6.1 Calibrating the refractometer

Before measuring, the instrument should be calibrated with the supplied test piece and immersion fluid, as described below:

1. Put some drops of the immersion fluid onto the surface of the primary prism (K).
2. Gently place the test piece into the fluid, with the polished side pointing downwards.
3. Peep through the eyepiece and turn the eyepiece until the image is sharply focused.
4. Now turn the adjustment knob F until the cross exactly separates the light and dark image in the field of view.
5. The scale should now read exactly the same value as mentioned on the test piece. If this is not the case, adjust the scale by turning the set screw (B) with the supplied driver.

6.2 Measuring liquid samples with the refractometer

1. Put some drops of the sample fluid onto the primary prism (K), and close the secondary prism (M) by means of the knob (P). Ensure the sample is homogeneous and without air bubbles.
2. Open the light cap (N) and close the reflection mirror (J).
3. Peep through the eyepiece (A) and focus the cross line.
4. Turn the illumination window (H) of the scale until the brightest image is reached.
5. Now move the cross with knob (F) until it is exactly at the border line of the dark and light image.
6. Colour shifting in the image can be corrected to "black/white" by means of the dispersion knob (C).
7. Now a last correction to get the cross exactly on the border line can be made with knob (F).

The refractive index value (nD) can now be read on the bottom part of the scale.

6.3 Measuring the sugar percentage in a liquid

1. Put some drops of the sample fluid onto the primary prism (K), and close the secondary prism (M) by means of the knob (P). Ensure the sample is homogeneous and without air bubbles.
2. Open the light cap (N) and close the reflection mirror (J).
3. Peep through the eyepiece (A) and focus the cross line.
4. Turn the illumination window (H) of the scale until the brightest image is reached.
5. Now move the cross with knob (F) until it is exactly at the border line of the dark and light image.
6. Colour shifting in the image can be corrected to "black/white" by means of the dispersion knob (C).
7. Now a last correction to get the cross exactly on the border line can be made with knob (F).

The sugar percentage (BRIX) can now be read on the upper part of the scale.

6.4 Measuring clear-transparent solid materials (e.g. glass)

Note! Make sure one of the sides of the sample is perfectly smooth.

1. Put some drops of the supplied immersion fluid onto the primary prism (K).
2. Carefully place the specimen with its smooth side into the fluid.
3. Open the light cap (N) and close the reflection mirror (J).
4. Peep through the eyepiece (A) and focus the cross line.
5. Turn the illumination window (H) of the scale until the brightest image is reached.
6. Now move the cross with knob (F) until it is exactly at the border line of the dark and light image.
7. Colour shifting in the image can be corrected to "black/white" by means of the dispersion knob (C).

The refractive index can now be read on the bottom part of the scale.

6.5 Measuring non-clear-transparent solid materials (e.g. satinized glass)

Note! Make sure one of the sides of the sample is perfectly smooth.

1. Put some drops of the supplied immersion fluid onto the primary prism (K).
2. Carefully place the specimen with its smooth side into the fluid.
3. Open the reflection mirror (J).
4. Peep through the eyepiece (A) and focus the cross line.
5. Turn the illumination window (H) of the scale until the brightest image is reached.
6. Now move the cross with knob (F) until it is exactly at the border line of the dark and light image.
7. Colour shifting in the image can be corrected to "black/white" by means of the dispersion knob (C).
8. Now a last correction to get the cross exactly on the border line can be made with knob (F).

The refractive index can now be read on the bottom part of the scale.

6.6 Establishing the dispersion value DFC

1. Put some drops of the sample fluid onto the primary prism (K), and close the secondary prism (M) by means of the knob (P). Ensure the sample is homogeneous and without air bubbles.
2. Open the light cap (N) and close the reflection mirror (J).
3. Peep through the eyepiece (A) and focus the cross line.
4. Turn the illumination window (H) of the scale until the brightest image is reached.
5. Now move the cross with knob (F) until it is exactly at the border line of the dark and light image.
6. Correct the dispersion with the knob (C) and write down the value "Z" (to read on the side of knob C). If "Z" is higher than 30, write "Z" as a negative number.
7. Now a last correction to get the cross exactly on the border line can be made with knob (F).
8. The refractive index can now be read on the bottom part of the scale.
9. Take the values of "A", "B" and "σ" over from the table on page 9 of this manual with the use of the values "Z" and nD, written down on point 6.
10. Use the values for the below formula:

DFC = A + σB

6.6a Calculation example 1, measured values with 2 decimals behind the comma:

Measured at 22°C:

nD liquid: 1.3300

Dispersion correction Z : 40.0

Found values A and B in the nD column in table 6.7:

A = 0.02484

B = 0.03304

Found value σ in the Z column in table Z:

σ = -0.500 (negative value for Z is higher as 30)

DFC = A + σB

DFC = 0.02484 + (0.03304 x -0.500)

DFC = 0.00832

6.6b Calculation example 2, measured values with more as 2 decimals behind the comma:

Measured at 20°C:

ND distilled water: 1.3330*

Dispersion correction Z : 41.62*

*In the table the measured values nD 1.3330 and "Z" value 41.62 are not included, therefor calculate "A", "B" and "σ" as follows:

Take the nD value 1.33 (or the corresponding "Z" value) from the table and read the correct value (in this case 5x10⁻⁶ per 0.001) and add it to the value of "A" given for 1.33.

1.3330 - 1.33 = 0.003 so the correcting value is: 3 x 5 x 10⁻⁶ = 0.000015.

The for 1.33 given "A" value is 0.02484 so the corrected "A" value for nD 1.3330 is: 0.02484 + 0.000015 = 0.024825.

Repeat these steps also for the "B" and "σ" values.

Results:

A = 0.024825

B = 0.032983

σ = -0.5716 (negative value for Z is higher as 30)

DFC = A + σB

DFC = 0.024825 + (0.032983 x -0.5716)

DFC = 0.005972

6.7 Table dispersion values

6.8 The use of circulating water

For use in so-called "on-line" situations, it can be important to keep the temperature of the sample fluid at a constant level. The refractometer can be linked to a water circulator to keep the prisms of the refractometer at a constant temperature. Therefore, the connection points of the circulation system should be connected to each other by means of flexible rubber hoses (not supplied). Proceed as follows:

• The water supply should be connected to connection point "I".
• Connection point "E" should be connected to one of the connection points "D".
• The last connection point should be used for the discharge.

6.9 Refractive indices and average dispersion values of distilled water

As example dispersion values and nD values corrected at temperatures of 10 - 40°C are given.

7.1 Cleaning the optics

If the eyepiece or prism surfaces are polluted, they can be cleaned with a lenspaper with a little alcohol. Never use a drop of alcohol directly on the lenses, since it can damage the coating.

Warning

Cleaning cloths containing plastic fibres can damage the coating of the lenses!

7.2 Maintenance of the stand

Dust can be removed with a brush. In case the stand is very dirty, the surface can be cleaned with a non-aggressive cleaning product.