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LVDT Sensitivity & Range

Calculate LVDT output voltage, sensitivity in mV/mm, and linear range from excitation voltage and stroke. Design displacement sensor signal chains.

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Formula

Vout=S×Vex×(x/FS)×100V_out = S × V_ex × (x/FS) × 100
S— Sensitivity (mV/V/%FS)
x— Core displacement (mm)

How It Works

This calculator computes LVDT (Linear Variable Differential Transformer) output voltage from displacement, essential for precision metrology engineers, aerospace actuator designers, and CNC machine developers. An LVDT is an electromechanical sensor that converts linear position into an AC voltage with essentially infinite resolution. It consists of a primary winding and two secondary windings on a cylindrical former with a free-moving ferromagnetic core. AC excitation (1-10 kHz typically) of the primary induces voltages in the secondaries; when the core is centered, secondary voltages are equal and opposite, giving zero differential output. Core displacement causes voltage imbalance proportional to position: Vout = S Vex (x/FS), where S is sensitivity in mV/V per mm (typically 1-5 mV/V/mm), Vex is excitation amplitude, x is displacement, and FS is full stroke. Per MIL-PRF-24042 (Performance Specification: Transducers, Linear Variable Differential, General Specification For) and SAE ARP4187 (Aerospace Recommended Practice for Linear Variable Differential Transformers), precision LVDTs achieve +/-0.1% linearity over +/-80% of stroke and infinite resolution (limited only by signal conditioning). LVDT calibration traceability follows NIST SP 811 (NIST Guide to the SI) and IEEE Standard 1451.4 (IEEE Standard for a Smart Transducer Interface for Sensors and Actuators — Mixed-Mode Communication Protocols and Transducer Electronic Data Sheet formats). Temperature coefficient is typically +/-0.02%/C per manufacturers Honeywell, Macro Sensors, and TE Connectivity.

Worked Example

Problem

Design signal conditioning for a Macro Sensors GHSA-750-500 LVDT (stroke +/-12.7 mm, sensitivity 2.5 mV/V/mm) in a hydraulic servo valve feedback system. Excitation is 3 Vrms at 5 kHz, target 10V output at full stroke.

Solution
  1. Full-stroke sensitivity: 2.5 mV/V/mm * 12.7 mm = 31.75 mV/V at full stroke
  2. Full-stroke output: Vout_fs = 31.75 mV/V * 3V = 95.25 mV rms
  3. Required demodulator + amplifier gain: G = 10V / 0.09525V = 105 V/V
  4. Use AD598 LVDT signal conditioner (excitation + demod + DC output in one IC)
  5. AD598 gain set: Rg = 62.5k / (G/10 - 1) = 62.5k / 9.5 = 6.58 kOhm
  6. Bandwidth: set by AD598 filter caps, use 10 Hz for servo stability (100 ms response)
  7. Resolution: AD598 noise is 15 uV rms -> 15 uV / (95.25 mV/12.7 mm) = 2 um
  8. Linearity error: +/-0.1% * 12.7 mm = +/-12.7 um
Result: AD598 with Rg = 6.8 kOhm provides +/-10V output over +/-12.7 mm stroke. Resolution is 2 um, limited by electronics noise, not LVDT resolution.

Practical Tips

  • ✓Use dedicated LVDT signal conditioner ICs (AD598, AD698, LDC1614) to provide excitation, phase-sensitive demodulation, and filtering in a single package; AD598 operates from single 9-36V supply per Analog Devices datasheet
  • ✓Match excitation frequency to LVDT specification: lower frequencies (100 Hz-1 kHz) reduce eddy current losses in the core; higher frequencies (5-10 kHz) improve bandwidth for dynamic position measurement; optimal is typically 2-5 kHz
  • ✓Ensure the core is guided mechanically to move axially only; lateral movement or tilting introduces nonlinearity and can cause premature wear in guide bearings; radial clearance should be <50 um per MIL-PRF-24042

Common Mistakes

  • ✗Applying DC excitation: LVDTs require AC excitation (typically 1-10 kHz sine wave) because transformer coupling only works with time-varying magnetic fields; DC produces no output per basic transformer theory
  • ✗Measuring LVDT output with DC voltmeter: raw output is AC proportional in amplitude to displacement; a phase-sensitive demodulator (AD598, AD698) converts it to bipolar DC proportional to signed displacement
  • ✗Exceeding linear stroke range: beyond +/-80% of rated stroke, output becomes increasingly nonlinear (2-5% deviation); use an LVDT with 25% larger stroke than required per Macro Sensors application guide

Frequently Asked Questions

LVDTs are non-contact (no friction between core and windings), have infinite resolution (no quantization), long life (>100 million cycles per MIL-PRF-24042 vs 1-10 million for potentiometers), and are immune to contamination. Potentiometers suffer wiper wear, finite resolution steps (dependent on winding pitch), and contact resistance variability. LVDTs cost $50-500 vs $5-50 for potentiometers but are required in high-reliability applications (aerospace, nuclear, medical devices) per SAE ARP4187 reliability specifications.
LVDT (Linear Variable Differential Transformer) measures linear displacement with typical strokes of +/-1 mm to +/-500 mm. RVDT (Rotary Variable Differential Transformer) measures angular rotation using the same principle with rotary core; typical range is +/-40 degrees for good linearity. For full 360-degree rotation measurement, resolvers (similar principle, multiple pole pairs) are used instead. Both LVDT and RVDT achieve +/-0.1% linearity per Honeywell and Moog specification sheets.
You can use rectified absolute-value detection for magnitude-only sensing (no direction information); output is always positive regardless of core direction. For bidirectional measurement required in servo systems, phase-sensitive detection (PSD) or lock-in amplifier is mandatory to determine displacement sign from the 0/180-degree phase relationship with excitation. Integrated signal conditioners (AD598, AD698) include PSD; for custom designs, use analog multiplier (AD633) or synchronous demodulation with reference from excitation oscillator.

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