The dust particle counter is based on light scattering technology to achieve precise detection of particles in the air. Its core principle is to use the scattering effect of particles on light, combined with photoelectric conversion and signal processing, to achieve quantitative analysis of particle quantity and size. The following is a detailed analysis of its working principle:
1. Light scattering phenomenon: interaction between particles and light
When light shines on particles in the air (such as dust, smoke, etc.), some of the light will deviate from its original propagation direction and scatter in all directions, forming scattered light. The intensity of scattered light is directly proportional to the surface area of the particles (i.e. the square of the particle size): the larger the particle size, the stronger the scattered light. For example, the scattered light intensity of 0.5 μ m particles is 2.78 times that of 0.3 μ m particles (with a surface area ratio of (0.5/0.3) ² ≈ 2.78). This law is the theoretical basis of light scattering particle counters.
2. Core components: Optical path and signal conversion system
Light source: Usually laser (wavelength 635nm) or ordinary iodine tungsten lamp is used. Laser light sources, due to their good monochromaticity and strong directionality, can detect particles larger than 0.1 μ m; Ordinary light sources are suitable for particles larger than 0.3 μ m.
Measurement chamber: Air passes through at a constant flow rate (such as 28.3L/min), where particles are illuminated by a light source and scatter light.
Photodetector: A photomultiplier tube or photodiode converts scattered light into an electrical pulse signal. For example, a 0.3 μ m particle may generate an electrical pulse of 69mV, while a 0.5 μ m particle may generate 531mV.
Signal processing unit: amplifies and identifies electrical pulses, counts the number of pulses (corresponding to the number of particles) and amplitude (corresponding to the size of particles).
3. Workflow: From light pulses to data output
Sampling: The vacuum pump extracts air and ensures uniform particle distribution through an isokinetic sampling head.
Light scattering: Particles scatter laser light inside the measurement cavity, forming a light pulse signal.
Photoelectric conversion: The photodetector converts light pulses into electrical pulses.
Signal processing: Electronic circuit amplification, identification of electrical pulses, and differentiation of particles of different sizes (such as 0.3 μ m, 0.5 μ m, 1.0 μ m, etc.).
Data display: The counting system counts the number of pulses in each particle size channel, calculates the particle concentration per unit volume of air, and displays the results.
4. Technical advantages and application scenarios
High sensitivity: capable of detecting particles at the 0.1 μ m level, meeting the monitoring requirements of clean rooms (such as ISO Class 5).
Real time performance: Sampling and data analysis are completed synchronously, suitable for dynamic environmental monitoring.
Multi scenario applications:
Pharmaceutical industry: Monitor GMP workshops to prevent microbial carriers (≥ 0.5 μ m particles) from contaminating drugs.
Electronic manufacturing: Detecting nanoscale dust in semiconductor workshops to ensure component yield.
Environmental monitoring: Evaluate indoor air quality (such as PM2.5, PM10 concentration).
5. Key parameters and performance indicators
Particle size resolution: usually divided into 6 levels (0.3 μ m, 0.5 μ m, 1.0 μ m, 3.0 μ m, 5.0 μ m, 10.0 μ m), the higher the resolution, the stronger the ability to distinguish small particles.
Flow stability: The sampling flow deviation should be ≤ ± 5%, otherwise it will affect the accuracy of concentration calculation.
Counting efficiency: Ideally, it should be close to 100%, but in reality, it is affected by factors such as optical systems and electrical noise, and usually requires regular calibration.
6. Calibration and maintenance points
Optical calibration: Use standard particles (such as polystyrene latex balls) to verify wavelength and light intensity uniformity.
Flow calibration: Check the sampling flow rate through a flow meter to ensure it is constant.
Environmental control: Avoid high concentrations or corrosive gases to prevent contamination of optical and gas components.
Regular self-cleaning: The instrument needs to self clean for 20 minutes before starting to remove residual particles and reduce background noise.