Humboldt H-4204 Proving Ring Penetrometer - Manual (Page 5)

Precautions
Keep the instrument vertical while taking the measurements.
Do not attempt readings higher than the capacity of the dial since this will
overstress the proving ring.
Do not withdraw the instrument by the ring but always by the rod.
Care and Adjustment
General Care
All parts of the penetrometer are plated for resistance to corrosion and should
be relatively maintenance free. The penetrometer needs little care beyond
keeping the instrument free from dirt & rust, keeping all parts tight and
frequently checking and if necessary rezeroing the instrument. Take particular
care to see that no grit is caught between the extensometer arm of the dial and
the lower mounting block.
Dial Indicator
The dial indicator is a sensitive instrument that should be protected against
water and rough usage. Never immersed it in water and wipe it dry as soon as
possible after its use in rainy weather. When transported truck, cushion the dial
by wrapping it in paper or cloth.
Mounting Block Adjustments
If either or both mounting blocks should become loosened and moved, the
entire ring assembly should be returned to the factory for calibration. Merely
readjusting and retightening these blocks may or may not return the ring to its
initial calibration and a calibration check is necessary in this case.
Cone Replacement
Considerable use of the same cone may result in a rounding of its points. This
will not affect the accuracy of the instrument necessarily, but if the base of the
cone has had excessive wear or is deformed by hard usage, the cone should be
replaced.
Proving Ring Recalibration
If the ring should have need of recalibration, services are available from
Humboldt Mfg. Company.
Special Note
In areas where the cone can be driven only through 1/2 or 1/4 of the cone
height (very high penetration resistance) with a force up to 220 pounds (safety
limit), the actual penetration resistance can be obtained by multiplying the
corresponding load reading by an appropriate factor. For example, if the cone
penetration is just 1/2 of the cone’s height, multiply the corresponding load by
4 to get the actual penetration resistance. (It is not generally recommended to
take readings at fractional cone penetrations; do so just when the penetration
reaches exactly 1/4, 1/2, etc., of the cone height).