US 5,308,973 A · Method and device for the measurement of force by a fiber optics system by evaluating phase shift of light waves

Abstract

A method and the device for fiber-optic measurement of the absolute value of the pretensioning in a highly loaded mechanical structural component part are based on the measurement of the phase displacement of a light wave caused by the strain-induced birefringence in a single-mode light waveguide 4 which is embedded between two metallic disks or washers 3a, 3b. Since the measurement results are ambiguous modulo-2.pi., serial or simultaneous measurement with two light wavelengths .lambda..sub.1, .lambda..sub.2 is used according to a first method variant of the invention. The quantity of 2.pi. periods can be unequivocally determined within a predetermined measuring range by means of comparing the two measurement results. The evaluation is preferably effected according to a quadrature or phase step method, known per se. According to second method variant, the light waveguide 4 is irradiated with polarized white light. The phase difference of the two linear modes due to the influence of force on the structural component part is compensated for in a compensation device 20. The control signal required for the compensation of the path difference is evaluated as a measurement for the force. The compensation method has the advantage that no monochromatic light sources are required.

Claims24

Dependent claims

A method for the absolute measurement of a force by fiber optics, based on the straininduced change in birefringence of a single-mode light waveguide wherein, in order to achieve unequivocal measurement results for said force:

two light waves having different wavelengths are beamed into one end of a light waveguide and the difference phase shifts of the two linear modes of said light exiting at an opposite end of said light waveguide, which is caused by the influence of force on said light waveguide and the consequent change in birefringence are detected photoelectrically, wherein the absolute values of said phase shifts are determined by means of phase comparison via a calibrated evaluating logic with an intermediate storage of said individual measurement values of said detected phase shifts, and further wherein said determined absolute value of at least one of said phase shifts is evaluated as a measurement for said force.

A device for the fiber-optic measurement of the absolute value of a pretensioning in a mechanical structural component part which is highly loaded by one of tensile and compressive forces, which comprises:

means for embedding a fiber-optic light waveguide in a pressure transmitting disk arranged transversely relative to a direction of force along a partial area of its length lying between its free ends;
two monochromatic light sources having different wavelengths;
means for introducing into one end of said light waveguide, in one of a simultaneously and a sequentially alternating manner, light waves from said light sources;
means for determining separately at an opposite end of said waveguide said two light waves having different wavelengths and converting same to electrical signals;
a phase comparison circuit and evaluating logic for determining the number of 2.pi. periods of phase shifts of at least one of said wavelengths and calculating the absolute value of one of said tensile and compressive forces from said determined absolute value of said phase shift;
and
means for feeding said electrical signals to said phase comparison circuit and evaluating logic.

4 more elements

Dependencies are inferred from the claim text.

Method and device for the measurement of force by a fiber optics system by evaluating phase shift of light waves

Life of this patent

Method and device for the measurement of force by a fiber optics system by evaluating phase shift of light waves

Life of this patent

Abstract

Claims24