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Design Guidelines

Magneto-elastic technology can be implemented using circular magnetism with either magnetic shafts or non-magnetic shafts and a magnetic ring. The material component of the steel alloy must contain at least 1.5% nickel and/or other alloying elements to allow the magnetic field to be maintained within the shaft. The magneto-elastic system measures changes in the magnetic field generated by the magneto-elastic ring, shaft, or area.

Individual Sensors are Comprised of 3 Basic Components:

  1. A metallic shaft that will accept and retain a defined magnetic field or a collar or ring assembly
  2. A pickup assembly that is capable of detecting a magnetic field and processing the information. The sensors are “hall devices”, precision coils or flux gates made of amorphous tape or wire
  3. An electronic module that provides the proper drive circuitry, a detection circuit with an amplifier

The simplicity of the design and minimum of components allows the magneto-elastic sensor to live in harsh environments where oil, dirt, water and large swings in temperature have a minimal effect on the sensor's performance.

The magnetic properties of the sensors are very stable and do not become weak with time, excess vibration, or impact loading. As a result, virtually all static and dynamic torque measurements are possible with the magneto-elastic sensors.

Shaft Configurations

RING DESIGN
  • Shaft diameter requires taper for ring press fit
  • Press fit endows ring with stress anisotropy
  • Shaft can be made of almost any material
  • Ring, typically 18% Ni maraging steel, is magnetized
  • Accuracies of .1% and .5%
COLLARLESS DESIGN
  • Material is locally magnetized (by a similar process as the ring design)
  • Shaft is a common alloy containing 1½% Ni or more
  • Select materials naturally exhibit magnetocrystalline anisotropy
  • Preponderance of local magnetic distributions lie within 90º quadrant symmetrically disposed in circular direction.
  • Materials used include 43XX, 48XX and 300M
  • Attainable accuracy = 0.5% to 2%

Magnetically Isotropic (Random orientation of magnetic moments). Initial State Region is magnetically isotropic in initial unconditioned state.

CIRCUMFERENTIAL POLARIZATION
Flux lines are all within the Magneto-elastic Ring. Region is magnetized via current, inducing circumferential polarization. For example:

 
HELICAL POLARIZATION (Application of Torque Results)
  • Applied torque tilts principal stress axis 45º
  • Moment (M R) tends to align with the principal stress axis
  • Resultant Moment (M R) has:
  • Axial Component (M A)
  • Circumferential Component (M C)
  • Flux lines are now external to the ring
OUTPUT SIGNAL VS. APPLIED TORQUE MAGNETIC STATES OF MAGNETO-ELASTIC RING
  • Sensor detects the external flux lines induced by torque
  • Magnetically Isotropic
  • Uniaxial Anisotropy
  • Circumferential Polarization
  • Helical Polarization Due to CCW Torque
®Copyright 2005