In industries with extremely high cleanliness requirements such as semiconductor manufacturing and pharmaceutical production, particle counters are core equipment to ensure the compliance of production environments. As a key parameter, sampling flow rate directly determines the reliability of monitoring data and environmental representativeness. A deep understanding of the mechanism of sampling flow rate is of great significance for accurately evaluating the environmental quality of cleanrooms.

The technical principle of sampling flow rate is based on the light scattering counting mechanism. Its core is to correlate particle counting efficiency with environmental representativeness through the sampling volume per unit time. A larger flow rate means more air volume collected per unit time, resulting in higher detection efficiency, which is suitable for scenarios requiring rapid acquisition of overall environmental status; a smaller flow rate is suitable for long-term monitoring of local areas or low-concentration environments. International standards have clear specifications for flow rate ranges: ISO 21501-4 requires that the deviation of instruments with flow control systems should be ≤±5%; ISO 14644-1 stipulates that a flow rate of ≥28.3L/min must be used for detecting large particles (≥5μm), and condensation nucleus laser particle counters are required for detecting small particles (<0.1μm), forming a flow rate standard system covering different particle sizes and scenarios.

The impact of sampling flow rate on monitoring results is reflected in three dimensions. Firstly, the accuracy of concentration measurement is directly affected by flow rate deviation. The concentration calculation formula is "number of particles / sampling volume". A lower flow rate will lead to an underestimation of the sampling volume, making the concentration result lower than the true value; conversely, a higher flow rate will overestimate the concentration. For example, if a 28.3L/min flow rate instrument has an actual deviation of 12%, the concentration measurement error will reach 12%, which is particularly critical for the assessment of sterile environments in the pharmaceutical industry. Secondly, the measurement of particle size distribution is affected by the coupling effect of particle inertia and flow rate. A high flow rate (28.3L/min) can reduce the sedimentation loss of large particles (≥5μm), while a low flow rate (2.83L/min) needs to be combined with isokinetic sampling to avoid missing small particles. For non-isokinetic sampling, the error of particles ≥5μm is significant, while particles <2μm are hardly affected. Thirdly, temporal representativeness depends on the balance between flow rate and sampling duration. Large flow rate instruments can quickly respond to environmental fluctuations, suitable for dynamic monitoring; small flow rate instruments need to extend sampling time to ensure data stability. For example, a 2.83L/min device takes 10 minutes to collect 28.3L of air to smooth out instantaneous interference.

Standardized application requires a three-in-one strategy of "calibration - selection - operation". In terms of calibration, it should be carried out every 6-12 months in accordance with ISO 21501-4, using standard particles traceable to SI units to ensure that flow rate accuracy and counting efficiency meet the standards. In terms of selection, 28.3L/min equipment is suitable for sterile workshops in the pharmaceutical industry; 2.83L/min equipment can be used for local monitoring in the electronics industry; small flow rates are needed for special scenarios such as biological safety cabinets to reduce air flow interference. In operation, the sampling port should be 1.2m above the ground and at least 0.5m away from obstacles. The sampling pipe should be made of stainless steel with a length of ≤1.5 meters, and the pipeline should be cleaned quarterly to avoid particle loss and contamination.

In conclusion, sampling flow rate is the core link connecting instrument performance and environmental authenticity. By strictly following standards and specifications and scientifically adapting flow rate parameters, particle counters can provide reliable data support for cleanroom quality control, contributing to product quality and safety assurance in high-cleanliness industries. You can learn more about Lumeley's particle counters~