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Paramagnetic O2 Purity Analyzer
4
Not used
5
Preamplifier output ~0- 1 Vdc
6
Not used
7
24 Vdc return, power ground
8
Collector of transistor switching heating element (Not con-
9
Fault signal: <0 Vdc= OK, >4.6 Vdc = Fault (Not connected)
10
Not used
11
Negative reference voltage (Not connected)
12
Positive reference voltage (Not connected)
13
Nominal temperature voltage signal (Not connected)
14
Actual temperature voltage signal (Not connected)
15
+24 Vdc power.
The Electronics and heating elements require a separate power supply
(also housed in the Control Unit) capable of delivering approximately 1.5
amps at 24 volts dc. The output of the sensor is roughly calibrated to be 0
to 1 volt DC for the range of 95 to 100% O
sensor is carried out by the microprocessor as described in Part I Chapter
4.
6.2.2 Cross Interference
As mentioned previously, the selectivity of the measuring system is
based on the extraordinarily high magnetic susceptibility of oxygen
compared to other gases. In most cases the presence of other gases can be
ignored but significant errors can occur when the sensor is calibrated with
a mixture of oxygen and nitrogen and the sample gas consists mainly of
other gases with considerable magnetic susceptibility. In this case, the
reading shows a measured value even if the sample gas contai ns no
Oxygen. It is actually displaying the cross sensitivity to another gas.
Table 6-2 shows the cross sensitivity of some gases when changing
from pure nitrogen to 100% of one of the gases listed.
With gas mixtures the components are weighted according to their
proportional volumes.
The cross interference with a gas mixture can be determined in
advance if the concentration of the individual background gases is known.
Teledyne Analytical Instruments
Analysis Unit
. The true calibration of the
2
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