Silicon Piezoresistive Pressure Diaphragm Encapsulation Selection Criteria
Encapsulation selection balances gel potting low cost against oil-filled cell thermal stability to control long term zero drift and field recalibration expenses.
Shore OO Hardness
Durometer Measurement
Soft elastomers and cellular plastics require a low-force measurement scale to quantify their resistance to surface indentation. The scale designated as Shore OO hardness provides this metric by using a standardized durometer equipped with a hemispherical indentor and a light spring load. This measurement ensures that soft materials can be sorted and specified without causing permanent damage to their physical structure.
Instrument Calibration
Calibrating a Shore OO durometer requires verifying both the spring force curve and the geometry of the indentor tip. The spring force must apply exactly zero point five eight Newtons of force at full scale, which is tested using a calibrated balance. The indentor diameter is verified under an optical comparator to confirm it meets the specification of two point three eight millimetres.
These calibrations are checked against reference test blocks of known hardness before each measurement campaign to maintain traceability. Any deviation in these dimensions or spring forces shifts the hardness reading, which could lead to accepting out-of-specification materials.
Indentation Drift
Indentation readings often exhibit a time-dependent decay called creep or indentation drift. When the indentor is first applied, the initial reading is higher because of the material’s viscoelastic resistance. Over a standardized period, typically fifteen seconds, the material flows around the indentor, which causes the hardness value to decrease to a stable plateau.
To ensure reproducibility, testers must use an automated operating stand that applies the force at a controlled rate and takes the reading at the exact specified time.
Material Boundary
Low-range scales are not suitable for rigid plastics or very soft gels that have no elastic recovery. For those materials, Shore A or Shore micro-scales must be used. This limitation ensures the instrument remains within its calibrated range.