Sensing mechanism of water turbidity using LED for in situ monitoring system

摘要

This paper investigates on the efficiency and suitability of an optical sensing mechanism for water quality monitoring. By using three types of optical sensors as detector and various colour of Light Emitting Diode (LED) as light transmitter, a real-time monitoring system is developed. The sensing mechanism works based on different absorbance properties of light as given by Beer-Lambert Law. A measurement and monitoring system is developed by using LABVIEW to measure the turbidity of the samples which are calibrated using a commercial turbidimeter. The use of different light sources; ultraviolet, white, red, green and blue LED paired with different photodetectors; phototransistor, photodiode and photoresistor are tested and analysed. White LED paired with phototransistor is found to have the best performance with sensitivity of 8 mV/NTU, shows the best linearity performance at 10% of error tolerance as well as having the least fluctuation reading during measurement.