An Electronic System to Heat MOX Sensors With Synchronized and Programmable Thermal Profiles

Metal oxide (MOX) sensors are widely used in several application fields: environmental monitoring, home automation, food control, and so on. Research activities in this topic are oriented toward new materials and nanotechnologies, thus requiring new instruments for the sensor characterization and management. Often, in order to improve selectivity, sensitivity, stability, the sensor is heated according to purposely designed profiles. The repeatability of the measurement conditions strongly depends on the ability to perform a sensor resistance measurement in a synchronous fashion with respect to the imposed thermal profile. This work proposes an electronic equipment for a complete management of a generic MOX sensor. The system is able to estimate the sensor resistance in a range varying from tens of kilohms up to tens of gigohms, while driving the sensor heater with a thermal profile designed by the user. Thanks to the short readout time (10 ms) and to the synchronism between the heater management and the sensor resistance measurement, the system is suitable for monitoring fast transients and thermal dynamics of the sensors. In addition, an estimation of the sensor parasitic capacitance, modeled in parallel with the resistive part and on the order of few picofarads, is provided for diagnostic purposes. Experimental results conducted on both commercial resistors/capacitors emulating the sensor, and on a real SnO₂ nanowire-based sensor for carbon monoxide detection have demonstrated the validity of the proposed approach. Broad topic: 17. Measurement Techniques.