A Scanning Infra-red Technique for Cigarette Coal Peak Temperature Measurements

Thermocouples were used in the past, with a few exceptions, for cigarette coal temperature measurements. The main shortcomings of this technique are: the cigarette is disturbed by insertion of the thermocouple, the position of the bead does not necessarily coincide with the location of the puff, heat transfer between tobacco shred and bead is poor, heat capacity and conductivity are orders of magnitude different for tobacco and metals. Methods employing x-ray observations of fusions of metal inclusions or cinematographic optical pyrometry also possess serious shortcomings. These shortcomings are eliminated by a non-contact technique based on radiometry. This method is applicable only to the measurement of surface temperature of the cigarette coal. By measuring the intensity of the emitted radiation, the temperature can be calculated or can be obtained by calibration with an artificial blackbody. Since the coal temperature is not stable even during the 2-second duration of a puff, the instantaneous response of an infra-red detector has to be coupled with a very fast recording system. An AGA Scanning Infra-red Camera was selected for the coal temperature measurements. The electronic system of the camera generates a waveform proportionaI to the 2-5.4 AAµ band of the infra-red radiation emitted by the coal. The peak value of the video signal, representing the hottest point of the coaI, is stored. At a command, given automatically by the smoking machine, the signal is digitized and printed out. Although the peak signal decreases with very small targets, evaluation of the system indicates acceptable accuracy for target sizes down to 3 mm in width. The cigarette coal fulfills this condition.