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FMS 375

FMS 375 Measuring System with dilution and sample switching for the determination of fractional separation efficiency of e.g. oil mist separators or filters

The fractional efficiency measurement system FMS 375 bundles core competences of Topas in one compact and robust instrument for highly-resolved aerosol analyses regarding particle size and concentration.
Fractional Efficiency Measurement System FMS 375, front view Fractional Efficiency Measurement System FMS 375 with accessory trolley, front view Fractional Efficiency Measurement System FMS 375, display
The FMS 375 enables an automated aerosol sampling as well as excess air refeeding via a switching unit, aerosol conditioning by two static dilution systems and a precise aerosol characterisation based on the aerosol spectrometer LAP 325.


ISO 21501-1
VDI 3867-4
ISO 17536
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  • operable at both over and lower pressure
  • automated and remote-controlled operation
  • mobile use (optional trolley kit)


  • characterisation of particle size distributions and particle numbers of aerosols
  • evaluation of fractional separation efficiency of oil mist separators and filters
  • compact design for the use at engine test stations or in laboratory test setups (e.g. SPT 140)

The FMS 375 has to be connected to the sampling points of a test set-up. These are then individually controlled via the automated switching unit. If necessary, the sample is conditioned before characterisation by means of the dilution systems. The dilution factor can be varied in three steps. The particle inlet concentration defines the necessity for none, one or two dilution systems for lowering the concentration towards the acceptable concentration range for the aerosol spectrometer. Afterwards, the conditioned aerosol passes the measuring cell of the aerosol spectrometer.\r\nThe measurement zone is illuminated by light of two different wavelengths, which originates from two laser diodes with high lifetime. The light, which is scattered by the particles or droplets, is collected and recorded by a photodetector. The optical signals are converted into electrical ones and are processed. Signal evaluation is performed by the firmware. Results like the particle size distribution and the particle number concentration are visualised on a display.

Parameter title Unit Value
measuring range, particle size µm 0,2 ... 40
measuring range, concentration #/cm³ < 4 × 10⁸
sample flow rate L/min 3
analytical flow rate L/min 0,1
operating medium, gas/air - compressed air supply bar 4 ... 8
power supply - 110 … 240 V, 50 … 60 Hz
communication interface - ethernet, USB
connector, sample inlet mm 8 (outer diameter)
aerosol temperature °C max. 120
environmental condition, ambient pressure bar +/- 0,8
dimensions (w × h × d) mm 530 × 440 × 500 (w/o grip); 650 × 570 × 500 (with grip)
weight kg 33

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