Piezoresistive Diaphragm Calibration Traceability and Proof Pressure Bounds
Calibration traceability requires unbroken deadweight references, while exceeding proof pressure bounds causes unrecoverable zero drift from metallic yielding.
Thin Plate Deflection
Mechanical Deformation
Mathematical modeling of the displacement of a flat boundary under uniform pressure relates the applied load to the resulting mechanical strain. In the design of capacitive and piezoresistive pressure sensors, thin plate deflection governs the sensitivity and linearity of the transducer.
Sensing Mechanism
The magnitude of the displacement is inversely proportional to the cube of the plate thickness and directly proportional to the applied pressure. As the plate deforms, the embedded strain gauges measure the surface stress or the capacitance of the gap changes. This mechanical response must remain purely elastic to prevent hysteresis and permanent zero-point shift.
Uncertainty Assessment
Non-linear effects can arise if the deflection exceeds a small fraction of the plate thickness. These non-linearities must be compensated by calibration algorithms to maintain accuracy.
Design Constraint
Material selection is constrained by the need for high tensile strength and low thermal expansion to minimize environmental sensitivity. The fabrication process must control the plate thickness with sub-micron precision to avoid unit-to-unit variation in sensitivity. Any variation in the thickness from the nominal design value shifts the calibration curve and requires custom adjustments for each sensor.
Therefore, automated optical inspection of the diaphragms is conducted before the final assembly of the pressure sensors.