MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 36

Riley 1991). In general, very sensitive LVDTs have small linear ranges,
whereas LVDTs with greater linear ranges are less sensitive. The sensitivity
and the linear range needed depend on the accuracy and the amount of dis-
placement required for the measurement.
Before use, the LVDT must be calibrated to determine the relation be-
tween the output voltage and the displacement. A calibration device con-
sisting of a micrometer, a voltmeter, and a holder is used to calibrate the
LVDT, as shown in Figure 1.27.
The shell and the core of the LVDT can be either separate or attached in
a spring-loaded arrangement (Figure 1.28). When the former type is used, a
nonmagnetic threaded connecting rod is attached to the core used to attach
the LVDT to the measured object. In either case, to measure the relative
movement between two points, the core is attached to one point and the
shell is attached to the other point. When the distance between the two
points changes, the core position changes relative to the shell, proportional-
ly altering the output voltage. Figure 1.29 shows an extensometer with an

Connecting rod

LVDT Micrometer

FIGURE 1.27 LVDT calibration device.

(a) (b)

FIGURE 1.28 Types of LVDT: (a) non-spring loaded (core and connecting
rod taken out of the shell), and (b) spring loaded (core and connecting rod inside
the shell).