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.
Zero Shift
Baseline Deviation
A measurement error occurs when the output of an instrument changes at the zero point of its scale without a corresponding change in the input variable. This zero shift typically results from thermal expansion or the mechanical aging of internal components. It appears as a constant offset across the entire measurement range and can be corrected by recalibrating the baseline.
The stability of the zero point is a primary indicator of the long term reliability of a sensor in the field.
Causal Mechanism
Variations in ambient temperature are the most frequent cause of these deviations as the internal electronics or sensing elements undergo physical changes. A zero shift may also occur if the sensor housing is subjected to torque or mounting stress during installation. These forces alter the bridge balance or the capacitance of the sensing element and create a false reading.
Proper isolation and the use of temperature compensation circuits help to minimize the impact of these external influences.
Detection Protocol
Technicians identify the error by venting the system to the atmosphere or applying a known zero reference gas.
Qualification Limit
Manufacturers specify the maximum allowable deviation over a given time period or temperature range in the product data sheet. This tolerance is verified during periodic maintenance to ensure the instrument remains within its accuracy specification. A persistent or large change in the baseline often signals the impending failure of the sensing element or a breach in the reference seal.