Can a Tee Rosette Be Used for Temperature Compensation?

A half-bridge in the form of a 0-90 degree Tee rosette can be used for a uniaxial strain measurement with excellent temperature compensation, but only under specific conditions.  These conditions are:

1. A uniaxial stress state exists.

2. Poisson’s ratio is known and Poisson strains exist in reality as in Poisson’s ratio.This is pointed out since there are some situations in mechanics where Poisson strain does not exist.

3. Of course, the standard conditions for half-bridge temperature compensation must exist; both strain gage grids are the same foil type, at the same temperature, and bonded to the same material.Since a Tee rosette has both grids on the same strain gage, this condition is usually assured unless there is a very steep temperature gradient.

   This figure illustrates the strain conditions and half-bridge wiring of the Tee rosette.

   

   If those three conditions are met, then a half-bridge using a Tee rosette will provide temperature compensation along with a measurement of uniaxial strain.  The number of active arms for a half-Poisson bridge is If the readout instrumentation is scaled to indicate in microstrain using the package gage factor for the Tee rosette, then a correction to the indicated strain is needed for .  The correct axial strain is given by:

   

   Where:

   

   

   

   Note that with the Micro-Measurements P3 Strain Indicator and Recorder, as well as StrainSmart data systems, an option is available to select the half-Poisson bridge type so that data is reduced directly into axial strain.