A traditional handheld refractometer is an analog instrument for measuring a liquid's refractive index. It works on the critical angle principle by which lenses and prisms venture a shadow line onto a small glass reticle inside the instrument, which is then viewed by the user through a magnifying eyepiece.
In use, a sample is placed between a measuring prism and a small cover plate. Light traveling through the sample is either passed through to the reticle or totally internally reflected. The net effect is that a shadow line forms between the illuminated area and the dark area. It is where this shadow line crosses the range that a reading is taken. Because refractive index is very temperature dependent, it is important to use a refractometer with automatic temperature compensation. Compensation is achieved through the use of a small bi-metallic strip that moves a lens or prism in response to temperature changes. The use of a hand refractometer facilitates opportune and speedy measurement of concentration in a number of liquid and semi-solid samples.
Food applications include the measurement of sugar in grape must and other fresh fruit, processed food, sugar solutions and beverages. Starch, honey and salt solutions may also be measured.
Hand held refractometers are also commonly used to control blend ratios of various industrial liquids. Chemical blends such as glycols, battery acid, heat exchange fluids, automotive antifreeze, aviation wing de-icing chemicals and jet fuel ice inhibitors can be controlled easily whilst measurement of industrial fluids such as coolants, quenchants and hydraulic oils are routine.
Digital handheld refractometers are generally more accurate than traditional handheld refractometers, but less precise than most benchtop refractometers. They also may require a slightly larger amount of sample to read from since the sample is not spread thinly against the prism.
Digital Hand-Held Refractometers
The digital handheld refractometer has more functions than a simple handheld refractometer and at the same time is more cost effective than a desktop unit. Besides the refractive index, sugar and salt scales, up to two other user-defined scales can be designed. To do this, a handheld refractometer can be connected to a PC via a serial interface. The software supplied with it allows outcomes to be managed and printed out.
Manual Hand-Held Refractometers
Manual handheld refractometers are for fast everyday use. They are particularly easy to use and very sturdy. Various scales and additional functions ensure that there is exactly the right handheld refractometer for many application areas. This makes for reliability when reading, as the measured value does not have first to be converted.
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