A refractometer is a handheld optical device that measures
the concentration of solids in a liquid. Light passes through a drop of the sample liquid, which
is spread onto the prism. The refracted light illuminates the scale inside the instrument.
The scale, when viewed through the eyepiece, gives a reading at the division of the blue and white
refracted light. Common sample liquids are fruit juice, sugar concentrations, salt water,
urine, and antifreeze.
We stock brix, salinity, clinical, and automotive refractometers, as described below.
For many of our models, you can choose the ATC (Automatic Temperature Compensation) option.
Brix refractometers are used for beverages,
sugars, and cutting fluids. Fruit growers, fruit packagers, and the wine industry use the brix scale. Because it covers largest refractive index range, brix is also useful for general purposes.
refractometers are used for aquaculture, hobbyist marine aquariums, and food processing (to control brine).
refractometers are used for urinalysis (urine specific gravity), blood analysis (i.e., total serum protein), refractive index (basic scale shows refractivity), or dilutions.
refractometers are used for antifreeze/coolant (Propylene Glycol and Ethylene glycol) and battery recharge level.
ATC is an abbreviation for automatic temperature
compensation. ATC allows the user to take accurate scale readings at varying ambient room temperatures.
Benefits of ATC:
Without ATC, if the temperature of the room changes by a degree or two, the
refractive index shifts. The scale is only accurate for the temperature at which calibration was done.
ATC allows the refractometer to maintain accuracy at a wider range of ambient temperature shifts (between
20-50 degrees Celsius). So ATC refractometers require calibration much less often than models without automatic temperature compensation.
Temperature of the sample:
The sample MUST be the same temperature as the prism for an accurate reading. ATC compensates for shifts in ambient temperature, not for the difference
between sample and prism temperature. If you are working with samples at a
temperature different than the ambient room temperature, leave the sample on the prism for 30 seconds before taking the reading.
This allows the sample to acclimate to the temperature of the prism
Ambient air temperature:
ATC models are best suited for settings where the room's air temperature may vary more than one degree. Even as much as a single degree of temperature
variation can affect the reading of a refractometer without ATC.
Calibration for non-ATC refractometers is only accurate for the temperature at which calibration was done. If the temperature of the room shifts 5 degrees, you must recalibrate. Even 1 degree affects the scale, so
if the measurement is critical, you should recalibrate. Even with ATC, it is good to recalibrate periodically.
Refer to your refractometer operation manual for your model's specific calibration instructions. If you
do not have the manual, here are basic calibration instructions. (Note that while distilled water works for most models,
a few models require calibration fluid. Refer to the Replacement Parts page to determine whether your refractometer needs
calibration fluid. The procedure is the same whether you use distilled water or calibration fluid.)
Open the daylight plate
and place 2-3 drops of distilled water on the main prism. Close the daylight
plate so the water spreads across the entire surface of the prism without
air bubbles or dry spots. Allow the sample to rest on the prism for
approximately 30 seconds before going to step #2. (This allows the sample
to adjust to the temperature of the refractometer.)
Hold the daylight
plate in the direction of a light source and look into the eyepiece. You
will see a circular field with graduations down the center (you may have to
focus the eyepiece to see the graduations clearly). The upper portion of
the field should be blue, while the lower portion should be white.
While looking into the
eyepiece, turn the Calibration Screw (on the top of the refractometer) until
the boundary between the upper blue field and the lower white field meet exactly on the 0.0° line.
After this calibration procedure, your instrument is calibrated for the current ambient room
temperature. When the working temperature of the room or environment (not the
sample) changes by more than 5°F, we recommend recalibrating to maintain
accuracy and reproducibility.
If you need a replacement part, you can look up the replacement part number
for your model on the Replacement Parts page. If you do not know your refractometer's
model number, phone Customer Service at 1-866-614-4022.
To avoid having to replace broken daylight plates frequently,
choose our Industrial or Lighted series models. These have drop-tested daylight plates, so they may be the most economical option if
your refractometer is at high risk of being dropped.
A scale used to measure the density of liquids. The Baumé scale is used in winemaking, brewing, and food processing. Our RHB-90 model includes a Baumé scale and a brix scale.
The percentage of sugar in a sample is expressed in degrees Brix (°Bx). A sample measured at 15 °Bx is 15% sugar.
Light at the critical angle reflects off the surface of the sample instead of refracting through it. If you do not get a good reading, adjust the angle of the
refractometer so the light can pass through the sample.
The change in the speed and angle of light moving through different materials. When light comes into
the refractometer prism and moves through materials of different densities, it bends toward the denser material.
Refractive index: The difference between the optical density
of the glass (known) and the density of the sample (measured) is the refractive index (shown on the scale). This difference in density causes different angles
of refraction, which appear on the refractometer's scale as blue and white light. The line between the blue and white light on the scale is the refractive
index of the sample. When the sample is a known value, such as distilled water, it is possible to calibrate the refractometer.
Salinity: The concentration of salt in a liquid.
If you still have questions, contact Customer Service.
Copyright © 2010 Westover Scientific, Inc.
All rights reserved.
Revised: Nov 9, 2010
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