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R
OUTINE
O
PERATION AND
T
HEORY
Rosemount Analytical
748460-A
January 2000
4-2
Next, a collimating mirror is used to focus and direct the pulsed UV energy. Just prior
to entering the sample cell, a planar, non-position-sensitive beam splitter is utilized to
direct 50 percent of the transmitted energy to the first detector block assembly.
In the detector block, transflective mirrors with selective wavelength reflection
characteristics are used instead of optical filters. These mirrors further isolate the
radiation into the required measurement and reference wavelengths, and reflect it onto
a matched set of silicon photodiode detector assemblies.
A second detector block, located just after the sample cell, is an exact duplicate of the
first. This dual detector array allows the signal processing circuitry to yield a highly
sensitive and accurate SO
2
analysis.
Additionally, utilizing this same technique on a second set of adjacent wavelengths,
allows accurate measurement and elimination of the effects of absorption by
interferent gas or gases such as nitrogen dioxide.
Coupled with the four-detector, multiple wavelength analysis technique described
above, a unique detector output signal integration and de-integration signal processing
scheme allows a continuous on-line correction of dark current and electronic noise
errors. This effectively resets the electronic zero every 30 milliseconds, and yields a
measurement which is virtually free of instability and drift. See Figure 4-1.
F
IGURE
4-1. M
ODEL
890 T
IMING
D
IAGRAM
f
-
+
-
+
-
+
-
+
+
-
+
-
+
-
+
E d = [ k * ( f * R b - S b ) - ( f * R a - S a ) ]
-
+
-
+
-
-
+
-
+
+
DIGITA
DISPLA
DIGITAL
CONTROLLED
GAIN AMPLIFIER
X1,2,4,8,16
B CHANNEL
MUX
ADC
12 BIT
MICRO
PROCESSOR
SPAN
DIGITAL
CONTROLLED
RESISTOR
R
C
RESET
DIGITAL
CONTROLLED
RESISTOR
REFERENCE A
Ra
SAMPLE A
Sa
REFERENCE B
Rb
SAMPLE A
Sa
DIGITAL
CONTROLLED
RESISTOR
INTERFERENCE
ADJUSTMENT
f
HIGH
LOW
BALANCE
ADJUSTMENT
DIGITAL
CONTROLLED
RESISTOR
LIGHT
THERMISTOR
SAMPLE CELL
SPAN
COMPENSATION
DARK
REFERENCE
REFERENCE
ZERO
COMPENSATION
THERMISTOR
BLOCK B
INTEGRATOR
SAMPLE/HOLD
ZERO
SUPPRESSION
DIGITAL
CONTROLLED
RESISTOR
THERMISTOR
BLOCK A
E o u t = - 1 / R * C E d d t
LAMP 30.75 Hz
LIGHT
DARK
SAMPLE/HOLD
RESET
12.1905 mSEC
16.2537 mSEC
12.1905 mSEC
12.1905 mSEC
16.2537 mSEC
12.1905 mSEC
12.1905 mSEC
0.5079 mSEC
1.0159 mSEC
0.5079 mSEC
1.0159 mSEC
0.5079 mSEC
1.0159 mSEC
LAMP 30.75 Hz
LIGHT
DARK
SAMPLE/HOLD
RESET
Содержание 890
Страница 1: ...Rosemount Analytical MODEL 890 UV ANALYZER INSTRUCTION MANUAL 748460 A ...
Страница 8: ...CONTENTS VI 748460 A Rosemount Analytical January 2000 NOTES ...
Страница 16: ...PREFACE Rosemount Analytical January 2000 748460 A P 8 NOTES ...
Страница 64: ...TROUBLESHOOTING Rosemount Analytical 748460 A January 2000 5 4 NOTES ...
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