Low-Cost Turbidity Sensor for Low-Power Wireless Monitoring of Fresh-Water Courses

This paper reports on a low-cost turbidity sensor design for continuous on-line water quality monitoring applications. The measurement of turbidity by agricultural and environmental scientists is restricted by the current cost and functionality of available commercial instruments. Although there are a number of low-cost turbidity sensors exploited within domestic `white-goods', such as dishwashers, the lack of sensitivity, and power-usage of these devices make them unsuitable for fresh-water quality monitoring purposes. The recent introduction of wireless protocols and hardware, associated with the `Internet-of-Things' concept for machine-to-machine autonomous sensing and control, has enabled the large-scale networked intelligent water turbidity monitoring system that implements relatively low-cost sensors to be developed. The proposed sensor uses both transmitted light and orthogonal (90 degrees) scattered light detection principles, and is 2-3 orders of magnitude lower in cost compared to the existing commercial turbidity sensors. With an 850-nm infrared LED, and dual orthogonal photodetectors, the proposed design is capable of measuring turbidity within the range of 0-1000 Nephelometric Turbidity Unit (NTU) with improved accuracy and robustness as compared with the existing low cost turbidity sensors. The combination of orthogonal and transmitted light detection unit provides both 0-200 NTU high resolution and accuracy sensing and 0-1000 NTU lower resolution and accuracy sensing capability. Results from calibration experiment are presented, which proved that the proposed sensor design produced comparable turbidity readings as that of a commercial turbidity sensor.