Quantifying Production Line Tooling Calibration Drift and Stoppage Costs
Tooling drift costs combine line stoppage labor, scrapped assemblies, and re-qualification fees, demanding automated inline sensor verification.
Strain Gage Creep
Meaning
A gradual change in the output signal of a resistive transducer under a constant, sustained load introduces measurement drift over time. This strain gage creep occurs when the organic adhesive layer or the carrier backing material undergoes viscoelastic deformation under stress. The strain experienced by the foil grid decreases even though the external load on the specimen remains constant.
Engineers must characterize this behavior to separate material deformation from sensor drift during long-term monitoring.
Adhesive Behavior
Viscoelastic behavior in the adhesive layer is the primary cause of signal decay under prolonged static load. The high shear stresses at the ends of the grid cause the polymer chains to slide past one another. This sliding action decreases the strain transferred from the test specimen to the sensing foil.
Choosing an adhesive with a high glass transition temperature minimizes the sliding effect at elevated operating temperatures.
Signal Compensation
Mathematical correction algorithms in the data acquisition system can compensate for the predictable portion of the signal drift. The system estimates the decay based on time under load and operating temperature. This corrected value prevents the control system from triggering false alarms during continuous loading cycles.
Calibration routines also periodically reset the baseline to restore measurement accuracy.
Material Selection
Epoxy-phenolic carriers and rigid adhesives exhibit the lowest creep rates during static measurements. They provide stable long-term data.