Abstract: A strain detector wherein the efficiency of a detecting coil is improved to improve the sensitivity of the strain detector. The strain detector comprises a magnetic layer made of a soft magnetic material having a high permeability and fixedly mounted on an outer periphery of a driven shaft strain of which is to be detected, and a detecting coil disposed around the magnetic layer with a gap left therebetween for detecting a variation of the permeability arising from strain of the magnetic layer caused by an external force applied to the driven shaft. The strain detector further comprises a metal layer made of a non-magnetic material having a high electric conductivity and disposed in the gap between the magnetic layer and the detecting coil. Or else, the detecting coil has a pair of coil portions connected to each other by way of an intermediate portion thereof, and an electric current flows in the same direction through the coil portions.

Abstract: A strain detector wherein external and internal magnetic fields are magnetically separated from each other to eliminate an influence of such disturbance magnetic field to assure accurate and stabilized detection of strain in a drive shaft. The detector comprises a magnetic layer made of a soft magnetic material having a high permeability and suitable magnetostriction fixedly mounted on an outer periphery of a driven shaft, a pair of bearings or bearing stands made of a soft magnetic material having a high permeability for supporting the driven shaft for rotation thereon, a detecting coil disposed around the magnetic layer for detecting a variation of the permeability of the magnetic layer arising from strain of the magnetic layer caused by an external force applied to the driven shaft, and a shield disposed on an outer periphery of the detecting coil and magnetically connected at the axial opposite end portions thereof to the bearings or bearing stands.

Abstract: A strain detector wherein the efficiency of a detecting coil is improved to improve the sensitivity of the strain detector. The strain detector comprises a magnetic layer made of a soft magnetic material having a high permeability and fixedly mounted on an outer periphery of a driven shaft strain of which is to be detected, and a detecting coil disposed around the magnetic layer with a gap left therebetween for detecting a variation of the permeability arising from strain of the magnetic layer caused by an external force applied to the driven shaft. The strain detector further comprises a metal layer made of a non-magnetic material having a high electric conductivity and disposed in the gap between the magnetic layer and the detecting coil. Or else, the detecting coil has a pair of coil portions connected to each other by way of an intermediate portion thereof, and an electric current flows in the same direction through the coil portions.

Abstract: A strain detector for detecting a strain developed in a shaft applied with a torque comprises strain-sensitive magnetostrictive elements attached to the shaft in two groups in a chevron pattern. A pair of annular detection coils are wound around a bobbin to surround respective one of the groups of magnetostrictive elements. Two annular yokes made of a soft magnetic material of high permeability are disposed around respective coils across radial gaps. A hollow cylindrical shield of non-magnetic material with a high electrical conductivity is disposed around the two yokes across radial gaps. The magnetostrictive elements may be made of a nickel-iron alloy of 45 to 55% Ni-Fe. The yokes may be made of a nickel-iron alloy of about 80% Ni-Fe or alternatively, of a 6.5% Si-Fe steel. The detector may comprise a second magnetic shield disposed around the first shield of non-magnetic material with a high electrical conductivity. The second shield may be made of the same magnetic material as the yokes.