A high accuracy fiber-optic level sensor

This paper describes a novel fiber-optic level sensor designed to measure the level of benzene, diesel oil and other chemical liquid discretely or continuously. It is an intensity-modulated on-off switching sensor whose operating principle is based on the frustrated-total-internal-reflection effect caused by the refraction index change of the surrounding medium. The sensor head is made from standard multi-mode communication silica fiber with a taper tip. Different tip shapes and fabrication methods were studied and the maximum signal contrast of 15 dB of the sensor tip has been obtained. The experiment results demonstrated that the resolution of the system of 10 mum and the level measurement accuracy of +/-0.5 mm have been achieved in a continuous measurement range of 2m.