We propose a novel relative-story displacement sensor for structural health monitoring. The sensor is composed of three pairs of position sensitive detector (PSD) units and light emitting diode (LED) arrays, and is capable of measuring both the local inclination angle of the PSD unit and the relative displacement between the PSD unit and the LED array. By immobilizing the LED arrays on the ceiling and the PSD units on the floor, we can accurately measure the relative-story displacement in real time. We have verified the measurement accuracy of the developed sensor using a shaking table and a θ stage, and the accuracy was evaluated to be approximately 0.15 mm in the displacement and 0.1 mrad in the local rotation angle. The results indicate that the developed sensor is applicable to the relative-story displacement measurement for the diagnostics of an actual building.
