Analysis of ultra-short pulse modulation for NDIR

In this research an infrared source which radiation is modulated by supplying the heater of source with an ultrashort alternating voltage are used in gas analyzer operating on the basis of non-dispersive infrared sensing. Beyond the conventional technique of constant periodic heating of infrared light source, we propose a new infrared delta-sigma architecture with closed-loop feedback system is built with the hybrid combination of a CO
₂
infrared sensor with a specific wavelength filter, an infrared MEMS heater, a chopper amplifier, threshold comparator, ARM based MPU and discrete electronic devices. The thermal properties of light source for ultra-short alternating modulation without the use of a mechanical chopper has been studied from the output signal of infrared sensor within the limit of modulation frequency and energetic efficiency. The numbers of heating and cooling of the heater are count and manipulated to give a ratio which will determine the gas concentration. After a modeling of system, we built a model for the description of relationship between gas concentration and sensor by the duty of heating. The measurement results show a good linear behavior of signal and it proves to be a practical for all the NDIR measuring techniques and this work also gives a new approach not only to measure gas concentration fast but also obtain the high resolution.