Servomex Servotough SpectraScan 2400, Руководство пользователя

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SERVOTOUGH SpectraScan User Manual
02400001A/1 9
2 SYSTEM OVERVIEW
This chapter introduces the Servomex SpectraScan Gas Analyzer and explains its basic principle of
operation.
2.0 Introduction to the Analyzer
The Servomex SpectraScan Gas Analyzer is a non-contact, light absorption based gas analyzer
capable of ppm to percent level concentration monitoring of multiple gas compounds. The system
consists of a light spectrometer, a flow-through sample cell, a single-element photo-detector and the
supporting electronics. The spectrometer uses a unique tunable Fabry-Perot assembly that
provides wavelength scanning with high optical throughput. An advanced spectral processing
algorithm computed in the embedded electronics provides highly accurate and robust quantitative
measurements.
The analyzer is configured and calibrated for a specific wavelength analysis region(s) depending on
the application for which it is intended. It is designed to be a dedicated on-line monitoring system
that is “plug and play,” not requiring any on-site configuration or calibration. The specific system
configuration and calibration is denoted by the application code “-xyz” that can be found in the
Calibration Verification Sheet delivered with the analyzer.
Example applications of the Servomex SpectraScan Gas Analyzer include:
Hydrocarbon gas composition monitoring
Petrochemical process monitoring
Specialty and chemical gas process and blending monitoring
Catalysis and combustion process monitoring
2.1 Measurement Principle
When a gas sample is introduced in the gas cell, the light radiation provided by a broadband light
source is partially absorbed by the gas species present. The light absorption occurs at specific
frequencies and magnitudes depending on the gas compound and the concentration of that
compound. The Servomex SpectraScan spectrometer module scans the wavelength and measures
the true absorption spectra and compares them with the pre-loaded calibration spectra. The on-
board analysis algorithm computes the gas concentrations in real-time, which can then be output
through the MODBUS TCP/IP protocol.
In principal, the absorption spectrum of each compound is unique which acts as a “fingerprint” for
identification or speciation analysis. In addition, the magnitude of the absorption is a function of the
number of molecules of the gas. With a known path length, pressure and temperature, the
magnitudes of the absorption spectra are then used to compute volumetric concentrations. This
first principle based technique provides accurate and robust measurements with minimal span and
baseline drifts.
The analyzer employs an internal pressure transducer to measure the sample pressure in real-time
enabling pressure variation corrections. The flow cell is heated to a constant temperature (default
value is 60
o
C) with a sample preheat module to maintain both sample and optical sensor
temperature at a constant calibrated temperature, thereby ensuring measurement accuracy and
stability despite sample and environmental variations.