Improved multi-sensor for force measurement of pre-stressed steel cables by means of the eddy current technique

Increasing demands on re-enforced concrete constructions (e.g. bridges) require long-term multi-sensor monitoring techniques. For failure prediction of components the continuous monitoring of force and stress in reinforced concrete components is required. Coils can detect very small stress variations in ferromagnetic steels due to the magneto-elastic effect. Their main advantage over strain gauges is the ability of a medium-free measurement. Environmental and real construction conditions led to a sensor arrangement with six individual eddy current coils. These coils were arranged around a strand wire and are also in direct contact with the material under testing. Due to changing magnetostriction coefficients of different structural steels an impedance calibration is necessary [D. Jiles, Introduction to Magnetism and Magnetic Materials, Chapman and Hall, London, 1991].