Gas Analyzer For Petrol, LPG & CNG Vehicles Instrument is easily upgradable to measure concentration of 6 gases (NOx, SOx in addition to CO, HC, CO2 and O2). AutoZero The accuracy of the NDIR sensor depends upon temperature factors. Any change in the temperature results in change in the measured values. AutoZero ensures to zero measured values for every 20 minutes by default or for every 2°C change in the temperature.