Nominal Efficiency

Canonical Definition

A non-standardised efficiency rating indicating that a filter removes a stated percentage of particles at a stated size under single-pass conditions, without defining the specific test method used. Unlike absolute efficiency (ISO 16889 multi-pass), nominal efficiency ratings are not comparable across manufacturers because test conditions vary. Nominal ratings are not used in ELIMFILTERS engineering documentation; all efficiency claims reference ISO 16889 Beta ratio.

Engineering Context

Nominal efficiency appears frequently in commodity filter datasheets as "90% at 10 micron" or similar claims. Because the test method is unspecified, two filters both rated "90% nominal at 10 µm" may have actual efficiencies ranging from 50% to 95% under identical real-world conditions. Use Beta ratio (ISO 16889) for accurate performance comparisons.

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