Operation
Calibration Factors Menu
Thermo Electron Corporation Model 42i Low Source Instruction Manual 3-19
NO and NO
x
Backgrounds The NO and NO
x
background corrections are determined during zero
calibration. The NO background is the amount of signal read by the
analyzer in the NO channel while sampling zero air. The NO
x
background
is the amount of signal read by the analyzer in the NO
x
channel while
sampling zero air. Although the background is expressed in terms of
concentration, the background signal is actually the combination of
electrical offsets, PMT dark current, and trace substances undergoing
chemiluminescence. Before the analyzer sets the NO and NO
x
readings to
zero, it stores these values as the NO and NO
x
background corrections,
respectively. The NO
2
background correction is determined from the NO
and NO
x
background corrections and is not displayed. NO and NO
x
background corrections are typically below 15 ppb.
The NO and NO
x
Background screens are used to perform a manual
adjustment of the instruments zero background. Before performing a
background adjustment, allow the analyzer to sample zero air until stable
readings are obtained. The NO channel should be adjusted first. Both the
NO and NO
x
Background screens operate the same way. Therefore, the
following description of the NO background screen applies to the NO
x
background screen as well. The first line of the display shows the current
NO reading. The second line of the display shows the NO background
correction that is stored in memory. The NO background correction is a
value, expressed in the current gas units, that is subtracted from the NO
reading to produce the NO reading that is displayed.
CALIBRATION FACTORS: CALIBRATION FACTORS:
>NO BKG 0.0 >NO BKG 0.0
NOx BKG 0.0 NOx BKG 0.0
NO COEF 1.000 HI NO COEF 1.000
NO2 COEF 1.000 HI NO2COEF 1.000
NOx COEF 1.000 HI NOx COEF 1.000
CAL PRESSURE 150.0 mmHg LO NO COEF 1.000
RESET USER CAL DEFAULTS
LO NO2 COEF 1.000
ª
RANGE AVG DIAGS ALARM
RANGE AVG DIAGS ALARM
LO NOx COEF 1.000
CAL PRESSURE 150.0 mmHg
RESET USER CAL DEFAULTS
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