Top “Ten” Strip Sensors - Un Pour Tous, Tous Pour Un
Measuring Strain Gradients Using Strip Gages
In this iNotes Video, Mike shows an example of a strain gradient and introduces Micro-Measurements strip gages. Strip gages have up to ten small strain gages spaced at even increments and allow the user to measure and define the existing strain gradient at a location on a structure. If you would like more information about how to use strip gages, please contact a Micro-Measurements Application Engineer, Technical Sales Manager, or independent Sales Representative at firstname.lastname@example.org.
A strip gage consists of ten strain-sensitive grids mounted on a common backing. This type of gage offers a number of advantages in the study of local strain distributions and strain gradients. As an example, it is much easier, faster, and more accurate to install the ten-grid strip in a single operation than it would be to align and bond ten individual gages for the same purpose. In addition, the optical tooling employed in the manufacture of the strip gage ensures that all grids are precisely located. Grid spacing is also closer than can usually be achieved with individual gages, thus yielding better resolution of nonuniform strain fields. Overall dimensions for the complete patterns vary with the grid and solder-tab configurations. When necessary, some types of the gages can be cut to produce smaller assemblies with fewer grids. Most sizes are offered in two different versions — with all grids oriented either parallel to, or perpendicular to, the long axis of the strip. As indicated in the gage listings, several types of strip gages are designed with a common tab, or bus, connected to all grids on one side. Since this arrangement affects measurement accuracy, and may not be compatible with some instrument systems, the following information should be considered when contemplating the use of such gages.
COMMON-TAB STRIP GAGES
Common-tab strip gages are generally not compatible with multi-channel instruments, particularly those incorporating individual bridge excitation supplies. When used with this type of instrumentation, they will yield significantly lower accuracy than a strip gage with electrically independent grids. Effects of the common tab include excessive initial unbalance of the Wheatstone bridge circuit (possibly beyond the balance range of the instrumentation), circulating currents when the grids are powered simultaneously from a common power supply, loss of leadwire temperature compensation, and reduced accuracy in shunt calibration. All of these effects should be carefully considered by the user before selecting strip gages with common tabs. Where greatest accuracy is required, strip gages with electrically independent grids should be employed, or common-tab strip gages may be used with single-channel instruments in conjunction with a switch and balance unit.