Civil Engineering Reference
In-Depth Information
FIGURE 1.31
Proving ring.
gauge reading is known, the proving ring can be used to measure the applied
force. Therefore, the proving ring comes with a calibration relationship, ei-
ther in a form of a linear equation or a table, that allows the user to deter-
mine the magnitude of the force based on measuring the deformation of the
proving ring. To avoid damage, it is important not to apply a force on the
proving ring higher than the capacity specified by the manufacturer. More-
over, periodic calibration of the proving ring is advisable to insure proper
measurements.
1.7.5 Load Cell
The load cell is an electronic force-measuring device used for many labora-
tory tests. In this device, strain gauges are attached to a member within the
load cell, which is subjected to either axial loading or bending. An electric
voltage is input to the load cell and an output voltage is obtained. If the re-
lation between the force and the output voltage is known, the force can eas-
ily be determined by measuring the output voltage.
Load cells are manufactured in different shapes and load capacities.
Figure 1.32(a) illustrates a tensile load cell fabricated by mounting four
strain gauges on the central region of a tension specimen. Figure 1.32(b)
shows an S-shaped load cell in which strain gauges are bonded to the cen-
tral portion and calibrated to measure the force applied on the top and bot-
tom of the load cell. Figure 1.32(c) illustrates a diaphragm strain gauge
bonded to the inside surface of an enclosure that measures the amount of
pressure applied on the load cell.
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