test facilities

Real-time measurement

ELPI (ELECTRICAL LOW PRESSURE IMPACTOR)

The ELPI(TM) Aerosol Sizer is used to measure the particle size, particle concentration and particle size distribution from 30 nm to 10 µm. The classification per size is obtained following inertial selection with a succession of impactors at low pressure. The concentration is calculated by measuring the electrical charges carried by particles with electrometer located at each impactor stages.

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Particle sizing and counting principle

T he ELPI(TM) operating principle can be divided into three major parts; particle charging in a unipolar corona charger, size classification in a cascade impactor and electrical detection with sensitive electrometers. The particles are first charged into a known charge level in the charger. After charging the particles enter a cascade low pressure impactor with electrically insulated collection stages. The particles are collected in the different impactor stages according to their aerodynamic diameter, and the electric charge carried by particles into each impactor stage is measured in real time by sensitive multichannel electrometers. This measured current signal is directly proportional to particle number concentration and size.

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T he particle collection into each impactor stage is dependent on the aerodynamic size of the particles. Measured current signals are converted to (aerodynamic) size distribution using particle size dependent relations describing the properties of the charger and the impactor stages. The result is particle number concentration and size distribution in real-time.

The base of the ELPI is maintained to low pressure (100 mbar) in order to increase the speed of the particles and to impact the smallest. Without such a low pressure, less than 300nm particles cannot be detected.

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Contact: frantz.gouriou@certam-rouen.com