The operation of 'a v ib ra tin g wire strain gauge is based on the
principle th a t the n atural frequency of v ib ra tio n of a stretched
wire depends upon the force stretching the wire. One end of
wire 1 is secured to movable prism 2; the other end passes
through a hole in stationary prism 3 and is secured to tensioning
screw 4. The movable prism is linked to tensioning screw 5
at the other end of the gauge by means of spring 6. The tension
of the wire can be regulated by tu rn in g n u t 7 or n u t 8. W ire 1
passes between two pairs of pole shoes of two polarized electromagnets
9 and 10. The purpose of the electromagnets is to set
wire 1 into mechanical v ib ratio n and to convert this v ib ratio n
into electrical oscillations, which are measured in some suitable
way. In measuring elongation, the strain gauge is mounted
on the workpiece w ith the points of prisms 2 and 3 engaging
indentations in the workpiece.
$4367$SmE,M$