Micromeritics TRISTAR II PLUS - Page 78

4 Parameter Files
Selections Description
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.
Experiment 1. There might be 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. There might be 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.
p° and T [button]
Click to select one option for obtaining the saturation pressure (Po)
and analysis bath temperature. Each selected option presents a
different set of parameters at the bottom of the window.
Options and descriptions:
1. Analysis bath temperature (not used for krypton analyses).
Measures the p
0
on a continuous basis. Allows the meas-
urement of each data point without slowing the analysis.
Analysis Conditions (continued)
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TriStar II Plus Operator Manual
303-42800-01 (Rev M ) — Sep 2023