156 Advanced Operation Manual
4 Columns and Oven
•Constant flow—Maintains a constant mass flow rate of
carrier gas in the column throughout the run. If the
column resistance changes due to a temperature program,
the column head pressure is adjusted to keep the flow
rate constant. This can shorten runs significantly.
• Ramped flow—Increases the mass flow rate in the column
during the run according to a program you enter. A
column flow profile can have up to three ramps, each
consisting of a programmed increase followed by a hold
period.
The pressure modes
The pressure modes are not available if the column is not
defined or the inlet’s mode is set to Flow control.
Pressures are gauge pressures—the difference between the
absolute pressure and the local atmospheric pressure.
Because most detectors present little resistance to the
column flow, the gauge pressure at the column head is
usually the same as the pressure difference between column
inlet and exit. The mass selective detector and the atomic
emission detector are the exceptions.
• Constant pressure—Maintains a constant gauge pressure
at the head of the column throughout the run. If the
column resistance and gas density changes during a run,
the gauge pressure does not change but the mass flow
rate does.
• Ramped pressure—Increases the column head gauge
pressure during the run according to a program you
enter. A column pressure profile can have up to three
ramps, each consisting of a programmed increase followed
by a hold period.
Select a column mode
The column’s mode parameter is not available if the inlet’s
mode parameter is set to Flow control.
When a splitter controlled by a PCM or AUX pressure is
used to divide flow between multiple columns, only the
mode setting of the lowest column number configured
determines the mode used. All other column mode settings
exiting the splitter are ignored by the GC.
1 Press [Col 1] or [Col 2], or press [Aux col #] and enter the
column number.
2 Scroll to the Mode line.
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