Statistical Acceptance Sampling for Incoming Transducer Lot Quality Audits
Variable acceptance sampling under ANSI ASQ Z1.9 reduces sample size by 70 percent while enforcing strict consumer risk bounds on transducer lot audits.
Strain Gauge Creep
Unintended Drift
Signal fluctuation in a sensor while the applied load remains constant. Strain gauge creep is caused by the viscoelastic behavior of the adhesive and the backing material used to mount the gauge. It appears as a slow decrease or increase in the measured strain even though the physical deformation has not changed.
Adhesive Influence
Polymer resins used for bonding the sensor to the surface tend to relax under stress. Strain gauge creep occurs as the bond layer slowly yields, allowing the gauge grid to contract independently of the substrate. The rate of this movement is dependent on the temperature and the thickness of the adhesive.
Selecting the correct bonding agent is essential for measurements.
Compensation Method
Manufacturers design gauges with specific grid geometries to counteract the relaxation of the glue. Strain gauge creep can be minimized by matching the gauge characteristics to the properties of the installation surface. In some cases, the sensor is designed to creep in the opposite direction of the adhesive to cancel out the error.
This ensures a stable reading over long periods.
Verification Protocol
Long term load tests are conducted to quantify the drift rate of the sensor system. Strain gauge creep is measured by applying a known weight to a load cell and monitoring the output for several hours. The resulting data is used to set the accuracy specifications for the instrument.
Understanding this behavior prevents errors in structural health monitoring.