18
7. Calibration (Scale adjustment)
CAUTION
Calibration with test piece
When measuring solid sample in main, calibrate the scale in this method.
There are two different methods for calibrating the refractometer scale as
mentioned below.
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Don't wet the refractometer except the prism surface with water or sample liquid
unreasonably. If the refractometer gets wet excessively, it may cause malfunction
and breakdown of the refractometer.
Don't tap or pick at the prism surface with a metal spoon, tweezers, etc. because
the prism surface is made of optical glass.
If the prism surface is scratched, the refractometer may fall in measurement.
Method
Calibration with distilled water
When measuring liquid sample in main, calibrate the scale in this method.
Turn the prism open/shut handle to open
the secondary prism (Fig.7-1). After wiping
down the main and secondary prism
surface, drip a small amount of distilled
water on it (Fig. 7-2). Gently close the
secondary prism .
a)
(1) Calibration with distilled water
Connect the refractometer with the
circulating constant temperature bath, and
set
the
measurement
temperature
(temperature indication of the digital
thermometer) to 20
Υ
.
While observing through the eyepiece,
turn the measurement knob to get the
Refractive Index
scale
to
indicate
approximately
1.3330
and
the
Brix
percent scale to indicate approximately
0.0% (the upper scale is for reading
Refractive Index while the lower scale is
for Brix percent). When the temperature is
other than 20
Υ
, the scale must read the
Refractive Index at the actual temperature
and Brix 0.0%.
b)
Fig. 7-1
Fig. 7-2
