VST Lab Coffee 2 Instruction Manual page 6

Calibration - Zero Set
The VST Coffee Refractometer MUST be Zero Set before
initial use and periodically thereafter for changes in ambient
temperature of more than 2 Deg C. It is recommended that a
Zero Set be performed at least once a day as well as prior to
performing tests requiring the highest accuracy, or when moving
between environments with changes in ambient temperature.
Distilled or deionized water is required for Zero Setting the
instrument. The water temperature for zero setting should
be between 15-30°C (59 to 86 °F). To ensure accuracy, it is
important to independently verify that you are calibrating the
instrument with distilled or deionized (DI) water and not just a
clear liquid which you think is DI water. RO (reverse osmosis)
water is not recommended for Zero Set.
Inspect the measuring surface to make
1
sure it is clean and dry. Place a few drops
of distilled water on the measuring surface.
Close the sample cover and allow some
2
time for the temperature to equalize. The
sample cover MUST be closed to calibrate
or take measurements.
Press and release <GO> to turn the instru-
3
ment on.
Press and release <MENU> until the
4
display reads:
Set Zero?
[GO] To Set
Press and release <GO> to automati-
5
cally zero the instrument. Remember
to clean and dry the measuring
surface after zero-set.
If the calibration was successful the instrument will display
"READY" or "nD 1.3330" otherwise, an error message will be
displayed. In later revisions, the backlight dims during reads.
Filtering Procedure
6
for Espresso or Coffee
Allow 2 minutes for espresso to cool
1
and CO
stir sample for 4-5 seconds.
Draw about 3-4 mL espresso with sy-
2
ringe tip under the crema, and without
touching the bottom
Attach syringe fi lter and tighten until
3
snug, about a quarter turn. Do not
over-tighten.
Slowly express about 2 mL into a clean,
4
dry glass. Allow 30-60 seconds to cool.
CONTINUE with Step 2 of Sampling
Procedure, below.
Sampling Procedure
Draw a 0.2 - 0.4 mL fi ltered sample
1
using a pipette and transfer to a clean
dry cup or glass that is at ambi-
ent temperature. Let cool for 30-60
seconds.
Using a fresh pipette, transfer the
2
cooled sample to the instrument
Sample Well. Close cover. Allow 20-
30 seconds to equibrilate.
Press GO to take a measurement.
3
to diffuse out of solution, and
2
11