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1.
Unscrew the lower end
2.
Fill the cap with the liquid
3.
Screw the filled cap back onto the electrode. Use a
cloth to wipe off any liquid that leaks out.
Preparation
Connect the oxygen probe (included in the scope of supply)
to the connector at the front of the sensor. Ensure that you
can hear that the outer metal ring of the connector locks in
place.
ATTENTION: Never turn the plug after it has been plugged
in. This can lead to the destruction of the sensor.
Calibration
It is not necessary to recalibrate the sensor for every meas-
urement. Especially if only the change in oxygen content is to
be demonstrated, an already existing calibration (the last cal-
ibration remains automatically stored in the sensor) or the
factory settings are usually sufficient. However, if absolute
values are required for your measurement, e.g. if you are de-
termining the oxygen content of bodies of water, or if you
want to optimise the accuracy of your measurement, we rec-
ommend calibrating the sensor. See section 5.4.
5.3 Recording of measurement data
Measurement:
Two types of measurements can be performed with the Co-
bra SMARTsense Oxygen: Measurement of the oxygen con-
tent, e.g. in the air (%), and a measurement of the oxygen
concentration in an aqueous solution (mg/l).
a)
Measurement of oxygen in the air
Select the "Air" mode in the software.
It takes approximately 1 minute for the value to settle.
b)
Measurement of dissolved oxygen
Select the "Fluid" mode in the software.
•
Plunge the oxygen probe into the solution so that
the temperature sensor is also covered (approxi-
mately. 5-6 cm). Do not immerse it completely in
the liquid. The handle is not waterproof.
•
Record the oxygen concentration with the aid of
the recording function of the software.
•
Ensure that the water sample that is to be ana-
lysed is slightly stirred in a continuous manner.
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Measuring principle:
This sensor type is an amperometric Clark sensor with a plat-
inum cathode and a silver anode.
A fixed voltage is applied at the platinum electrode. When
oxygen diffuses through the membrane and to the cathode,
the latter will be reduced:
1/2 O
The reference electrode (anode) is subject to oxidation:
Ag + Cl
Correspondingly, a current flows and this current is propor-
tional to the oxygen diffusion and, thereby, to the oxygen
concentration. The current is converted into a voltage signal
that is then received by the sensor.
5.4 Calibration
Ensure to perform the calibration at a temperature that is sim-
ilar to the temperature of the sample. Like in the case of a
measurement, wait for approximately 1-2 minutes after the
connection of the sensor until the measurement value has
settled. Then, perform the calibration.
Oxygen in air
A two-point calibration is performed.
Select the "Air" mode.
Use a commercial zero-oxygen calibration solution.
First calibration point
Select "Configuration/Calibration" from the software menu
(APP). Immerse the measuring probe into the calibration liq-
uid and wait approx. 2 minutes until the measurement values
have settled. Enter the 0% value as set point 1 and send it to
the sensor.
Second calibration point
Hold the sensor in the ambient (outdoor) air since, in this
case, the oxygen content will be constantly at 20.9%. Wait
approx. 2 minutes until the measurement values have settled.
Enter the 20.9% value as set point 1 and send it to the sen-
sor.
Dissolved oxygen
A two-point calibration is performed.
Use a comercial zero-oxygen calibration solution.
First calibration point
Select "Configuration/Calibration" from the software menu
(APP). Immerse the measuring probe into the calibration liq-
uid and wait approx. 2 minutes until the measurement values
have settled. Enter the 0 mg/l value as set point 1 and send it
Temperature sensor
to the sensor.
Second calibration point
Hold the oxygen probe into a receptacle fill with distilled wa-
ter. The measurement value should have settled after ap-
prox. two minutes and the calibration can be performed. Set
point 2 can be found in the table below.
This is important since the sensor consumes oxy-
gen during the measurement. Without stirring, it
would seem as if the oxygen concentration de-
creases.
→
–
e–
+ H
O + 2
2 OH
2
2
–
→
AgCl + e–
3
12933-01 / 4521
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