Quantifying Water Vapor Diffusion across Elastomer Pressure Sensor Seals
Water vapor diffusion across elastomer seals causes reference cavity pressurization and dielectric drift, requiring coulometric ISO 15105-2 verification.
Dielectric Distortion
Electromagnetic Alteration
Signal interference occurs when the electric field within a sensing element is modified by external forces or material non-uniformities. Such dielectric distortion changes the capacitance or impedance of a sensor relative to its nominal factory calibration. This effect is particularly prevalent in high frequency applications where the geometry of the insulator influences the propagation of the signal.
The resulting measurement error persists until the field geometry is restored to its reference state.
Capacitance Variation
Changes in the permittivity of the surrounding medium or physical shifts in the sensor housing create unintended paths for electrical flux. In moisture probes, dielectric distortion may arise from the presence of polar contaminants that align with the applied electric field. These contaminants increase the apparent capacitance and lead to an overestimation of the moisture content.
Designing sensors with guarded electrodes helps to contain the electric field and minimize the impact of external dielectric shifts.
Frequency Sensitivity
The magnitude of the error depends on the frequency of the excitation signal and the relaxation time of the interfering molecules.
Calibration Correction
Technicians account for these variations by performing a multi point calibration that spans the expected range of environmental conditions. If the dielectric distortion is non linear, the sensor requires a complex compensation algorithm to maintain accuracy. Proper shielding and the use of low loss materials in the sensor construction provide the most effective defense against this type of interference.