Compact Analog Refractometers

An analog handheld refractometer is an instrument for measuring a liquid's refractive index. It works on the critical angle principle by which lenses and prisms project a shadow line onto a small glass reticle inside the instrument, which is then viewed by the user through a magnifying eyepiece. Most refractometers measure on the brix scale and the number taken to be a good indication of % of sugar content in a given sample. When used to test the juice from your fruits and vegetables it is often taken to be a good sign of  taste and quality.

To use one of these a sample is placed between a measuring prism and a small cover plate. The light traveling through the prism casts a shadow line between the illuminated area and the dark area. It is where this shadow line crosses the scale that a reading is taken. Because refractive index is very temperature dependent, it is important to use a refractometer with automatic temperature compensation (ATC). Compensation is accomplished through the use of a small bi-metal strip that moves a lens or prism in response to temperature changes.

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