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RF40 V1.2 4/04

Operation

The instrument measures the refractive index of the sample.

1. Zero Adjustment

Place one or two drops of distilled water on the prism. Close the cover plate and

rotate the adjusting screw so that the light/dark boundary lines up with the

“waterline”. Once the zero adjustment has been completed, clean the prism with soft

cloth

2. Sample Preparation and Reading

To take a sample reading, simply place a few drops of a sample liquid on the

measurement prism at the end of the instrument. Lower the cover plate onto the

sample and prism.

While holding the instrument under a light source, look through the eyepiece. The

freezing point of the liquid or the state of the battery liquid is determined by the

intersection of the boundary of the light and dark fields (known as the shadowline)

on the printed scale. If the scale appears out of focus, the eyepiece may be adjusted

by rotating the knurled portion. The instrument also features an eye guard to prevent

stray light from entering the eyepiece and causing reflections.

It may be necessary to adjust the position of the light source to maximize the

contrast of the shadowline. Under normal conditions, optimal contrast is obtained by

holding the instrument underneath and perpendicular to a light source.

Once a reading has been taken, wipe dry with a clean cloth (do not wash or rinse)

and place the instrument in the supplied plastic case. Store the instrument in a safe,

dry environment.

Temperature is one of the single most important factors influencing accurate

refractometer readings and is one of the largest sources of error in measurement.

Temperature compensation relieves the user of the responsibility to measure

temperature and apply a correction factor when taking readings. This refractometer

makes this correction automatically. When ambient temperature varies from 68°F

(20°C), readings are automatically adjusted to compensate for temperature variance

between 50°F to 86°F (10°C to 30°C).

Open the prism cover and

place 2 or 3 drops on the

prism. Close the cover so the

liquid spreads across the entire

surface of the prism without air

bubbles or dry spots. Allow the

sample to remain on the prism

for approximately 30 seconds.

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Extech Instruments RF40 User Manual

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