UNISENSE HYDROGEN SENSOR, User Manual

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must be polarized for at least 1 hour before it can be calibrated
and used . After shorter periods without polarization, the sensor
should be polarized until it has exhibited a stable signal for 10
minutes .
The signal depends on the specific sensor (see the value in the
specifications that came with the sensor) .
If the signal does not stabilize or is too high or too low, refer to the
‘Trouble-shooting’ section of this manual .
c
alibration
Calibration must be performed after the sensor signal has
stabilized during pre-polarization .
z
ero hydrogen reading
Place/keep the sensor tip in water and read the signal . This signal is
your calibration value for zero hydrogen conditions .
h
ydrogen reading
The hydrogen sensor responds linearly, and consequently, a
two-point calibration is sufficient . Prepare a water phase with
a defined hydrogen concentration, which is slightly above
the maximum expected hydrogen to be measured . A defined
hydrogen concentration can be obtained by 2 different
procedures:
1 . Use a gas mixture controller to obtain a
defined mixture of hydrogen and hydrogen
free inert gas from a gas tank (e .g . N
2
) as bulk
carrier gas . For instance, to obtain a hydrogen
concentration of 40,25 µM in the calibration
chamber at 20 °C, bubble the water in the
calibration chamber vigorously with a gas
mixture containing a 95 % N
2
and 5 % H
2
. The
hydrogen partial pressure is in this case 0 .05
atm, and the Solubility is 805 μmol/L/atm .
Multiplying the solubility with the partial
pressure results in the concentration: 805
µmol/L/atm * 0,05 atm = 40,25 µM .
See Table 1 for more values of the solubility .
IMPORTANT
Hydrogen sensors
are sensitive to
temperature and
salinity,
IMPORTANT
Calibration must
be performed after
pre-polarization
when the sensor
signal has
stabilized.
Always use
a calibration
solution with the
same temperature
and salinity as the
sample solution.