Reducing Variability in Multi-Pass Filter Test Results Among Laboratories

In 1999, three new ground-breaking hydraulic filter test standards were adopted: ISO 11171 provides NIST (National Institute of Standards and Technology) traceable calibration of automatic particle counters (APCs); ISO 11943 establishes procedures for calibrating on-line particle counters; and ISO 16889 updates the multi-pass filter test method. Together, these standards ensure the generation of meaningful, reproducible multi-pass filter data and, for the first time, provide NIST traceability for particle size data obtained using APCs. In the global marketplace where data may be generated by different laboratories, personnel and/or equipment, companies face special challenges in obtaining consistent, quality filter test results. This paper addresses three questions: (1) what are significant differences in filter performance data, (2) what are the sources of inter-laboratory variability, and (3) what can be done to reduce variability.