Temperature compensation for magnetostrictive position detectors

Abstract

The present disclosure relates to temperature compensation for magnetostrictive position detectors. The present disclosure provides a system, method, and apparatus for compensating fluid plane measurements of a magnetostrictive position detector for temperature conditions associated with a process without the use of built-in or external standalone temperature sensors. An algorithm is also disclosed for compensating for temperature conditions associated with a process by determining a thermal compensation factor proportional to the process temperature for temperature compensation by digitally processing the signal of the position detector.

Description

Technical Field

[0001] This disclosure generally relates to magnetostrictive position detectors, and more particularly to compensation for position measurements obtained by magnetostrictive position detectors due to temperature variations associated with the environment in which the magnetostrictive position detector is located. Background Technology

[0002] Magnetostrictive position detectors can be used in process control and other applications to measure the position of a movable float in order to determine the fluid level in a container, such as a tank. Temperature variations during the process can cause inaccurate float position detection, resulting in inaccurate fluid level measurements. This is typically addressed by using a temperature sensor built into the detector, or by using a dedicated external temperature sensor to measure temperature changes and then determining temperature compensation errors for the position measurements based on the measured temperature.

[0003] Using a stand-alone temperature sensor to determine and compensate for position measurement errors has several disadvantages. For example, instrumentation is more expensive due to the need to provide separate instruments and / or sensors, coupled with additional costs for installation, wiring, additional process connections, and additional inputs to the control system. Magnetostrictive position detectors with built-in sensors can mitigate some of these additional costs, but still require the addition of a temperature sensor component to the magnetostrictive position detector. Such detectors may also only provide limited temperature range capability. This disclosure relates to a system, method, and / or apparatus for providing temperature compensation for position measurements from a magnetostrictive position detector without the need for a temperature sensor. Summary of the Invention

[0004] According to this disclosure, a system, method, and / or apparatus are provided for compensating for position measurements of a magnetostrictive position detector with respect to temperature conditions without using built-in and / or external stand-alone temperature sensors. As a result, cost savings with respect to the magnetostrictive position detector and / or the ability to integrate the magnetostrictive position detector into, for example, process control systems can be achieved. This disclosure provides an algorithm for compensating for temperature conditions associated with the environment in which the magnetostrictive position detector is located by determining a thermal compensation coefficient proportional to the ambient temperature through digital processing of the magnetostrictive position detector's signal. According to this disclosure, a computer system operable to perform the foregoing is also provided.

[0005] This summary is provided to introduce the selection of concepts further described below in the illustrative embodiments. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid to limiting the scope of the claimed subject matter. Further embodiments, forms, objects, features, advantages, aspects, and benefits will become clear from the following description and drawings. Attached Figure Description

[0006] The features, aspects, and advantages of the invention will become better understood with reference to the following description, the appended claims, and the accompanying drawings, in which:

[0007] Figure 1 A schematic diagram of an exemplary system is shown, which utilizes a magnetostrictive position detector in conjunction with a controller configured to compensate for temperature to determine position measurements.

[0008] Figure 2 A signal graph is shown for determining the measured distance to the probe tip of the magnetostrictive position detector; and

[0009] Figure 3 This is a flowchart of the process used to compensate for the temperature effect on position measurements obtained by a magnetostrictive position detector. Detailed Implementation

[0010] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the accompanying drawings, and specific language will be used to describe these embodiments. However, it will be understood that this is not intended to limit the scope of the invention, and any changes and further modifications to the illustrated embodiments, as well as any further applications of the principles of the invention as illustrated herein, are contemplated herein.

[0011] refer to Figure 1 The diagram illustrates a magnetostrictive position detector 20 for measuring position 12 in an environment, such as container 10. In one embodiment, position 12 is a liquid level, container 10 is a tank or other object containing liquid, and the environment is a process involving the liquid in container 10. However, this disclosure is applicable to determining position 12 in any application or environment in which the magnetostrictive position detector 20 is employed.

[0012] The magnetostrictive position detector 20 includes a sensor 22 connected to a sensor tube or probe 24. The probe 24 contains sensor wires 26 connected to electronic circuitry 30 in the magnetostrictive position detector 20. A position marker (such as a magnetic float 28) is mounted around the probe 24 and is movable along the probe 24 in response to changes in the plane or position 12 of the liquid, as indicated by the position of the float 28' along the probe 24.

[0013] In operation, the electronic circuitry 30 in the magnetostrictive position detector 20 generates low-energy current pulses 32 at fixed intervals. These pulses travel at the speed of light along a wire 26 in the probe 24, thereby generating a magnetic field around the wire 26. The interaction between the magnetic field around the wire 26 and the magnet associated with the float 28 induces a torsional stress wave in the wire 26, which propagates along the wire 26 from the float 28 toward the sensor 22 at a known speed. The sensor 22 is configured to convert the received mechanical torsional stress wave into an electronic return pulse. Electronic devices (such as a computer system 50) are connected to the sensor 22, measure the time elapsed between the initial pulse and the return pulse (time of flight), and convert this measurement into a position measurement of position 12, which is proportional to the plane of the float 28 and indicates the liquid level in the container 10.

[0014] Computer system 50 receives input signals from sensor 22 and is configured to output a position determination value for float 28 compensated for temperature effects. Variations in ambient temperature and / or liquid temperature cause inaccuracies in the position measurements obtained by time-of-flight determination as described above. Computer system 50 may be incorporated into magnetostrictive position detector 20 or may be a stand-alone device connected to magnetostrictive position detector 20 in any suitable manner, including wired and wireless connections. Computer system 50 may also be connected in any suitable manner to a process controller (not shown) or may be part of a process controller (not shown) that can use the compensated position measurement value of position 12 in process control. Computer system 50 and / or process controller may provide the temperature-adjusted position measurement determination value according to this disclosure as alarms, readings, printouts, emails, text messages, process variables, signals, etc., without requiring the use of a temperature sensor to determine temperature compensation. As a result, the operation of computer system 50 is improved, and the cost of magnetostrictive position detector 20 and / or associated process hardware is reduced.

[0015] Computer system 50 may include one or more computers for performing one or more tasks related to the production process and / or computers that may be dedicated to magnetostrictive position detector 20. At least one of these computers in computer system 50 may include a user interface device (UI) 52, which includes: one or more display devices, such as monitors (with or without touchscreens) or handheld devices (such as smartphones, tablets, laptops, or other mobile devices for displaying graphics); and one or more input devices, such as keyboards, mice, trackballs, joysticks, handheld devices, and / or voice-activated devices.

[0016] Computer system 50 can be configured to compensate for any one or more factors contributing to temperature errors. For example, the material of probe 24 (such as a metal) can contribute to temperature errors because the material may stretch or contract depending on the direction of the process or changes in ambient temperature. Density changes in the process material (liquid) due to temperature fluctuations can also introduce temperature errors, affecting the buoyancy of float 28. The propagation speed of torsional waves can also be affected by the temperature of the process and / or environment.

[0017] These error sources each possess linear characteristics with respect to temperature changes. The computer system 50 is configured to compensate for errors introduced by temperature changes by using a temperature factor without requiring any temperature sensors, thereby reducing the cost of the instrument and corresponding installation. The computer system 50 is operable to determine, for example,... Figure 2 The probe length PL shown is constant at any given temperature and is independent of the position of the magnet.

[0018] exist Figure 2 In the diagram, the transmitter signal reflected by the magnet of float 28 travels a distance R from the end of probe 24 to the sensor 22, and the distance L from the magnet of float 28 back to the sensor 22 is also considered. The measurement distance to the end of the probe (also called the probe length PL) can be determined by averaging L and R as follows:

[0019] Equation 1

[0020] The average flight time measured for the first reflected signal generated by the magnet of float 28 (which travels from the magnet of float 28 to the end 34 of probe 24 and back to sensor 22) and the second reflected signal (which travels from the magnet of float 28 to sensor 22) is equal to the flight time for the length of the probe. During factory configuration, computer system 50 calculates the thermal error coefficient (CTE) as the measured PL compared to a reference PL previously measured at a calibration temperature (e.g., room temperature). REF The ratio between ).

[0021] Equation 2

[0022] Then, the thermal error coefficient can be applied as an inverse correction factor to the parameters of measurement position 12 and also to float 28 to compensate for buoyancy error as follows:

[0023] Equation 3

[0024] L COMPENSATEDHere, L is the compensated position measurement, H is the immersion height of float 28 at room temperature, and K is the buoyancy coefficient determined by the float design. Parameters H and K can be retrieved by computer system 50 from, for example, one or more lookup tables stored in memory and containing design details of various floats 28, or, if float 28 is a custom-designed float, parameters H and K are directly input into computer system 50.

[0025] The probe length PL can be calculated at any given ambient temperature and at any position of the float 28 along the probe 24. Additionally, for applications where a magnetostrictive position detector 20 is used to measure distance or position rather than a liquid plane, the buoyancy correction factor H can be disabled. K / CTE.

[0026] refer to Figure 3 An embodiment of a method for compensating for the temperature effect on position measurements obtained by a magnetostrictive position detector 20 is shown. Method 300 includes the following operation 302: transmitting a current pulse generated by electronic circuitry 30 along a wire 26 to a magnetic position marker (such as a float 28 in a liquid application).

[0027] Method 300 further includes operation 304 to induce torsional stress waves in the conductor 26 by the interaction of current pulses with the magnetic position marker. Method 300 continues at operation 306 to measure a first distance and a second distance based on the time of flight of the induced stress waves traveling along the conductor 26, which generate reflected signals detected by sensor 22. The first measured distance is measured along the path of the first reflected signal from the magnetic position marker to the end 34 of the probe 24 and from the end 34 of the probe 24 back to sensor 22. The second measured distance is measured along a second reflected signal from the magnetic position marker back to sensor 22.

[0028] Method 300 continues at operation 308 to determine the measured probe length of probe 24 by averaging the first and second measurement distances. Method 300 continues at operation 310 to determine the CTE in response to the ratio of the measured probe length to the reference probe length. The reference probe length can be determined in a factor at a predetermined calibration temperature and stored in computer system 50. Method 300 continues at operation 312 to compensate the position measurement of the magnetic position marker based on the determined CTE.

[0029] In environments where magnetic position markers are used to determine the liquid level of a float, the float's buoyancy error can also be temperature-compensated using CTE. The buoyancy error is the product of the float's immersion height at room temperature and the float's buoyancy coefficient, divided by a thermal error factor. The immersion height and buoyancy coefficient can be retrieved from a lookup table based on the design of float 28, or, if float 28 is custom-made, the immersion height and buoyancy coefficient can be entered by the user.

[0030] This document provides a general overview of the diagrams and processes described above. Therefore, the depicted order and labeled steps indicate representative embodiments. Other steps, sequences, combinations of steps, and methods are conceivable that are functionally, logically, or effectively equivalent to one or more steps or portions thereof of the methods illustrated in the diagrams.

[0031] Additionally, the formats and symbols used are provided to interpret the logical steps of the diagrams and are understood not to limit the scope of the systems, devices, and methods illustrated in the figures. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. It will also be noted that each block of the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, may be implemented by a system based on dedicated hardware or a combination of dedicated hardware and program code that performs the specified function or behavior.

[0032] Many of the functional units described in this specification have been labeled to more specifically emphasize their implementation independence. For example, one or more aspects of the magnetostrictive position detector 20 and / or the computer system 50 may be implemented as hardware circuitry including custom VLSI circuitry or gate arrays, off-the-shelf semiconductors (such as logic chips), transistors, or other discrete components. The magnetostrictive position detector 20 and / or the computer system 50 may also be implemented in programmable hardware devices (such as field-programmable gate arrays, programmable array logic, programmable logic devices, etc.).

[0033] One or more aspects of the magnetostrictive position detector 20 and / or computer system 50 may also be implemented in a machine-readable medium executable by various types of processors. In some cases, the machine-readable medium executable by various types of processors may be implemented in the aforementioned hardware circuitry. The identification module of the executable code may, for example, include one or more physical or logical blocks of computer instructions, which may be organized, for example, as objects, procedures, or functions. However, the executable files of the identification circuitry do not need to be physically located together, but may include completely different instructions stored in different locations, which, when logically linked together, include the circuitry and achieve the stated purposes of the magnetostrictive position detector 20 and / or computer system 50.

[0034] For example, computer-readable program code can be a single instruction or many instructions, and can even be distributed across several different code segments, across different programs, and across several memory devices. Similarly, operational data (such as measurements) can be identified and illustrated herein within modules, monitors, or circuits, and can be embodied in any suitable form and organized within any suitable type of data structure. Operational data can be collected as a single dataset or can be distributed across different locations (including on different storage devices), and can exist at least in part solely as electronic signals on a system or network. Where a module, monitor, or circuit, or part thereof, is implemented in a machine-readable medium (or computer-readable medium), computer-readable program code can be stored and / or distributed on one or more computer-readable media.

[0035] A computer-readable medium may be a tangible computer-readable storage medium that stores computer-readable program code. A computer-readable storage medium may be, for example, but not limited to, electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor systems, devices, or apparatuses, or any suitable combination thereof.

[0036] More specific examples of computer-readable media include, but are not limited to, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), portable optical disc read-only memory (CD-ROM), digital versatile optical disc (DVD), optical storage devices, magnetic storage devices, holographic storage media, micromechanical storage devices, or any suitable combination thereof. In the context of this document, computer-readable storage media can be any tangible medium that can contain and / or store computer-readable program code for use by and / or in conjunction with an instruction execution system, device, or apparatus.

[0037] Computer-readable media can also be computer-readable signal media. Computer-readable signal media may include, for example, data signals propagated in baseband or as part of a carrier wave, in which computer-readable program code is embodied. Such propagated signals may take any of a variety of forms, including but not limited to electrical, electromagnetic, magnetic, optical, or any suitable combination thereof. Computer-readable signal media may be any computer-readable medium other than computer-readable storage media, which can convey, propagate, or transport computer-readable program code for use by or in connection with an instruction execution system, device, or apparatus. Computer-readable program code embodied on a computer-readable signal medium may be transmitted using any suitable medium, including but not limited to wireless, wired, fiber optic cable, radio frequency (RF), or any suitable combination thereof.

[0038] In one embodiment, a computer-readable medium may include a combination of one or more computer-readable storage media and one or more computer-readable signal media. For example, computer-readable program code may be transmitted as an electromagnetic signal via an optical fiber cable for execution by a processor, or it may be stored in a RAM storage device for execution by a processor.

[0039] Computer-readable program code for implementing the operations of various aspects of this disclosure can be written using any combination of one or more programming languages, including object-oriented programming languages ​​(such as Java, Smalltalk, C++, etc.) and conventional procedural programming languages ​​(such as Java, Python, Matlab, R, or similar programming languages). The computer-readable program code can be executed entirely on the user's computer, partially on the user's computer, as a stand-alone computer-readable package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer can be connected to the user's computer via any type of network (including a local area network (LAN) or a wide area network (WAN)), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0040] Program code may also be stored in a computer-readable medium that can instruct a controller, computer, other programmable data processing device or other means to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of writing including instructions that implement the functions / behaviors specified herein.

[0041] Various aspects of this disclosure are intended as indicated in the appended claims.

[0042] Throughout this specification, the terms "an embodiment," "an embodiment," or similar language refer to a particular feature, structure, or characteristic described in connection with that embodiment being included in at least one embodiment of the invention. The use of the phrases "in one embodiment," "in one embodiment," and similar language throughout this specification may, but not necessarily all, refer to the same embodiment.

[0043] Therefore, this disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be regarded in all respects as illustrative rather than restrictive. Therefore, the scope of this disclosure is indicated by the appended claims rather than by the foregoing description. All variations falling within the equivalent meaning and scope of the claims are to be included within its scope.

[0044] While the invention has been illustrated and described in detail in the accompanying drawings and the foregoing description, it is to be considered illustrative in nature rather than restrictive, and it should be understood that only certain exemplary embodiments have been shown and described. Those skilled in the art will appreciate that many modifications are possible in the exemplary embodiments without substantially departing from the invention. Therefore, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

[0045] When reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one part” are used, there is no intention to limit the claims to only one item unless expressly stated otherwise in the claims. When the language “at least a part” and / or “part” is used, the item may include a part and / or the entire item unless expressly stated otherwise.

Claims

1. A method for compensating for the temperature effects of position measurements from a magnetostrictive position detector, the magnetostrictive position detector comprising a sensor, a probe extending from the sensor, and a magnetic position marker movable along the probe in accordance with the position, the method comprising: The thermal error coefficient is determined in response to the ratio between the measured probe length and the reference probe length; as well as The position measurement value is compensated based on the thermal error coefficient, wherein the thermal error coefficient is applied as an inverse correction factor to the position measurement value. The measured probe length is based on the average of a first measurement distance associated with the end of the probe and a second measurement distance associated with the position of the magnetic position marker along the probe.

2. The method of claim 1, wherein the first measurement distance and the second measurement distance are determined in response to the flight time of the reflected signal from the magnetic position marker.

3. The method of claim 2, wherein the first measurement distance is measured along a path traveled by the first reflected signal from the magnetic position marker to the end of the probe and from the end of the probe to the sensor, and the second measurement distance is measured along a second reflected signal from the magnetic position marker to the sensor.

4. The method of claim 2, wherein the reflected signal is a torsional stress wave induced in a wire within the probe, the torsional stress wave being generated by a current pulse transmitted by the wire and interacting with the magnetic position marker.

5. The method of claim 1, wherein the length of the reference probe is determined at the calibration temperature.

6. The method of claim 1, wherein the magnetic position marker is a float, and the method further comprises compensating the position measurement with the thermal error coefficient for buoyancy error of the float.

7. The method of claim 6, wherein the buoyancy error is the product of the immersion height of the float at room temperature and the buoyancy coefficient of the float divided by the thermal error coefficient.

8. The method of claim 7, wherein the immersion height and buoyancy coefficient are retrieved from a lookup table.

9. The method of claim 1, wherein the position measurement is a fluid plane.

10. A computer system operable to compensate for the temperature effects of position measurements from a magnetostrictive position detector, the magnetostrictive position detector comprising a sensor, a probe extending from the sensor, and a magnetic position marker movable along the probe in accordance with position, the computer system operable to: The thermal error coefficient is determined in response to the ratio between the measured probe length and the reference probe length; and The position measurement value is compensated based on the thermal error coefficient, wherein the thermal error coefficient is applied as an inverse correction factor to the position measurement value. The measured probe length is based on the average of a first measurement distance associated with the end of the probe and a second measurement distance associated with the position of the magnetic position marker along the probe.

11. The computer system of claim 10, wherein the first measurement distance and the second measurement distance are determined in response to the flight time of the reflected signal from the magnetic position marker.

12. The computer system of claim 11, wherein the first measurement distance is measured along a path traveling from the magnetic position marker to the end of the probe and from the end of the probe to the sensor along a first reflected signal, and the second measurement distance is measured along a second path traveling from the magnetic position marker to the sensor along a second reflected signal.

13. The computer system of claim 11, wherein the reflected signal is a torsional stress wave induced in a wire within the probe, the torsional stress wave being generated by a current pulse transmitted by the wire and interacting with the magnetic position marker.

14. The computer system of claim 10, wherein the length of the reference probe is factory calibrated.

15. The computer system of claim 10, wherein the magnetic position marker is a float, and the computer system is operable to compensate for buoyancy errors of the float in relation to the position measurement.

16. The computer system of claim 15, wherein the buoyancy error is the product of the immersion height of the float at room temperature and the buoyancy coefficient of the float divided by the thermal error coefficient.

17. The computer system of claim 16, wherein the computer system is part of or connected to the magnetostrictive position detector.

18. The computer system of claim 10, wherein the position measurement is a fluid plane.

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