I. Introduction: Why Sampling Flow Rate Matters

In high-cleanliness industries (e.g., semiconductor manufacturing, pharmaceutical production), particle counters are core equipment for ensuring production environment compliance. Sampling flow rate—a key parameter—directly determines monitoring data reliability and environmental representat. Understanding its mechanism is critical for accurately evaluating cleanroom quality.

II. Technical Principles & International Standards for Sampling Flow Rate

1. Light Scattering Mechanism & Flow Rate Correlation

The technical principle of sampling flow rate is based on the light scattering counting mechanism. Its core is correlating particle counting efficiency with environmental representat via sampling volume per unit time:

Larger flow rate: Collects more air per unit time → higher detection efficiency, suitable for rapid overall environmental status assessment.

Smaller flow rate: Ideal for long-term local monitoring or low-concentration environments.

2. ISO Standards for Flow Rate Specifications

International standards define clear flow rate ranges:

ISO 21501-4: Requires instruments with flow control systems to have a deviation ≤±5%.

ISO 14644-1: Mandates a flow rate ≥28.3L/min for detecting large particles (≥5μm); condensation nucleus laser particle counters are required for small particles (<0.1μm).

These form a standard system covering different particle sizes and scenarios.

III. Impact of Sampling Flow Rate on Monitoring Results

Sampling flow rate affects results in three key dimensions:

1. Concentration Measurement Accuracy

Concentration is calculated as "number of particles / sampling volume."

Lower flow rate: Underestimates sampling volume → concentration result lower than the true value.

Higher flow rate: Overestimates concentration.

Example: A 28.3L/min instrument with a 12% actual deviation leads to a 12% concentration error—critical for pharmaceutical sterile environment assessment.

2. Particle Size Distribution Measurement

Affected by the coupling of particle inertia and flow rate:

High flow rate (28.3L/min): Reduces sedimentation loss of large particles (≥5μm).

Low flow rate (2.83L/min): Requires isokinetic sampling to avoid missing small particles

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Note: Non-isokinetic sampling causes significant errors for particles ≥5μm but minimal impact for particles <2μm.

3. Temporal Representativeness

Depends on balancing flow rate and sampling duration:

Large flow rate: Rapidly responds to environmental fluctuations → suitable for dynamic monitoring.

Small flow rate: Requires extended sampling time for data stability.

Example: A 2.83L/min device needs 10 minutes to collect 28.3L of air to smooth instantaneous interference.

IV. Standardized Application: Calibration, Selection, and Operation

A "three-in-one" strategy ensures reliable results:

1. Calibration Requirements

Conduct calibration every 6–12 months per ISO 21501-4.

Use SI-traceable standard particles to verify flow rate accuracy and counting efficiency.

2. Equipment Selection Guidelines

28.3L/min: Suitable for pharmaceutical sterile workshops.

2.83L/min: Ideal for electronics industry local monitoring.

Small flow rates: Required for special scenarios (e.g., biological safety cabinets) to reduce airflow interference.

3. Operational Best Practices

Sampling port: 1.2m above ground, ≥0.5m from obstacles.

Sampling pipe: Stainless steel, length ≤1.5m; clean quarterly to avoid particle loss/contamination.

V. Conclusion: Sampling Flow Rate – The Core of Reliable Monitoring

Sampling flow rate is the critical link connecting instrument performance and environmental authenticity. By adhering to standards and scientifically adapting flow rate parameters, particle counters provide reliable data for cleanroom quality control—supporting product quality and safety in high-cleanliness industries. Learn more about Lumeley's particle counters~

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