The Evolution of ISO 11171
ISO 11171:1999 and subsequent revisions have introduced a number of modifications to help clarify the steps required to minimize variability.
- Automated liquid particle counter (APC) definition added (1999 )
- How to construct a calibration curve guidance introduced
- Additional direction on detecting APC calibration changes provided
- Defined sequence of calibration steps no longer mandated
- Acceptable APC system resolution increased from 10% to 15%
- At least 5,000 particles must be counted for statistically valid data (by channel setting)
- ISO UFTD verification no longer acceptable. NIST RM 8632 dust mandated for verification of counting accuracy
- 0% sample analysis replaced with regression equation for coincidence error (B.7)
- Additional detail to distinguish between fixed and adjustable flow rate bottle samplers (Annex C)
- Fixed flow rate instruments require validation of capability to consistently deliver a constant flow rate within 3%
- Adjustable flow rate instruments require working flow rate and flow rate limits be determined AND validation of capability to consistently deliver a constant flow rate within 3%
- ISO 11171:2016 calibration procedure has not changed. Tools have been provided to enable proper interpretation of results. Specifics include:
- Changes should lead to fewer failures to meet cleanliness/product specs
- Standardized method for distinguishing SRM 2806a from SRM 2806b results
- Defines mathematical relationship between μm(b) and μm(c) sizes
- Historical data, standards and specs referring to μm(c) are unaffected provided they reference most ISO 11171 Standard (e.g., pre-2016 standards, specs use μm(c) and can be used with ISO 11171:2016)
- Although no direct mathematical conversion for μm(b)-counts-to-μm(c)-counts, sizes can be converted
- – μm(c) if SRM 2806a calibration
- – μm(c) if SRM 2806b calibration with sizes converted to μm(c)
- – μm(b) if SRM 2806b calibration
