Movable Core: Core Diameter 3-25 mm

Q: What is the main function of the movable core in an LVDT?

The movable core converts mechanical linear displacement into proportional electrical signals by altering magnetic coupling between primary and secondary coils, enabling precise position measurement.

Q: Why are nickel-iron alloys preferred for movable cores?

Nickel-iron alloys (80/20) provide high magnetic permeability, low coercivity, and minimal hysteresis losses, ensuring accurate signal generation with excellent temperature stability and linearity.

Q: Can movable cores be replaced independently in LVDT sensors?

Typically no - movable cores are precision-matched to specific LVDT assemblies during manufacturing. Replacement requires complete sensor recalibration due to critical magnetic and mechanical tolerances.

Component Specifications

Definition

The movable core is a precisely manufactured ferromagnetic component that slides axially within the primary and secondary coils of a Linear Variable Differential Transformer (LVDT). Its position relative to the coils creates differential voltage outputs proportional to displacement, enabling accurate linear position measurement with high resolution and repeatability in industrial feedback systems.

Working Principle

The movable core moves linearly within the LVDT's electromagnetic field. As it displaces, it changes the magnetic coupling between the primary excitation coil and two secondary coils, creating differential AC voltage outputs. The phase and amplitude of these voltages indicate both direction and magnitude of displacement, with null position occurring when the core is centered between secondary coils.

Materials

High-permeability nickel-iron alloys (typically 80% Ni, 20% Fe), laminated silicon steel, or ferrite materials with low coercivity and high magnetic saturation to minimize hysteresis and eddy current losses.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Linearity	±0.1% to ±0.5% of full scale
Resolution	Theoretically infinite (limited by electronics)
Null Voltage	<0.5% of full scale output
Core Diameter	3-25 mm
Stroke Length	±0.5 to ±500 mm
Frequency Response	50 Hz to 20 kHz
Operating Temperature	-55°C to +150°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 16063-21, DIN 43760, IEC 60668

Parent Products

This component is used in the following industrial products

Feedback Sensor (e.g., LVDT)

A sensor that provides real-time position feedback for servo control valve spools.

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Feedback Device (e.g., LVDT)

A sensor component in servo valves that provides real-time position feedback of the valve spool to the control system.

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Engineering Analysis

Risks & Mitigation

Magnetic saturation at extreme positions
Mechanical wear from continuous sliding
Temperature-induced dimensional changes
Contamination affecting smooth movement
Demagnetization from shock or excessive heat

FMEA Triads

Trigger: Abrasive particles in operating environment
Failure: Increased friction and wear, leading to position measurement errors and reduced lifespan
Mitigation: Implement protective bellows or seals, use filtered air systems, select hardened core materials, establish regular maintenance schedules

Trigger: Excessive operating temperature beyond specifications
Failure: Material expansion/contraction altering magnetic properties and dimensional tolerances, causing measurement drift
Mitigation: Install temperature sensors with compensation circuits, ensure proper cooling, select materials with low thermal expansion coefficients

Trigger: Mechanical misalignment during installation
Failure: Binding or uneven movement, creating nonlinear output and premature wear
Mitigation: Use precision alignment fixtures during installation, implement run-in procedures, verify perpendicularity with laser alignment tools

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Diameter tolerance: ±0.005 mm, Straightness: <0.01 mm/100 mm, Surface finish: Ra 0.4 μm max

Test Method

Magnetic permeability testing per ASTM A342, dimensional verification with coordinate measuring machines (CMM), linearity testing with laser interferometers, thermal cycling per MIL-STD-810

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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CNFX does not score or rank suppliers. Buyers must verify all claims and documents with the legal manufacturer before ordering.

Manufacturers of Movable Core

Manufacturer profiles associated with Movable Core.

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Frequently Asked Questions

What is the main function of the movable core in an LVDT?