User guide

286 Advanced User Guide
9 Columns and Oven
• 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.
3 Press [Mode/Type] to see the column mode list.
4 Scroll to the column mode you want. Press [Enter].
This completes column mode selection. Next you must specify
the inlet conditions either during the entire run (if you selected
either of the constant modes) or at the beginning of the run (if
you selected either of the ramped modes).