Civil Engineering Reference
In-Depth Information
FIGURE 1.25
Extensometer with
a dial gauge.
core is moved slightly in one direction, an output voltage is obtained. Dis-
placing the core in the opposite direction produces an output voltage with
the opposite sign. The relationship between the core position and the out-
put voltage is linear within a certain range determined by the manufacturer.
If this relation is known, the displacement can be determined by measuring
the output voltage using a voltmeter or a readout device. LVDTs can measure
both static and dynamic movements.
LVDTs vary widely in sensitivity and range. The sensitivity of commer-
cially available LVDTs ranges from 0.003 to 0.25 V/mm (0.08 to 6.3 V/in.) of
displacement per volt of excitation. Normal excitation supplied to the pri-
mary coil is 3 Vac with a frequency ranging from 50 Hz to 10 kHz. If 3 V is
used, the most sensitive LVDTs provide an output of 18.9 mV/mm (Dally and
Secondary
coil
Primary
coil
Secondary
coil
Secondary
coil
Output
voltage
Input
voltage
Primary
coil
Core
Secondary
coil
FIGURE 1.26
LVDT circuit.
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