E C O P H Y S I C S Operating Guide
CLD 780 TR / July 2000 73
Note: The count values for pre-chamber and main chamber should always
be very close to values previously measured under identical conditions. If
this is not the case, the instrument has not been sufficiently flushed, poor
quality zero gas is being used or possibly the flow restrictor or main
chamber is contaminated (see chapter 7).
Press the “YES“ key to end the calibration. The new calibration factors are
now displayed in window (58). The user is given the option of observing,
accepting, rejecting or manually overwriting the given values with his
own.
Press “NO“ to abort. The “Exit“-window (60) appears, allowing the op-
tion to return to the start of the calibration (window (51)).
Press “MEAS“ to abort and return to measure (window 1a).
(58) “Valid“ window.
Accept calibration as valid.
“Valid(Y/N)“: allows the user to accept or reject the calibration.
Press “YES“ to accept the new calibration factors.
Note: The number shown in the display under the heading “ZEROnet“
(S
Null
in the formula) represents the main chamber signal during the “Zero
calibration“ (i.e. measuring high-quality zero air), and should lie between
500 and 1000 cps. The number shown under the heading “fNO“ repre-
sents the number of counts/sec per ppb, and should lie between 1500
and 2500. The number shown under the heading “
λ
NO“ represents the
fractional reduction in signal between pre-chamber and main chamber
measurements. During an “NO Calibration“ with good quality zero air
this value should lie above 0.95 ( i.e. >95 %).
Press “NO“ to reach the “Enter Value!“ window (59).
Press “YES“ and “MEAS“ to return to measure mode.
Caution:
λ
NO is remeasured every time an AIC determination is
made (window(7)). When measuring air samples containing interfer-
ing substances, an AIC should be made at the start of measurement,
to adjust the
λ
NO value to that appropriate for the gas mixture. Oth-
erwise, the Automatic Interference Correction calculation will not give
accurate values for the interval up to the first AIC determination.
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