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Operation and Maintenance Manual 75
Typical Operating Conditions
The Controller is calibrated at the factory for flow rates to deliver gas in sccm
units. The following table summarizes the typical operating conditions:
Table 1 Typical Operating Conditions
Condition SCD NCD
Detector Pressure (Torr) 4-8 (6-12
*
)
* Oil-free pump
Thermocouple lifetime at 950 °C is diminished.
The recommended conditions should yield satisfactory results for most
applications and should be used as a typical starting point for any method
development. Like any detector, however, there are optimum conditions which
may very somewhat from the recommended conditions. In optimization of
conditions for the Dual Plasma Burner and Controller the following guidelines
should be considered:
High flow rates of hydrogen and oxidant can release enough heat at high
temperature to vaporize combustion tubes and cause blockages downstream
where the materials condense. High flow rates will eventually cause the
pressure in the Burner to exceed its fault cut-off limit of about 600 Torr. For
this reason, do not exceed the recommended flow rate by more than about
25%.
A higher hydrogen to oxidant ratio may initially show higher response but
later yield a reduced response because of the accumulation of contaminants,
such as soot or other active species, that reduce the Detector response.
Operating the Burner at higher temperatures will place more demand on the
heater, thermocouple and seal materials, effectively shortening their lifetime.
In general, when making any parameter change, keep in mind that the system
may require time to reach equilibrium.
4-10
Dual Plasma Controller
Pressure (Torr)
300-400 100-250
Burner Temperature (°C) 800 900-950
Hydrogen Flow Rate (sccm) 40-50 4-6
Oxidant Flow Rate (sccm) 60-65 (air) 8-12 (oxygen)
Background Noise (mV) 0.3-2.0 0.3-1.0