Calibration Procedure of a Fiber-Optic Refractometric Sensor

To ensure the accuracy of measuring the refractive indices of liquids, the quality of which is determined, all refractometric instruments undergo a calibration procedure to reduce the calibration error, which is up to $70 \%$ of the basic error. In some cases, it is necessary to carry out the calibration procedure under ideal conditions, avoiding sudden temperature changes, since the refractive index of liquids decreases with increasing temperature, and increases with decreasing temperature. The complexity and long duration of the calibration procedure reduces the value of known refractometric measuring instruments. The aim of the study is to reduce the basic error of the new fiber-optic refractometric sensor (FORS), which implements a modified refractometric method for diagnosing the quality of liquid media of various applications. Results. It is proved that the use of first a transparent calibration substance with a known refractive index placed in a cylindrical transparent microtubule, and then a transparent test substance with the desired refractive index, allows you to change the contour of the image of the radiating end of the incoming optical fiber in the plane where the receiving ends of the outgoing optical fibers are located, and, accordingly, change the output signal of the sensor. A simple FORS calibration technique has been developed, which eliminates the disadvantages of the calibration procedure inherent in known refractometric measuring instruments, which reduces the basic error of the FORS by reducing the calibration error.