ISO 21501-4:2018 specifies calibration and performance-verification requirements for light-scattering airborne particle counters used in clean spaces. A quality reviewer should not stop at a generic pass statement. The certificate must identify the instrument, model, serial number, nominal flow rate, size channels, method and test conditions. The tested scope should match the intended pharmaceutical use.

A certificate may be formally valid while covering only part of the operating range. If the site uses 0.5 micrometre and 5.0 micrometre channels for classification or monitoring, evidence for those channels should be understood. The reviewer should separate a tested parameter from a value stated only in a product specification.

Size-setting error or size calibration indicates how the instrument responds to reference particles around defined size thresholds. Counting efficiency compares particle detection with a reference method or instrument under controlled conditions. Size resolution describes the ability to distinguish a known particle population without excessive spreading around its nominal size.

These parameters are related but not interchangeable. Good counting efficiency at one size does not demonstrate appropriate sizing across all channels. The certificate should show actual results and acceptance criteria, not only the final conclusion.

False-count testing evaluates counts reported when suitably clean air is supplied under the defined method. Unexpected background can be associated with the optical chamber, leaks, tubing, clean-air source or electrical noise. Maximum particle concentration is also important because coincidence can cause undercounting or incorrect sizing when multiple particles cross the sensing volume together.

Sample-flow error directly affects calculated concentration because the count is divided by sampled volume. Review the nominal flow, measured result, reference standard and any as-found and as-left values. Fixed sensors using external vacuum also require field controls for tubing, vacuum and flow alarms.

The certificate should identify reference standards, calibration status, method, environmental conditions, calibration date and the responsible laboratory or technician. If adjustment was required, as-found and as-left results should be distinguishable because an out-of-tolerance as-found condition may trigger a retrospective data-impact assessment.

Calibration does not replace pre-use checks. Operators should confirm instrument condition, self-test, zero count or purge where required, flow status, tubing, power, clock, location identification and data transfer. Calibration intervals should be justified from manufacturer guidance, use frequency, transport, criticality and historical drift rather than assumed to be universally fixed.

SAO NAM is the Authorized Sales and Service Center of Particle Measuring Systems specializing in Life Science applications in Vietnam. Support may include certificate review, application assessment, calibration, preventive maintenance and troubleshooting according to the instrument and service scope.

Before releasing the instrument for use, the reviewer should connect the certificate to the approved asset record, calibration procedure, intended size channels and current configuration. Any limitation, missing channel, out-of-tolerance as-found result or unexplained adjustment should have a documented assessment. Transport after calibration, tubing changes and repairs may also require checks before use. The site should define who reviews the certificate, how discrepancies are escalated and how superseded certificates are retained. Trending calibration history can reveal gradual drift that a single pass result does not show. This controlled review turns the certificate from a purchasing document into lifecycle evidence supporting reliable cleanroom data and defensible GMP decisions.