Annual Drift Extrapolated from a Four Week Test Bench
Linear annual drift extrapolation from four-week test bench data produces severe forecast errors by ignoring logarithmic relaxation and test fixture noise floors.
Logarithmic Relaxation
Structural Stability
Time-dependent decay in the internal stress of a material follows a non-linear path where the rate of change decreases as time progresses. Many precision components exhibit logarithmic relaxation after they are formed or machined into a final shape. This behavior means that most of the dimensional change occurs shortly after manufacturing.
Material Creep
Atoms within a crystal lattice or molecules in a polymer chain slowly rearrange themselves to reach a lower energy state. In the context of logarithmic relaxation, the displacement is proportional to the logarithm of the elapsed time. This specific curve is common in spring materials and high-precision mechanical supports.
Sensor Drift
Load cells and pressure transducers often show a shift in their zero point due to the slow movement of their internal structures. When logarithmic relaxation affects a sensing element, the output signal changes even if the physical input remains constant. Designers often pre-age these components to reach the flatter part of the decay curve.
Calibration Interval
Maintaining accuracy requires understanding how quickly a device deviates from its reference value. Because logarithmic relaxation slows down over months and years, a sensor becomes more stable as it ages. The timing of the first calibration check is critical.