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.Industry Standards ISO 11171

  • 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