Xylem ECLIPSE PROFESSIONAL HAND-HELD REFRACTOMETER - Manual (Page 4)

Precautions to improve accuracy
Make sure that the prism is cleaned and dried between each reading, using a little clean water at
room temperature, and a soft cloth to dry.
Make sure the scale of the instrument is in sharp focus before taking readings, adjust the eyepiece if
necessary.
Look at the quality of borderline obtained. Poor sharpness may indicate insufficient sample on
prism, or temperature gradients across the prism, or that the prism was not properly cleaned and
dried after the last reading.
If in doubt, clean and dry the prism, leave for a while, and repeat measurements from the start.
Measuring the same sample twice in quick succession is a useful indication of the reliance that
should be placed on the results obtained. Always clean the plastic illuminator plate when cleaning
the prism.
Adjusting the Calibration
All Eclipse refractometers are calibrated to read correctly at 20°C. The refractive index of the
measured sample will vary with temperature and the calibration should be adjusted to take account
of this prior to taking any initial readings. The calibration method and Certified Reference Material
(CRM) to use will depend on the scale range of the Eclipse refractometer.
Calibration Method – low range models able to measure water
Firstly loosen the adjuster locking nut (the larger diameter knob). Next apply distilled
water at 20°C to the prism and rotate the smaller knob to adjust the reading until
correct, then carefully retighten the locking nut.
Alternative Method for low range models
1. Stabilise the instrument at ambient temperature.
2. Apply distilled water to the prism and adjust the reading to zero as described above.
3. Sample readings will then be correct at the ambient temperature.
Calibration Method – high range models unable to measure water
Unscrew the protective cap. Apply the appropriate CRM at 20°C and rotate the
knob to adjust the reading until correct, then replace the protective cap.
Notes
• It is also recommended that periodically the higher end of the scale is verified using a
suitable CRM.
• The ATC models are corrected for ambient temperatures in the range 10-30°C, and so
should never require adjustment.
• The R.I. Aviation Eclipse refractometer (code 45-66) has a fixed calibration at 20°C
• Further information on CRM’s can be found on our website at: -
http://www.bellinghamandstanley.com/ltd/newcalibration/materials.html
• The Eclipse User Guide is also available in other languages at: -
http://www.bellinghamandstanley.com/ltd/literature.html
• If the flap should become damaged, a replacement can be clipped on easily – part number
45-003 (pack of 5).
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