Rosemount 890, Инструкция по эксплуатации

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I
NTRODUCTION
Rosemount Analytical 748460-A January 2000
1-2
transmit the remaining, higher wavelengths, all with much lower energy loss than the
more commonly used bandpass interference filters.
Four detectors are used in this system, two before the sample cell (sample before [S
b
]
and reference before [R
b
]) and two after (sample after [S
a
] and reference after [R
a
]).
S
b
and S
a
receive energy in the specific wavelength regions depending on the
application (265 to 310 nm for SO
2
, 310 to 355 nm for Cl
2
), R
b
and R
a
in the 310 to 355
nm region for SO
2
and 355 to 400 nm for Cl
2
.
These four detectors measure the component of interest (COI) concentration and
correct for NO
2
interference and UV lamp fluctuations. The difference between
detector determinations is the COI concentration, following this formula:
COI = [f(R
b
)-S
b
]-[f(R
a
)-S
a
]
where:
Ra, Rb, Sa, Sb = signals from those detectors so identified
f = attenuation factor for the reference signal, adjusted to compensate for NO
2
interference.
The sample gas is introduced to the sample cell, and the COI absorbs ultraviolet
energy in proportion to the concentration in the gas. The difference between the
signals of the detectors located at both ends of the sample cell determines the
concentration of COI
in the sample.
F
IGURE
1-2. M
ODEL
890 O
PTICAL
B
ENCH
R a
DETECTORS
MIRRORS
TRANSFLECTANCE©
MIRRORS
DETECTORS
MIRROR
TRANSFLECTANCE©
MIRRORS
SAMPLE CELL
UV LAMP
BEAM SPLITTER
Sa
Sb
Rb