Linear variable differential transformers for temperature measurement and related methods

Abstract

A linear variable differential transformer ("LVDT") configured to measure temperature is provided. The LVDT includes a ferromagnetic core, a primary coil surrounding the ferromagnetic core, and a secondary coil surrounding the ferromagnetic core. An AC driver is configured to provide an AC current to the primary coil. A first switch is configured to selectively connect and disconnect the AC driver to the primary coil. One or more data acquisition units is configured to measure a resistance of at least one of the primary coil or the secondary coil when the AC driver is disconnected from the primary coil. Methods for measuring temperature with an LVDT are also provided.

Description

[0001] LINEAR VARIABLE DIFFERENTIAL TRANSFORMERS FOR TEMPERATURE MEASUREMENT AND RELATED METHODS

[0002] PRIORITY CLAIM

[0003] This application claims the benefit of the filing date of United States Provisional Patent Application Serial No. 63 / 549,266, filed February 2, 2024, for “LVDT Intrinsic Temperature Measurement,” the disclosure of which is hereby incorporated herein in its entirety by this reference.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0005] This invention was made with government support under Contract No. DE-AC07- 05-ID14517 awarded by the United States Department of Energy. The government has certain rights in the invention.

[0006] TECHNICAL FIELD

[0007] This disclosure relates generally to linear variable differential transformers (LVDTs). More specifically, this disclosure relates to LVDTs used and operated in environments where temperatures may vary.

[0008] BACKGROUND

[0009] An LVDT is a type of electrical transformer that is used to measure linear displacement. LVDTs are considered highly robust for providing accurate measurements in a variety of extreme environmental conditions. LVDTs are known for providing relatively high degrees of reliability, stability, consistency, and accuracy for measuring linear displacement. LVDTs are thus used in a variety of applications such as in power turbines, hydraulics, automation, aircraft, nuclear reactors, and the like.

[0010] While LVDTs are highly robust, LVDTs are also temperature dependent. Thus, when an LVDT is used in an environment subject to large changes in temperature, the output of the LVDT must be compensated for temperature to ensure accurate outputs. This requires the use of temperature sensors to measure the temperatures near the LVDT. In some applications, the added instrumentation due to the need for temperatures sensors may increase the cost and complexity of the overall instrumentation used in a given application. Furthermore, many temperature sensors may not have a lifespan equivalent to that of an LVDT. limiting the lifespan of the instrumentation in a given application.

[0011] DISCLOSURE

[0012] According to some aspects of the disclosure, a linear variable differential transformer (“LVDT”) configured to measure temperature is provided. The LVDT includes a ferromagnetic core, a primary coil surrounding the ferromagnetic core, and a secondary coil surrounding the ferromagnetic core. An AC driver is configured to provide an AC current to the primary coil. A first switch is configured to selectively connect and disconnect the AC driver to the primary coil. One or more data acquisition units is configured to measure a resistance of at least one of the primary coil or the secondary coil when the AC driver is disconnected from the primary coil.

[0013] According to some aspects, a method of measuring temperature with an LVDT is provided. The method includes placing an LVDT in a variable temperature environment. The LVDT includes an AC driver, a primary’ coil, and a secondary coil. The method further includes disconnecting the AC driver from the primary coil of the LVDT and measuring resistance across at least one of the primary coil or the secondary coil of the LVDT. The measured resistance is correlated with temperature.

[0014] According to some aspects, a method of measuring temperature w ith an LVDT is provided. The method includes delivering an AC energy pulse to a primary coil of the LVDT to generate sound waves within a ferromagnetic core of the LVDT and correlating a timing of the sound waves w ithin the ferromagnetic core to temperature.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a detailed understanding of the present disclosure, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements have generally been designated with like numerals, and wherein:

[0017] FIG. 1 shows a perspective, section view of an LVDT according to some embodiments;

[0018] FIG. 2 shows a schematic view of an LVDT according to some embodiments;

[0019] FIG. 3 show’s a schematic view of resistances of the secondary’ coils of an LVDT according to some embodiments; FIG. 4 shows a schematic view of an LVDT with electronics for temperature measurements according to some embodiments:

[0020] FIG. 5 shows a method for measuring temperature with an LVDT according to some embodiments;

[0021] FIG. 6 shows a schematic view of an LVDT with electronics for temperature measurements according to some embodiments:

[0022] FIG. 7A. FIG. 7B, and FIG. 7C show schematic views of utilizing a pulse echo method for determining temperature using an LVDT according to some embodiments;

[0023] FIG. 8 shows an exemplary output of a wave in a pulse echo method for determining temperature using an LVDT according to some embodiments;

[0024] FIG. 9 shows a schematic view of coils and a core of an LVDT; and

[0025] FIG. 10A and FIG. 10B show an exemplary input signal and a frequency output signal based on resonant frequency for temperature measurement in an LVDT.

[0026] MODE(S) FOR CARRYING OUT THE INVENTION

[0027] The illustrations presented herein are not actual views of any LVDT, or any component thereof, but are merely idealized representations, which are employed to describe embodiments of the present invention.

[0028] As used herein, the singular forms following "a." “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0029] As used herein, the term “may” with respect to a material, structure, feature, or method act indicates that such is contemplated for use in implementation of an embodiment of the disclosure, and such term is used in preference to the more restrictive term “is” so as to avoid any implication that other compatible materials, structures, features, and methods usable in combination therewith should or must be excluded.

[0030] As used herein, any relational term, such as “first,” “second,” “top,” “bottom,” “upper,” “lower,” “above,” “beneath,” “side,” “upward,” "downw ard." etc., is used for clarity and convenience in understanding the disclosure and accompanying drawings, and does not connote or depend on any specific preference or order, except where the context clearly indicates otherwise. For example, these terms may refer to an orientation of elements of any LVDT when utilized in a conventional manner. Furthermore, these terms may refer to an orientation of elements of any LVDT as illustrated in the drawings. As used herein, the term “substantially” in reference to a given parameter, property, or condition means and includes to a degree that one skilled in the art would understand that the given parameter, property, or condition is met with a small degree of variance, such as within acceptable manufacturing tolerances. By way of example, depending on the particular parameter, property7, or condition that is substantially met, the parameter, property, or condition may be at least 90.0% met, at least 95.0% met. at least 99.0% met, or even at least 99.9% met.

[0031] As used herein, the term “about” used in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter, as well as variations resulting from manufacturing tolerances, etc.). For example, “about” in reference to a numerical value may include additional numerical values within a range of from 90.0 percent to 108.0 percent of the numerical value, such as within a range of from 95.0 percent to 105.0 percent of the numerical value, within a range of from 97.5 percent to 102.5 percent of the numerical value, within a range of from 99.0 percent to 101.0 percent of the numerical value, within a range of from 99.5 percent to 100.5 percent of the numerical value, or within a range of from 99.9 percent to 100.1 percent of the numerical value.

[0032] FIG. 1 shows a perspective, section view of an LVDT according to some embodiments. In FIG. 1, an LVDT 10 may comprise a housing 102 having a first end 104 and a second end 106. The housing 102 may comprise a body 108 that includes a cavity that houses a cylindrical ferromagnetic core 1 10. The cylindrical ferromagnetic core 110 may be configured to translate axially within the body 108 and may protrude from the first end 104 of the housing 102. The cylindrical ferromagnetic core 110 may comprise a core holder 112 at a distal end thereof. The core holder 112 may be configured to attach to an object or surface such that the LVDT 10 may measure a linear displacement of the object or surface.

[0033] The LVDT 10 may comprise magnetic shielding 114 on an interior surface of the body 108 of the housing 102. The magnetic shielding 114 may be configured as a Faraday cage around internal components of the LVDT. The LVDT 10 may further comprise a primary coil 116, a first secondary7coil 1 18a on a first side of the primary coil 116, and a second secondary coil 118b on a second side of the primary7coil 116. In some embodiments, the LVDT 10 may comprise a cable input 120 that facilitates introduction of electrical leads to and from the LVDT 10. The LVDT 10 may also comprise a helium leaktest nipple 122 to ensure adequate sealing of the LVDT 10.

[0034] FIG. 2 shows a schematic view of an LVDT according to some embodiments. As shown in FIG. 2, the LVDT 10 may comprise an AC driver 124 that drives the primary coil 116. The alternating current drives the primary7coil 116 and causes a voltage to be induced in the first secondary coil 118a and the second secondary coil 118b proportional to a length of the cylindrical ferromagnetic core 110 linking the primary7coil 116 to the first and second secondary coils 1 18a, 118b. The voltage across the first secondary coil 1 18a may be measured by voltage between the leads 126 and 128. The voltage across the second secondary coil 118b may be measured by a voltage between the leads 128, 130.

[0035] A difference between the induced voltages in the first secondary coil 118a and the second secondary coil 118b may be correlated with a displacement of the cylindrical ferromagnetic core 110 relative to the primary7coil 116 and secondary coils 118a, 118b, and thus to a displacement of the object (not shown) being measured by the LVDT 10. As the cylindrical ferromagnetic core 110 moves relative to the primary coil 116, the first secondary coil 118a. and the second secondary coil 118b. the primary coil’s 116 hnkage to the two secondary coils 118a, 118b changes and causes the induced voltages to change, which correlates to the change in position of the cylindrical ferromagnetic core 110 relative to the primary coil 116 and secondary coils 118a, 118b.

[0036] While the induced voltages in the secondary coils 118a. 118b are dependent on a position of the cylindrical ferromagnetic core 110, the induced voltages are also affected by temperature. Thus, to ensure an accurate measurement of displacement, the position output by the LVDT 10 may be calibrated based on the temperature of the LVDT 10. This may be especially applicable when operating the LVDT 10 in an environment where the temperature may change by a relatively large amount, such as in a high temperature environment or a low temperature environment, such as environment 180 shown in FIG. 2.

[0037] With conventional LVDTs, a temperature sensor is added to the instrumentation and is placed near the LVDT to measure the temperature near the LVDT. The output of the LVDT may then be calibrated based on the temperature measured by the temperature sensor. However, by adding additional sensors and corresponding electrical leads to an instrumentation setup, the cost of the instrumentation setup may increase. It is also possible that the other sensor’s temperature measurement will induce additional error in the LVDT. Furthermore, the lifespan of the instrumentation setup in an extreme environment, such as within a nuclear reactor, a power turbine, or the like, may be limited by the temperature sensor rather than the LVDT.

[0038] Accordingly, in some embodiments, the LVDT 10 itself may be used to measure the temperature, eliminating the need for a separate temperature sensor. In some embodiments, the resistances across the secondary7coils 118a, 118b may be used to calculate the temperature of the LVDT 10. This temperature measurement may then be used, among other things, to calibrate the LVDT 10 to accurately measure linear displacement.

[0039] FIG. 3 shows a schematic view of resistances of the secondary7coils and associated electrical leads of an LVDT according to some embodiments. In FIG. 3, R is the conductor resistance of each of the leads 126, 128. 130 in ambient conditions. This conductor resistance in ambient temperatures may be a known value and is substantially equal in each of the leads 126, 128, 130. Rm is the conductor resistance of each of the leads 126, 128, 130 within the elevated temperature environment 180 (wi thin the elevated temperature boundary 182). This conductor resistance is unknown because it is based on the temperature of the leads 126, 128. 130 within the elevated temperature environment 180. Rm may be equal in all three of the leads 126, 128, 130. RA is the resistance within the first secondary7coil 118a (see FIGS. 1 and 2), which is unknown and which is dependent on temperature of the first secondary coil 118a within the elevated temperature environment 180. RB is the resistance within the second secondary coil 118b (see FIGS. 1 and 2), which is unknown and which is dependent on temperature of the second secondary coil 118b within the elevated temperature environment 180.

[0040] Using the leads 126, 128, 130 of the LVDT 10, resistance measurements of different portions of the LVDT 10 may be obtained at various temperatures. For example, a resistance Ri may be obtained between leads 126 and 128, a resistance R2 may be obtained between leads 128 and 130, and a resistance Rs may be obtained between leads 126 and 130. By measuring the resistances Ri, Rs. and Rs. the resistances RA of the first secondary coil 118a and the resistance RB of the second secondary coil 118b and the resistance Rin of the leads within the elevated temperature environment 180 may be calculated by the following system of equations:

[0041] R = 2R + 2Rin+ RAR2= 2R + 2Rin+ RB

[0042] R3— 2R + 2Rin+ RA+ Rg By obtaining the resistances Ri, R2. and Rs at several different known temperatures and calculating the resistances RA of the first secondary coil 118a and the resistance RB of the second secondary coil 118b for each of the known temperatures, the resistances RA of the first secondary coil 118a and the resistance RB of the second secondary coil 118b may be correlated with temperature for future use in measuring the internal temperature of the LVDT 10. Thus, once the correlation between the resistances RA of the first secondary coil 118a and the resistance RB of the second secondary coil 118b is established, the LVDT 10 may be used to calculate temperature in addition to measuring linear displacement.

[0043] In some embodiments, an LVDT may be configured to switch from measuring linear displacement and measuring temperature. FIG. 4 shows a schematic view of an LVDT 20 with electronics for so-called '‘intrinsic temperature measurements” according to some embodiments. By “intrinsic temperature measurement,” it is meant that portions of an LVDT 20 used for measuring linear displacement may also be used to measure temperature. To avoid repetition, not all features shown in FIG. 4 are described in detail herein. Rather, unless described otherwise below, in FIG. 4, a feature designated by a reference numeral that is a 100 increment of the reference numeral of a feature previously described with reference to FIGS. 1-3 will be understood to be substantially similar to the previously described feature. By w ay of non-limiting example, unless described otherwise below, features designated by the reference numerals 210, 216 in FIG. 4 respectively will be understood to be substantially similar to the cylindrical ferromagnetic core 110 and the primary coil 116 previously described herein with reference to FIGS. 1-3.

[0044] As shown in FIG. 4, the LVDT 20 is a 5-wire LVDT. However, this is merely exemplary and other ty pes of LVDTs may be used, such as a 4-wire LVDT or a 6-wire LVDT. In the LVDT 20, a first switch 232 may be provided in a lead connected to the primary coil 216. The first switch 232 may be operable to selectively connect the primary coil 216 to the AC driver 224. A second switch 234 may be provided on a lead 226 connected to the first secondary coil 218a. The second switch 234 may be operable to selectively connect the lead 226 with a first resistance data acquisition unit 250 and with a linear displacement sensor 227. A third switch 236 may be provided on a lead 228 that connects between the first and second secondary coils 218a, 218b. The third switch 236 may be operable to selectively connect the lead 228 to a first resistance measurement lead 246 and a ground 229. A fourth switch 238 may be provided on a lead 230 connected to the second secondary coil 218b. The fourth switch 238 may be operable to selectively connect the lead 230 to the first resistance measurement lead 246 and to a linear displacement sensor 231.

[0045] The LVDT 20 may also comprise a fifth switch 240 connected to a second resistance measurement lead 248 and the first resistance data acquisition unit 250. The fifth switch 240 may be operable to selectively connect the first resistance data acquisition unit 250 to the first secondary coil 218a (e.g., via lead 226) or the second secondary coil 218b (e g., via lead 230). A sixth switch 242 may be provided that is connected to the first resistance measurement lead 246 at a second resistance data acquisition unit 252. The sixth switch 242 may be operable to selectively connect the first resistance measurement lead 246 to the second secondary coil 218b (e.g., via lead 230) and to between the first and second secondary coils 218a, 218b (e.g., via lead 228).

[0046] Each of the switches 232, 234, 236, 238, 240, 242 may be operable to allow the LVDT 20 to switch betw een a linear displacement measurement mode and a temperature measurement mode. For example, in the linear displacement measurement mode, the first switch 232 may be in position 1 to connect the primary coil 216 to the AC driver 224. The second, third, and fourth switches 234, 236, 238 may each be in position 1 so that the induced voltages across each of the secondary' coils 218a, 218b may be measured at the leads 226, 228, 230 via the linear displacement sensors 227, 231, thereby allowing the linear displacement to be determined.

[0047] To configure the LVDT 20 in temperature measurement mode, the first switch 232 may be moved to position 3 to disconnect the primary' coil 216 from the AC driver 224. With the primary' coil 216 disconnected from the AC driver 224, no induced voltages are generated in the first and second secondary coils 218a, 218b. The switches 234, 236. 238 may be moved to position 3 such that the first and second secondary coils 218a, 218b may connect to the first and second resistance measurement leads 246, 248. The switches 240, 242 may be used along with the first and second resistance data acquisition units 250, 252 to measure resistance from the first resistance measurement lead 246 to the second resistance measurement lead 248 across each of the first and second secondary coils 218a, 218b, respectively, and across both of the first and second secondary coils 218a, 218b. By using the measured resistances, the resistance of the first and / or second secondary' coils 218a, 218b may be detenwined as outlined above. One or both resistances may be correlated to temperature to determine the temperature of the LVDT 20. In some examples, the first data acquisition unit 250 may be used to verify the current through the system in the temperature measurement mode. For example, a known resistance 244 may be used to verify the current through the system by measuring a voltage drop across the resistor at the first data acquisition unit 250 to calculate the exact current through the system.

[0048] In some examples, the LVDT 20 may be configured to measure the resistance from the first resistance measurement lead 246 to the second resistance measurement lead 248 across the first secondary coil 218a. In this configuration, the fifth switch 240 may be in position 3 while the sixth switch 242 may be in position 1, allowing the first resistance data acquisition unit 250 to measure the resistance across the first secondary' coil 218a.

[0049] The LVDT 20 may be configured to measure the resistance from the first resistance measurement lead 246 to the second resistance measurement lead 248 across the second secondary coil 218b. In this configuration, the fifth switch 240 may be in position 1 while the sixth switch 242 may be in position 1, allowing the first resistance data acquisition unit 250 to measure the resistance across the second secondary coil 218b.

[0050] The LVDT 20 may be configured to measure the resistance from the first resistance measurement lead 246 to the second resistance measurement lead 248 across both first secondary coil 218a and the second secondary' coil 218b. In this configuration, the fifth switch 240 may be in position 3 while the sixth switch 242 may be in position 3, allowing the first resistance data acquisition unit 250 to measure the resistance across the first secondary coil 218a and the second secondary coil 218b.

[0051] FIG. 5 shows a method for measuring temperature with an LVDT according to some embodiments. In act 305, the LVDT may be initially operated in a linear displacement measurement mode in which the LVDT is operated with the AC driver providing an AC current to the primary coil. In act 315, the linear displacement may be measured based on an output of a difference in the induced voltages of the secondary' coils. The difference in the induced voltages of the secondary' coils may be based on the position of the cylindrical ferromagnetic core relative to the primary and secondary coils.

[0052] The LVDT may be switched from the linear displacement measurement mode to a temperature measurement mode. In act 325, the AC Driver may be disconnected from the primary' coil such that no AC current is delivered to the primary' coil and no voltages are induced in the secondary coils. In some embodiments, the secondary coils may be disconnected from voltage measurement leads, and may be connected to a current source and a data acquisition unit operable to measure resistance through one or both of the secondary coils. In act 335, the resistance across one or both of the secondary’ coils may be measured using the data acquisition unit.

[0053] In act 345, the measured resistance across one or both of the secondary coils may be correlated with temperature to determine the temperature of the LVDT. This temperature may be output as a temperature reading to an external device. In some examples, in act 355, the temperature reading from the LVDT in the temperature measurement mode may be used to calibrate the output of the LVDT in the linear displacement measurement mode. For example, the output of the LVDT in the linear displacement measurement mode may be calibrated (e g., adjusted) based on the temperature of the LVDT as measured by the LVDT when operating in the temperature measurement mode.

[0054] After using the LVDT in the temperature measurement mode and optionally calibrating the LVDT based on temperature, the LVDT may be switched back to the linear displacement measurement mode. In act 365, the AC driver may be reconnected to the primary coil such that the LVDT operates in the linear displacement measurement mode. The method may then be repeated, as desired.

[0055] While the above-described LVDT and method describe using both the first secondary coil and the second secondary coil to measure temperature within the LVDT, this is not intended to be limiting. In some examples, instead of measuring resistance in both of the secondary coils, resistance may be measured in a single secondary coil. In some examples, instead of using the resistance of the secondary coils, the LVDT may be configured to measure the resistance of the primary coil and correlate the measured resistance to temperature.

[0056] FIG. 6 shows a schematic view of an LVDT 60 with electronics for temperature measurements according to some embodiments. The LVDT 60 shown in FIG. 6 may be a 4-wire LVDT. In the LVDT 60, a first switch 632 may be provided on a first lead connected to the primary coil 616, and a second switch 634 may be provided on a second lead connected to the primary coil 616. The first switch 632 and the second switch 634 may be operable to selectively connect the primary coil 616 to the AC driver 624 and to a first resistance data acquisition unit 650 and a second resistance data acquisition unit 652.

[0057] A third switch 638 may be provided on a lead 626 of secondary' coil 618. The third switch 638 may be operable to selectively connect the secondary coil 618 with the first resistance data acquisition unit 650. A fourth switch 640 may be provided on a lead 628 connected to the secondary coil 618. The fourth switch 640 may be operable to selectively connect the secondary coil 618 with the second resistance data acquisition unit 652.

[0058] Each of the switches 632, 634, 638, 640 may be operable to allow the LVDT 60 to switch between a linear displacement measurement mode and a temperature measurement mode. For example, in the linear displacement measurement mode, the first switch 632 and the second switch 634 may each be in position 1 to connect the primary coil 616 to the AC driver 624. The third switch 638 and the fourth switch 640 may each be in position 1 so that the induced voltages across the secondary coil 618 may be measured at a linear displacement sensor 654, thereby allowing the linear displacement to be determined.

[0059] To configure the LVDT 60 in temperature measurement mode, the first switch 632 and the second switch 634 may each be moved to position 3 to disconnect the primary coil 616 from the AC driver 624 and to connect the primary coil 616 to the first resistance data acquisition unit 650 and the second resistance data acquisition unit 652. With the primary coil 616 disconnected from the AC driver 624, no induced voltages are generated in the secondary coil 618. The third switch 638 and the fourth switch 640 may each be moved to position 3 such that the secondary coil 618 connects to the first resistance data acquisition unit 650 and the second resistance data acquisition unit 652. The first resistance data acquisition unit 650 and the second resistance data acquisition unit 652 may be used to measure resistance across each of the primary coil 616 and the secondary coil 618. One or both resistances may be correlated to temperature to determine the temperature of the LVDT 60.

[0060] In some examples, it has been found that by using resistance measurements of one or more of the coils within the LVDT to measure temperature, an accuracy similar to a Type K thermocouple may be achieved. For example, in a 5-wire or 6-wire LVDT, a temperature reading accuracy of within 1% may be achieved. In a 4-wire LVDT, a temperature reading accuracy of within about 10% or better may be achieved. In some examples, because the LVDTs may be “self-calibrating” for temperature (e.g., may be calibrated to temperature based on using the LVDT itself to measure temperature), LVDTs may be used in environments where temperature drift has excluded their use in the past. Further, because the LVDT may measure temperature, the need for added thermocouples, such as for irradiation testing, is eliminated, which may decrease the cost of irradiation testing, which may be conducted for extended periods of time. In some examples, other methods may be used to measure temperature with an LVDT. such as LVDT 10, 20 described above. FIGS. 7A-7C show schematic views of utilizing a pulse echo method for determining temperature using an LVDT according to some embodiments. In FIG. 7A, through switches 732, 734, a primary coil 716 of an LVDT may be disconnected from the AC driver 724 and may be connected to a high power pulser 760. The high power pulser 760 may generate a high frequency pulse in the primary coil 716. The energy pulse in the first primary coil 716 may excite a cylindrical ferromagnetic core 710 to generate sound waves within the cylindrical ferromagnetic core 710. The sound waves are shown in FIG. 7A as a first primary' wave 762a and a second primary' wave 762b.

[0061] As the sound waves within the cylindrical ferromagnetic core 710 reflect from each end of the cylindrical ferromagnetic core 710, the sound waves 762a, 762b again pass by the primary coil 716. As they pass through the primary coil 716, the inverse magnetostrictive effect w ill generate a small amount of current in the primary' coil 716. The time between successive reflections of the sound waves 762a, 762b is dependent on the temperature of the cylindrical ferromagnetic core 710 because the speed of sound within the cylindrical ferromagnetic core 710 changes with temperature. Therefore, the time betw een reflections of the sound w aves 762a, 762b within the cylindrical ferromagnetic core 710 may be correlated with temperature to determine the temperature within the LVDT. The reflections of the sound waves 762a, 762b, may be detected via an oscilloscope 768.

[0062] Given that the primary sound waves 762a, 762b are generated in both directions along the axis of the cylindrical ferromagnetic core 710, the timing of primary reflections 762a, 762b will depend on the core position relative to the primary coil 716 where the center of the primary coil 716 is shown by axis A in FIGS. 7B and 7C. However, as each primary reflection 762a, 762b passes through the cylindrical ferromagnetic core 710 a second time where the reflected wave may be termed a secondary' w ave 764a, 764b as shown in FIGS. 7B and 7C. the total distance traveled will be the same for waves propagating in each direction, so the secondary waves 764a, 764b or reflections will not depend on the core position. As shown in FIG. 8, the first signal 872 and second signal 874 shown correspond to the primary' waves 762a, 762b, while the third signal 876 shown corresponds to the secondary w aves 764a, 764b. Therefore, the time of flight for the secondary waves 764a, 764b is dependent on temperature only. The secondary waves 764a, 764b may be reflected several times and may be interpreted as a frequency. Therefore, in some embodiments, the frequency of the secondary waves 764a, 764b may be correlated to a temperature of the LVDT. After the measurement is made, the LVDT will be switched from a high frequency pulse back into normal AC mode for measuring linear displacement via the switches 732, 734.

[0063] The above-described LVDTs and methods for measuring temperature using an LVDT may be incorporated in a variety of applications. The LVDTs may be used, for example, in nuclear reactors to determine irradiation effects on nuclear fuel and cladding. The LVDTs enable real-time data acquisition in such a fluctuating temperature environment. In addition, LVDTs configured to measure temperature and methods for measuring temperature using an LVDT may be incorporated in medical equipment such as LINAC, manufacturing equipment such as in automotive or aerospace applications, flight control systems where temperature variations based on altitude may be present, research and development labs where precise accuracy over a range of temperatures may be desired, and / or military applications.

[0064] In some examples, a resonant frequency of the cylindrical ferromagnetic core of the LVDT may be used to determine temperature. The AC driver of the LVDT may be configured to provide a “frequency sweep” input signal to the primary coil 916 (e.g., the middle coil shown in FIG. 9). The frequency sweep input signal may be similar to that shown in FIG. 10A. The primary coil 916 may drive a frequency in a cylindrical ferromagnetic core 910, which induces a voltage in the secondary coils 918. As the frequency of the input signal to the primary coil 916 changes, the cylindrical ferromagnetic core 910 may be driven into a resonant oscillation, which may be detected in the secondary' coils 918. Such a detection of the resonant oscillation is shown in FIG. 10B. The thermal expansion of the cylindrical ferromagnetic core 910 causes the resonant frequency to decrease as temperature increases. Therefore, the resonant frequency detected by the secondary coil may be correlated with the temperature of the LVDT. In some embodiments, the primary coil 916 may be disconnected from the AC driver of the LVDT and connected to a different AC source in order to provide a frequency sweep in the range of the resonant frequency of the cylindrical ferromagnetic core 910 at the expected operating temperatures.

[0065] The embodiments of the disclosure described above and illustrated in the accompanying drawings do not limit the scope of the disclosure, which is encompassed by the scope of the appended claims and their legal equivalents. Any equivalent embodiments are within the scope of this disclosure. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternate useful combinations of the elements described, will become apparent to those skilled in the art from the description. Such modifications and embodiments also fall within the scope of the appended claims and equivalents.

Claims

CLAIMSWhat is claimed is:

1. A linear variable differential transformer ( ‘LVDT”) configured to measure temperature, the LVDT comprising: a ferromagnetic core; a primary coil surrounding the ferromagnetic core; a secondary coil surrounding the ferromagnetic core; an AC driver configured to provide an AC current to the primary coil; a first switch configured to selectively connect and disconnect the AC driver to the primary coil: and one or more data acquisition units configured to measure a resistance of at least one of the primary coil or the secondary' coil when the AC driver is disconnected from the primary’ coil.

2. The LVDT of claim 1, wherein the secondary coil comprises a first secondary coil and a second secondary' coil, and wherein the one or more data acquisition units are configured to measure a first resistance of the first secondary coil and a second resistance of the second secondary coil when the AC driver is disconnected from the primary coil.

3. The LVDT of claim 2, wherein the one or more data acquisition units are configured to measure a combined resistance across the first secondary coil and the second secondary coil.

4. The LVDT of claim 2, further comprising: a first lead connected to the first secondary coil: a second lead connected to the second secondary coil: and a third lead connected between the first secondary' coil and the second secondary coil.

5. The LVDT of claim 4, wherein: the one or more data acquisition units are configured to measure the first resistance (“RA”) and the second resistance C‘RB”) by detecting a first total resistance (“Ri”) from the first lead to the third lead, a second total resistance (“R2”) from the second lead to the third lead, and a third total resistance (“R3”) from the first lead to the third lead, and the one or more data acquisition units are configured to calculate R and RB by solving the following system of equations:R2= 2R + 2Rin+ RBR2= 2R + 2R in+ RA+ RgRin is an unknown value of a lead resistance within a high-temperature environment and R is a known value of a lead resistance at ambient temperature conditions; and the one or more data acquisition units correlate RA and RB to a temperature.

6. The LVDT of claim 4, further comprising: a second switch connected to the first lead; a third switch connected to the second lead; and a fourth switch connected to the third lead, the second, third, and fourth switches being configured to selectively operate the LVDT in a linear displacement measurement mode and a temperature measurement mode.

7. The LVDT of claim 6, wherein: the second switch selectively connects the first lead to a linear displacement sensor and the one or more data acquisition units; the third switch selectively connects the second lead to the linear displacement sensor and the one or more data acquisition units; and the fourth switch selectively connects the third lead to the one or more data acquisition units and a ground.

8. The LVDT of claim 7, further comprising: a fifth switch electrically connected to the one or more data acquisition units, the fifth switch selectively connecting the one or more data acquisition units to the second switch and the third switch; and a sixth switch electrically connected to the one or more data acquisition units, the sixth switch selectively connecting the one or more data acquisition units to the third switch and the fourth switch.

9. The LVDT of claim 8, wherein the one or more data acquisition units comprise a first data acquisition unit connected to the fifth switch and a second data acquisition unit connected to the sixth switch.

10. The LVDT of claim 1 , further comprising a second switch connected to the primary coil, the first switch and the second switch configured to selectively connect the primary coil to the AC driver and to the one or more data acquisition units.1 1. The LVDT of claim 10, further comprising a third switch and a fourth switch connected to the secondary coil, the third switch and the fourth switch configured to selectively connect the secondary coil to a linear displacement sensor and the one or more data acquisition units.

12. A method of measuring temperature w ith a linear variable differential transformer (“LVDT”), the method comprising: placing an LVDT in a variable temperature environment, the LVDT comprising an AC driver, a primary coil, and a secondary coil; disconnecting the AC driver from the primary coil of the LVDT; measuring resistance across at least one of the primary coil or the secondary coil of theLVDT; and correlating the measured resistance with temperature.

13. The method of claim 12, wherein the secondary coil comprises a first secondary coil and a second secondary coil, and wherein measuring resistance across at least one of the primary coil or the secondary coil comprises measuring resistance across the first secondary coil and the second secondary coil.

14. The method of claim 13, wherein measuring resistance across the first secondary coil and the second secondary coil comprises: detecting a first total resistance (“Ri”) from a first lead connected to the first secondary coil to a third lead connected between the first secondary' coil and the second secondary’ coil; detecting a second total resistance (“R2”) from a second lead connected to the second secondary coil to the third lead; detecting a third total resistance (“R3”) from the first lead to the third lead; determining a resistance of the first secondary coil (“RA”) and a resistance of the second secondary coil (“RB") by solving the following system of equations:R2= 2R + 2Rin+ RBR3= 2R + 2Rin+ RA+ RBwherein Rin is an unknown value of a lead resistance within a high-temperature environment and R is a known value of a lead resistance at ambient temperature conditions; and correlating RA and RB to a temperature.

15. The method of claim 12, wherein measuring resistance across at least one of the primary coil or a secondary coil comprises measuring resistance across both the primary' coil and the secondary' coil.

16. The method of claim 12, wherein disconnecting an AC driver from a primary coil of the LVDT comprises switching a first switch and a second switch to electrically7connect the primary coil to a data acquisition unit.

17. The method of claim 12, further comprising disconnecting the secondary coil from a linear measurement sensor.

18. The method of claim 17, wherein measuring resistance across at least one of the primary coil or a secondary coil comprises connecting the secondary coil to a data acquisition unit and detecting the resistance at the data acquisition unit.

19. The method of claim 18, wherein connecting the secondary coil to a data acquisition unit comprises switching a third switch and a fourth switch to disconnect the secondary coil from the linear measurement sensor and connect the secondary coil to the data acquisition unit.

20. A method of measuring temperature with a linear variable differential transformer ('‘LVDT”), the method comprising: delivering an AC energy pulse to a primary coil of the LVDT to generate sound waves within a ferromagnetic core of the LVDT; and correlating a timing of the sound waves within the ferromagnetic core to temperature.

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