The REST ASR unit or (Air Scent Regulator) was developed to produce real-time samples for training without the need of sample tanks and laboratory pumps.
Samples produced in laboratory tanks have a background odour of the laboratory and not the cargo shed or warehouse. The ASR unit allows you to precisely control the flow of air past the odour and how much is placed on the filter.
The ASR screws straight onto the front of the filter holder much the same as the DFTs TASP unit, but allows you to adjust the airflow to balance resistance in accordance with the strength of the odour or resistance in the material texture.
In terms of equipment cost, it is cheaper to use samples tanks, but with the ASR you will produce accurate real-time samples.