The dust particle counter is the "eye" of clean environment monitoring, and its core lies in converting the physical signals of microscopic particles into statistically significant digital data. The entire process is a precise physical measurement and electronic processing link.
1. Light scattering sensing: core detection
The counter adopts the principle of light scattering. Clean air is sucked into the detection chamber under the action of a vacuum pump, intersecting perpendicularly with a precisely focused laser beam (usually a semiconductor laser). When particles pass through a beam of light, they cause the incident light to scatter in all directions. A high-sensitivity photodetector located at a specific angle (such as 90 ° lateral) captures these weak scattered light pulses and converts them into electrical signals. Key point: A single particle generates a pulse signal, and the amplitude of the signal pulse (voltage peak) is positively correlated with the particle size, which is the basis of particle size grading.
2. Signal processing and particle size grading
The original electrical signal output by the detector is very weak and contains noise, which needs to be amplified by a preamplifier and then processed by a pulse height discriminator. The system has pre-set voltage thresholds corresponding to different particle size thresholds. The pulse signal is classified into different particle size channels (such as ≥ 0.3 μ m, ≥ 0.5 μ m, ≥ 5.0 μ m) by comparing with these threshold values. This step achieves the "optical equivalent" measurement and graded counting of particle size.
3. Flow control and data statistics
To ensure the accuracy of counting concentration, it is necessary to strictly control the sampling flow rate (such as the common 1CFM, which is 2.83L/min). The flow sensor and feedback circuit maintain a constant flow rate. Meanwhile, high-precision clock controls the sampling time. Finally, the internal processor of the counter calculates the particle concentration per cubic meter of air by combining the number of particles counted in each channel during a specific time with a constant sampling volume, and displays or outputs the data.
4. Calibration and Limitations
The accuracy of the instrument depends on regular calibration using standard particles (such as polystyrene latex balls) to establish a standard curve between particle size and signal amplitude. It should be noted that the measurement results are based on the equivalent diameter of light scattering, which is affected by the particle material, shape, and refractive index, and may differ from the actual physical dimensions.
Summary: This technology chain is precisely coupled with four modules: optical sensing, electronic processing, flow control, and data computation, achieving real-time, quantitative, and rapid statistical analysis of invisible particles in the air. It is the cornerstone of clean technology.