RADIOMETER ABL800 FLEX, Reference Manual

Page: 44 / 206

ABL800 FLEX Reference Manual 2. Amperometric measuring principles
pO
2
electrode,
Continued
The Ag
+
ions are released into the electrolyte solution where they react with the
Cl
−
ions present, producing AgCl which is insoluble and forms a layer on the silver
rod:
Description
(continued)
Ag
+
+ Cl
−
→
AgCl
Not all Ag+ ions can be removed from the solution. Some reach the cathode where
they are converted back to Ag and form a deposit of silver. This deposit must be
periodically removed with the brush provided in the electrode box.
Designations The following designations are used to describe sensitivity, zero point and drift:
I(O
2
,gas1)
= Current recorded at the p O
2
electrode from a measurement on
Gas 1
I(O
2
,gas2)
= Current recorded at the p O
2
electrode from a measurement on
Gas 2
p O
2
(gas1)
= Partial pressure of O
2
in Gas 1
p O
2
(gas2)
= Partial pressure of O
2
in Gas 2
F O
2
(gas1) = Fraction of O
2
in Gas 1
F O
2
(gas2) = Fraction of O
2
in Gas 2
B
= Ambient pressure
p H O
2
= Water vapor pressure =6.2571 kPa at 37
o
C.
Sens( p O
2
,
prev)
= Sensitivity of the p O
2
electrode measured at the previous 2-
point calibration
I(O
2
,gas2,
prev)
= Current recorded at the p O
2
electrode from the previous
measurement on Gas 2
The p O
2
electrode is calibrated on two gases with known O
2
content. Sensitivity
Gas 1 contains 19.76 % O
2
and Gas 2 contains 0.0 % O
2
.
The exact composition of the calibration gases is contained in their bar codes.
The sensitivity of the p O
2
electrode, Sens( p O
2
), is calculated as follows:
pA/kPa
(gas2) O (gas1) O
gas2) , I(O gas1) , I(O
) O Sens(
2 2
2 2
2
p p
p
−
−
=
Continued on next page
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