24
Appendix 1
Determining When to
Replace Cone
Repeated soil sampling will wear down the metal cone.
Periodically measure the diameter of the cone using a
dial caliper or micrometer that allows you 0.001-inch
measurements.
Place the caliper/micrometer on the shoulder of the
cone. Figure 1 shows the proper placement and Figure
2 the layout of the shoulder.
Figure 1
Shoulder
Figure 2
The determination as to when to replace the cone will
depend on how the user is applying the meter.
If you are using the meter to get absolute compaction
readings, replace the cone when there is a “wear factor”
of 3%. Three percent wear affects the cone index
measurements by 5%. A new cone has a diameter of
0.505“, see Figure 3. When the cone diameter reaches
0.490“ (3% wear), replace the cone.
5
An ultrasonic sensor lo-
cated at the base of the
meter is used to measure
the depth of penetration.
The field of view ex-
tends about 30
o
from the
shaft. The sensor meas-
ures distance by emit-
ting a sound wave and
measuring
the
travel
time of the first reflected
wave. Usually, this first
reflection
will
come
from the ground just ad-
jacent to the shaft.
However, if an object
with a surface oriented
toward the sensor is
within the field of view,
an
erroneous
depth
measurement may be
made. This can lead to
depth error messages (see Warning Messages p. 18). If
possible, try to remove the object and/or smooth the sur-
face. Repositioning your feet and knees may also elimi-
nate these errors. If the problem persists, use a flat target
surface with a hole slightly large than the diameter of the
cone to test the depth sensor and, if necessary, to take
measurements. This target should be about 1 foot wide
and can be made out of cardboard or something sturdier if
more durability is required. To test the sensor, lay the tar-
get on the ground and place the shaft in the hole. Have
another person slowly raise the target while you verify the
meter is incrementing the depth.
Depth
Sensor
Depth Sensor