2. Amperometric measuring principles ABL800 FLEX Reference Manual
pO
2
electrode, Continued
Sensitivity
(continued)
The partial pressures of O
2
in the gas mixtures Gas 1 and Gas 2 are calculated from
the following equation:
The sensitivity of the pO
2
electrode should fall between 5 - 40 pA/mmHg or 37.5 -
300 pA/kPa.
The zero point of the pO
2
electrode is the electrode current at pO
2
=0. It is
calculated from the current measured at the electrode with Gas 2 (0 % O
2
), and the
sensitivity:
Zero point
kPa
prev),OSens(
gas2),I(O
)Opoint Zero
2
2
2
p
(p =
The zero point value of the pO
2
electrode should be less than 6.0 mmHg or 0.80 kPa.
The zero point current is the current measured at the pO
2
electrode with Gas 2 in
the measuring chamber. When the measurement on Gas 2 begins, a relatively high
current is recorded due to residual O
2
from the rinse solution in the measuring
chamber. This current falls exponentially with time while Gas 2 is present in the
measuring chamber.
Forty seconds into the measurement the
current reaches a steady state which is
then considered as the zero point
current.
Time (secs)
Current (pA)
Drift
Drift 1 is a measurement of the difference between two consecutive measurements
on Gas 1, and is calculated from the following equation:
kPa)gas1(O
)prev,OSens(
)prevgas1,,I(O)gas1,I(O
)O1(Drift
2
2
)22
2
p
p
p −
=
Drift 2 reflects the change in sensitivity between 2-point calibrations and is
calculated from the following equation:
Drift 2( O
I(O gas2 I(O gas2,prev
Sens( O prev
Ogas2 kPa
2
22)
2
2
p
p
)
,) , )
,)
()=
− p
The default drift tolerances set by Radiometer are ± 0.80 kPa (6.0 mmHg) for Drift
1 and Drift 2. The Drift tolerances can, however, be user-defined in the Setup
program.
Continued on next page
2-6
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