Abstract: An ion mobility spectrometer for detecting substances such as narcotics and explosives, has inlets for a sample gas and a drift gas. The gas can be ambient air, bottled air, or another gas source. To ensure accuracy and prevent drifting of analyte peaks, the air is dried. A two stage dryer is provided comprising a first dryer, preferably a dryer which chills the air and removes water by condensation. This removes the bulk of the water. The second dryer includes a suitable absorbent, and reduces the water content to around 1-10 .mu.g/L, i.e. a level which will not substantially affect the performance of the IMS apparatus. The first dryer substantially reduces the load on the second dryer, and enables an extended period of use before the absorbent material in the second dryer either needs to be replaced or regenerated. The increased stability of calibrant and analyte peak positions allows detection windows to be narrowed, resulting in significantly lower false alarm rates.

Abstract: An apparatus for reading variable area optically encoded soundtracks has a light source, a lens system and a detector. The detector can be a linear array, for example a CCD array, with an integral slit, with the lens system imaging the soundtrack in the plane of the slit. The apparatus includes circuitry for processing the detector output signal. The processing circuitry can be provided with a feedback control circuit to condition the detector output signal so that the resulting audio signal is not affected by variations in the film or electronic components. Further, a circuit can be included for detecting whether an analogue or digital soundtrack is present, and automatically switching the output of an amplification circuit between analogue and digital outputs.