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Palas - Fidas® mobile Fine Dust Monitor System

The Fidas® mobile is designed to be a portable, hand-held, battery-operated device that can also be plugged into the power supply It simultaneously measures PM1, PM2.5, PM4, PM10, and TSP environmental mass fractions or respirable, thoracic, and inhalable mass fractions as per DIN EN 481. In addition, it measures the particle number and particle size distribution (upon request) in up to 64 size classes within the particle size range of 0.18 – 18 μm or 0.4 – 40 μm. The time resolution can be adjusted from one second to hourly or daily mean values for continuous measurements.

A filter holder was intentionally omitted from this model. Based on the WHO air quality guideline of 50 μg/m3 for PM10 as a daily average limit for ambient air with a volume flow of 1.4 L/min, a 48-hour measurement would have to be carried out in order to gather a concentration of 200 μg on the filter (two times the detection limit of a 100-μg laboratory scale), with the sampling time extended accordingly in the case of half the average concentration.

The Fidas® mobile is equipped with a data logger with 4 GB Compact Flash storage and WLAN support. The firmware supports complete remote access with remote maintenance and optional data storage at In addition, the Fidas® mobile can be equipped with additional sensors for environmental conditions, temperature, atmospheric pressure, and relative humidity.

The Fidas® mobile can be connected to an isokinetic sampling probe that measures emissions in exhaust air ducts.

Principle of measurement

The Fidas® mobile measures aerosol particles based on Lorenz-Mie scattered light analysis of single particles. The single particles move through an optically differentiated measurement volume (see Fig. 1) that is homogeneously illuminated with polychromatic light.

The patented T-stop provides a precisely defined optical measurement volume and enables particle measurement without border-zone errors, resulting in a precise size measurement. The new, digitized, electronic signal analysis system enables the rapid identification and correction of coincidence, as necessary.

Fig. 1: Schematic diagram of scattered light detection with the patented T-stop

Each particle generates a scattered light impulse that is detected at an angle of 85° to 95° degrees. The particle number is measured based on the number of scattered light impulses. The level of the scattered light impulse is a measure of the particle size diameter.

Using a polychromatic light source enables a precise and unambiguous calibration curve to be obtained, resulting in an extremely high size resolution (see Fig. 2).

Fig. 2: Scattered light intensity of a white light source compared with a monochromatic light source (angle 85° – 95°, respectively; m = 1.59 + 0i)

The measured light intensities are classified to a particle diameter and combined into a histogram (corresponding to the size classes) using this unambiguous calibration curve.

In order to convert the measured particle size distribution into a mass or mass fraction, the distribution in each value is multiplied by a correlation factor that reflects the different sources (e.g. combustion aerosols, tire wear, pollen) of the environmental aerosol (see Fig. 3). A mass fraction is obtained by additionally applying the separation curve (see DIN EN 481) to the determined particle size distribution.

Fig. 3: Comparison of the algorithms for conversion of the particle size distribution by PM values

Multiple separation curves can be used simultaneously for the same size distribution, which enables the simultaneous output of PM10, PM2.5, PM1 (and others).


Based on continuous customer feedback, the user interface and software have been optimized for intuitive operation and real-time control of measurement data and parameters (see Fig. 4).

Fig. 4: Standard data screen and graphic display measurement on the integrated touch screen

In addition, the software provides data management with the integrated data logger, sophisticated export capabilities, and network support. The measured data are able to be displayed and evaluated with many available options. If a specific display is desired, we can implement it for you.

Fig. 5: Typical use of the Fidas® mobile for indoor air quality measurements


Particular Advantages

  • Online display of dust values and particle size distribution
  • Counting measurement method, optimal resolution
  • Real-time measurement
  • Light source: LED
  • Up to four hours of measurement time in battery mode
  • Fidas® data analyzer software for individual analysis of your measurement data on an external PC
  • Low maintenance
  • Easy to operate
  • Reliable function
  • Cloud zone via Palas server for worldwide data retrieval
  • Reduces your operating expenses






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