Micromeritics ASAP 2460, Operator'S Manual

Page: 114 / 468

Analysis Conditions Files ASAP 2460 Operator’s Manual
3-20 246-42800-01 - Aug 2013
Target Pressures
Options
button
(continued)
•
Absolute / Relative pressure tolerance
- values used to determine how
close the actual pressure must be to each target pressure from the
pressure table. At lower pressures, the relative tolerance value is lower.
At higher pressures, the absolute tolerance value is lower. For example:
Experiment 1:
You have an absolute tolerance of 5 mmHg, a relative
tolerance of 5%, and a target pressure of 40 mmHg; 5% of 40 mmHg is

2 mmHg. Since 2 mmHg (relative tolerance) is lower than 5 mmHg
(absolute tolerance), 2 mmHg is used. Therefore a minimum pressure of
38 mmHg (40 - 2) must be attained to collect data for a target pressure of
40 mmHg.
Experiment 2:
You have an absolute tolerance of 5 mmHg, a relative
tolerance of 5%, and a target pressure of 200 mmHg; 5% of 200 mmHg
is 10 mmHg. Since 5 mmHg (absolute tolerance) is lower than

10 mmHg (relative tolerance), 5 mmHg is used. Therefore a minimum
pressure of 195 mmHg (200 - 5) must be attained to collect data for a
target pressure of 200 mmHg.
Normally, surface area measurement points are widely spaced and the
resulting measurement is not very sensitive to the precise location of
points so wider tolerances may be used. Unnecessarily tight tolerances
lengthen the analysis.
•
Low Pressure incremental dose mode
- Choose this option when you
are performing an analysis of microporous materials. At low pressures
on Type 1 isotherms, the pressure points are very closely spaced, making
a useful pressure table difficult to define. Choosing this mode enables
you to measure equilibrium points at approximately equal intervals on
the quantity adsorbed axis. Each dose is fully equilibrated and recorded
as a data point.
In this mode, the sample is successively dosed with a specified amount
of gas until the first pressure point is reached. The first point is the
threshold value, triggering the transition from Incremental Dose Mode
to Pressure Table Mode. When the first pressure table value is reached,
Incremental Dose Mode is disabled, and points are recorded in
accordance with the specified pressure table. Because the data points
recorded during Incremental Dose Mode may define most of the
analysis, one point on the pressure table can be sufficient and serve as
the end point for the analysis.
This field is disabled if
First Pressure Fixed Dose Mode
is selected.
Dose amount
- Enter the amount of gas to be added to the sample for
each data point until the first point on the pressure table is reached.
Enabled when
Low pressure incremental dose mode
is selected.
Field or Button Description (continued)