is an estimated value stored in memory that approximates the ideal zero value. These values ​​will vary based on the details of the flowmeter, such as shape, size, constituent materials, transducer arrangement, and type. In one embodiment, one or more zero variables may 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 solely for clarity and should not be interpreted as limiting. 【0068】 The first step is to check for density changes using density ratios. 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 logic can be applied. ρ'r <= (1 - ρ l ) case Check status = "Transition" Otherwise ρ' r <= (1 + ρ l ) case Check status = "Transition" Otherwise Check status = "Normal" Here, ρ l = density range limit. 【0069】 Another output check can be a 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 When the average drive gain ratio is established, the following example of logic can be applied. Dg m = 100 case Check status = "Transition" Otherwise Dg r <= (1 - Dg l ) case Check status = "Transition" Otherwise Dg r <= (1 + Dg l ) case Check status = "Transition" Otherwise Check status = "Normal" Here, Dg l = drive gain range limit. 【0070】 Finally, as shown in equation (2), the pick-off ratio logic is applied. PO r < (PO ZERO - PO limit)in the case of Check status = "flag" PO r <(PO ZERO + limit )in the case of Check status = "flag" If not Check status = "Normal" Here, PO limit =PO range limit. 【0071】 An example of the coupling logic, illustrated using pseudocode, is shown in Figure 8. Note that the flow rate, density, and drive gain variables may or may not be present in some embodiments, and the order in which they are analyzed may differ. Referring to Figure 9B, it will be clear that applying the above flow condition logic to the PO ratio data in Figure 9A results in significantly fewer false check values ​​("false flags") than using the pick-off ratio alone for a given PO limit. 【0072】 The detailed description of the embodiments described above is not an exhaustive description of all embodiments that the inventors intend to include within the scope of this description. Indeed, those skilled in the art will understand that further embodiments can be created by combining or omitting certain elements of the embodiments described above, and that such further embodiments will fall within the scope of this description and teachings. It will also be apparent to those skilled in the art that further embodiments can be created within the scope of this specification and teachings by combining the embodiments in whole or in part. 【0073】 Therefore, although specific embodiments are described here for illustrative purposes, 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 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 embodiments described above should be determined by the following claims.

Claims

[Claim 1] Flow conduits (103A, 103B), Driver (104) and pick-off sensors (LPO, 105; RPO, 105') connected to the flow conduits (103A and 103B) and Meter electronic equipment (20) configured to drive the driver (104) to vibrate the flow conduits (103A, 103B) and to receive signals from the pick-off sensors (105, 105'). Equipped with, The meter electronic equipment (20) acquires the voltages of both of the pick-off sensors (105, 105') and PO ＲＡＴＩＯ It is configured to determine, The meter electronic equipment (20) ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ It is configured to determine whether it is inside or not. The meter electronic equipment (20) ＲＡＴＩＯ The predetermined PO ＬＩＭＩＴ A Coriolis flow meter (5) is configured to indicate the presence of an external magnetic field when it is located outside. [Claim 2] The first process variable is collected and compared with the first confidence interval. The meter electronic device (20) determines that the first process variable is within the first confidence interval and the PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ The Coriolis flow meter (5) according to claim 1, which is configured to indicate the presence of an external magnetic field when it is located outside. [Claim 3] A second process variable is collected and compared with a second confidence interval. The meter electronic device (20) is 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. [Claim 4] A third process variable is collected and compared with a third confidence interval. The meter electronic device (20) determines that the first, second, and third process variables are within their respective confidence intervals, and the PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ The Coriolis flow meter (5) according to claim 3, which is configured to indicate the presence of an external magnetic field when it is located outside. [Claim 5] The Coriolis flow meter (5) according to any one of claims 2 to 4, wherein the first, second, and third process variables each include one of the flow tube frequency, drive gain, fluid density, and damping coefficient. [Claim 6] PO ＺＥＲＯ The PO is collected by the meter electronic equipment (20) ＺＥＲＯ At least one of the mean and standard deviation is determined by the meter electronic equipment (20), The meter electronic equipment (20) ＺＥＲＯ The PO includes the allowable deviation from ＬＩＭＩＴ A Coriolis flow meter (5) according to claim 1, configured to determine the following. [Claim 7] The Coriolis flow meter (5) according to any one of claims 2 to 4, wherein the meter electronic equipment returns a “transition” state if any of the first, second, and third process variables are outside their respective confidence intervals. [Claim 8] All of the first, second, and third process variables are within their respective confidence intervals, and the PO ＲＡＴＩＯ The predetermined PO ＬＩＭＩＴ The Coriolis flow meter (5) according to any one of claims 2 to 4, wherein the meter electronic equipment returns a "normal" state when it is inside. [Claim 9] A method for operating a Coriolis flow meter, Steps include flowing the fluid material through the flow conduit of the flow meter, A step of driving a driver connected to the flow conduit to vibrate the flow conduit in a first bending mode, The step of receiving a signal from a pick-off sensor connected to the flow conduit, The voltage of the aforementioned pick-off sensor is obtained and PO ＲＡＴＩＯ Steps to determine The aforementioned PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ Steps to determine whether it is inside and The aforementioned PO ＲＡＴＩＯ The predetermined PO ＬＩＭＩＴ Steps to indicate the presence of an external magnetic field when it is outside. Methods that include... [Claim 10] Step 1: Collect the first process variables. Step of comparing the first process variable with the first confidence interval. and The first process variable is within the first confidence interval, and the PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ Steps to indicate the presence of an external magnetic field when it is outside. A method for operating a Coriolis flow meter according to claim 9, including the method described in claim 9. [Claim 11] Step 2: Collect the process variables. and Step of comparing the second process variable with the second confidence interval. Includes, The meter electronic equipment (20) determines that both the first and second process variables are within their respective confidence intervals, and the PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ A method for operating a Coriolis flow meter according to claim 10, configured to indicate the presence of an external magnetic field when it is located outside. [Claim 12] Step to collect the third process variable and Steps to set the third process variable as a confidence interval. Includes, The meter electronic equipment (20) determines that both the first and third process variables are within their respective confidence intervals, and the PO ＲＡＴＩＯ is the specified PO ＬＩＭＩＴ A method for operating a Coriolis flow meter according to claim 10, configured to indicate the presence of an external magnetic field when it is located outside. [Claim 13] A method for operating a Coriolis flow meter according to any one of claims 10 to 12, wherein the first, second, and third process variables each include one of the flow tube frequency, drive gain, fluid density, and damping coefficient. [Claim 14] PO ＺＥＲＯ Steps to collect The aforementioned PO ＺＥＲＯ A step to determine at least one of the mean and standard deviation. and The aforementioned PO ＺＥＲＯ The PO including the allowable deviation from ＬＩＭＩＴ Steps to determine A method for operating a Coriolis flow meter according to claim 9, including the method described in claim 9. [Claim 15] A method for operating a Coriolis flow meter according to any one of claims 10 to 12, comprising the step of returning a “transition” state if any of the first, second, and third process variables are outside their respective confidence intervals. [Claim 16] All of the first, second, and third process variables are within their respective confidence intervals, and the PO ＲＡＴＩＯ The predetermined PO ＬＩＭＩＴ A method for operating a Coriolis flow meter according to any one of claims 10 to 12, comprising the step of returning a “normal” state if it is in the state.