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Maintenance Schedule & Procedures Teledyne API T802 Paramagnetic O
2
Analyzer Operation Manual
219
12. PRINCIPLES OF OPERATION
The T802 parametric oxygen analyzer is a microprocessor-controlled analyzer
that determines the percent concentration of molecular oxygen (O
2
) in a sample
gas drawn through the instrument. It uses a paramagnetic sensor that relies on the
relatively high reactivity of O
2
molecules to magnetic fields to generate a current
that is proportional to the amount of O
2
present in the sensor chamber.
Calibration of the instrument is performed in software and does not require
physical adjustments to the instrument. During calibration the microprocessor
measures the current state of the O
2
Sensor output and various other physical
parameters of the instrument and stores them in memory. The microprocessor
uses these calibration values, measurements made on the sample gas along with
data regarding the current temperature and pressure of the gas to calculate a final
O
2
concentration.
The optional CO
2
sensor allows the T802 to measure both O
2
and CO
2
simultaneously. This option includes a CO
2
sensor probe, a Logic PCA that
conditions the probe output and issues a 0-5 VDC signal to the analyzer’s CPU
that is used to compute the CO
2
concentration. The T802 receives this input,
scales it based on the values of the CO2_SLOPE and CO2_OFFSET Recorded
during calibration (see Section 9.5).
12.1. PARAMAGNETIC OXYGEN MEASUREMENT
12.1.1. MAGNETIC PROPERTIES OF O
2
GAS
Molecular oxygen, O
2
, displays a particularly strong susceptibility to the effect of
magnetic fields. This is due to the behavior of the electrons of the two oxygen
atoms that make up the O
2
molecule.
When the electrons in an orbital are paired, they spin in opposite directions from
each other thereby canceling any magnetic field effects. On the other hand,
unpaired electrons, such as those of an O
2
molecule, spin in the same direction as
each other, increasing the aggregate magnetic field.
12.1.2. PRINCIPLE OF MEASUREMENT
The type of paramagnetic sensor used in the T802 analyzer is called a magneto-
mechanical sensor. This type of sensor consists of a small dumbbell-shaped body
(a sphere on either end) made of glass and filled with a gas of negative
paramagnetic characteristic (in this case, N
2
). The dumbbell body is suspended
on a platinum fiber within the magnetic field of a permanent magnet, in such a
way that it is free to rotate. Because the N
2
inside the spheres has a small
opposite magnetic charge from the field of the permanent magnet, the
dumbbell’s resting (neutral) position is slightly deflected away from the
strong point of the field.
07275B DCN6418