GRPM ISWSAMPLE CELL I PYROELECTR/C MIRROR 20 DETECTOR m CHOPPER SOURCE 75 k 24 Lu 5] t3 MAGNET/C. m D: P/CggUP 26 s T l: Q ONE SHOT /46 MULT/V/BRATOR /25 I /53 SYNC. LOG/C COUNTER COMPUTER ANALOG POS/T/ON INTERRUPT COUNTER F/Gl sum 2 or z SCANNING INFRARED SPECTROSCOPIC ANALYZER USING ROTATING VARIABLE FILTER BACKGROUND OF THE INVENTION The invention relates to an apparatus that is particularly ad