Teledyne T802 12. PRINCIPLES OF OPERATION

Maintenance Schedule & Procedures Teledyne API T802 Paramagnetic O2 Analyzer Operation Manual

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12. PRINCIPLES OF OPERATION

The T802 parametric oxygen analyzer is a microprocessor-controlled analyzer

that determines the percent concentration of molecular oxygen (O2) in a sample

gas drawn through the instrument. It uses a paramagnetic sensor that relies on the

relatively high reactivity of O2 molecules to magnetic fields to generate a current

that is proportional to the amount of O2 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 O2 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

O2 concentration.

The optional CO2 sensor allows the T802 to measure both O2 and CO2

simultaneously. This option includes a CO2 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 CO2 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).

Molecular oxygen, O2, 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 O2 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 O2 molecule, spin in the same direction as

each other, increasing the aggregate magnetic field.

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, N2). 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 N2 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.

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