The work demonstrates a simple, handheld, micro-heater integrated MOX-based gas sensor interface system that includes digital set point, a precise closed loop temperature controller and a wide range resistance readout circuit. The implementation of the proposed system constitutes two circuits. The temperature control loop circuit is able to set the platinum microheater temperature over a range for ambient temperature to 300°C, with a peak to peak deviation less than 2.0°C. An accurate closed proportional control loop is used for controlling the temperature of the microheater. A resistance to the time conversion based resistance readout circuit that measures the resistance over a range of 1KΩ to 100MΩ. The overall system is flexible and can be interfaced with integrated sensors having different power requirements and fabrication parameters. At varied temperatures, it can measure different gases like ammonia (NH3) at 230°C, nitrogen dioxide (NO2) at 80 °C and carbon mono-oxide (CO) at 270 °C. Various experiments were conducted to test the circuit by first connecting discrete known resistive components and also, its response to different gases is recorded by passing the gases with various concentrations. The resistance readout circuit output has an excellent accuracy with an error of less than 2%.
Fig. 89 shows the gas characterisation setup developed for testing the MOX-based gas sensor interface system. Fig. 90 shows the portable smart interface electronic system for sensing ammonia gas. Fig. 91 shows the relative error between set temperature and measured temperature is less then 2°C and Fig. 92 shows the sensor resistance read out response.
Gas sensing systems were handed over to sponsoring agency DietY (MCIT). Fig. 93 shows the handing over of portable systems by Dr. Chandra Shekhar, director CSIR-CEERI to Dr. S.C. Gadkri, chairman, Review Committee.
Fig. 89: Gas sensor characterisation set-up
Fig. 90: Portable smart interface electronics for sensing ammonia
Fig. 91: Temperature obtained Vs desired temperature with relative error
Fig. 92: Readout circuit response with discrete resistive values
Fig. 93: Dr. Chandra Shekhar, director CSIR-CEERI handing over prototypes of the Gas sensor to Dr. S.C. Gadkari, Chairman, Review Committee