Jeulin Ex.A.O. 453 076 Mode D'emploi page 17

Data logging
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Ref : 453 076
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
in the water and 5.82% CO
The slope S
to the difference in concentration:
The correction factor = 1 in the air and 1.09 in a solution.
Example: voltage in the air (0.03 % CO
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:
wherein: log p
example:
ENGLISH
in the air. The concentration in the ambient air is 0.03%.
2
of the probe can be determined by the ratio of the difference in voltage read
t
= U /  (log pCO2)
S
t
voltage in the solution (5.82 %) = -108 mV
S = (-233 - (-108)) / (log 0.03 - log 5.82) = 54.63 x 1.09 = 59.5 mV/decade
t
log p = log p - ( U - U
M 1 1 M
: 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
log p = log 0.03
1
U = -233 mV
1
U = -133 mV
M
log p = log (0.03) - (( -233 - (-133))/59.5 = 0.16
M
therefore, the gas contains 10
x correction factor
) = -233 mV
2
) / S
t
in the air (log 0.03)
2
in the unknown gas
2
0.16
% or 1.44 % CO
16
dissolved
2
.
2