Stability Degradation
Continuous output bias changes over time alter transducer baseline calibration independently of applied process pressure. Capacitive pressure sensor drift occurs when mechanical relaxation of diaphragm materials or contamination of internal dielectric cavities shifts the reference zero. The resulting bias shifts the calculated pressure reading away from true physical values over months of continuous service.
Standard recalibration routines restore zero accuracy but do not stop underlying structural creep in internal components.
Electrode Displacement
Sub-nanometer shifts in electrode gap distance produce measurable zero shifts due to the inverse relationship between capacitance and separation distance. Mechanical strain relief in welded housing assemblies slowly changes initial electrode spacing under sustained line pressure. Silicon micro-machined structures display lower mechanical creep than welded stainless steel diaphragms.
Thermal stress cycles accelerate structural relaxation, making initial burn-in testing essential for long-term stability.
Dielectric Alteration
Ingress of polar molecules like water vapor into internal sensing cavities modifies the dielectric constant of the gap space. Even trace amounts of moisture elevate cavity permittivity, generating positive baseline zero shifts. Hermetic sealing under vacuum or dry nitrogen purging eliminates atmospheric humidity interference inside the cavity.
Verification Method
Periodic reference pressure application confirms whether total output changes stem from zero shift or span change. Bench testing against primary pressure standards isolates sensor output changes from electronic signal conditioning errors.
