Research And Design Of Optical Fiber Turbidity Sensor

Turbidity is one of the important parameters of water quality monitoring,whose measurement trends are real-time online monitoring and early warning,reducing the measurement threshold to improve the sensitivity and accuracy, andimproving anti-jamming capability.Based on turbidity measurement trends, a fiber optic sensing online monitoringsystem was proposed. According to the turbidity measurement requirements ofreducing the threshold to improve the sensitivity and accuracy, and improvinganti-jamming capability, three types of optical fiber turbidity sensor was researchedand developed. By simulating and experimental studying their sensing characteristics,these optical fiber turbidity sensors have been optimized to conform to the turbiditymeasurement trends.Monte Carlo simulation of optical fiber turbidity sensor: By configuring a planemirror in front of the Y-shaped optical fiber bundle probe tip, a backscatteringturbidity sensor was proposed. Applying Monte Carlo method, detected light intensityreceived by sensor was simulated in different situations, and the distance betweenfiber bundle and plane mirror was optimized. This simulation provided a reference toimprove the design of an optical fiber turbidity sensor.To reduce turbidity measurement threshold, and improve low turbiditymeasurement sensitivity and accuracy, a double right-angle prism reflecting chamberwas designed, which combined with optical fiber sensing technology for photometricanalysis of solution. By measuring the absorbance of trace substances, theconcentration and extinction coefficient could be calculated, which estimatedturbidity and other characteristics of water. Analysis and experimental results showedthat by changing the distance between the two prisms, optical path was adjustable,and then the sensor sensitivity could change; the sensitivity of the sensor with prismschamber was enhanced by a factor of4with reference to the chamber without prisms,which made it more suitable for the detection of trace substances.To reduce light fluctuations, detector differences and water bubbles interference, a dual-channel optical fiber turbidity sensor was designed, which utilized a singlelight source but dual-channel light emitting, and a single spectrometer butdual-channel detection system. The light source channel was chosen by thephotoswitch alternately, and the corresponding scattered light or transmitted light wastransported to the same spectrometer by time division multiplexing effect of the otherphotoswitch. Turbidity was estimated in terms of the average of the scattered lightand transmitted light ratio, the linear correlation coefficient was0.9909, and theturbidity measurement stability and anti-jamming capability were enhanced.This study finally completed a fiber optic online turbidity monitoring system andthree types of fiber optic turbidity sensor. According to the turbidity measurementtrends, simulations and experiments were carried out systematically. Feasibilitystudies results showed that compared to conventional turbidity sensor, the sensingproperty of optical fiber turbidity sensor has improved in reducing measurementthreshold, and improving the sensitivity, accuracy and anti-interference ability.