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iG l a fr.cI on reducer (an oversized collar) to be welded onto the push pipe above the probe in order to limit the build-up of pipe-soil friction. With the larger probe, no friction _ reducer is needed because the probe diameter is larger than the push pipe diameter, and thus the probe itself acts as a friction reducer. 2.1.4 Data Acquf_141on The millivolt output signals from the electric friction cons are amplified, converted to digital data, and translated to appropriate measurement units by means of an on-board computerized data acquisition systern (OAS). A 12-bit OAS analog-to cligital converter was used with a programmable gain amplification capability to enhance the lower range measurement sensitivity. A depth encoder,which is mechanically triggered by the downward movement of the electric friction cone probe' sends pulses to the OAS, instructing it to record the data as a function of the penetrated depth. An automatic depth adjustment is made to the sleeve friction data to compensate for the vertical offset of approximately ':2 cm (5 in) between the cone tip and friction sleeve center. Cone tip resistances can range from less than 2 tons/ft2 in very soft clays to over 700 tons/ft2 in dense granular soils or heavily overconsolidated or cemented materials. Sleeve friction values are usually less than 10 percent of the cone tip resistance value. To maintain enough measurement accuracy in soft soils, digital increments of 0.1 ton/ft2 in the cone tip resistance measurements were maintained at the lower end of the measurement range, where sensitivity is most criticai. Negative cone tip and sleeve friction readings, while generally not expected, are recordable in order to - accurately monitor the zero-load outputs of the electric friction cone probe for quality control purposes. Piezocone pore pressures can range from about -1 ton/ft2 to over 36 tons/ft2. Pore pressures over 36 tons/ft2 (500 psi) can seldom be reliably measured because of the limited capacity of the built-in pore pressure transducer. 5 i~