Development of optical instrument as turbidimeter: a comparative study

• Published in: Sensor review 2012-01, Vol.32 (2), p.134-141
• Main Authors: Fairuz Omar, Ahmad, Zubir MatJafri, Mohd
• Format: Article
• Language: English
• Subjects: Design engineering; Design specifications; Detectors; Drinking water; Electric currents; Fiber optics; Guidelines; Instrumentation industry; ISO standards; Light emitting diodes; Noise; Sediments; Sensors; Standard error; Studies; Technological change; Turbidimeters; Turbidity; Water quality
• ISSN: 0260-2288; 1758-6828
• DOI: 10.1108/02602281211209428

Purpose - The purpose of this paper is to present a comparative study between two low-cost turbidimeter designs using a multi purpose Optical Fiber NIR System (OF-NIRS), Optical Fiber NIR System-Modified (OF-NIRS-M) and High Sensitivity NIR System (HS-NIRS) conducted in the development of a turbidimeter by closely replicating the existing standard design guideline. Optical method is a typical measuring technique that has been applied intensively for the measurement of water turbidity.Design methodology approach - Comprehensive guidelines for the development of turbidimeter have been stated by the United States Environmental Protection Agency (EPA Method 180.1) and the International Organization for Standardization (ISO 7027) and have been used as standards by instrument's manufacturers world wide, including the designs presented in this work. The development commonly does not only establish through physical instrumentation aspects, but also emphasizes on the physics of light-matter interaction such as scattering and absorption that is embedded within the science of turbidity. The individual system design is the assembly of light emitting diode (LED) and photo detector with near infrared (NIR) band, amplifier, 12-bit analogue to digital converter (ADC) and Basic Stamp 2pe microcontroller.Findings - The measurement by OF-NIRS produces coefficient of determination, R2=0.8881 with standard error of 20.33 NTU while HS-NIRS produces higher precision result with R2=0.995 with standard error of 1.809 NTU. A modified version of OF-NIRS (OF-NIRS-M) has been introduced and consists of direct emission of NIR radiation to the sample. OF-NIRS-M produces R2=0.9921 with standard error of 2.37 NTU, a high linearity result, comparable to HS-NIRS.Originality value - This research introduced a fundamental design of a turbidimeter by following closely to the existing standards at much lower cost. This work presents a comparative study between two main designs that utilize different types of photo detector and amplification circuitry and enables related industry to develop their own in-house turbidity monitoring system with flexible sensitivity.