WPI APOLLO 4000, Instruction Manual

Page: 52 / 74

APOLLO 4000
OXYGEN DETECTION
World Precision instruments d-4
the physical interpretation of the
% oxygen is the percentage of
atmospheric pressure that the oxygen
present exerts. For example, in a
00% oxygen environment a reading
of 00 means that the partial pressure
of oxygen is atm (760 mm Hg). A
reading of 2 means that the partial
pressure of oxygen is 0.2 atm (60
mm Hg).
Fig. D2 shows a record of the
calibration procedure described
above. Before point the record
displays the background current
of the oxygen sensor in air. this
current value may vary from sensor
to sensor. At point the sensor is
exposed to 0 % oxygen. At point 2
the background is zeroed using the software. At point 3 and point 4 the sensor is
exposed to air (2% oxygen) and 00% oxygen, correspondingly. By using the
current at 0% (0 nm) and 00% (236 nA), a two-point calibration curve is built and
the slope is determined at 2.36 nA/%. Alternatively, a three-point calibration can be
implemented by adding the information for the current of the sensor in air and by
using linear regression software.
to present the data in % oxygen you may use the Setup/Unit conversion option
from the menu. A new unit for the oxygen-measuring channel must be created by
setting up 2360 pA to correspond to % oxygen (
Fig. D3 ). switch to % unit as
shown in Fig. D4 and all recorded data as well as incoming data will be displayed
in % oxygen unit.
Note: After the calibration the trace should not be re-zeroed as this will invalidate
the calibration.
Fig. D3 —
Creating a new unit
(% oxygen).