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Teledyne API Model 200A NO
X
Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
7.6 Calibrate on NO
2
Permeation Tube
If the M200A is equipped with the IZS option, is possible to span the instrument on the
permeation tube. If this feature is enabled, the instrument internal valves are set so that gas is
routed through the permeation tube, then the moly converter, thus producing NO gas. The
software is programmed to use this known NO gas concentration to span both the NO and NO
x
channels of the instrument. Thus, if CAL-ON-NO2 is enabled, the CALS button now will span
both the NO and NO
x
channels of the instrument.
CAUTION
This feature has some unexpected side effects.
If CAL-ON-NO2 is enabled and you do a SPAN CHECK or SPAN CAL, the NO
2
concentration
will be reported as ZERO! This is because all of the NO
2
gas is being routed through the
molybdenum converter during both the NO and NO
x
portions of the measurement cycle. Thus
the instrument sees the SAME concentration of NO gas in the NO and NOx channels, and
reports a NO
2
concentration of zero.
As long as CAL-ON-NO2 is enabled the instrument will never report any NO
2
during span
calibration. This feature should be enabled only when a calibration is desired, otherwise leave it
disabled so that NO
2
concentrations are reported correctly. See Table 7-7-9 to enable this
feature.
NOTE
Note that this method of calibration is NOT approved by the USEPA.
Permeation tubes are known to change as temperatures are cycled,
and as they age. Also, this calibration relies on the moly converter
to be working properly. (Converter efficiency can be compensated
by enabling the Converter Efficiency option.) It is recommended that
if CAL-ON-NO2 is used, the instrument calibration be checked
frequently by independent means to assure accurate data.
7-9
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