Teledyne gfc 7000ta Oxygen Sensor OPT, Theory of Operation, Paramagnetic measurement of O2

FAQ Model GFC7000TA Carbon Dioxide Analyzer

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 O2

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 O2 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).

Teledyne Analytical Instruments 58