SPECIFICATIONS :
- Zero reading 0.25 division
- Spring constant 120.25 lb/inch (2.142.045 kg/cm)
- Load required to read 3.0 ton/ft2 (3kg/cm2 ) 11.250.55 lb (5.1040.249 kg)
- Load required to read 4.5 ton/ft2 (4.5kg/cm2 ) 170.85 lb (7.7130.386 kg)
- Foot Dia. 0.25 inch (6.35 mm)
The pocket penetrometer has a spring constant of 12 pounds/inch. One ton/ft interval on the scale is equivalent to 8mm. Therefore, a compressive force of 3.78 pounds on the foot is required to read 1 ton/ft. The equivalent of 3.78 pounds on a .049 in (1/4 Diameter foot) is 5.58 tons/ft. Why does the Penetrometer need this very high force to read 1 ton/ft? The penetrometer reading is taken by pushing its foot into the material to a depth of . For a depth of , the cylindrical surface area of the material to be sheared is 0.196 in, just 4 times the area of the foot. This accounts for the large value of compressive force.
The pocket penetrometer is calibrated by correlation studies relating the effective spring compression to unconfined compressive strength values determined by other methods. The pocket penetrometers are not individually calibrated; therefore, no calibration certificates are supplied with them. An error of up to division on the scale equivalent to 0.125 TSF is possible with the instrument. The data given above under specifications will be helpful for users of the instrument to check the accuracy of their units. The pocket penetrometer can be compressed to any desired reading and the corresponding applied load can be determined using a platform scale or any compression machine having a readability better than 0.5 lb (0.25 kg)
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