With the help of a particle counter calibrated in compliance with ISO 21501-4, the size and number of particles in gases can be determined. It often goes about optical particle counters in accordance with the scattered light method. The essential components of the particle counter with appropriate measuring method are a measuring cell with a light source and detector. The particles are sucked in by means of a vacuum pump and are passed through the measuring chamber. In principle, these components are arranged in such a way, that no light gets on the detector as long as there is no particle in the measuring volume or in the measuring chamber. If a particle passes through the measuring chamber, the light is deflected towards the detector because of the optical effects such as diffraction, scattering or reflection, which causes formation of a signal at the detector depending on the size of the particle.

In order to be able to reliably determine the relationship between the signal strength at the detector and the particle size, particle measuring devices for demanding applications, such as e.g. classification of the clean rooms calibrated in compliance with the standard 14644-1 according to the specifications ISO 21501-4. ISO 21501-4 is an internationally established standard for ensuring the measurement accuracy and comparability of the measurement results of different particle counters.

ISO 21501-4 is one of 4 sections of the ISO standard for particle size distribution. The main goal of introducing the new version in 2007 was to improve the accuracy of the measurements and exclude, or at least significantly eliminate the differences occurring in the result of measurements by different devices.

ISO 21501-4 uses several parameters, the comparison of which provides meaningful results. These parameters include the size calibration of each channel, the corresponding channel error (false count rate), the counting efficiency and the size resolution. In addition, the sampling flow rate in the particle counter is checked to control the performance of the vacuum pump. The basic requirement for the calibration according to ISO 21501-4 is the availability of the pulse height analyser (PHA). This pulse height analyser must either be integrated directly into the device or, due to the connection to the particle counter, be able to analyse the signal strengths and raw signals within the individual size channels. Only then the calibration and possibly the necessary adjustment of the individual channels is feasible.

The PCE - PQC series particle counters from PCE Instruments meet all the above-mentioned requirements for the calibration in compliance with ISO 21501-4. The devices are operated via a 4.3" colour touch display. The measurement data can be stored in a large memory, evaluated by means of the software and, for example, presented in the form of ISO14644-1 or EU GMP reporting format. The measuring devices can detect different particle sizes in the range between 0.3 ... 25 μm and determine the mass concentration. The handheld and table measuring devices are equipped with an internal vacuum pump with an automatic flow rate control. The remote particle collectors are connected to an external source.

Fine dust originates in the natural sources such as forest fires, volcanic eruptions, sea salt, whirled sand, plants or even microorganisms. Nowadays, due to the increasing industrialization, humans also contribute a lot to locally significantly increased particulate matter emissions. Through traffic, energy production, agriculture and industry, the fine dust levels are increasing immensely. No matter whether the origin is natural or man-made, in various areas an increased particle concentration or the presence of the particles is undesirable and harmful.
Fine dust gauges calibrated in compliance with ISO 21501-4 are suitable for numerous applications in the field of clean room technology, such as the monitoring of clean workbenches or clean rooms, clean room qualification or filter control and monitoring in the area of supply air and exhaust air systems. Also, in the field of environmental metrology, building renovation or industrial manufacturing of electronic components as well as in the area of the pharmaceutical industry, ISO 21501-4 calibrated particle counters guarantee product quality and process reliability.