Abstract: A pneumatic detector, non-dispersive infrared analyzer employing detector cell chambers in optical series. The invention having an auxiliary chamber communicating with the front chamber to increase the rear chamber's signal so as to balance the signals from the front and rear chambers. The use of xenon as a diluent gas in the detector chambers in combination with a mass flow detector to improve the sensitivity. The use of an improved synchronous detection method employing a voltage-to-frequency circuit to convert the detector signal to a synchronous high resolution digital signal. The use of an improved source electrically pulsed having low thermal mass and a large radiating area.