Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 289)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 269
The following table lists the gas flow rates of the critical flow orifices in the standard
9110TH/M
Table 8-3: 9110TH/M Critical Flow Orifice Diameters and Gas Flow Rates
LOCATION PURPOSE
ORIFICE DIAMETER
NOMINAL FLOWRATE
(cm³/min)
9110TH 9110TM 9110TH 9110TM
Bypass manifold 1 out
to NO/NO
x
valve and
NO
2
converter
Controls rate of flow of sample gas into the NO
2
converter and reaction cell.
0.003” 0.007” 40 250
Vacuum manifold:
Bypass manifold 1 Port
Controls rate of sample gas flow that bypasses
the analyzer when bypassing the reaction cell
during the auto-zero cycle.
0.007” N/A 250 N/A
TOTAL INLET GAS FLOW – Standard Configuration 290 250
Vacuum manifold: O
2
sensor port
Controls rate of flow of zero purge gas through
the O
2
sensor (when installed and enabled) when
inactive.
0.004" 0.004" 80 80
TOTAL INLET GAS FLOW – With O
2
Sensor Option 370 330
O
3
supply inlet of
reaction cell.
Controls rate of flow of ozone gas into the
reaction cell.
0.007” 0.007” 250 250
Dry air return of Perma
Pure ® dryer
Controls flow rate of dry air return / purge air of
the dryer.
0.004" 0.004" 80 80
1 Bypass manifold is built into the 3-port reaction cell.
In addition to controlling the gas flows, the critical flow orifices at the inlets of the
reaction cell also maintain an under-pressure inside the reaction cell, effectively
reducing the number of molecules in the chamber and therefore increasing the
chemiluminescence yield as the likelihood of third body quenching is reduced (Section
8.2.4.1). The 9110TH/M sensitivity reaches a peak at about 2 in-Hg-A, below which the
sensitivity drops due to a low number of molecules and decreased yield in the
chemiluminescence reaction.
EFFECT OF TEMPERATURE ON CRITICAL FLOW
Changes in temperature will cause the critical flow orifice materials to expand or
contract. Even though these changes are extremely small, they can alter the diameter of
the critical flow orifice enough to cause noticeable changes in the flow rate though the
orifice. To alleviate this problem the two most important of the flow assemblies (those
controlling the sample gas an O
3
gas flow)in the 9110TH/M are maintained at a constant
temperature.
8.3.4. SAMPLE PARTICULATE FILTER
To remove particles in the sample gas, the analyzer is equipped with a PTFE membrane
filter of 47 mm diameter (also referred to as the sample filter) with a 1 µm pore size.
The filter is accessible through the front panel, which folds down (after removal of the