UNISENSE N2O-50, Руководство пользователя

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Therefore, it is ideal also for shipping to field work, research cruises
etc. The detailed calibration procedure can be found in the
Calkit-subscript Manual (
https://www.unisense.com/manuals/ )
A
LTERNATIVE CALIBRATION
Z
ERO CALIBRATION POINT
Place/keep the sensor tip in nitrous oxide free water and
record the signal. This signal is your calibration value for
zero nitrous oxide. The temperature in the solutions for zero
calibration and for known N
2
O concentration must be the
same.
K
NOWN CONCENTRATION CALIBRATION POINT
The nitrous oxide sensor responds linearly to N
2
O within
its measuring range (see Table 1 for the measuring range
for your type of sensor). Therefore, a two-point calibra-
tion is sufficient. Prepare water with a defined nitrous oxide
concentration (partial pressure), which is slightly above the
maximum expected nitrous oxide concentration (partial
pressure) in the samples. Never expose the sensor to con-
centrations more than the specified measuring range - it
may cause irreversible damage to the sensor (see Table 1 for
the measuring range for your sensor).
A defined nitrous oxide concentration can be obtained by
two different procedures:
a) Use a gas mixture controller to obtain a defined mixture
of nitrous oxide and nitrous oxide-free inert bulk carrier gas
from a gas tank (e.g. N
2
) . For instance, to obtain a nitrous
oxide concentration of 100 µM in the calibration chamber
at 22°C, bubble the water in the calibration chamber with
a gas mixture containing 1 atm N
2
and 0,003679 atm N
2
O
(nitrous oxide partial pressure 0.003679 atm × solubility
27,05 × 10-3 mol/liter/atm. = 100 µmol/liter, see Table 2).
For a Unisense 300 ml calibration chamber CAL300, 5
minutes of bubbling at a rate of 5 L per minute is sufficient
time to achieve 99% of the concentration. If the equipment
(gas mixture controller) is available, this method can be
WARNING
Never expose
the
N
2
O sensors
to concentra-
tions above their
measuring range.
This will destroy
the senor! See
Table 1 for the
measuring range
for each type of
N
2
O sensor.
WARNING
Bubbling of
water with any
gas may cause
the water to cool
considerably.
Monitor the
temperature to
find a suitable
bubbling rate,
which does not
cool the water
significantly.