ABSTRACT
A refractometer measures the refractive index of a liquid sample. Refractive index is the ratio of the velocity of light in a vacuum to the velocity of light in the material. Some industries that are users of refractometers prefer to use their own units instead of the index of refraction. Two types of process refractometers have evolved, one based on refraction angle changes, and one based on critical angle changes. The differential refractometer measures the refraction angle changes as a function of sample refractive index. The two-pass differential refractometer uses a triangular-shaped reference cell and a reflecting mirror. The range of this refractometer is determined by the shape of the reference cell, the thickness of the zero restorer glass and the span attenuation in the meter circuit. The critical angle refractometer uses the reflected light from a prism interface with the sample. Some refractometers measure the total amount of reflected light, which varies with refractive index of the process fluid.
