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.
Silicone Oil Fill Fluid
Force Transmission
An incompressible synthetic liquid transmits applied pressure from an external isolating diaphragm to an internal sensing element. Utilizing silicone oil fill fluid in pressure transmitters ensures that the deflection of the metal diaphragm is instantly and accurately transferred to the silicon chip. This fluid must be highly pure and free of dissolved gases to prevent any loss of sensitivity.
Viscosity Properties
The performance of the transmitter depends on the viscosity of the fluid remaining relatively constant across the operating temperature range. If the viscosity increases too much at low temperatures, the sensor’s response time will become unacceptably slow. Choosing the correct grade of fluid ensures that the instrument responds quickly and accurately in both hot and cold environments, and it prevents the dynamic response from lagging during rapid changes in process flow.
High Temperature
In high-temperature applications, the fluid must resist thermal expansion to prevent generating an artificial back-force on the diaphragm. When the fluid expands, it can cause a zero shift that degrades the accuracy of the measurement. Specialized fluids are formulated to minimize this expansion and maintain stable performance at elevated temperatures.
Stability Verification
Manufacturers test the stability of the filled sensor by cycling it through extreme temperatures and monitoring the output for drift. Any unexpected change in pressure indicates the presence of air or fluid degradation. This testing ensures that only sensors with stable fill fluids are shipped to customers, maintaining the high quality of the product line.