This paper proposes a safety monitoring system by small number of autonomous sensors. High-reliable safety monitoring system is vital to operate large-scale systems, such as nuclear power plants. Monitoring by multiple and fixed sensors is effective, but it requires large cost. Also, in nuclear systems, there are difficult places to fix sensors for long time since a sensor has weakness for radiation near a nuclear reactor. Thus, this paper proposes a reliable autonomous and distributed monitoring system by small number of sensors.
There are three requirements for the autonomous monitoring system from aspect of reliability. The first one is that several sensors should aggregate to prevent false alarms when a sensor detects abnormal situation, and that then they should diffuse efficiently all over the objected area to prevent lack of alarms. The second is that a frequency of sensors' visit should be constant for every point in area when the monitored area is homogeneous. The last is that the frequency should be controllable depending on the priorities when the monitored area is heterogeneous. The monitoring system that this paper proposes is an Ant-like Sensor System (ASS) that consists of autonomous sensors communicating by pheromone. In ASS, each sensor agent moves around leaving the markings of repulsive pheromone that means that some sensor has visited the surveillance point. Such pheromone communication makes sensors system satisfy the above three requirements.
Two experiments are conducted to clarify the condition to assign optimal parameters for ASS, such as quantity of sprayed pheromone and evaporation speed of pheromone. The optimal parameters are determined dependent on the number of sensors and the characteristics for monitored area.