The temperature‐dependent sensing properties of metal‐oxide semiconductor gas sensors (MOX), based on SnO2 and WO3, to measure triacetone triperoxide (TATP), diacetone diperoxid (DADP), and di‐tert‐butyl‐peroxide (DTBP) and acetone are described. Conductivity measurements in the range from 100 to 400 °C operating temperature show two different reaction pathways on the surface for WO3 sensors. At temperatures below 150 °C organic peroxides react as an oxidizer which leads to an increase in the sensor resistance. Above 200 °C they react as a reducing agent that leads to a decrease of the sensor resistance. This effect is caused by two different, peroxide dependent reaction paths. The unique behavior of WO3‐based sensors can be used for selectivity enhancements in temperature cycle operation mode. With this method gas concentrations down to a few ppb are detectable.
Scheme of TATP reacting on tungsten oxide semiconductor gas sensor. TATP decomposes and this leads to an increase of the sensor resistance at low temperatures and a decrease of resistance at high temperatures.
The choice of suitable semiconducting metal oxide (MOX) gas sensors for the detection of a specific gas or gas mixture is time-consuming since the sensor’s sensitivity needs to be characterized at multiple temperatures to find its optimal operating conditions. To obtain reliable measurement results, it is very important that the power for the sensor’s integrated heater is stable, regulated and error-free (or error-tolerant). Especially the error-free requirement can be only be achieved if the power supply implements failure-avoiding and failure-detection methods. The biggest challenge is deriving multiple different voltages from a common supply in an efficient way while keeping the system as small and lightweight as possible. This work presents a reliable, compact, embedded system that addresses the power supply requirements for fully automated simultaneous sensor characterization for up to 16 sensors at multiple temperatures. The system implements efficient (avg. 83.3% efficiency) voltage conversion with low ripple output (<32 mV) and supports static or temperature-cycled heating modes. Voltage and current of each channel are constantly monitored and regulated to guarantee reliable operation. To evaluate the proposed design, 16 sensors were screened. The results are shown in the experimental part of this work.
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