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.
Gas Solubility Outgassing
Fluid Release
The release of dissolved gases from a liquid medium occurs when the surrounding pressure drops below the saturation threshold of the fluid. This gas solubility outgassing can create bubbles within the filled cavity of a pressure sensor, altering its mechanical behavior. This release must be prevented to ensure the transmission of pressure remains direct and uncorrupted.
Pressure Effects
When pressure is reduced, the dissolved air or nitrogen forms micro-bubbles that are highly compressible. These bubbles act like springs, absorbing a portion of the applied pressure instead of transmitting it directly to the internal silicon chip. This compressibility reduces the sensitivity of the sensor and introduces a non-linear response that cannot be easily compensated for.
Sensor Drift
The presence of gas bubbles inside the transmitter housing leads to significant errors in zero-point stability and span accuracy. As the temperature rises, the bubbles expand and apply a force to the diaphragm, creating a false reading. This thermal drift can make the sensor unsuitable for precise industrial measurements.
Degassing Process
Manufacturers prevent this issue by subjecting the fill fluid to a rigorous vacuum degassing process before it is injected into the sensor. This process removes almost all dissolved gases, ensuring the oil remains a pure, incompressible liquid. Testing the completed sensor under vacuum confirms that no residual gas remains to threaten the long-term stability of the device, and that it can operate reliably in low-pressure and vacuum applications without the risk of bubble formation.