Encapsulation Instability
Gradual changes in the output signal of a protected transducer result from mechanical stresses exerted by the surrounding potting compound. Potted sensor drift often appears after thermal cycling as the resin expands or contracts at a different rate than the electronic components. This mismatch places pressure on sensitive elements like resistors or microchips.
The effect is most pronounced in high-precision analog circuitry.
Material Selection
Hardness and the coefficient of thermal expansion of the epoxy or silicone determine the severity of the signal shift. When potted sensor drift occurs, it is frequently linked to the glass transition temperature of the polymer. Above this temperature, the physical properties of the material change rapidly.
Soft gels are sometimes used to decouple the electronics from the rigid outer housing.
Extended Stability
Moisture absorption into the potting material can lead to swelling and altered dielectric properties over several months. This form of potted sensor drift is difficult to distinguish from electronic component aging without controlled environmental testing. Regular recalibration in the field identifies the magnitude of the error.
High-quality resins are formulated to minimize shrinkage during the curing process.
Mitigation Strategy
Burn-in periods and thermal conditioning help to stabilize the mechanical interface before the final calibration of the unit.
