Multiple tin-oxide gas sensing system to monitor the indoor of the aged of solitary living

Abstract

Four kinds of tin-oxide gas sensors are installed in a home of a solitary elderly person and the sensor outputs are monitored to know the activity of the aged. These sensors are designed to detect a combustible gas(CGS), ammonia(AMS), carbon monoxide(COS) and nitrogen dioxide(NXS), respectively. As the monitoring results indicate, outputs of the sensors are related with daily living patterns. NDVA indeces especially have periodicity. NDVA is a value which is obtained by an output of AMS divided by an output of CGS, namely NDVA=V(AMS)/V(CGS). The periodical characteristics indicate the daily living patterns of the aged and the system can judge whether the person has been spending a normal life or not. The indoor activity(IA) is derived as a sum total of square of each slipped value from a mean value of a daily sensor-level. The average of IA is about 12 in the experimental house.