MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 34

FIGURE 1.24 Dial gauge.

range of measurement of the dial gauge. Dial gauges used in civil engineer-
ing material testing frequently have sensitivities ranging from 0.1 mm to
0.002 mm. The dial gauge shown in Figure 1.24 has a sensitivity of 0.001 in.
and a range of 1 in. The gauge can be “zeroed” by rotating the large scale in
order to start the reading at the current pointer position.
Dial gauges can be attached to frames or holders with different configu-
rations to measure the deformation of a certain gauge length or the relative
movement between two points. For example, the extensometer shown in
Figure 1.25 is used to measure the deformation of the gauge length of a metal
bar during the tensile test. Note that because of the extensometer configura-
tion shown in the figure, the deformation of the bar is one-half of the read-
ing indicated by the dial gauge.

1.7.2 Linear Variable Differential Transformer (LVDT)
The linear variable differential transformer (transducer), or LVDT, is an elec-
tronic device commonly used in laboratory experiments to measure small
movements or deformations of specimens. The LVDT consists of a nonmag-
netic shell and a magnetic core. The shell contains one primary and two sec-
ondary electric coils, as illustrated in Figure 1.26. An electric voltage is
input to the LVDT and an output voltage is obtained. When the core is in the
null position at the center of the shell, the output voltage is zero. When the