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Theory of Operation Teledyne API - Model 200EH/EM Operation Manual
200
Figure 10-10-10: Flow Control Assembly & Critical Flow Orifice
The actual flow rate of gas through the orifice (volume of gas per unit of time), depends on the size and shape of
the aperture in the orifice. The larger the hole, the more gas molecules, moving at the speed of sound, pass
through the orifice.
With nominal pressures of 28 and 4 in-Hg-A for the sample and reaction cell pressures, respectively the
necessary ratio of sample to reaction cell pressure of 2:1 is largely exceeded and accommodates a wide range
of possible variability in atmospheric pressure and pump degradation extending the useful life of the pump.
Once the pump does degrades to the point where the vacuum pressure exceeds 14 in-Hg-A so that the ratio
between sample and vacuum pressures is less than 2:1 a critical flow rate can no longer be maintained. At this
point, the instrument will display “
XXXX" indicating an invalid sample flow rate.
The following table lists the gas flow rates of the critical flow orifices in the standard M200EH/EM
Table 10-3: M200EH/EM Critical Flow Orifice Diameters and Gas Flow Rates
ORIFICE DIAMETER
NOMINAL FLOWRATE
(cm³/min)
LOCATION PURPOSE
M200EH M200EM M200EH M200EM
Bypass Manifold 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 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
04521C (DCN5731)