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The sample gas flow can be adjusted, when a preset gas flow is present. The correction
factor for the flow rate can also be changed in the channel specific settings list (see page
42 ‘Fig. 42 Channel-specific settings list’)
After leaving the section M5/S2, the set points will adopt the actual values shown on the
screen. If you open this section again, the actual values and the set points will have the
same values.
10.5 Cross-sensitivity of coexisting gases
Oxygen is a paramagnetic gas, which means that oxygen molecules are attracted into a
strong magnetic field. This paramagnetic susceptibility distinguishes oxygen from most
other gases.
The PMC uses this paramagnetic characteristic to measure the concentration of oxygen in
a gas mixture.
Here are two examples of coexisting gases which have an effect on the accuracy of the
oxygen concentration measurement.
Example 1
To determine the residual oxygen content of a 100% carbon dioxide (CO
2
) inert gas atmo-
sphere at +20 °C (+68 °F), please take a look at the table in this chapter.
If the PMA1000 is calibrated at zero point with nitrogen the reading will show -0.27 %. Then
due to the Cross-sensitivity of CO
2
at +20 °C (+68 °F) the analyzer shows a value of -0.27 %.
This means, if you calibrate the analyzer with 100 % N
2
, the zero point needs to be set to
+0.27 %. This zero point adjustment compensates the effect of CO
2
in the measurement
and 100 % CO
2
show a reading of 0 %.
This is an example for a gas composition with CO
2
and O
2
only. To eliminate the cross-sen-
sitivity effects, we can simply use CO
2
instead of N
2
for the zero point adjustment.
Example 2:
To determine the oxygen content of a gas mixture at +20 °C (+68 °F), please take a look at
the following values from the table.
C2H6
(Ethane)
1 vol%
O2
5 vol%
CO2
40 vol%
N2
54 vol%
N
2
will be used for the zero point adjustment. The cross-sensitivity values from the table
are referring to 100 vol% of the corresponding gases.
To estimate the actual cross-sensitivity of the existing gases, the values need to be adjust-
ed to the real concentrations in the gas mixture.