Teledyne T400, Руководство пользователя, Страница: 90 / 177

88 Teledyne API – Model T400 O
3
Analyzer 083730400A DCN8130
4.1.3 C
ALIBRATION
(S
PAN
) G
AS
Span Gas is a gas specifically mixed to match the chemical composition of the type of
gas being measured at near full scale of the desired measurement range and should be
certified traceable to NIST Standard Reference Materiald (SRM). It is recommended that
the span gas used have a concentration equal to 80% of the full measurement range. (For
example, if the application is to measure between 0 ppm and 500 ppb, an appropriate
span gas would be 400 ppb; between 0 ppb and 1000 ppb, an appropriate Span Gas would
be 800 ppb).
If Span Gas is sourced directly from a calibrated, pressurized bottle, use the exact
concentration value printed on the bottle.
Because of the instability of O
3
, it is impractical, if not impossible, to produce stable
concentrations of bottled, pressurized O
3
. Therefore, when varying concentrations of O
3
is required for span calibrations they must be generated locally. We recommend using a
gas dilution calibrator with a built in O
3
generator, such as a Teledyne API Model T700,
as a source for O
3
span gas.
4.1.4 I
NTERFERENTS
The detection of O
3
is subject to interference from a number of sources including SO
2
,
NO
2
, NO, H
2
O and aromatic hydrocarbon meta-xylene and mercury vapor. The Model
T400 successfully rejects interference from all of these with the exception of mercury
vapor.
If the Model T400 is installed in an environment where the presence of mercury vapor is
suspected, steps should be taken to remove the mercury vapor from the sample gas before
it enters the analyzer.
For a more detailed discussion of this topic, see Section 6.1.4.
4.1.5 D
ILUTION
R
ATIO
O
PTION
S
OFTWARE
S
ET
U
P
If your application involves diluting the sample gas before it enters the analyzer, and the
Dilution Ratio Option is enabled:
1. Set the appropriate units of measure (Setup>Vars>User Units).
2. Select the reporting range mode (Setup>Vars>Range Mode [Single or Dual]).
3. Set the reporting range (Setup>Analog Outputs>Analog Output[#]>O3 Concentration, Min
Max). Ensure that the upper span limit entered for the reporting range (in the Max field) is
the maximum expected concentration of the undiluted gas.
4. Set the dilution factor as a gain, e.g., a value of 20 means 20 parts diluent and 1 part sample
gas (Setup>Vars>Dilution Factor).
5. Calibrate the analyzer; ensure that the calibration span gas is either supplied through the
same dilution system as the sample gas or has an appropriately lower actual concentration.
EXAMPLE: If the reporting range limit is set for 100 ppm and the dilution ratio of the
sample gas is 20 gain, either:
•
a span gas with the concentration of 100 ppm can be used if the span gas passes
through the same dilution steps as the sample gas, or;
• a 5 ppm span gas must be used if the span gas IS NOT routed through the dilution
system.