Operating Instructions
Handheld Analog Refractometers
Operation
Preparation. Hold the refractometer in a horizontal position. Aim the front end of the
refractometer in the direction of a bright light, and use the adjusting ring of diopter
until the reticle can be seen clearly.
Zero % adjust with distilled water. Place a few drops of pure water on the prism
surface and close the prism cover. If bubbles form, gently pressing the cover will
remove the bubbles and help disperse the water over the entire surface.
Hold the refractometer up to natural light or an incandescent bulb to obtain the
reading. Looking into the eyepiece, you should see a distinct separation between a
blue and white section, often called a “contrast” line. If the contrast line is not directly
at zero, then adjust by turning the calibration screw on the top of the refractometer
until it reads zero. Replace the plastic cap after adjusting the screw to prevent water
from entering the refractometer.
Adjust the focus by twisting the eyepiece until the scale can be seen clearly. Once the
refractometer is calibrated to zero with pure water, dry the surfaces with a clean cloth.
– For models with 28% to 62% Brix range: Open cover plate, drop one or two drops of
saturated sodium chloride (table salt) solution on the prism surface, close cover
plate. Adjust to 29.9% at 15°C, 29.6% at 20°C, 29.2% at 25°C.
– For ATC models with 58 to 92% Brix range: Owing to the remarkably consistent
properties of extra-virgin olive oil, one drop of it on the slide will always read
between 71% and 72% on the Brix scale. If you set the calibration screw to show any
such oil at 71.5%, you will have correctly calibrated the water content scale at the
same time.
– For models with multiple Brix scales: These units have been adjusted at the factory.
To use multiple scales, rotate the adjusting wheel (model 81150-30) or adjusting knob
(model 81150-33) to change scales. To reduce chromatism, rotate the adjusting ring.
Measurement. Open the cover plate, clean the surface of prism with a piece of soft
paper or cotton, then drop 1 to 2 drops of the solution to be measured. Close the
cover plate, and press it lightly, then read the corresponding scale of light and dark
boundary. The reading is the Brix, salinity concentration, or refractive index (RI) of
measured solution.
Storage. After measurement, clean the surface of prism and cover plate with moist
gauze, and store carefully. Do not immerse or dip in water so that water does not
enter the inside of the unit.
Refractometers with Automatic Temperature Compensation (ATC)
The reference of temperature is 20°C. In operation, the temperature should be made
according to the Correction Table below. The automatic temperature compensation
(ATC) function enables users to concentrate on measurements without worrying about
the temperature. Compensation range is 10 to 30°C.
Abbreviated International Temperature Correction Table for a Refractometer Tested at 20°C
Temperature
Dry substance content in percent
°C
°F
0
5
10
15
20
10
50
Substract 0.50 Brix
Substract 0.54 Brix
Substract 0.58 Brix
Substract 0.61 Brix
Substract 0.64 Brix
15
59
Substract 0.27 Brix
Substract 0.29 Brix
Substract 0.31 Brix
Substract 0.33 Brix
Substract 0.34 Brix
20
68
None required
25
77
Add 0.33 Brix
Add 0.35 Brix
Add 0.36 Brix
Add 0.37 Brix
Add 0.38 Brix
30
86
Add 0.72 Brix
Add 0.74 Brix
Add 0.77 Brix
Add 0.78 Brix
Add 0.79 Brix
Description
1) Prism
2) Cover plate
3) Calibration screw
4) Mirror tube
5) Eyepiece (adjusting ring of diopter)
Accessories (not shown)
Eyeshade
Suction tube
Screwdriver
Adjusting wheel
Adjusting ring
Adjusting knob
Model 81150-30
Model 81150-33
Zero calibration
