PMX offers a suitable glyph for stress analysis using rosette SGs. The block returns the two principal stresses, the angle of the first principal stress, the maximum shear stress and the von Mises reference stress. In this example three fixed resistors are added to a rosette to form half bridges. The temperature compensation of the rosette SG can be based on either the rosette temperature or a reference SG that is mounted stress-free.
The rosette temperature is provided by an external Pt100 module in this case (for example from LKM electronic) for a 10-V input of the PX401 card. The polynomial for the rosette data sheet returns the temperature-dependent apparent strain with which compensation is performed.
The actual stress calculation takes place in the "SG stress analysis" glyph. It requires the following inputs:
epsA_raw... epsB_raw are the raw values of the rosette strains. The unit must be μm/m. (Note: 0°/60°/120° rosettes are currently not supported.)
The temperature compensation SG returns the reference stress. If this option is not used, as in this case, the input should be continuously connected with 0.
The apparent strain eps_p is returned by the temperature polynomial in μm/m. (If it is not used, this input should also be continuously connected with 0.)
The modulus of elasticity and transverse contraction index should be set as parameters (in this case for aluminum). The unit of measure for the modulus of elasticity is user-defined. The calculated outputs have the unit of the modulus of elasticity.
The block returns the following quantities:
Temperature response: The range -30° ... +70°C is mapped to 0 ... 10 V.
To calculate the apparent strain eps_p, the polynomial coefficients are transferred from the rosette data sheet to the "Polynomial" block:
Scaling of the rosette inputs is some what more complicated. The gauge factor is given and strain in μm/m is required.
The first scaling point is simple: 0 mV/V corresponds to 0 μm/m.
The second point is specified at a misalignment of 1 mV/V.
The actual gauge factors are listed on the rosette data sheet. In this case the setting for k= 2.08, 2.10 and 2.12:
The output values can be reset with the "Reset" button or by a digital signal that is defined under "Reset by".
This makes it possible to restore the zero point.
These examples are simply for the purpose of illustration. They cannot be used as the basis for any warranty or liability claims.