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Data logging
CO
probe
2
Ref :
453 076
ENGLISH
13- Rinse the probe with distilled water, dry it (avoid touching the membrane)
and let it in the air.
The value displayed must be around 0.
5
Using the probe with a pHmeter
You can use the probe with a high impedance pH meter. Proceed according
to the following instructions:
- Set the pH meter to read in mV.
- Hold the probe in the air vertically with the head pointing downwards.
Record the value indicated.
- Place 25 ml of base solution in a 30 ml bottle and add 3 ml of reactive
solution.
- Shake the bottle to homogenize the mixture.
- Insert the electrode into the bottle in such a way that there is no air in the
bottle (see Figure 1).
- Record the value indicated by the pH meter (ca. 2 minutes after immersing
the probe).
Remember that the calibration and the measurement must be performed at
the same temperature.
It is very important to prepare the calibration solution immediately before
beginning the calibration. The solution can only be used once and it is only
good for about 10 to 15 min.
Determining the slope:
The calibration solution with 3 ml of acid added corresponds to 89 mg/L of
CO
dissolved in the water and 5.82% CO
2
the ambient air is 0.03%.
The slope S
of the probe can be determined by the ratio of the difference in
t
voltage read to the difference in concentration:
= ∆U / ∆ (log pCO2)
S
t
The correction factor = 1 in the air and 1.09 in a solution.
Example: voltage in the air (0.03 % CO
voltage in the solution (5.82 %) = -108 mV
S
= (-233 - (-108)) / (log 0.03 - log 5.82) = 54.63 x 1.09 = 59.5
t
mV/decade
The probe signal increases by 59.5 mV when one increases the
concentration by a factor of 10.
Measurement:
The concentration of an unknown gas can be calculated by the following
formula:
log p
= log p
- ( U
M
1
wherein: log p
: logarithm of the partial pressure of CO
1
U
: voltage read in the air
1
S
: slope
t
U
: voltage read in the unknown gas
M
log p
: logarithm of the partial pressure of CO
M
example:
log p
= log 0.03
1
18
in the air. The concentration in
2
x
correction factor
) = -233 mV
2
- U
) / S
1
M
t
2
in the air (log 0.03)
2
in the unknown gas
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