purchased for geotechnical engineering laboratories since AC signal conditioning is difficult and AC noise is often encountered Ac when AC LVDTs are used in the laboratory. With LVDTs. it is always recommended that a dial gage be used in series in or parallel in the measuring system to provide a cross-check of measured displacement values as well as a backup system should the LVDT fail. Spring-loaded LVDTs are often convenient to mount and may be used if the spring force is not so large that it prevents proper measurement of other parameters such as load values. Pore water pressures are measured with pore water pressure transducers. which are generally of the strain gage or solid sat type. outputs of such devices are on the order of 2 to 100 mv volt of excitation full scale. It is important that the per transducer be stiff enough to accurately monitor the pore pressure response of the specimen. To achieve reliable measurements it is recommended that pore water pressure transducer volume changes not exceed 2.5 x 10-6 cm3/k Pa (1.0 x 10-6 in. 3 psi). Only small-displacement. small-volume transducers are able to meet this specification. Additional transducers are sometimes required for specific test procedures. To cite just two examples. clip gages are used for measuring lateral displacements and rotational LVDTs are used to masurc torsional displacements.