Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 76)

FAQ Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 58
Figure 5-4: Multi-drop/LVDS PCA Seated on CPU
5.6. Oxygen Sensor (OPT 65)
5.6.1. Theory of Operation
5.6.1.1. Paramagnetic measurement of O
2
The oxygen sensor used in the GFC 7000TA analyzer utilizes the fact that oxygen is attracted into strong
magnetic field; most other gases are not, to obtain fast, accurate oxygen measurements.
The sensor’s core is made up of two nitrogen filled glass spheres, which are mounted on a rotating
suspension within a magnetic field (Figure 5-7). A mirror is mounted centrally on the suspension and light
is shone onto the mirror that reflects the light onto a pair of photocells. The signal generated by the
photocells is passed to a feedback loop, which outputs a current to a wire winding (in effect, a small DC
electric motor) mounted on the suspended mirror.
Oxygen from the sample stream is attracted into the magnetic field displacing the nitrogen filled spheres
and causing the suspended mirror to rotate. This changes the amount of light reflected onto the
photocells and therefore the output levels of the photocells. The feedback loop increases the amount of
current fed into the winding in order to move the mirror back into its original position. The more O
2
present, the more the mirror moves and the more current is fed into the winding by the feedback control
loop.
A sensor measures the amount of current generated by the feedback control loop which is directly
proportional to the concentration of oxygen within the sample gas mixture (see Figure 5-7).