Side-polished fiber sensor for measurement of the color concentration in lubricant products

Color concentration is a key parameter to mark lubricant product specifications. Lubricant color does not necessarily indicate product quality, but the grade's color range can indicate possible contamination by another product. This study aims to design a side-polished fiber to measure color concentration in lubricants. The sensor is obtained by stripping the cladding of 1 mm polymer optical fiber. The side-polished fiber weaken light intensity due to the absorptive properties of color concentrate for visible light. The light source in this study is tri-color LED and the OPT101 as a light detector. Light passing through the fiber is converted by the detector into a voltage output. The results showed that the sensor is capable of detecting the concentration of color with measurement ranging from 10 mg/L to 200 mg/L. The output voltage of sensor's sensitivity is up to 0.039 (mg/L)/mV, 0.042 (mg/L)/mV and 0.047 (mg/L)/mV for the red, green and blue light sources respectively. The average linear correlation is 97.3 % in liquid lubricants. The designed sensor could be applied in ASTM D-1500 for color scale measurement of lubricant oil products.