JP2015148623A - Method and apparatus for maintaining flow meter tube amplitude over variable temperature range - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for keeping a flow meter flow tube amplitude constant over a variable temperature range.SOLUTION: A flow meter includes a driver and pickoff sensors coupled to a flow tube. The driver is adapted to vibrate the flow tube in response to a drive signal. The method and apparatus comprise setting a target pickoff voltage, measuring a flow meter temperature, and controlling the drive signal to generate a temperature compensated target pickoff voltage to maintain a temperature compensated flow tube amplitude.

Description

  The present invention relates to a flow meter, and more particularly to a flow meter that can maintain a constant flow tube amplitude over a varying temperature range.

  It is generally known to use mass flow meters that use the Coriolis effect to measure the mass flow and other information of material flowing through a conduit in the flow meter. A typical Coriolis flow meter is described in J.A. E. U.S. Pat. No. 4,109,524, U.S. Pat. No. 4,491,025 and Re 31,450, all assigned to Smith et al. These flow meters include one or more conduits that have a linear or curved structure. The structure of each conduit in a Coriolis mass flow meter has a set of natural vibration modes, such as simple bending, torsional, or combinational modes. Each conduit can be vibrated to vibrate in a preferred mode.

  Material flowing into the flow meter from a pipeline connected on the inlet side of the flow meter exits the flow meter from the outlet side of the flow meter through one or more conduits. The natural vibration mode of a system filled with oscillating material is determined in part by the sum of the mass of the conduit and the mass of material flowing in the conduit.

  If vibration force is applied to the conduit when nothing is flowing through the flow meter, all sites along the conduit will vibrate in the same phase, or with the fixed phase slightly offset in the initial stage. To do. This offset can be corrected. As material begins to flow through the flow meter, Coriolis forces cause each point along the conduit to have a different phase. For example, the phase of the inlet end of the flow meter is delayed from the phase of the center driver position, and the phase of the outlet is advanced from the phase of the driver position. A pickoff sensor on the conduit is adapted to generate a sinusoidal signal representative of the motion of the conduit. The signal output from the pick-off sensor is processed to obtain the phase difference between the pick-off sensors. The phase difference between two or more pickoff sensors is proportional to the mass flow rate of the material flowing through the conduit.

  The meter electronics generates a drive signal for operating the driver and determines the mass flow rate and other characteristics of the material from the signal received from the pickoff sensor. The driver may have one of a plurality of known configurations. However, configurations in which the magnet is attached to one conduit and the opposing drive coil is attached to the other conduit or fixed substrate have been very successful in the flow meter industry. An alternating current is passed through the drive coil to cause both conduits to vibrate at the desired flow tube amplitude and frequency. It is also known in the art that a pick-off sensor is configured as having a magnet and a coil, similar to the configuration of the driver. However, the driver can receive a current that causes movement, and the pickoff sensor can use the movement imparted by the driver to induce a voltage. The general operating principles of such drivers and pickoff sensors are generally known in the art.

In most applications, the drive signal is determined at least in part by the pickoff signal. Once an initial drive signal is applied to the driver to vibrate the meter, the pickoff sensor maintains a certain speed. It is known in the art that meter electronics control drive signals according to “displacement” type control or “position” type control. In other words, the meter electronics generates a drive signal and applies it to the driver so as to maintain a certain amplitude of the pickoff signal. The amplitude of the voltage signal generated by the movement of the pickoff sensor is usually designed to be proportional to the amplitude of the sinusoidal displacement of the flow tube, and this relationship is often expressed in volts / hertz. . The amplitude of the pickoff signal is a function of each component of the pickoff vibration frequency, pickoff magnetic field, pickoff coil wire length, and pickoff vibration amplitude. It is common in the art that the system operating frequency is measured by the electronics, assuming that both the magnetic field and the coil wire length are constant. Accordingly, control of the amplitude of the flow tube displacement is achieved by maintaining the amplitude of the voltage of the pickoff signal, often expressed in volts / hertz.

A problem with the amplitude relationship arises when the flow meter is exposed to high ambient or high process fluid temperatures. In either case, the temperature of the driver and the temperature of the pickoff sensor are increased. When the temperature rises in this way, the magnetic fields of the driver and the pickoff sensor are weakened, so that the pickoff output voltage is lowered. If the drive signal is set to maintain the pickoff output voltage so that the volt / hertz relationship remains constant, the drive signal will increase, thereby increasing the flow tube displacement to increase the amplitude of the pickoff voltage. Amplitude increases. Larger flow tube amplitudes will have some undesirable consequences. From a structural point of view, the tube stress increases as the tube amplitude increases. Also, different flow tube amplitudes induce undesirable vibration modes that are added to the pickoff signal, resulting in measurement errors. In addition, as the flow tube amplitude increases, more drive power is required. In many cases, the available power may be limited by safety approval ratings, or may be limited by manufacturing specifications. In a high temperature environment, the efficiency of the drive magnet is reduced, so the drive power requirement is increased considerably. There is a need in the art to provide a method for maintaining a constant flow tube amplitude even at high temperatures.
The present invention overcomes the above and other problems and achieves technological advancement.

In accordance with one aspect of the present invention, a driver is coupled to the flow tube and is configured to vibrate the flow tube in response to a drive signal, and a pickoff sensor coupled to the flow tube. The way to operate the flow meter is
The steps include: setting a target pickoff voltage; measuring a flow meter temperature; generating a temperature compensated target pickoff voltage; and controlling the drive signal to maintain the temperature compensated target pickoff voltage. doing.

  Preferably, such method further comprises identifying the magnetic material of the pickoff sensor, wherein generating the temperature compensated target pickoff voltage comprises compensating for a change in the magnetic field strength of the pickoff sensor. That is.

  Preferably, generating the temperature compensated target pickoff voltage includes adjusting the target pickoff voltage using the Br coefficient of the magnetic material of the pickoff sensor.

Preferably, generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
Using the formula represented by:

  Preferably, such method further comprises the step of setting a design temperature, and if the measured meter temperature is within the threshold limits of the meter design temperature, the temperature compensated target pickoff voltage is the target pickoff. It is almost equal to the voltage.

  Preferably, the threshold limit includes a value that can be set by a user.

  Preferably, the threshold limit includes a predetermined value based on a pickoff sensor.

  Preferably, generating the temperature compensated target pickoff voltage includes retrieving the stored value based on the difference between the meter design temperature and the measured meter temperature.

According to another aspect of the present invention, a driver coupled to the flow tube and configured to vibrate the flow tube in response to a drive signal, and a pickoff sensor coupled to the flow tube. How to operate the flow meter
Setting the target pickoff voltage, measuring the flow meter temperature, comparing the measured flow meter temperature to the meter design temperature, and the measured flow meter temperature differ from the meter design temperature by a threshold limit A step of generating a temperature compensated target pickoff voltage.

  Preferably, such a method further comprises the step of controlling a drive signal to maintain the temperature compensated target pickoff voltage.

  Preferably, such method further comprises identifying the magnetic material of the pickoff sensor, and generating the temperature compensated target pickoff voltage comprises compensating for changes in the magnetic field strength of the pickoff sensor. It is that you are.

  Preferably, generating the temperature compensated target pickoff voltage includes adjusting the target pickoff voltage using the Br coefficient of the magnetic material of the pickoff sensor.

Preferably, generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
Using the formula represented by:

  Preferably, generating the temperature compensated target pickoff voltage includes retrieving a stored value based on a difference between the meter design temperature and the measured meter temperature.

  Preferably, the threshold limit includes a value that can be set by a user.

  Preferably, the threshold limit includes a value that is predetermined based on a pickoff sensor.

In accordance with another aspect of the present invention, a method of maintaining flow meter amplitude of a flow meter over a varying temperature range, comprising:
Applying a drive signal to a driver coupled to the flow tube and configured to maintain a target pickoff voltage of a plurality of pickoff sensors coupled to the flow tube; and measuring a flow meter temperature; Using the Br temperature coefficient of the magnetic material of the multiple pickoff sensors to generate a temperature compensated target pickoff voltage and the difference between the measured flow meter temperature and the meter design temperature exceeds a threshold limit And controlling the drive signal to maintain a temperature compensated target pickoff voltage.

  Preferably, the step of controlling the drive signal includes adjusting drive power.

  Preferably, the threshold limit includes a value that can be set by a user.

  Preferably, the threshold limit includes a value that is predetermined based on a pickoff sensor.

Preferably, generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pick-off voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
Using the formula represented by:

  Preferably, generating the temperature compensated target pickoff voltage includes retrieving a stored value based on the difference between the meter design temperature and the measured meter temperature.

In accordance with another aspect of the present invention, a flow meter is coupled to a flow tube, a driver coupled to the flow tube and configured to vibrate the flow tube in response to a drive signal, and the flow tube. A plurality of pick-off sensors and meter electronics,
The meter electronics is configured to set the pickoff voltage, monitor the flow meter temperature, generate a temperature compensated pickoff voltage, and control the drive signal to maintain the temperature compensated target pickoff voltage. .

  Preferably, the meter electronics is configured to generate a temperature compensated pickoff voltage by identifying the magnetic material of the pickoff sensor and compensating for changes in the magnetic field strength of the pickoff sensor.

  Preferably, the meter electronics is configured to adjust the target pickoff voltage using the Br coefficient of the magnetic material of the pickoff sensor.

Preferably, the meter electronics is
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
Is further configured to generate a temperature compensated target pickoff voltage using the formula:

Preferably, the meter electronics is further configured to set the meter design temperature, and if the measured meter temperature is within the threshold limit of the meter design temperature, the temperature compensated target pickoff The voltage is approximately equal to the target pickoff voltage.

  Preferably, the meter electronics is configured to accept a user settable value for the threshold limit.

  Preferably, the meter electronics is further configured to store a predetermined value for the threshold limit based on the pickoff sensor.

  Preferably, the meter electronics retrieves a stored value based on the difference between the meter design temperature and the measured temperature and uses the stored value to generate a temperature compensated pickoff voltage It is further configured to do.

It is a figure showing flow meter 100 concerning one embodiment of the present invention. It is a flowchart which shows each operation performed by meter electronic equipment. FIG. 6 is another flow chart illustrating an operation performed by the meter electronics that represents how the control algorithm maintains the flow tube amplitude after setting the initial operating conditions of FIG. 2. 6 is an initialization flowchart illustrating operations performed by meter electronics according to one embodiment of the present invention.

  1-4 and the following description depict specific embodiments to teach those skilled in the art how to make and use the best mode of the invention. To teach the principles of the invention, some of the prior art has been simplified or omitted. As will be apparent to those skilled in the art, variations on these embodiments are also within the scope of the present invention. Also, as will be apparent to those skilled in the art, the components described below can be combined in various ways to form multiple variations of the invention. Accordingly, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents.

  FIG. 1 shows a flow meter 100 and meter electronics 20 according to an embodiment of the present invention. According to one embodiment of the invention, the flow meter 100 comprises a Coriolis flow meter. However, the present invention is not limited to applications using Coriolis flow meters, and it will be appreciated that other types of flow meters may be used. The meter electronics 20 is connected to the flow meter assembly 100 via lead wires 110, 111, 111 ′, 112 and via path 26, temperature, density, mass flow, volume flow, total mass flow. Configured to provide. Meter drive signals and meter pick-off signals are also transmitted over path 26.

The flow meter assembly 100 includes a spacer 103 that accommodates the lower portion of the flow tubes 101 and 102. In the flow tube 101 and 102, the left ends of the flow tubes 101 and 102 are connected to the flange 104 through the neck portion 108, and the right side. The end is attached to the flange 105 and the manifold 107 via the neck 120. Further, FIG. 1 shows the outlet 106 of the flange 105, the left pickoff LPO, the right pickoff RPO and the driver D. The flow meter assembly 100 is configured to be connected to a pipeline or the like through flanges 104 and 105 in use. The right pickoff RPO is shown in detail and includes a magnet structure 115 and a coil structure 116. Although only two pickoff sensors LPO, RPO are shown, it goes without saying that any number of pickoff sensors may be used. A temperature measuring device such as an RTD sensor is further attached to the flow meter assembly 100. Although the flow meter assembly 100 is shown as having only one RTD attached, this is merely for clarity, and of course, as a matter of fact, the RTD or other temperature measuring device is It may be connected to each of the pick-off sensors LPO, RPO and the driver D. Each of the RTD sensors may be connected to the meter electronic device 20 via a lead wire such as the lead wire 112.

  The meter electronic device 20 is configured to give a drive signal to the driver D via a lead wire 110. Since the polarity of the drive signal is alternately changed, the tubes 101 and 102 can be vibrated according to a given flow tube amplitude and flow tube frequency. The flow tube amplitude and flow tube frequency vary depending on the drive signal provided by the meter electronics 20. Also, in response to the flow tube vibration, the magnet and coil assembly of the pickoff sensors LPO, RPO induce a voltage received by the meter electronics 20 via the lead wires 111, 111 '. According to embodiments of the present invention, meter electronics 20 is adapted to control meter assembly 100 according to a “displacement” type or “position” type control technique. Therefore, the meter electronics 20 sets the drive signal to maintain the target pickoff voltage. The target pickoff voltage may be set in the field by the user or may be selected in advance. In some embodiments, the default target pickoff voltage is set based on the detected flow meter and / or is set based on the process fluid. There is also. The drive power provided by the meter electronics 20 must be large enough to overcome the meter damping and spring forces to maintain sufficient tube amplitude to maintain the target pickoff voltage. The pickoff voltage can be calculated as follows.

When the flow tubes 101 and 102 are vibrated by the driver D, the pickoff LPO and RPO magnets and coil assemblies generate a pickoff voltage. The resulting pickoff voltage is a function of the four attributes of the meter assembly and can be expressed as equation (1) below:
(Pickoff voltage) = (Tube amplitude x Frequency x Magnetic field strength x Coil length) (1)

However, the frequency varies depending on the density and temperature of the process fluid, causing problems when controlling the pickoff voltage. On the other hand, if the meter electronics 20 attempts to maintain a pick-off voltage expressed in units of voltage / hertz instead of attempting to maintain a target pick-off voltage, this representation can be expressed in terms of process fluid density and It will be automatically compensated for changes in sensor frequency due to temperature variations. Therefore, the pickoff voltage may be expressed as the following equation (2):
(Pickoff voltage) / (Frequency) = (Tube amplitude x Magnetic field strength x Coil length) (2)

The relationship expressed by equation (2) is an appropriate representation of pickoff voltage for multiple applications. Assuming that the magnetic field strength is constant and the coil length is constant, the pickoff voltage can be maintained at its target value by adjusting only the tube amplitude. As is generally known in the art, tube amplitude can be controlled by a drive signal.

FIG. 2 is a flowchart illustrating an initialization algorithm 200 that is executed by the meter electronics 20 to operate the flow meter assembly 100. The algorithm 200 may be stored in a processor or the like and searched by the meter electronic device 20, another processor, or a software program. The initialization algorithm 200 ensures the start of the flow meter assembly 100 regardless of the type of flow meter or process fluid being measured. Process 200 begins at step 201 with identifying a flow meter in which meter electronics 20 is used. This specification may be realized by transmitting / receiving a signal to / from the flow meter 100, or the user may specify the flow meter 100 manually. Once the flow meter 100 is identified, a target pickoff voltage is set at step 202. The target pickoff voltage may be set according to the flow meter actually used, or the target pickoff voltage may be set manually based on a parameter input value from the user. In step 203, the tube period is determined. In order to properly control the drive, a tube period is required along with a pickoff voltage. In step 204, the drive power is adjusted to maintain the target pickoff voltage. This is a setting value of the drive algorithm and may be called a displacement target value. Once the drive power is set, the initialization routine 200 is complete.

  FIG. 3 illustrates a process 300 for normal operation of the flow meter 100 performed by the meter electronics 20. Once the drive target value is set in the process 200, the meter electronics 20 transmits the desired drive target value to the driver D in step 301. The drive target value is a drive signal that is transmitted to the driver D and vibrates the flow tubes 101 and 102. In step 302, the pick-off sensors LPO and RPO continue to send a signal indicating the pick-off voltage to the meter electronic device 20. This pick-off voltage is converted into a pick-off voltage as shown in the above equation (2). In step 303, the meter electronics 20 determines whether the actual pickoff voltage is equal to the target pickoff voltage. If the answer is “yes”, the process returns to step 302 and checks the pickoff voltage again. The meter electronics 20 can continue to measure the pickoff voltage and compare it to the target pickoff voltage. However, if the actual pickoff voltage is different from the target pickoff voltage or exceeds a predetermined threshold difference, process 300 proceeds to step 304 to adjust the desired drive target value. Thus, if the actual pickoff voltage is not equal to the target pickoff voltage, the process 300 changes the amplitude of the tube, the only known variable, by changing the drive signal. The modified drive signal is sent to driver D at step 305. Process 300 returns to step 302 and the pickoff voltage is measured once again.

The process 300 described above provides proper flow meter operation as long as the temperature of the system is maintained substantially constant or within a threshold difference in meter design temperature. However, problems arise when the temperature of the pickoff sensor LPO, RPO or driver D exceeds the ambient meter design temperature, typically 20 ° C. (68 ° F.). Needless to say, the flow meter 100 may have a design temperature different from 20 ° C. (68 ° F.), and the technical scope of the present invention is limited by the design temperature. is not. Similarly, although the following description is primarily related to a temperature increase, the correction is equally applicable to a temperature decrease. The reason why the temperature change occurs is that when the temperature of the pickoff sensors LPO, RPO and the magnet of the driver D rises, the magnetic field strength of these magnets decreases. Similarly, when the temperature of the pickoff sensor, LPO, RPO and driver D permanent magnets decreases, the magnetic field strength of those magnets increases. Recall from equation (2) that the pickoff voltage is partially determined by the magnetic field strength. Therefore, in a high temperature environment, as the magnetic field strength decreases, the “pickoff voltage” programmed to be maintained by the meter electronics 20 also decreases. In order for the pickoff voltage to generate the same amplitude signal (mV / Hz), the flow tubes 101, 102 must travel a longer distance, i.e., the flow tube amplitude must increase. Increasing the flow tube amplitude is not always desirable. This is because it causes the pick-off signal to change in relation to vibration and further tube stress. In addition, the drive signal must be increased to increase the flow tube amplitude. Therefore, a large amount of power is consumed during operation at a high temperature.

  In addition to the magnetic field of the pick-off sensor decreasing at high temperature, the magnetic field strength of the drive magnet also decreases at high temperature. Therefore, the pick-up sensors LPO and RPO are efficient to meet the high amplitude requirements so as to respond at low temperature. Cannot respond to. When the drive becomes inefficient, more drive current is required from the transmitter, and thus intrinsically safe drive current accumulation that can be utilized to vibrate the tubes 101, 102 under high fluid damping conditions. The amount will decrease.

  The decrease in magnetic field strength accompanying the temperature increase is well known as “Br (residual magnetic flux density) temperature coefficient” in the magnetic industry. The decrease in magnetic field strength is not permanent and returns to its previous value as the temperature drops. The Br temperature coefficient is based on the magnetic material used and constitutes part of the material specification for all magnets produced. The temperature coefficient of a common magnet is well known, and is expressed as a −% magnetic field density per 1 ° C. For example, it is known in the industrial field for Coriolis flow meters to use samarium-cobalt magnets having a Br temperature coefficient of about -0.35% / ° C. Needless to say, the exact Br temperature coefficient depends on the actual magnet used, and the scope of the present invention is not limited to the use of a samarium-cobalt magnet.

In accordance with one embodiment of the present invention, temperature changes are compensated by generating a temperature compensated target pickoff voltage. This temperature compensated target pickoff voltage may be adapted to compensate for changes in the pickoff voltage due to temperature changes in the flow meter. The temperature compensated target pickoff voltage may be calculated using a Br temperature coefficient or may be calculated using other temperature compensation values. Further, the temperature compensated target pickoff voltage may be obtained from a stored value. The stored value may be based on the difference between the measured meter temperature and the meter design temperature. According to other embodiments, the stored values may be based on previously obtained data. Of course, the present invention should not be limited to the use of the Br temperature coefficient. However, by incorporating the Br temperature coefficient of the magnet used for the pick-off sensors LPO and RPO and the driver D into the above-mentioned “expression (2)”, the temperature-compensated target pick-off voltage is expressed by “expression (3)” described below. Can be calculated as:
(Br temperature coefficient x pick-off voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length) (3)

When the temperature compensated target pick-off voltage is obtained using the above-mentioned “formula (3)”, the tube amplitude can be stabilized even in a high temperature environment. This is because the temperature-compensated target pickoff voltage of the “formula (3)” compensates for a decrease in magnetic field strength even if the magnetic field strength decreases with increasing temperature. Therefore, the meter electronic device 20 does not increase the pick-off voltage that decreases due to a temperature increase. Instead, the meter electronics 20 determines a new temperature compensated target pickoff voltage that takes into account temperature changes.

FIG. 4 illustrates a process 400 performed by meter electronics 20 to operate flow meter 100 in accordance with one embodiment of the present invention. Process 400 begins with initializing flow meter operation at step 401. The initialization may include the steps of the process 200 shown in FIG. 2 or may include other initialization routines that identify the flow meter and set an initial target pickoff voltage. Process 400 continues to step 402 to identify the magnetic material used for pickoff sensors LPO, RPO and driver D. If the magnetic material is already known, step 402 may not be necessary. Once the magnetic material is known, at step 403, meter electronics 20 obtains the Br temperature coefficient of the magnet. The Br temperature coefficient may be acquired from a stored value, or may be manually input by a user. Needless to say, in many applications, the type of magnet used for the pick-off sensor and the driver is made of the same material, but different types of magnets may be used, in which case multiple compensations for temperature changes are required. It is necessary to use the Br temperature coefficient. In step 404, a target pickoff voltage is set. The target pickoff voltage may be a value that can be set by the user or may be based on the meter design temperature. As described above, a flow meter such as flow meter 100 can have a meter design temperature. Thus, the target pickoff voltage may be based on the magnetic properties of the driver coil and pickoff coil at the meter design temperature.

  In step 405, the flow meter temperature is obtained using, for example, an RTD sensor. The flow meter temperature may be a process fluid temperature. According to other embodiments of the present invention, the flow meter temperature may be the temperature of the driver D or the temperature of the pickoff sensors LPO, RPO. According to yet another embodiment, the flow meter temperature may be the temperature of the flow tubes 101, 102.

  Based on the temperature received in step 405, a temperature compensated target pickoff voltage may be generated in step 406. According to one embodiment, the temperature compensated target pickoff voltage is generated at step 406 only if the difference between the meter design temperature and the temperature measured at step 405 exceeds a threshold limit. It has become. The threshold limit may be settable by the user. Alternatively, the threshold limit may be based on the flow meter used. In still other embodiments, the threshold limit may be based on the magnetic material used for the pickoff sensors LPO, RPO. Using the measured temperature, meter design temperature and equation (3) above, a temperature compensated pickoff voltage can be calculated. In step 407, the drive power is adjusted to achieve the temperature compensated target pickoff voltage. This new drive power is sent to driver D at step 408. The process 400 can be repeated by continuously acquiring new flow meter temperatures until a predetermined time or until the user exits the process 400.

  Process 400 can be used to control the drive signal transmitted by meter electronics 20 to maintain the temperature compensated target pickoff voltage rather than the default target pickoff voltage. Therefore, although the pickoff voltage changes with temperature, the target pickoff voltage is adjusted in order to compensate for the change in the pickoff voltage caused by the temperature change. According to one embodiment, the temperature compensated target pickoff voltage is generated using the Br temperature coefficient to compensate for changes in the magnetic field characteristics of the magnets used in the pickoff sensors LPO, RPO. Yes. Thus, the meter electronics 20 does not increase the tube amplitude in response to a drop in pickoff voltage caused by a temperature rise, but generates a new temperature compensated target pickoff voltage that takes into account changes in magnetic field strength. It has become. The present invention provides a method that can reduce the power required by the flow meter and further extend the life of the flow tube.

The above detailed description of the embodiments does not completely cover all embodiments considered by the inventor to be within the scope of the present invention. More precisely, as will be apparent to those skilled in the art, some embodiments of the above-described embodiments may be variously combined or removed to create further embodiments. Such further embodiments are also within the scope and teachings of the present invention. Also, as will be apparent to those skilled in the art, the above-described embodiments may be combined in whole or in part to create further embodiments that fall within the scope of the technology and teachings of the present invention.

  Although specific embodiments or examples of the invention have been described for purposes of illustration as described above, various modifications may be made within the scope of the invention, as will be apparent to those skilled in the art. The teachings described and taught herein can be applied not only to the embodiments described above and corresponding figures, but also to other embodiments. Accordingly, the scope of the invention is determined by the following claims.

Claims (30)

A method of operating a flow meter, comprising: a driver attached to a flow tube and configured to vibrate the flow tube in response to a drive signal; and a pickoff sensor attached to the flow tube,
The method comprises
Setting a target pickoff voltage;
Measuring the flow meter temperature;
Generating a temperature compensated target pickoff voltage;
Controlling the drive signal to maintain the temperature compensated target pickoff voltage;
Have The method further comprises identifying a magnetic material of the pickoff sensor;
The method of claim 1, wherein generating the temperature compensated target pickoff voltage comprises compensating for a change in magnetic field strength of the pickoff sensor.   The method of claim 2, wherein generating the temperature compensated target pickoff voltage comprises adjusting the target pickoff voltage using a Br coefficient of the magnetic material of the pickoff sensor. Generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
4. The method of claim 3, comprising using the formula represented by:   The method further includes setting a meter design temperature, and if the measured meter temperature is within a threshold limit of the meter design temperature, the temperature compensated target pickoff voltage is the The method of claim 1, wherein the method is approximately equal to a target pickoff voltage.   6. The method of claim 5, wherein the threshold limit includes a user configurable value.   The method of claim 5, wherein the threshold limit includes a predetermined value based on the pickoff sensor.   The method of claim 1, wherein generating the temperature compensated target pickoff voltage comprises retrieving a stored value based on a difference between a meter design temperature and the measured meter temperature. . A method of operating a flow meter attached to a flow tube and configured to vibrate the flow tube in response to a drive signal and a pickoff sensor attached to the flow tube. ,
The method comprises
Setting a target pickoff voltage;
Measuring the flow meter temperature;
Comparing the measured flow meter temperature with a meter design temperature;
Generating a temperature compensated target pickoff voltage if the measured flow meter temperature differs from the meter design temperature by a threshold limit;
Having a method.   The method of claim 9, further comprising controlling the drive signal to maintain the temperature compensated target pickoff voltage. The method further comprises identifying a magnetic material of the pickoff sensor;
The method of claim 9, wherein generating the temperature compensated target pickoff voltage comprises compensating for a change in magnetic field strength of the pickoff sensor magnet.   The method of claim 11, wherein generating the temperature compensated target pickoff voltage comprises adjusting the target pickoff voltage using a Br coefficient of the pickoff sensor magnet. Generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
13. The method of claim 12, comprising using a formula represented by:   The method of claim 9, wherein generating the temperature compensated target pickoff voltage comprises retrieving a stored value based on a difference between a meter design temperature and the measured meter temperature. .   The method of claim 9, wherein the threshold limit comprises a user configurable value.   The method of claim 9, wherein the threshold limit comprises a value that is predetermined based on the pickoff sensor. A method of maintaining flow meter amplitude of a flow meter over a varying temperature range, comprising:
This method supplement is
Applying a drive signal to a driver attached to the flow tube and configured to maintain a target pickoff voltage of a plurality of pickoff sensors coupled to the flowtube;
Measuring the flow meter temperature;
Generating a temperature compensated target pickoff voltage using the Br temperature coefficient of the magnetic material of the plurality of pickoff sensors;
Controlling the drive signal to maintain the temperature compensated target pickoff voltage when a difference between the measured flow meter temperature and a meter design temperature exceeds a threshold limit;
Having a method.   The method of claim 17, wherein controlling the drive signal includes adjusting the drive power.   The method of claim 17, wherein the threshold limit comprises a user configurable value.   The method of claim 17, wherein the threshold limit comprises a value that is predetermined based on the pickoff sensor. Generating the temperature compensated target pickoff voltage comprises:
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
18. The method of claim 17, comprising using the formula represented by:   The method of claim 17, wherein generating the temperature compensated target pickoff voltage comprises retrieving a stored value based on a difference between the meter design temperature and the measured meter temperature. Method. Flow tubes (101, 102);
A driver (D) attached to the flow tube (101, 102) and configured to vibrate the flow tube (101, 102) in response to a drive signal;
A plurality of pickoff sensors (LPO, RPO) coupled to the flow tubes (101, 102);
Meter electronic equipment (20),
The meter electronics is configured to set a pickoff voltage, monitor a flow meter temperature, generate a temperature compensated pickoff voltage, and control the drive signal to maintain the temperature compensated target pickoff voltage A flow meter (100).   The meter electronics (20) identifies the magnetic material of the pickoff sensor (LPO, RPO) and generates the temperature compensated pickoff voltage by compensating for changes in the magnetic field strength of the pickoff sensor (LPO, RPO). 24. A flow meter (100) according to claim 23, configured to:   25. A flow meter (100) according to claim 24, wherein the meter electronics (20) is configured to adjust the target pickoff voltage using a Br coefficient of the magnetic material of the pickoff sensor (LPO, RPO). ). The meter electronics (20)
(Br temperature coefficient x pickoff voltage) / (frequency) = (tube amplitude x magnetic field strength x coil length)
26. The flow meter (100) of claim 25, wherein the flow meter (100) is configured to generate a temperature compensated target pickoff voltage using an equation represented by:   If the meter electronics (20) is further configured to set a meter design temperature and the measured meter temperature is within a threshold limit of the meter design temperature, the temperature compensated target 24. A flow meter (100) according to claim 23, wherein a pickoff voltage is approximately equal to the target pickoff voltage.   28. A flow meter (100) according to claim 27, wherein the meter electronics (20) is configured to accept a user settable value for the threshold limit.   28. The flow rate of claim 27, wherein the meter electronics (20) is further configured to store a predetermined value for the threshold limit based on the pickoff sensor (LPO, RPO). Meter (100).   The meter electronics (20) retrieves a stored value based on the difference between the meter design temperature and the measured temperature, and uses the stored value to determine the temperature compensated pickoff voltage. 24. The flow meter (100) of claim 23, further configured to generate.

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