A fiber optic current sensor on tunnel boring machine for current measurement application in tunnel geological prediction

摘要

A fiber optic current sensor (FOCS) used for current measurement application on tunnel boring machine (TBM) in tunnel geological prediction is proposed in this paper. Compared with the FOCS designed for power gird, the sensor developed in this paper is especially suitable for measuring the current which flows in a large diameter conductor, such as TBM. Aiming at solving the signal fading problem and sensitivity drift induced by the harsh working environment, the proposed FOCS utilizes a technique which is based on rotatable half-wave retarder and alternated current measurement. Verified by mathematical analysis and laboratory test, the rotatable half-wave retarder technique has been proved to be effective in solving the signal fading. The alternated current measurement method has been employed by a TBM which works for a water-diversion tunnel project, and the measurement record of field test suggests that the method reduces the sensitivity drift in long time measurement. Comparing with direct measurement, the coefficient of variance of the measuring result has been reduced significantly.