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.
ISO 20485 Leak Verification
Standard Procedure
Standardized metrological protocols govern the assessment of gas leakage in sealed industrial enclosures and instrumentation. The protocol designated as ISO 20485 leak verification defines the requirements for calibrating helium leak detectors using external reference standards. This standard ensures that leak-rate measurements are comparable across different laboratories and testing facilities by specifying correct correction factors for temperature and tracer gas concentration.
Traceability Chain
Implementing this standard requires a continuous chain of calibration for the reference leaks used in testing. The reference leak is a physical device that releases a known flow rate of helium, typically calibrated by a national standards laboratory. Under ISO 20485 leak verification, the test system must undergo calibration before and after every testing sequence to account for any thermal or sensor drift.
The operator must record the ambient temperature and atmospheric pressure during each test, as these parameters affect the gas flow through the micro-channels of the leak.
Uncertainty Assessment
Calculating the total uncertainty of a leak test involves assessing the response time of the mass spectrometer and the background concentration of helium. For high-reliability electronic assemblies, the permissible leak rate has a narrow tolerance that leaves little margin for instrumentation error. Standard formulas provide the mathematical equations needed to combine these uncertainty components into a single confidence interval.
Method Boundary
Liquid leak testing methods are excluded from this protocol, which focuses exclusively on tracer gases. When testing very large volumes, the response time of the system becomes too long for this technique to be practical. That limitation necessitates alternative test setups.