Silicon Pressure Cell Fill Oil Volume Verification Methods
Confirm fill oil volume using pre- and post-injection micro-gravimetric mass checks combined with non-contact laser interferometric diaphragm dome profiling.
Vacuum Oil Filling
Assembly Process
Industrial fabrication of sealed sensors requires the complete evacuation of air from the internal cavity before fluid injection. During vacuum oil filling, the pressure transmitter housing is subjected to a deep vacuum to draw out all gases. This process is critical for producing oil-filled capillary lines and pressure capsules.
It prevents the formation of bubbles that could compromise pressure transmission.
Air Removal
Incomplete evacuation leads to gaseous voids that remain inside the fluid channel. Because the presence of air increases the compressibility of the fill medium, vacuum oil filling must be maintained at pressures below one millibar for a prolonged period. This extraction is monitored by a vacuum gauge to ensure that all outgassing has ceased.
The subsequent fluid injection is carried out under the same vacuum to prevent re-introduction of gas.
Metrological Quality
Sensor accuracy depends on the high stiffness of the fluid column. When vacuum oil filling is done correctly, the sensor maintains high frequency response and low temperature dependence. This calibration is verified by testing the zero point of the transmitter across a wide temperature range.
Any residual air would cause a non-linear shift in the pressure readings due to thermal expansion of the bubbles.
Sealed Design
Hermetic sealing is the final step, where the fill port is welded or pinched off while the fluid is under pressure. This secure closure prevents the ingress of atmospheric air and retains the oil for the entire service life of the transmitter.