There are basically two different methods to sample airborne particultes on a filter. The first is with moving filter the second with fixed filter A sample of air is drawn via a sampler head through a glass fiber filter tape, which retains particulates. Downstream of the filter a flow measurement system is located and a lateral blower pump. The filter tape is advanced in the same manner as the tape on a tape recorder. The difference between the tape recorder and the particulate monitor lies in the position of the detector head and the dual function of the capstan. The capstan of the moving filter monitor is provided with slits, which allow the sample air to pass through them at the collection area. At the same time it ensures a continuous motion of the filter tape and thus a homogeneous deposition of particles, both radioactive and non-radioactive. The advantage of this technique lies in the fact that, with proper choice of filter speed and flow rate, clogging problems no longer occur. The disadvantage of fixed filters which require frequent changing ; hence mechanisms to overcome the radon in growth to equilibrium problem (false alarms ! ), is eliminated with the use of a moving filter tape. Another feature of interest for stand-alone systems is the autonomy of more than 200 days obtained by the use of a 50-m filter tape.