Principle and usage of refractometer
When a fixed medium is used, there is a simple functional relationship between the critical refractive angle rc and the refractive index. Beijing Million Electronics specializes in producing Abbe refractometers (i.e. handheld refractometers, handheld refractometers, handheld sugar meters, handheld salinity meters, sugar refractometers, sugar meters, alcohol meters, refractometers, freezing point meters, concentration meters, salinity meters, alcohol refractometers, battery detectors, sugar meters, emulsion concentration meters, cutting fluid concentration meters, refractometers) Abbe refractometers are designed based on this principle.
Its main components are two right angled prisms PI, PII. There is a gap of approximately 0.1 to 0.15mm between the rough surface of the prism PI and the optical plane mirror AD of PII, which is used to hold the liquid to be tested and lay a thin layer between PI and PII. After the light enters the prism PI through the reflector, it diffuses due to the rough ground glass surface, passing through the measured liquid from various angles through the gaps; Entering the prism PII, as previously known, the light rays entering the prism PII from all directions are refracted, and their refractive angles fall within the critical angle rc (because the refractive index of the prism is greater than that of the liquid, all light rays from to can be refracted through the prism). The light with a critical angle of rc passes through the prism PII and is directed onto the eyepiece. If the crosshair of the eyepiece is adjusted to the appropriate position, the upper half of the eyepiece will be visible.
From the principles of geometric optics, it can be proven that the refractive index of a liquid in a gap, n liquid, and the relationship between the refractive index and the refractive index of the liquid in the gap is: n liquid=sinB B, which is a constant for a certain prism, and n prism is also a constant at a constant temperature. So the refractive index n of a liquid is a function of the angle r. The refractive index of liquids can be calculated using RC. The reading rc has been converted to the value of n liquid on the refractometer, and the value of n liquid can be directly read. Under specified conditions, the refractive index of a liquid varies depending on the wavelength of the monochromatic light used. If ordinary white light is used as the light source, colored light bands will appear at the light dark boundary due to dispersion, making the light dark boundary unclear. In order to use white light as the light source, the instrument is also equipped with two "Amixi" prisms composed of three prisms each as compensation prisms (the upper "Amixi" prism can rotate), and their relative positions can be adjusted. When properly oriented, the scattered light from the refracting prism below can be turned back into white light, eliminating color bands and making the light dark boundary clear. At this point, the refractive index measured with white light is equivalent to the refractive index nD measured with sodium light D-line (wavelength 5890 people).
The refractive index is one of the characteristic constants of matter, and its value is related to temperature, pressure, and the wavelength of the light source. The symbol refers to the refractive index of a substance when using sodium light D-line as the light source. Temperature has an impact on refractive index. Most liquid organic substances have a decrease in refractive index as the temperature increases, while the relationship between the refractive index of solids and temperature is irregular and generally does not exceed. Usually, changes in atmospheric pressure have little effect on the numerical value of refractive index, so the influence of pressure is only considered in very precise work.
