E C O P H Y S I C S Operating Guide
CLD 780 TR / July 2000 69
5.2.2.7.3 NO and Zero gas calibrations in “CONT“ mode
Calibrations made in the “CONT“ operating mode are different from
those described above in that frequently, even during sample data acqui-
sition, pre-chamber measurements are seldom made, only main chamber
values. Additionally, three additional calibration parameters are defined:
–S
Null
(= ZEROnet) is the signal value in counts when actual zero gas is
measured. When the counts value is converted into ppb at the end of
the calibration, S
Null
is subtracted first from the NO counts value.
– fNO is the factor by which the count value must be divided to give the
concentration value in ppb.
–
λ
NO is the factor by which the signal is reduced when the ozone flow
is added to the sample flow in the pre-chamber instead of the main
chamber.
The displayed concentration value B in ppb is calculated as follows:
B = ( S - S
Null
) x
λ
NO / fNO
Note: The values of S
Null
(= ZEROnet),
λ
NO and fNO are displayed in
window (58), and may be modified manually in window (59).
S is the total signal from the detector when ozone is added to the sample
flow in the main chamber.
(51) “Zero Calibration“ window
Allows the user to determine S
Null
(= ZEROnet).
“Zero Calibration (Y/N)“: Certified, or extremely good quality zero air is
necessary for this calibration step.
Press “YES“ to proceed with the zero point determination. Window (52)
appears.
Press “NO“ to proceed directly to the NO calibration step. Window (54)
appears.
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