Quantifying Long Term Sensor Drift Driven by Viscoelastic Strain Redistribution
Viscoelastic stress relaxation in packaging adhesives redistributes mounting strains over time, driving zero drift that requires thermal pre-aging to stabilize.
Microstrain Drift
Sensor Instability
A gradual change in the zero-point output of a strain gauge occurs over time without any change in the applied mechanical load. This slow, unwanted shift is termed microstrain drift and directly limits the long-term accuracy of high-precision structural health monitoring systems. Standard strain sensors must resolve changes of less than one part per million, making them highly susceptible to this form of instability.
Sensor datasheets quantify this factor as a rate of change per thousand hours of continuous operation.
Physical Cause
Relieving of internal stresses within the gauge backing material or the adhesive layer can cause the grid to deform slightly. This slow physical relaxation produces a false signal that the conditioning electronics interpret as real mechanical strain. Microstrain drift is particularly pronounced in newly installed sensors that have not undergone thermal stabilization.
Environmental Influence
Moisture absorption by the protective coating or the adhesive matrix swells the polymer, which transfers a spurious strain to the sensing element. Since microstrain drift is also driven by temperature fluctuations, compensation resistors or dummy gauges are integrated into the Wheatstone bridge circuit to balance out these thermal offsets. Unprotected sensors operating in humid outdoor environments exhibit rapid drift rates that obscure the actual mechanical load profiles.
In contrast, hermetically sealed metallic enclosures protect the sensor from environmental humidity to stabilize the baseline.
Calibration Protocol
Periodic baseline checks and offset adjustments are necessary to maintain the integrity of long-term structural measurements. Specialized field calibration procedures isolate microstrain drift by temporarily relieving the load or using reference transducers to reset the null point. Technicians apply these corrections during scheduled maintenance intervals to prevent cumulative errors from triggering false alarms.