If the tester consistently exhibits a tendency towards a
avoids the possibility of a single rock skewing the results.
low deviation, that is more towards the 0.75 end for the
calculator or more towards a 2 out or 1 out for the
manual method, then the tester is picking up some
periodic count rather than purely random count, tester
CPN advocates statistical testing wherein the average of
repair may be required.
several test sites is used to accept or disapprove the
project. The nuclear tester is much faster than the older,
This smooth tendency is probably due to a failing filter
conventional test methods and statistical programs may
network in some supply system which would allow a
steady noise to creep into the system, a noise not
subject to the variation of a random source.
Using the CPN Random Selection Cards, (See Appendix
J) select five site locations and take one test on each
Using either of these techniques, either calculator or
location. Average the sites for a statistically valid
manual evaluation, the operator can maintain a close
evaluation of the project.
watch on his tester and can be confident that his field
work is accurate without electronic error or decay drift.
Each site must be free from major protuberances
reasonably smooth, and should be representative of the
It is not adequate to merely run the automatic standard
count and not run the periodic evaluation.
The daily automatic standard count will serve to verify
general good operation, but it will also mask minor
Using the CPN Cast Aluminum Guideplate, smooth the
variations between counts that are indicators of potential
surface, removing large stones or surface debris which
would prevent the tester from sitting flat. Any technique
of smoothing, pounding, or other flattening will be
The standard count in the automatic mode can cover up
adequate. It is impossible for the operator to pound the
erratic tendencies such as a noisy detector, or other
site so hard as to compact the site. He can only flatten
problems. The tester may appear very normal under
down the top 1/16" or so to provide a good surface.
Using a sieve, shake some native fines or sands over the
We must maintain a professional attitude about our
site to fill in any remaining air voids to remove possible
equipment and its operation at all times.
errors from surface roughness.
This means frequent checking of standard count and
The tester must rest upon native promontories, however,
with only the voids filled in. The tester must not rest
upon a "cushion" of filler material.
1-13. SITE PREPARATION
If the test site is asphaltic concrete, (AC), a coffee can
"salt shaker" with fine sand may be used to fill in the
Tests will only be as good as the quality of site
preparation. The site must be flat, free of voids, with
surface irregularities filled with native fines or sand.
The tester has a reduced bottom surface to provide the
best possible seating under adverse conditions. This
If transmission is used, the hole must be neat and
facilitates seating the tester on AC where a rubber tired
square to the surface, and protected from puffing or
roller has been used.
movement during the drilling of the transmission hole or
retraction of the drill pin.
1-14. SEATING QUALITY EXPERIMENT
It is desirable to rotate the tester 900 or more on rocky
soils to obtain the largest sample size practicable. This
An experiment can be run to test the required effort