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Optional Hardware and Software Teledyne API - Model 200EH/EM Operation Manual
46
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).
Figure 5-7: Oxygen Sensor - Principle of Operation
5.8.1.2. Operation Within the M200EH/EM Analyzer
The oxygen sensor option is transparently integrated into the core analyzer operation. All functions can be
viewed or accessed through the front panel, just like the functions for NO
X
.
The O
2
concentration is displayed in the upper right-hand corner, alternating with NO
X
, NO and NO
2
concentrations.
Test functions for O
2
slope and offset are viewable from the front panel along with the analyzer’s other
test functions.
O
2
sensor calibration is performed via the front panel CAL function and is performed in a nearly
identical manner as the standard NO
X
/NO calibration. See Chapter 0 for more details.
Stability of the O
2
sensor can be viewed (see 3.3.2.1)
The O
2
concentration range is 0-100% (user selectable) with 0.1% precision and accuracy and is available to be
output via one of the instrument’s four user selectable analog outputs (see Section 6.13.4).
The temperature of the O
2
sensor is maintained at a constant 50° C by means of a PID loop and can be viewed
on the front panel as test function O2 TEMP.
The O
2
sensor assembly itself does not have any serviceable parts and is enclosed in an insulated canister.
5.8.1.3. Pneumatic Operation of the O
2
Sensor
Pneumatically, the O
2
sensor is connected to the bypass manifold and draws a flow of about 80 cm³/min in
addition to the normal sample flow rate (See Table 10.-3 for nominal sample inlet gas flow rates) and is
separately controlled with its own critical flow orifice located inside the vacuum manifold.
Figures 15-8 shows the internal pneumatics of the M200EH with the O2 Sensor installed.
Figures 15-9 shows the internal pneumatics of the M200EM with the O2 Sensor installed.
04521C (DCN5731)