Patent Description:
Electronic sensors may detect various environmental parameters and generate a response signal. For example, pressure sensors may detect pressure in industrial pipelines. Temperature sensors may detect an ambient environmental temperature or may detect, for example, a temperature in a chamber. Accelerometers may detect vibration or shock, and may, for example, deploy automobile airbags. Displacement sensors may detect linear or angular displacement. Motion sensors may turn on lights in response to detecting the motion of people, for example.

Displacement sensors may be implemented in a variety of applications. In pressure measurement applications, a pressurized vessel, for example, an oil line, may include a diaphragm that moves outward in response to pressure and inward in response to vacuum. A displacement sensor may be coupled to the diaphragm to measure the pressure in the line, by measuring the displacement of the diaphragm. <CIT> discloses a linear displacement sensor, which determines a linear extension of the core element depending on the movement of a detected object, based on the alterations of the inductivity in coils. <CIT> discloses a core consisting of a sleeve which is wound out of a sheet-metal strip and which has a continuous slit and can be clamped onto a nonferromagnetic guide rod as a friction fit. <CIT> discloses an electromagnetic motion responsive device. <CIT> discloses a sensor device for detecting a position in an axial direction of a shaft moving and rotating in a longitudinal direction and rotating is provided to perform a translational motion and a rotational motion of a rotatable shaft and to detect an axial direction and position of the rotatable shaft. <CIT> discloses a solenoid coil connected in series with an electric motor. The solenoid plunger is formed of a flat sheet of magnetic material curled into the shape of a hollow cylindrical shell. The solenoid frame has a forked portion through which the plunger extends, the forked portion having sufficient depth to minimize side loading of the plunger. <CIT> discloses a sensor including a core and a coil. The core includes a rectangular substrate, a layer of magnetically-permeable material disposed on the substrate, and an adhesive rigidly coupling two ends of the substrate so as to form a tube with the rectangular substrate. The coil is wound on the tube. The core further includes a layer of radiopaque material. The core further includes a flex pad for electrically coupling the coil with an external system. <CIT> discloses a solenoid structure and mounting means.

Examples of apparatuses relate to a linear variable differential transformer (LVDT) probe including a plunger rod and a metal sheet formed into a cylinder with a C-shaped cross-section, configured to couple to the plunger rod. In an illustrative example, the coupling may be an interference fit aided by spring retention forces of the metal sheet. The metal sheet may be stamped, formed and applied to the plunger rod without annealing. One or more longitudinal metal sheet edges may be rounded. The C-shaped metal sheet may be welded to the plunger rod at a distal and/or proximal end. In some examples, the longitudinal edges of the metal sheet may be welded together and/or to the plunger rod. The ratio of relative electromagnetic permeability of the metal sheet to the plunger rod may be greater than <NUM>. Various implementations may advantageously reduce lot-to-lot variability and reduce the cost of producing LVDTs.

Various examples may achieve one or more advantages. For example, some examples may improve durability, reducing the risk of damage during manufacture and during field use. Some implementations may increase reliability especially in high-vibration environments. In dual channel LVDT examples, higher channel-to-channel correlation (e.g., better tracking) may be achieved. Some examples may exhibit lower variability of output sensitivity and/or linearity due to temperature extremes (e.g., lower temperature coefficient). In various examples, overall outer diameter may decrease, which may reduce apparatus weight and may reduce overall size and weight of end-use applications. Some examples may enable low cost manufacturing processes such as metal stamping, forming and press-fitting. These manufacturing processes may be automated, further reducing cost.

The details of various examples are set forth in the accompanying drawings and the description below.

To aid understanding, this document is organized as follows. First, a use-case scenario illustrating an exemplary C-shaped core retained on a plunger rod of a linear variable differential transformer (LVDT) is briefly introduced with reference to <FIG>. <FIG> further explains the construction of an exemplary LVDT. Next, with reference to <FIG>, the discussion turns to an exemplary embodiment that illustrates the C-shaped core and its relationship to the plunger rod within an LVDT. Next, various exemplary rounding features of the corners and edges of the core materials are detailed in <FIG> and <FIG>. Next, <FIG> show various exemplary retention methods. Specifically, <FIG>, <FIG> and <FIG> depict exemplary end-welds, <FIG> an exemplary longitudinal weld in accordance with the invention, <FIG> an exemplary retention clip, <FIG> an exemplary static friction enhancement feature, <FIG> exemplary adhesive, and <FIG> an exemplary end-stop feature.

<FIG> depicts an exemplary C-shaped probe core within a linear variable differential transformer (LVDT) measuring a deployment status of a landing gear assembly on an aircraft. An LVDT use-case scenario <NUM> includes an LVDT <NUM>. The LVDT includes a plunger-probe <NUM>. A C-shaped core <NUM> is coupled to the plunger-probe <NUM>. In some examples, the C-shaped core <NUM> may couple to the plunger-probe <NUM> with an interference fit. The C-shaped core <NUM> may possess an electromagnetic permeability greater than unity. In some examples, the C-shaped core <NUM> may possess electromagnetic permeability at least <NUM> times greater than the electromagnetic permeability of the plunger-probe <NUM>.

In some examples, the C-shaped core <NUM> may be fabricated from a sheet of metal that is substantially thin. The substantially thin sheet of metal may advantageously minimize an outer diameter of the C-shaped core <NUM> assembled onto the plunger-probe <NUM>. The plunger-probe <NUM> coupled to the C-shaped core <NUM> is slidably engaged with a core housing <NUM>. The core housing <NUM> includes an excitation-sense harness <NUM>. The minimized outer diameter of the C-shaped core <NUM> may be a starting point for optimizing the overall diameter of the core housing <NUM>. Accordingly, the substantially thin sheet of metal included in the C-shaped core <NUM> may advantageously enable designs of LVDTs <NUM> with small outer diameters.

The LVDT <NUM> is coupled to a landing gear assembly <NUM>. The deployment state of the landing gear assembly <NUM> may be sensed by the LVDT <NUM>. The LVDT <NUM> may be coupled to a flight control panel within an aircraft to indicate the deployment state of the landing gear <NUM>.

<FIG> depicts an exemplary LVDT. The LVDT <NUM> includes the plunger-probe <NUM>. The plunger-probe <NUM> couples to the C-shaped core <NUM>. The plunger-probe <NUM> extends outside the core housing <NUM>. The C-shaped core <NUM> is surrounded by an excitation winding <NUM> (primary) and a pair of sense windings 140A, 140B (secondary). The windings <NUM>, 140A an 140B are coupled to the excitation-sense harness <NUM>. The windings <NUM>, 140A and 140B reside inside the core housing <NUM>. The excitation-sense harness <NUM> extends from external to the core housing <NUM> to the windings <NUM>, 140A and 140B inside the core housing <NUM>.

The excitation winding <NUM> may produce a magnetic field in response to an excitation signal. The sense windings 140A and 140B may be magnetically coupled to the magnetic field, and may produce an electrical output signal in response to the magnetic field coupling. The magnetic field coupling may vary based on the location of the C-shaped core <NUM> within the core housing <NUM>. Accordingly, the electrical output signal from the sense windings 140A and 140B may vary in response to the longitudinal location of the C-shaped core <NUM> relative to the windings <NUM>, 140A and 140B.

In an illustrative example, an excitation signal is applied to the excitation winding <NUM> via the excitation-sense harness <NUM>. As the plunger-probe <NUM> slides within the core housing <NUM>, the electrical output signal produced is sent out from the excitation-sense harness <NUM>. In some examples, a processing module may be electrically coupled to the excitation-sense harness <NUM>. The electrical output signal produced by the LVDT may be detected by the processing module. Accordingly, the processing module may determine a linear position of the plunger-probe <NUM>. In the LVDT use-case scenario <NUM>, an aircraft pilot may determine the deployment status of the landing gear assembly <NUM> based on a resulting output from the processing module.

<FIG> depicts a perspective exploded view of an exemplary LVDT probe. An LVDT probe rod <NUM> couples to a core <NUM>. The core <NUM> may be stamped from a metal sheet. In some examples, the core <NUM> may be die cut from a metal sheet. Further, the core <NUM> may be laser cut from a metal sheet.

The core <NUM> is further formed into a cylindrical shape. By way of example and not limitation, the forming process may include die forming, stamping or pressing. In some examples, the forming process may include rolling. In further examples, the forming process may include electrical discharge machining (EDM).

The inner diameter of the core <NUM> in a cylindrical shape may be smaller than the outer diameter of the probe rod <NUM>. The cross-section of the core <NUM> may be a C-shape. The core <NUM> may be press-fit using an arbor press, for example, onto the probe rod <NUM>. In some examples, the core <NUM> may be press-fit using an automated method. The spring force inherent in the metal sheet may provide the grip to hold the core <NUM> onto the probe rod <NUM>. Use of the core <NUM> fabricated from a metal sheet, may reduce a final outer diameter of an LVDT assembly (e.g., <FIG>, item <NUM>). The spring force may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>).

In some examples, the core <NUM> may be assembled onto the probe rod <NUM> without press-fitting. For example, the core <NUM> may be wrapped around the probe rod <NUM>. After the wrapping operation, the core <NUM> may be squeezed to secure it to the probe rod <NUM>. The core <NUM> may be cinched to firmly bind the core <NUM> to the probe rod <NUM>.

In some examples, the core <NUM> may be slid onto the probe rod <NUM> without press-fitting. The slid-on core <NUM> may be welded to the probe rod <NUM>. In some examples, the core <NUM> may be crimped to the probe rod <NUM>.

The wrapping operation may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>). The squeezing operation may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>). Cinching may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>). Welding may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>). Crimping may retain the core <NUM> on the cylindrical rod (e.g., the probe rod <NUM>).

In an illustrative example, an LVDT assembly (e.g., <FIG>, item <NUM>) including the core <NUM> coupled to the probe rod <NUM> may be placed in an aircraft engine to measure oil pressure. The LVDT assembly within the aircraft engine may experience substantially high vibrations. The term "substantially" in this case may be up to <NUM> (acceleration due to gravity). The core <NUM> may be retained on the probe rod <NUM> by the spring force within the metal of the core <NUM> in conjunction with the static friction between the probe rod <NUM> and the core <NUM>.

Some examples may improve durability of the core <NUM>, which may advantageously reduce the risk of damage to the core <NUM> during manufacture and during field use. In an illustrative example, characteristics of a core (e.g. <NUM>) may be resistant to the effects of scratches, along the core surface, due to an anneal-free process. The anneal-free process may mitigate the enlargement of grains contained within the core. Mitigation of grain enlargement may produce a more consistent permeability within a core. Further, by retaining finer grains the grain distribution is averaged out, which may advantageously reduce the lot-to-lot variation, making the cores consistent from part-to-part and lot-to-lot.

<FIG> depicts a perspective view of a distal end of an exemplary LVDT probe. An LVDT probe assembly <NUM> includes a shaft <NUM> and a slug <NUM>. In some examples, the slug <NUM> may be a core (e.g., <FIG>, item <NUM>). The slug <NUM> includes a longitudinal slotted opening <NUM>. The slug <NUM> includes a longitudinal edge <NUM> on each side of the longitudinal slotted opening <NUM>. The longitudinal edges <NUM> may be rounded. In various embodiments, the rounding of the edges <NUM> may be completed with a manufacturing process that removes material on the corners of the edges <NUM>, creating an edge <NUM> with a radius. The radius on the longitudinal edges <NUM> may advantageously allow welding to both edges <NUM> with a single weld, if welds are implemented. In addition, the radius may provide a groove to reduce the profile of a weld, if welds are implemented. Further, rounded edges <NUM> may advantageously reduce weld stress.

<FIG> depicts a perspective view of a distal end of an exemplary LVDT probe illustrating chamfered corners on a probe core. An LVDT probe assembly <NUM> includes a shaft <NUM> and a slug <NUM>. The slug <NUM> includes a longitudinal slotted opening <NUM>. The slug <NUM> includes a corner <NUM> on a distal end of each side of the longitudinal slotted opening <NUM>. The corners <NUM> are rounded (include a radius). The radius on the corners <NUM> may advantageously provide space for an end-weld, if one is implemented.

<FIG> depicts a perspective view of a distal end of an exemplary LVDT probe illustrating a single weld. An LVDT probe assembly <NUM> includes a shaft <NUM> and a C-shaped core <NUM>. The C-shaped core <NUM> includes a longitudinal gap <NUM>. The C-shaped core <NUM> includes a radial weld <NUM> on a distal end of the longitudinal gap <NUM>. The radial weld <NUM> may advantageously secure the core <NUM> to the shaft <NUM>. In some examples, the LVDT probe assembly <NUM> may be a plunger assembly. In some examples, the radial weld <NUM> may be an end-weld. Various radial welds <NUM> may retain the C-shaped core <NUM> on the cylindrical rod (e.g., shaft <NUM>).

<FIG> depicts a perspective view of exemplary distal and proximal point welds between an LVDT core and rod. An LVDT probe assembly <NUM> includes a rod <NUM> and a C-shaped core <NUM>. The C-shaped core <NUM> includes a longitudinal gap <NUM>. The C-shaped core <NUM> includes a weld <NUM> on a distal end of the longitudinal gap <NUM>. The C-shaped core <NUM> includes a weld <NUM> on a proximal end of the longitudinal gap <NUM>. The welds <NUM> and <NUM> may be keyhole welds. In some examples, the welds <NUM> and <NUM> may be various other welds (e.g., spot, machine, laser, Tungsten Inert Gas (TIG), Gas Tungsten Arc Welding (GTAW)). In some examples, the welds <NUM> and <NUM> may be laser welds. In some examples, the welds may bond the rod <NUM> to the C-shaped core <NUM>.

<FIG> depicts perspective views of exemplary distal and proximal circumferential welds between an LVDT core and shaft. An LVDT probe assembly <NUM> includes a shaft <NUM> and a core sleeve <NUM>. The core sleeve <NUM> includes a longitudinal gap <NUM>. A perimeter weld <NUM> is implemented on the distal end of the core sleeve <NUM>. A perimeter weld <NUM> is also implemented on the proximal end of the core sleeve <NUM>. The perimeter welds may advantageously prevent slippage of the core sleeve <NUM> from the shaft <NUM>. Various perimeter welds <NUM> may retain the core sleeve <NUM> on the cylindrical rod (e.g., shaft <NUM>).

In various examples, the distal perimeter weld <NUM> may exist without the proximal perimeter weld <NUM>. Implementation of the distal perimeter weld <NUM> without the proximal perimeter weld <NUM> may reduce the profile of the LVDT probe assembly <NUM>.

Further, the proximal perimeter weld <NUM> may exist without the distal perimeter weld <NUM>. Implementation of the proximal perimeter weld <NUM> without the distal perimeter weld <NUM> may provide additional spacing from the distal end of the LVDT probe assembly <NUM> to a core housing (e.g., <FIG>, item <NUM>). Placing the welds <NUM> and <NUM> on one end may save cost, reduce the risk of foreign object debris (FOD), yet securely hold the core sleeve <NUM> onto the shaft <NUM>. In some implementations, no additional welds may be applied, which may advantageously further reduce cost, and further reduce the risk of FOD. Due to the spring retention along the length of the core sleeve <NUM>, the core sleeve <NUM> may be held securely to the shaft <NUM>.

<FIG> depicts a perspective view of an exemplary longitudinal weld between an LVDT core and rod in accordance with the invention, An LVDT probe assembly <NUM> includes a shaft <NUM> and a core sleeve <NUM>. The core sleeve <NUM> includes a longitudinal gap (e.g., <FIG>, item <NUM>). A longitudinal weld <NUM> is implemented along the longitudinal gap of the core sleeve <NUM>. As shown in DETAIL B-B, the longitudinal weld <NUM> may penetrate the core sleeve <NUM> and into the shaft <NUM>. The longitudinal weld <NUM> may securely hold the core sleeve <NUM> to the shaft <NUM>. Various longitudinal welds <NUM> may retain the core sleeve <NUM> on the cylindrical rod (e.g., shaft <NUM>).

<FIG> depicts a perspective view of an exemplary core clip applied to an LVDT core. An LVDT probe assembly <NUM> includes a shaft <NUM> and a core sleeve <NUM>. The core sleeve <NUM> includes a longitudinal gap <NUM>. On the distal end of the LVDT probe assembly <NUM>, a groove <NUM> is circumscribed around the core sleeve <NUM>. The groove <NUM> retains a clip <NUM>. The core sleeve <NUM> may be advantageously secured to the shaft <NUM> at least in-part by the spring force of the clip <NUM>. Various clips (e.g., <NUM>) may retain the core sleeve <NUM> on the cylindrical rod (e.g., the shaft <NUM>).

<FIG> depicts a perspective view of an exemplary LVDT probe with a knurled rod for retention of a core. An LVDT probe assembly <NUM> includes a rod <NUM> and a core sleeve <NUM>. The core sleeve <NUM> includes a longitudinal gap <NUM>. The rod <NUM> includes a knurling pattern <NUM>. The knurling pattern <NUM> may advantageously increase the static friction between the rod <NUM> and the core sleeve <NUM>. The increased friction may hold the core sleeve <NUM> securely in place in high vibration environments. Various knurling patterns (e.g., <NUM>) may retain the core sleeve <NUM> on the rod <NUM>. Further, various friction enhancement methods (e.g., sanding, sandblasting, soda-blasting, laser etching, chemical etching) may retain the core sleeve <NUM> on the cylindrical rod <NUM>.

<FIG> depicts a perspective view of an exemplary LVDT probe illustrating application of adhesive for retention of a core. An LVDT probe assembly <NUM> includes a rod <NUM> and a core sleeve <NUM>. The core sleeve <NUM> includes a longitudinal gap <NUM>. The rod <NUM> includes adhesive <NUM>. The adhesive <NUM> may advantageously increase the bond between the rod <NUM> and the core sleeve <NUM>. The increased bond may hold the core sleeve <NUM> securely in place in high vibration environments. Adhesives (e.g., <NUM>) may retain the core sleeve <NUM> on the rod <NUM>.

<FIG> depicts a perspective view of an exemplary LVDT probe illustrating use of an end-stop and a press-fit application of a core from a proximal end. An LVDT probe assembly <NUM> includes a plunger rod <NUM> and a sleeve core <NUM>. The sleeve core <NUM> includes a longitudinal gap <NUM>. The plunger rod <NUM> is fixedly coupled to an end-stop <NUM>. The diameter of the end-stop <NUM> may be less than or equal to the outer diameter of the sleeve core <NUM> when the sleeve core <NUM> is in an assembled state press-fit onto the plunger rod <NUM>.

During assembly of the LVDT probe assembly <NUM>, the sleeve core <NUM> is press-fit onto the plunger rod <NUM> until it seats against the end-stop <NUM>. The end stop may be configured to prevent movement of the sleeve core <NUM> off the end of the plunger rod <NUM>. In some examples, the plunger rod <NUM> may be tapered such that the narrower end is the distal end with the end-stop <NUM>. Movement of the sleeve core <NUM> toward the proximal end may be mitigated by a larger outer diameter on the plunger rod <NUM>. Further, movement of the sleeve core <NUM> toward or off from the distal end may be mitigated by the end-stop <NUM>.

Once the sleeve core <NUM> is press-fit onto the plunger rod <NUM>, a probe coupling <NUM> may be coupled to the plunger rod <NUM>. The plunger rod <NUM> includes a threaded end <NUM>. In some examples, the plunger rod <NUM> and the threaded end <NUM> are unitary in construction. Various end-stop features (e.g., <NUM>) may retain the sleeve core <NUM> on the plunger rod <NUM>.

Although various examples have been described with reference to the figures, other examples are possible. For example, early in the fabrication process, a LVDT core in a flat sheet state may be stamped with a press. The press may stamp the core one or more times. The multiple stamping process may cause the grains within the LVDT core in the flat sheet state to break up and become finer. The fine grains may average out the grain domains within the LVDT core in the flat sheet state. This averaging may advantageously mitigate lot-to-lot variations in the magnetic properties of the LVDT core in the flat sheet state. Low lot-to-lot variations may advantageously allow field repair personnel to, for example, swap out failed LVDTs for new LVDTs without calibration and without sorting for electrical characteristics.

Various implementations may mitigate null shifting. An LVDT C-shaped core may be interference fitted to a plunger rod. The interference fit may enable an inherent spring force within the core material to retain the core on the plunger rod without welding. When the welding operation is omitted, ionic carbide lines may be avoided. Without ionic carbide lines, the stresses involved in high temperature applications may also be reduced, which may advantageously mitigate null shifting (e.g., shifting of the core). In an illustrative example, a dual channel LVDT is installed in a turbine generator. The design may rely on the tracking between the two channels for detection of minute differences in linear displacement. As the temperature within the generator rises, the weldless design of the dual channel LVDT allows the C-shaped cores to stay in place on the plunger rods. The mitigated null-shift effect provides monitoring electronics to detect true differential movement between the LVDT channels.

According to the invention, a starting core material is a metal sheet. By way of example and not limitation, the metal sheet may be about <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", <NUM>", or up to at least about <NUM>" or more. The sheet metal may be substantially thin. The term "substantially thin" may be defined as falling within the described thicknesses of the metal sheet.

The metal sheet may be any ferromagnetic or martensitic material. In some examples, the core material may be a high permeability material. By way of example and not limitation, the material may include iron and nickel. The material may further include, for example, cobalt, gadolinium, dysprosium, permalloy, awaruite, wairakite, magnetite, copper, chromium, molybdenum and/or silicon. Accordingly, various alloys may be employed in various cores.

The metal sheet may be formed by various methods. By way of example and not limitation, the forming process may include die forming, stamping, pressing, rolling or electrical discharge machining (EDM).

In some examples, a deep-draw forming process may be used on the metal sheet. In such examples, the high permeability metal sheet may be placed into a deep-draw stamping machine. The resulting deep-drawn part may be press-fit onto a plunger rod, and welded at the end. In some examples, the deep-drawn part may provide an interference fit with the plunger rod, and may be press-fit without the weld.

In various embodiments, an LVDT rod may include a longitudinal rib. The longitudinal rib may mate with a longitudinal gap on an LVDT core. The longitudinal rib and gap may advantageously key the assembly to ensure a consistent assembly orientation of the rib and gap. In some examples, the rib may mitigate rotational motion of the LVDT core. Various rib features may retain the LVDT core on the LVDT rod.

An LVDT with a plunger rod coupled to a C-shaped core, may be used in various aircraft flight controls, general engine controls, and within various power generation turbines. The C-shaped core may be used advantageously in high-vibration environments, and in high temperature applications. The C-shaped core may provide a high retention force on the plunger rod mitigating displacement on the rod in high vibration environments. The fine grains within the stamped core mitigates lot-to-lot variability, even in high temperature applications.

The C-shaped magnetic core design may reduce weight and may improve vibrational performance. The C-shape magnetic core may include a dual retention method when welded to the probe rod.

The magnetic core may be stamped in a press to be blanked and formed into a C-shaped cylinder. The stamping process may control the grain direction in the core blanks. Further, the C-shape magnetic core may be left in the un-annealed state. The un-annealed C-shape magnetic core may mitigate the effects of handling, scratching, dropping, mechanical endurance, and vibration on the sensitivity, linearity, and/or the output of an LVDT into which the C-shape magnetic core is assembled. In various examples, the C-shape magnetic core may be annealed to advantageously increase working voltage. Accordingly, the C-shape magnetic core may exhibit superior temperature performance and vibrational performance. Further the C-shape magnetic core may be produced with fewer processing steps, and may be low-cost.

An LVDT core may be "blank stamped" and "form stamped" which may advantageously control grain direction. After stamping and forming, the core may be pressed onto a probe rod to a desired position. In some examples, the core and probe rod assembly may include redundant retaining features (e.g., weld, braze, glue). The C-shape core may be welded on one or both ends, with either a single or multiple weld or braze pass. In some examples, a single pass weld and welding both ends with a single pass may reduce process cycle time. The C-shape core may be moved to a precise position on a rod prior to welding, brazing, and/or gluing. The C-shaped core may be positioned with a tool and/or embedded features such as threads on the probe rod or a probe fitting. Various LVDT core designs may be implemented on single or multi-channel LVDTs.

The core <NUM> is fixedly coupled to the cylindrical rod <NUM> in a non-slidable (e.g., retaining) relationship, which prevents displacement of the core <NUM> relative to the cylindrical rod <NUM> during operation. The present disclosure includes several ways/mechanisms for achieving this non-slidable (e.g., retaining) relationship between the core and the cylindrical rod. For example, <FIG> show various ways for configuring the core and cylindrical rod in a non-slidable relationship. These include: end-welds (in <FIG>, <FIG> and <FIG>), a longitudinal weld in accordance with the invention (in <FIG>), a retention clip (in <FIG>), a static friction enhancement feature (in <FIG>), adhesive (in <FIG>), and an end-stop feature (in <FIG>).

Claim 1:
An apparatus for use in a linear variable differential transformer (<NUM>), LVDT, the apparatus comprising:
a core (<NUM>) extending along a first longitudinal axis and having a C-shaped cross section in a plane normal to the first longitudinal axis and being made of sheet metal, the core (<NUM>) having a core inner diameter defining an inner surface of the core and defining a central lumen extending along the first longitudinal axis, and the core having a core outer diameter defining an outer surface of the core; and
a cylindrical rod (<NUM>) extending along a second longitudinal axis, wherein the cylindrical rod (<NUM>) is received in the central lumen of the core (<NUM>), such that when the cylindrical rod (<NUM>) is received in the central lumen of the core (<NUM>), the first and second longitudinal axes align with one another,
wherein the C-shaped core (<NUM>) includes a longitudinal gap (<NUM>) which extends from a proximal end of the core to a distal end of the core,
characterized in that
the C-shaped core (<NUM>) includes a longitudinal weld (<NUM>) implemented along the longitudinal gap and penetrating the C-shaped core (<NUM>) and into the cylindrical rod (<NUM>), such that the core (<NUM>) is fixedly coupled to the cylindrical rod (<NUM>) in a non-slidable relationship.