Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 297)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 277
Figure 8-13: Dilution Manifold
Please inquire with Teledyne sales if the analyzer can be modified to fit your
application.
8.4. OXYGEN SENSOR (OPT 65A) PRINCIPLES OF OPERATION
8.4.1. PARAMAGNETIC MEASUREMENT OF O
2
The oxygen sensor used in the 9110TH/M analyzer utilizes the fact that oxygen is
attracted into strong magnetic field (in contrast with most other gases) 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 8-14). A mirror is mounted
centrally on the suspension and light is shone onto the mirror, which reflects the light
onto a pair of photocells that then generate a signal. 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 wire 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 wire 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 8-14).