Patent ID: 9632025
Date: 2017-04-25
CPC Classifications: G01N

Claim:
1. A method for continuously measuring the Abbe number in a process liquid, the method comprising the steps of: generating light and directing the light through a measuring window in contact with the process liquid to the process liquid such that total reflection occurs on the surface of the measuring window and the process liquid, directing the part of the light that has been totally reflected to a sensor, whereby an image is formed on a light-sensitive surface of the sensor, the boundary between a light region and a dark region in the image corresponding to a critical angle at which the total reflection occurs, and detecting the dependency between the boundary of the light and the dark regions and the refractive index of the process liquid to be measured, wherein the light is generated successively at wavelengths of substantially 486.1 nm, 589.3 nm and 656.3 nm and the light of different wavelengths is directed successively to the measuring window by means of optics to provide a suitable angular distribution for the light and directed through the measuring window in contact with the process liquid to the process liquid, and the part of the light totally reflected at each wavelength is directed to the sensor, wherein the boundary between the light and the dark regions is detected at each wavelength by means of an image analysis, the dependency between the boundary of the light and the dark regions and the refractive index of the process liquid to be measured is determined at each wavelength, and the Abbe number is calculated by means of the refractive index values obtained from the aforementioned three wavelengths by using the formula known per se: where n D is the refractive index of the process liquid to be measured at a wavelength of 589.3 nm, n F is the refractive index at a wavelength of 486.1 nm, and n C is the refractive index at a wavelength of 656.3 nm.