Teledyne T400, Руководство пользователя, Страница: 145 / 177

083730400A DCN8130 Teledyne API – Model T400 O
3
Analyzer 143
6.1.4 I
NTERFERENT
R
EJECTION
The detection of O
3
is subject to interference from a number of sources including: SO
2
,
NO
2
, NO, H
2
O, aromatic hydrocarbons such as meta-xylene and mercury vapor. The
Model T400’s basic method or operation successfully rejects interference from most of
these molecules.
The O
3
scrubber located on the reference path (see Figure 6-2) is specifically designed
ONLY to remove O
3
from the sample gas. Thus, the variation in intensities of the UV
light detected during the instrument’s measurement phase versus the reference phase is
ONLY due to the presence or absence of O
3
. Thus, the effect of interferents on the
detected UV light intensity is ignored by the instrument.
Even if the concentration of interfering gases were to fluctuate so wildly as to be
significantly different during consecutive reference and measurement phases, this would
only cause the O
3
concentration reported by the instrument to become noisy. The
average of such noisy readings would still be a relatively accurate representation of the
O
3
concentration in the sample gas.
Interference from SO
2
, NO
2
, NO and H
2
O are very effectively rejected by the Model
T400. The two types of interferents that may cause problems for the Model T400 are
aromatic hydrocarbons and mercury vapor.
6.1.4.1 AROMATIC HYDROCARBONS
While the instrument effectively rejects interference from meta-xylene, it should be noted
that there are a very large number of volatile aromatic hydrocarbons that could
potentially interfere with ozone detection. This is particularly true of hydrocarbons with
higher molecular weights. If the Model T400 is installed in an environment where high
aromatic hydrocarbon concentrations are suspected, specific tests should be conducted to
reveal the amount of interference these compounds may be causing.
6.1.4.2 MERCURY VAPOR
Mercury vapor absorbs radiation in the 254nm wavelength so efficiently that its presence,
even in small amounts, will reduce the intensity of UV light to almost zero during both
the Measurement and Reference Phases rendering the analyzer useless for detecting O
3
.
If the Model T400 is installed in an environment where the presence of mercury vapor is
suspected, specific steps MUST be taken to remove the mercury vapor from the sample
gas before it enters the analyzer.
6.2 PNEUMATIC OPERATION
CAUTION
It is important that the sample airflow system is both leak tight and
not pressurized over ambient pressure.
Regular leak checks should be performed on the analyzer as
described in the maintenance schedule, Table 5-1.
Procedures for correctly performing leak checks can be found in
Section 5.6.3.