Oil Cavity Volumetric Expansion Mitigation in Piezoresistive Transducers
Minimizing fluid volume below five microliters and matching diaphragm spring rate eliminates thermal zero shift in isolated piezoresistive pressure cells.
Henrys Law Fluid Degas
Gas Extraction
The process of removing dissolved gases from a liquid relies on the principle that gas solubility is directly proportional to its partial pressure above the liquid. Applying henrys law fluid degas to the sensor fill fluid involves subjecting the oil to a high vacuum to force the dissolved air to escape. This extraction is critical for producing stable and reliable pressure transmitters.
Pressure Saturation
When the fill fluid is exposed to a vacuum, the partial pressure of the gas above the liquid falls to near zero, causing the dissolved gas to leave the solution. If this step is bypassed, the gas will eventually form bubbles when the transmitter experiences high temperatures or low operating pressures. These bubbles compress under load, causing a significant loss of measurement accuracy.
Cavity Filling
Once the fluid is fully degassed, it must be transferred into the sensor cavity under a continuous vacuum to prevent any re-absorption of air. This process ensures that the cavity is filled entirely with incompressible liquid, with no trapped micro-bubbles at the corners. Any remaining air would dissolve back into the fluid and then outgas during operation, leading to drift and non-linear behavior under temperature changes.
This careful filling sequence is verified by measuring the frequency response of the sensor after sealing.
Metrological Benefit
Removing dissolved gases ensures that the sensor has a highly linear response and excellent zero-point stability over its operating life. Because the fluid remains fully incompressible, it transmits pressure changes instantly and accurately to the internal silicon chip. This predictability allows the sensor to meet the highest accuracy classifications in industrial applications.