Investigation of the response of high-bandwidth MOX sensors to gas plumes for application on a mobile robot in hazardous environments

A custom sensor module has been developed comprising high-bandwidth metal oxide (MOX), low-cost non-dispersive infra-red (NDIR) and miniature solidly mounted resonator (SMR) acoustic sensors for use on a mobile exploration robot. The module has been tested in a wind tunnel in order to evaluate the performance of three MOX sensors (with coatings of PdPt SnO2, WO3 and NiO) to plumes of 2-propanol (concentration < 2.5 ppm). The formation of the VOC (volatile organic compound) plumes was verified through mapping of sensor responses across a grid of 9 positions in the wind tunnel. Fluctuating sensor responses were observed (±5%), demonstrating variation of VOC concentration within the gas plumes. Higher sensor responses were demonstrated with the n-type SnO2 and WO3 based devices (80% and 40% change relative to baseline, respectively) compared to the p-type NiO device (10%). Short plumes of VOC demonstrated the effect of gas pulse broadening, where longer duration responses (10% greater) were observed at locations further from the VOC source (∼0.4 m distance variation tested). Finally, the module was tested in a real-world environment, where plumes of VOC were observed using the MOX sensors and verified using a commercial Photoionization Detector (PID).