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Emerson Process Management GmbH & Co. OHG 3-1
X-STREAM X2
Instruction Manual
HASX2E-IM-HS
02/2012
3
Measuring Principles
Chapter 3
Measuring Principles
3.1 Infrared Measurement (IR)
Ultraviolet Measurement (UV)
3.1.1 IntrinzX Technology
X-STREAM series analyzers support several
measuring principles depending on the gas
component of interest. This provides best
possible results, as the measurement can be
chosen to optimally t the characteristics of
the gas to be measured with respect to the ap-
plication. The following sections introduce the
available measuring principles highlighting
their specic characteristics.
The non-dispersive measurement methods
described in this section utilize gas specic
light absorption in order to discriminate bet-
ween different gases. This is possible, as
any gas possesses distinct absorption cha-
racteristics. Selective measurement of these
so called absorption lines can be used to
identify gas components: The amount of light
absorpted by the absorption lines, is a direct
measure of the gas concentration.
One can distinguish between two different
types of non-dispersive measurements, dif-
fering in the way, wavelength selectivity is
accomplished. It is essential for gas specic
concentration measurements, to selectively
detect only light of the absorption line wave-
lengths of the gas of interest. Typically a gas
selective detector is used for NDIR measure-
ments,
3-3. For NDUV the selectivity
is achieved by an additional optical lter, as
the detector itself is broadband sensitive. In
some applications, a pyrodetector is used for
NDIR measurements. This type of detectors
is not wavelength selective, hence these se-
tups also use an optical lter to narrow their
wavelength response function.
The assembly of a NDIR and NDUV channel
is shown in
Fig. 3-3. For NDIR a broad-
band IR light source is used to generate the
light, while NDUV measurements utilize a UV
narrowband uorescence source or an EDL
(Electrodeless Discharge Lamp), already
adopted for the absorption lines of the gas
of interest. Part of this adoption is done by a
specially selected optical lter in the adaptor
cell.
The diameter of the light beam emitted from
the sources is adjusted to completely ll the
opening of the split analysis cell. After traver-
sing the analysis cell, the light passes through
a lter cell which adjusts the beam diameter to
the chopper opening and the diameter of the
active detector area. The chopper wheel used
is designed to allow an intrinsically referenced
measurement. The details of this new method
are described in
section 3.1.1.
The decision, which measurement (UV / IR)
to be used for a specic application depends
on the gas component to be measured, and
the required measurement performance.
The IntrinzX technology is an enhancement of
the well established “proof peak” technology
with automatic sensitivity control, known from
the MLT gas analyzer series. While the “proof
peak” provided one reference measurement
per chopper wheel revolution only, the IntrinzX
technology provides four reference measure-
ments per revolution. This IntrinzX technology
has been introduced into the market with the
launch of the X-STREAM X2 gas analyzers.
Using the new IntrinzX chopper wheel, the
reference and the measurement signal are
modulated with 4 and 5 times the basic revo-
lution frequency. As a result, the proof peak