- Abbe refractometer
An Abbe or laboratory refractometer is a bench-top
There have been many refinements regarding ease of use and precision to these instruments over the decades, but they still operate on the same principle. They are still used today as an inexpensive alternative to digital laboratory refractometers. They are also possibly the easiest method to find the refractive index of solid samples, such as
glass, plastics, and polymerfilms. Some Abbe refractometers utilize a digitaldisplay for the measurement, to eliminate the need for discerning between small graduations. The user still has to adjust the view to obtain the reading, however.
The first truly digital laboratory refractometers began appearing in the late 1970s and early 1980s, and no longer depended on the user's eye to determine the reading. They still required the use of circulating water baths to control instrument and fluid temperature. They did, however, have the ability to electronically compensate for the temperature differences of many fluids where there is a known concentration to refractive index conversion. Most digital laboratory refractometers, while much more accurate and versatile than their analog Abbe counterparts, are not capable of reading solid samples.
In the late 1990s, Abbe refractometers with the capability to read at wavelengths other than the standard 589
nanometersbecame available. These instruments utilize special filters of the desired wavelengthof light, well into the near infrared(though a special viewer is required to see the infrared rays). Multi-wavelength Abbe refractometers can be used to very easily determine a sample's Abbe number.
The most advanced instruments of today use solid-state
Peltier effectdevices to heat and cool the instrument and the sample, eliminating the dependence on an external water bath. The software on most of the current instruments is now very advanced and offers features such as programmable user-defined scales and a history function that recalls the last several measurements. Several manufacturers provide easily usable controls, with the capability to operate from and export readings to a linked computer.
Traditional handheld refractometer
Digital handheld refractometer
Inline process refractometer
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