RF20 Version 1.1 September 2003

3

Operation

The instrument measures the refractive index of the sample and displays the result in parts

per thousand (

1. Zero Adjustment

Put distilled water on the prism; enough to cover the entire prism. Close the cover plate

and rotate the adjusting screw so that the light/dark boundary line (known as the

shadow-line) evens up with the zero line. After the zero adjustment, clean the prism with

soft cloth.

2. Sample Preparation and Reading

To take a reading, place a few drops of a sample liquid on the measurement prism.

Ensure that enough solution is added to the prism in order to cover the entire prism.

Close the prism so that the liquid spreads across the entire surface of the prism without

air bubbles or dry spots (see diagrams below). Allow the sample to remain on the prism

for approximately 30 seconds.

While holding the instrument under a light

source, look through the eyepiece. The

salinity concentration is determined by the

intersection of the boundary of the light

and dark fields (known as the shadow-

line) on the printed scale. The left side of

the scale indicates the specific gravity and

the right side parts per thousand. 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 shadow-line. 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 the single most important factor influencing refractometer readings and

is one of the largest sources of measurement error. However, this device incorporates

automatic temperature compensation and the concern for temperature fluctuations in

sample liquids is alleviated. 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).

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