Fiber optic salinity sensor using beam-through technique

Abstract

A fiber optic displacement sensor is proposed to sense salinity based on different concentration of sodium chloride (NaCl) in de-ionized water using the beam-through technique. The performance of a 594nm and 633nm He–Ne laser as the light source are compared. For a concentration change of sodium chloride from 0 to 12% in de-ionized water, the output voltage increase linearly and the sensitivity is dependent on the displacement position of the receiving fiber from the quartz cell containing the sodium chloride solutions. Measurements taken at higher displacement positions contribute to lower sensitivity with the highest sensitivity of 0.0237mV/% and 0.0412mV/% occurring at the 0mm displacement position for the 594nm and 633nm He–Ne lasers, respectively. Furthermore, a better limit of detection of 1.44% is achieved when the 633nm He–Ne laser is used compared to the 1.28% limit of detection achieved by using the 594nm He–Ne laser. The main novelty of this sensor is that it is contactless and non-destructive which are attractive features for applications involving delicate and hazardous processes.