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•
Using a small screwdriver, turn the "Zero"
calibration trimmer until the display reads
zero.
•
If the zero point is
passed, "1" will appear
on the display.
If you cannot get zero reading, the probe
is probably defective. Check the mem-
brane, electrode and electrolyte solution.
After the zero calibration has been completed,
rinse the probe thoroughly with tap water.
SLOPE CALIBRATION
In order to perform a highly
accurate calibration, take a
B.O.D. bottle and fill with
water to a depth of 1-2 cm
(½ - ¾"). Seal the bottle with
the probe inside.
If this calibration is carried out with the bottle
opened to air rather than according to the
conditions described above, the margin of
error is approximately 0.1 ppm.
•
Switch the instrument to
"°C", wait for reading to
stabilize and note the
temperature of the water.
•
See Table 1 on page 12
for the DO reading corre-
sponding at the noted
temperature.
•
Switch to "O
" position
2
and adjust the "Slope"
trimmer until the correct
reading is displayed.
10
STB
°C
O
OFF
2
STB
°C
O
OFF
2
E.g. at 20.5°C the trimmer should be ad-
justed to read 9.08.
ALTITUDE COMPENSATION
If the calibration is not performed at sea level,
a correction should be made for the altitude
effect according to Table 2 on page 13.
E.g. at 20.5°C and at an altitude of 300 m
above sea level, the "Slope" trimmer should
be adjusted to read 9.08 x 0.96 = 8.72.
SALINITY COMPENSATION
An additional correction has to be performed
if the sample presents significant salinity con-
centrations. In such case, the reading has to
be adjusted according to Table 3 on page 14.
E.g. at 20.5°C and if the sample has a salin-
ity content of 3 g/L, the "Slope" trimmer
should be adjusted to read 9.08 - (3 x 0.0478)
= 8.94.
11
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