Micromeritics GEOPYC 1365 Operator's Manual page 75

The first conversion factor (calculated factor) is derived from geometry and mechanical
couplings and relates the plunger movement to chamber volume as if there were no sample
shape influence. The second factor (adjusted factor) is modified to include an average shape
influence experimentally determined from many different shapes. Neither is likely to apply
precisely to any particular specimen. True calibration for shape can be achieved only when the
predetermined envelope density of a representative specimen of the material in question is
used.
The representative specimen preferably is one from an evaluation procedure that was being
followed before GeoPyc introduction. GeoPyc results can be expected then to track prior
records. A completely nonporous specimen of the same shape as the material in question
affords a degree of calibration but, because it is nonporous, cannot have the same surface
texture and cannot be as satisfactory. Because in the final analysis the GeoPyc operates best
as a comparison device, there is no real substitute for a truly representative specimen for
calibration. A GeoPyc operator should set aside enough of the selected calibration material to
be able to recheck the calibration from time to time.
Guideline 1. Select for calibration a quantity of the material in question and determine its
envelope density by the prior test procedure or some other method.
2. Calibration itself will only be reproducible to the degree the guidelines given earlier for repro-
ducibility are followed. Accordingly, the weight of the representative sample, the quantity of
Dry Flo, and the sample chamber size should be selected on the basis of the amount of
sample to be used later. Also, all calibration tests should be made with the same consolidation
force and the same number of preparation and test cycles to be used in analyses.
Guideline 2. Conduct calibration tests using parameters identical to those to be used in
analyses.
3. Finally, a number of calibration tests should be made and the median selected as the con-
version factor.
Guideline 3. Use the median value from a number of calibration tests as the conversion factor
for the material to be analyzed.
GeoPyc 1365 Operator Manual
136-42800-01 (Rev -) — Dec 2016
C Envelope Density
C - 3