A short pre-use check can detect expired calibration, low battery, incorrect location, damaged tubing, clock error, abnormal zero count or flow alarms before the instrument enters a controlled area. Seven minutes is a suggested operating rhythm, not an ISO or manufacturer requirement. The approved site procedure and the specific instrument define the actual steps and acceptance criteria.

Do not release an instrument when identification or calibration is invalid, zero count remains unacceptable after permitted troubleshooting, flow alarms recur, probe or tubing is damaged, the clock is uncontrolled, or records cannot be stored and traced.

Confirm model, serial number, asset ID, calibration label and due date. Inspect housing, screen, ports, probe, tubing and connectors for impact, moisture or chemical residue. Verify battery capacity for the planned route and contingency time, as well as storage and data-transfer availability.

Check date, time, timezone, user login, area, room, location, batch and recipe. A correct particle result assigned to the wrong location is a data-integrity problem that may be difficult to repair later.

Install the zero-count filter, purge and run the test according to the model and SOP. If it fails, check connections, filter, tubing and environment. Do not repeat indefinitely or subtract background without an approved method. Preserve failed records and actions.

Confirm self-test, actual flow and alarm status. Sample concentration depends on sampled volume, so unstable or low flow can invalidate the result. Probe orientation, tubing length, bends and cleanliness should match the evaluated configuration.

Review completed locations, sample volume, alarms and invalid runs. Record repeat measurements and reasons without deleting failed records. Clean the exterior and sampling assembly using compatible approved methods. Transfer data, confirm location and batch mapping, charge batteries and document handover condition.

Pre-use checks do not replace ISO 21501-4 calibration, and current calibration does not replace daily condition and configuration checks. SAO NAM is the Authorized Sales and Service Center of Particle Measuring Systems specializing in Life Science applications in Vietnam. Support may include SOP review, training, calibration, preventive maintenance and troubleshooting according to service scope.

The checklist should be short enough for routine use but specific enough that two trained operators reach the same decision. Use defined evidence such as a displayed flow status, retained zero-count record, inspected tubing and confirmed location rather than vague statements such as machine looks normal. Supervisors can periodically observe execution and review whether operators skip steps under time pressure. Recurrent zero or flow problems should be trended by instrument and configuration. A checklist that repeatedly identifies the same issue should trigger maintenance or process improvement, not simply more signatures. When models or accessories change, revise the checklist through change control and train users before the new configuration enters routine cleanroom work. Retain completed checks when required by the site quality system and approved record-retention procedure when applicable.