Ten Steps to Success

Follow these ten steps to guide you towards a successful strain gage installation.

1. Determine what temperature(s) will be encountered during the test. Operating temperatures will dictate the foil strain sensor series, adhesive, and environmental protection during the sensor selection process, as well as the type of lead wire and solder.

2. Define the anticipated elongation. Foil strain sensor types and bonding adhesives have different elongation capabilities.

3. Define the number of loading cycles. Select the sensing foil type and sensor construction that is compatible with the required strain level and number of loading cycles.

4. Select the correct gage STC number based on the test material type. If there is a temperature change during the test any thermal output of the strain sensor will be minimized/eliminated.

5. Select the active gage length. Strain gages are averaging devices and the gage length needs to be sized commensurate with any stress concentrations, if present.

6. Select the pattern based on the type of measurement. If you know the direction of the principal strain then a single linear grid will suffice. If the strain field is a known direction bi-axial strain, then a 90° tee rosette, aligned with the principal strains, is appropriate. If the strain field is unknown then a three element rosette should be used to calculate the maximum and minimum principal strains and directions in relation to grid #1.

7. Select a grid resistance appropriate for the application. This is sometimes dictated by the instrument or by stock availability (350Ω is generally preferred over 120Ω).

8. Select the desired options. Options like integral lead wires or terminals can simplify foil sensor installation or wiring.

9. After foil sensor bonding and wiring perform an electrical check to ensure the gage is wired correctly and has sufficient insulation resistance. The GIT-1300 is helpful for this evaluation.

10. Select and apply a gage protection system based on the operating environment and test duration.