The measurement of strain using resistive elements is a well established technique. An electrical resistance strain gauge consists of a conductor in the form of a resistance element attached to a thin insulating backing. To make a measurement, the strain gauge must be bonded to the component or structure under test. Since the strains experienced in most structures and components are small (μm/m), so are the resulting resistance changes in the strain gauge (μohms/ohm). To measure these very small changes, a Wheatstone Bridge is used.
In an application where the direction of principal strain is known, a single gauge with its axis lined up in this direction can be bonded to the structure to form one arm of the Wheatstone Bridge, the remaining three arms being provided by the measuring equipment. This single active gauge arrangement is known as a quarter bridge. If the principal strain direction is not known, a gauge configuration known as a rosette must be used. A rosette consists of a number of independent gauge grids – normally three – mounted on a common backing. Taking readings from a strain gauge involves the measurement of very small changes of resistance, therefore a suitable signal conditioning system is required.
Fylde also offer Dynamic Strain Measurement using the constant current system. This measures the variation of strain with time and disregards the static strain or very slowly varying strain. The constant current system uses a precise and stable constant current and provides excellent signal-to-noise ratio. This system avoids the need for bridge completions and balance required by bridge transducers. It also allows single element gauges to be connected using only a two wire twisted pair connection instead of the usual 3 wire connection.