Dust particle counter is an important instrument widely used in the field of cleansing. It is mainly used to assess the cleanliness level of clean rooms. It can also be used to detect the filtration efficiency of filters and the amount of dust generated by clean fabrics. The industries used include electronics factories, pharmaceutical factories, medical device factories, testing laboratories, etc. The dust particle counter uses the principle of light scattering to measure the number and particle size of the dust particles in the air. The working principle (Figure 1): the light from the light source is focused on the detection area by the perspective lens group. Air passes through the area. When a dust particle (particle for short) passes through, it scatters the incident light once to generate an optical pulse signal. After amplification and screening, the desired signal is selected and then displayed by the counting system. The height of the electrical pulse signal reflects the particle ’s height. The size and number of signals reflect the number of particles. The main technical indicators concerned are the size and number of particles.

The size of the particles can be traced back to standard particles, usually using polystyrene plastic latex beads (PLS: Polymer Latex Suspensions), which can be traced to the size through scanning electron microscopy. However, it is difficult to have a reliable method for traceability of the number of particles. The particles detected by the dust particle counter are difficult to capture, and there is no effective way to count and count. Even if each step of sampling is performed well, the count display of different dust particle counters will still be very different. The main reason is that there are differences in the design and performance of various dust particle counters, so the calibration of dust particle counters has always been a hot and difficult point of research at home and abroad.

A large number of foreign literatures [2-5] mentioned the concept of counting efficiency. The counting efficiency is the ratio of the number of particles displayed by the dust particle counter to the number of standard particles obtained from the aerosol sampled from the air inlet of the dust particle counter. The instrument with the smallest measurable particle size <0.2 μm is classified as Class A, and the one with ≥ 0.2 μm is classified as Class B. The class A particle counter is a condensing nuclear counter or a similar counter with no less than the same performance. The class A counter can be used as the standard to obtain the counting efficiency of the class B counter. The problem of the traceability of the lower counting efficiency should not be solved, it is just the tacit approval of everyone, and it has not become a benchmark. The literature also mentions the response voltage of the particle size file. This method requires connecting a multi-channel pulse amplitude analyzer to the output of the dust particle counter to be detected (the output of the preamplifier or the input of the main amplifier). A standard particle generator is used to generate experimental aerosols suitable for standard particles of different particle sizes, and the pulse signals corresponding to different particle size files are analyzed to produce a pulse frequency curve to determine the response voltage of different standard particles. It also mentions the use of a dust particle counter to calibrate by comparison.

According to the traceability requirements of the dust particle counter, JJG547-88 "Dust Particle Counter" was formulated in 1988, which used polydisperse standard particles to verify the particle size distribution accuracy of the dust particle counter and the dispersion of monodisperse particle measurement. This regulation avoids the direct verification of particle concentration, adopts the division method, and all its indexes are indirect values. In 2008, after years of hard work, the regulation was revised and changed to JJF1190-2008 "Dust Particle Counter" [7]. The main technical indicators of the specification include appearance requirements, insulation resistance, electrical strength, self-purification time, flow error, timing error, repeatability, particle size distribution error, and particle concentration indication error, which cover the basic performance of the measuring instrument. Taking into account factors such as the scientificity and operability of the verification work. This specification innovatively proposes that standard particle aerosols are used to generate standard particle aerosols, and precision dust particle counters are used as the standard to calibrate the avoidance but an extremely important indicator: particle concentration indication error. The key to the calibration of the dust particle counter is the standard particle generator, precision dust particle counter, and data processing.

In the 1970s, China developed the first dust particle counter in China and began research on the dust particle counter and calibration methods. In 1985, GB6167.1 ~ GB6167.2-85 "Dust Particle Counter Performance Test Method" was formulated, which was revised in 2009 [6]. The standard mainly refers to relevant foreign literature, and puts forward counting efficiency, particle size response voltage and comparison method. It has a very positive significance for the factory debugging of the products of the manufacturer and the improvement of the product quality, but it is not suitable for the measurement and certification department to carry out the value traceability.

The calibration of the dust particle counter has not established a national base standard (also not seen abroad), so the calibration of the dust particle counter is very special and very difficult. The implementation of the national measurement and calibration standard JJF1190-2008 "Dust Particle Counter" is beneficial to ensure the consistency of the national value and suppress the current market laissez-faire.

Article link: China Chemical Instrument Network http: //Tech_news/Detail/417165.html

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