Hydrocarbon concentration measurement by using fiber optic displacement sensor

Abstract

Hydrocarbon is an organic water pollution. It can harm the environment as well as human being. Therefore a feasible way should be identified to detect the hydrocarbon level in water. In this study a fiber optic displacement sensor was introduced as a technique to determine the concentration of hydrocarbon in water. A reflective configuration technique was developed and the concentrations of hydrocarbon were studied in the range of 0% to 20%. In order to validate the system two unknown concentrations were selected representing the lower region and the higher region. In principle this sensor is using the concept of intensity modulation as a function of displacement. The optimum displacement between the reflecting target and the fiber optic probe was found to be at 1.5 mm for all the concentration tested. The intensity of light received by sensor was connected to a voltmeter. The voltage measured from different hydrocarbon concentration was initially calibrated by displacement measurement. The fingerprint for hydrocarbon solution was revealed in the calibration curve which had fast response in the front part and a slow response at the back part. The peak voltage from each fingerprint was found to be inversely proportional to the tested concentration. This means the higher concentration of hydrocarbon the weaker is the signal detected. The sensitivity of the fiber optic displacement sensor was found to be 0.12 mV/wt% with a repeatability of 96%. The resolution of the sensor was 0.027 mV, with a limit of detection of 0.23%. The linearity index was found to be 93.9% for 6% hydrocarbon concentration and 105.2% for 14% hydrocarbon concentration. The simplicity and the creditability of such system offer a good opportunity for industrial applications in the environmental sector.