Page 92 - Mechanical Engineers' Handbook (Volume 2)

4 The Wheatstone Bridge 81

Figure 7 Bridge excitation versus grid area for various power densities and 350- gages. (Courtesy
of Measurements Group, Inc., Raleigh, NC.)

Committee on Strain Gages (TCSG) of the Society for Experimental Mechanics (SEM). The
SEM is the premier organization in the United States involved with strain gages and exper-
imental mechanics in general. The SEM (formerly Society for Experimental Stress Analysis)
was founded by William Murray at the Massachusetts Institute of Technology. Publications
of this society include Experimental Mechanics and Experimental Techniques. A similar
European organization is the Joint British Committee for Stress Analysis, whose publication
is The Journal of Strain Analysis for Engineering Design.
By 2004, essentially the entire strain gage manufacturing capability in the United States
was consolidated by Vishay Measurements Group, corporate headquarters at Vishay Inter-
technology, Inc., 63 Lincoln Highway, Malvern, Pennsylvania 19355-2120. Its associated
website has an extensive array of in-depth articles on strain gage technology.

4 THE WHEATSTONE BRIDGE
Best transducer performance can be achieved by minimizing the strain level in the transducer
flexure. Lower strains allow increased safety without mechanical overload protection. Effec-
tive overload stops are usually troublesome to design and an added expense to make. Re-
duced strain levels almost always produce an improvement in linearity accompanied by a
reduction in the hysteresis originating in the transducer flexure material.