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24 Operation and Maintenance Manual
Dual Plasma Controller
The Dual Plasma Controller provides all operational parameters of the Dual
Plasma Burner except for the Detector base temperature. The Detector base
temperature is controlled by circuitry in the GC. Parameters monitored or
regulated by the Controller include Burner temperature, Burner temperature
set-point, hydrogen and oxidant flow rates, and Burner pressure. The
temperature set-point, actual pressure, oxidant and hydrogen flow rates are
displayed by rotation of a 4-position switch. Power, valve operation,
temperature within set-point range and fault conditions are indicated with
LED illumination on the front display panel.
The Dual Plasma Controller incorporates several safety features. The safety
circuitry detects faults such as power loss, vacuum loss, thermocouple failure,
heater element failure, broken ceramic tube, or high temperature. When a fault
is detected, the Fault LED illuminates and hydrogen and oxidant flow is
stopped by normally-closed solenoid valves.
Dual Plasma Burner with the 355 SCD
The Dual Plasma Burner is based on the same chemistry and basic principles
of earlier SCD Burner designs. A key difference, however, is the addition of a
second “flame” or “plasma,” the lower is oxygen-rich and the upper is
hydrogen-rich. The Burner consists of a tower assembly that contains an outer
sheath for burn protection, a heating element, thermocouple, and combustion
tubes. Conversion of sulfur containing compounds to SO occurs within the
ceramic reaction chamber housed in the Burner assembly. Agilent also
provides a Flame Ionization Detector (FID) option for the simultaneous
collection of hydrocarbon and sulfur chromatograms for some GCs.
Dual Plasma Burner with the 255 NCD
Compounds eluted from the GC column are combusted in the Dual Plasma
Burner first by an oxygen rich flame (plasma) followed by catalytic combustion
on a Noble metal screen. For hydrocarbons, this two stage combustion
technique results in complete conversion of the matrix to products, such as
carbon dioxide and water, which do not chemiluminesce with ozone. Nitrogen
atoms in a compound are converted into nitric oxide and potentially other
nitrogen oxide species. In the second stage, the catalyst is used to convert
other nitrogen oxide species to nitric oxide, resulting in a high efficiency of
conversion.