Micromeritics ASAP 2020 Confirm Operator's Manual page 102

ASAP 2020 Confirm
First Pressure Fixed
Dose
(continued)
Maximum volume
increment
Absolute and Relative
pressure tolerance
4-26
The first point on the pressure table is the threshold value,
triggering the transition from the Fixed Dose Mode to
Pressure Table Mode. When the first pressure table value is
reached, Fixed Dose Mode is disabled, and points are
equilibrated and recorded in accordance with the specified
pressure table. In the field adjacent to this option, enter the
amount of gas that is to be added to the sample for each dose
cycle.
This option is disabled if Low pressure incremental dose
mode is selected.
Select this option to determine when additional data points
are collected between target pressures in regions of
adsorption. When the maximum increment has been adsorbed
since the last collected data point, another point is
equilibrated and collected.
During desorption, this field is treated as a maximum volume
"decrement" value.
The values entered in these fields are 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 smaller, and at higher pressures the absolute
tolerance value is smaller. The lesser (or more stringent) of
these two criteria are used to determine the tolerance
For example, with relative tolerance = 5% and absolute
tolerance = 5 mmHg, the relative tolerance at 40 mmHg
target pressure is 5% of 40 mmHg, or 2 mmHg; 2 mmHg is
smaller than the absolute tolerance of 5 mmHg, so 2 mmHg is
used. At 200 mmHg target pressure, the relative tolerance is
5% of 200 mmHg, or 10 mmHg; in this case, the absolute
tolerance of 5 mmHg is smaller and is used.
In the above example, a minimum pressure of 40 - 2 = 38
mmHg must be attained to collect data for a target pressure of
40 mmHg. For a target of 200 mmHg, 200 - 5 = 195 mmHg
must be attained.
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.
New
202-42811-01 - Mar 2011