Humboldt H-4204 Proving Ring Penetrometer - Manual (Page 4)

Rezeroing the Instrument
When reading has changed at any time or if any part is changed in the
penetrometer, the instrument should again be zeroed as described in the
Zeroing Instrument section above.
Operation
Be certain that the dial indicator has been set to zero position. Select the site to
be tested and clear the test location so that a flat and clean surface is available
for testing.
Hold the assembly vertically on the test location. Grasping the handle firmly,
push the cone point down into the soil at a steady uniform rate until the top of
the cone goes just below the surface.
Determine the dial indicator reading as follows:
Each subdivision has a value of one. The small dial reads from 0 to 10 with one
division being equal to one full rotation of the large dial. Each value on the small
dial has a value of 100. Thus, one complete rotation of the large dial is 100 and
is recorded as 1 on the small dial.
To determine the penetration resistance (bearing capacity) in pounds per square
inch, record the dial reading of both the inner and outer dials. Use this number
in refering to the Proving Ring Calibration Chart provided to determine the pen-
etration resistance (bearing capacity) in pounds force at the depth being tested.
In order to measure the penetration resistance at 6", 12" or other depths, push
the cone point down into the soil until the 6", 12" or other marks on the rod
just hit the surface and record the dial indicator reading. Refer to the calibration
table to read the pounds force value.
Note: An approximate resistance (bearing capacity) is obtained by dividing the
penetration load by the cone base area. The cone base area is actually 0.983
square inch. But in order to make correction for the cone soil friction, the base
area should be taken as 1 square inch. Hence the penetration load reading
in pounds is numerically equal to the penetration resistance or cone index
in pounds per square inch.
Return the dial indicator reading to zero position by pressing the release
button on the pointer stem housing. Support the release button from behind
while pressing.
In soils of very low resistance, it maybe desirable to utilize a deeper penetration.
The 6" marks or other marks, which the user may wish to scribe on the
extension, may be used as the stopping point rather than the top of the cone.
These penetration depths allow correlation with laboratory tests as well as the
standard penetration depth.