Endress+Hauser SpectraSensors SS2100i-1, Обзорное руководство

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Sample Conditioning System
SCS Overview Manual 3
–
3
Sample dryer
All trace measurement applications require the use of a dryer. Typically, these
devices are switched into the flowing sample going to the measurement cell to
remove the desired component. A spectrum of the sample gas free of H
2
O is
acquired and saved in the analyzer controller memory. This is the “Dry”
spectrum. The dryer is then bypassed and the sample spectrum is acquired
with H
2
O in the sample. This is the “Wet” spectrum. The analyzer controller
subtracts the Dry spectrum from the Wet spectrum and the concentration of
trace moisture is measured. The same Dry spectrum is typically used for 10 to
30 minutes, depending on logic programmed into the controller before a new
Dry spectrum is acquired.
The automatic valves that control switching the sample stream into the dryer
or bypassing the dryer may be either electric solenoid valves or pneumatically
operated valves, depending on the application.
Validation systems
System validation is accomplished by the use of a permeation device. Refer to
the system drawings for your analyzer and “Permeation Validation for
Trace Moisture (0-10 ppm H
2
O)” on page 4-1.
Sample return/vent
Tunable diode laser absorption spectroscopy is inherently sensitive to sample
pressure in the measurement cell, so all SpectraSensors analyzers are
calibrated for a range of sample pressures. Most applications benefit from
operation at low pressures instead of high pressures. Sometimes the analyzer
is designed to vent the sample to atmosphere or an atmospheric pressure
return system. Return to a flare or other sample return must recognize the
pressure limitations of the cell and also the calibration of the analyzer. Refer to
the system drawings for your analyzer for the maximum sample return
pressure for your system.
SCS heaters
Many trace gas measurement analyzers have heated SCS enclosures. In some
cases, this is only to avoid condensation of sample components. However, in
cases such as trace measurements, temperature stability of the sample
measurement cell is critical to the measurement. In these applications, the
temperature control is very precise and a proportional, integral, derivative
(PID) temperature controller is used to maintain very close tolerance on the
temperature of the system.
To connect electrical power to the enclosure heater
Units with an enclosure heater will have an additional power connection
through a conduit hub located at the bottom right of the enclosure.