A wide dynamic range and high resolution all-fiber-optic turbidity measurement system based on single photon detection technique

Abstract

A high-resolution fiber-optic detection system has been developed to measure the wide dynamic range of turbidity. To obtain high-resolution measurement results, a high sensitive single photon detection technique (SPDT) has been used in the system. Based on fiber characteristics, a compact probe structure for fiber-optic integrated transceiver (FITP) is designed to transmitting and collection light signal, which has the capability of detecting turbidity in the narrow workspace. By combining the Beer-Lambert (B-L) law transmission law with single photon counting theory, a novel turbidity measurement theoretical model has been proposed, which shows a good exponential relationship over the whole measurement range from 0.01 to 1000 NTU (Nephelometric Turbidity Units). However, when detecting 0.01–0.1 NTU low turbidity, the experimental results turn into an approximate linear relationship, which good agrees with the proposed theoretical model. Last, some issues about the optimization of light intensity and requiring attention on constructing a practical distributed multi-point water turbidity remote monitoring system in the outdoors are also discussed. It was found that the system can achieve a measurement dynamic range as wide as 50 dB with a resolution better than 0.01 NTU in the range of 0.01–1000 NTU, which is suitable for some specific turbidity measurement in remote and narrow workspace.