Proving Ring





The Proving Ring Penetrometer is a 30 degree cone penetrometer used to determine the bearing capacity of subgrades or to measure soil compaction. The penetrometer also serves as a rapid means of determining the penetration resistance of soil in shallow exploration work.


  1. The dial indicator set to zero position.
  2. The test location should be flat and clean surface.
  3. Hold the assembly vertically on the test location.
  4. 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.
  5. 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 referring to the Proving Ring Calibration Chart provided to determine the penetration resistance (bearing capacity) in pounds force at the depth being tested.
  6. 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.

Equipment Specifications

Model no. : Humboldt (H-4204)
Proving Ring : 220 lb. (99.79 kg)
Dial Indicator : With continuous graduations,revolution Counter and brake
Shaft : 3/4″ (19mm) dia. x 18″ LG. (457mm); graduated at 6” (152mm) intervals
Extension Rod : 3/4″ (19mm) dia. x 36″ LG. (914mm) graduated at 6″ (152mm) intervals
Cone : 30 degree; 1 sq. in.
Handle : Cast Aluminum
Weight : Net 12 lbs. (5.4 kg)