Agilent Technologies G6600-90006 - Manual (Page 28)

28 Operation and Maintenance Manual
temperature, hydrogen and oxidant flow rates, and Burner pressure. The
temperature, actual pressure, oxidant and hydrogen flow rates are selected for
display by rotation of a 4-position control knob. 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.
Ozone Generator
The SCD and NCD produce ozone by corona discharge using a clean,
pressurized air or oxygen source. Use of oxygen should increase ozone
production and, hence, Detector response. High voltage to the ozone generator
is applied only when the reaction cell pressure is less than 100 torr in the SCD
and less than 200 torr in the NCD. Gas flow through the ozone generator is
controlled by a pressure regulator and flow restrictors.
Chemiluminescence Reaction Cell and Photomultiplier Tube
Sulfur monoxide (formed in the Burner) and ozone (produced in the ozone
generator located in the Detector) are mixed in the reaction cell. The cell is
designed such that the reaction between SO and O
3
occurs directly in front of
the photomultiplier tube (PMT). A UV band pass filter (300 - 400 nm) located
between the reaction cell and the PMT selectively transmits the light emitted
by the SO/O
3
reaction. Efficient combustion in the ceramic tubes coupled with
the UV band pass filter eliminates interference from non-sulfur containing
analytes (e.g. nitric oxide, olefins, etc.) which also undergo chemiluminescent
reactions with ozone. A background signal is typically present as a result of
ozone-wall interactions and low level sulfur contamination of Detector gases.
This background signal can be used as a troubleshooting aid (see Section 10).
WA R N I N G
Ozone is a hazardous gas and a strong oxidant. Exposure to ozone should be minimized by
using the instrument in a well ventilated area, changing the chemical trap regularly, and
venting the exhaust of the vacuum pump. The ozone generator should be turned off when
the instrument is not in use to reduce maintenance requirements.