PEN3, the Electronic Nose, is a small and fast odor monitoring and recognition system for gases and gas mixtures. PEN3 finds its use for Quality Control in a wide range of sectors: food, chemical, pharmaceutical industries (quality control purposes). In these sectors, it is important that the finished product meets precise standards: the PEN3 electronic nose is able to control, for example, the expiry date of food and other foods and substances. Detection is performed by means of an array of gas sensors. Single compounds or mixtures of gases can be identified after a training step by using the pattern generated by the sensors.