Development Of An Indoor Toxic Gas Monitoring System

With the improvements of the standard of living and the condition of housing in recent years, a lot of new-style decorating materials are widely used in house decoration, which caused the indoor environment deteriorated. Those poisonous gases have caused great harm to human health. So it is of great importance to develop the high quality and low cost monitoring system by combining multi-sensor and intelligence technology. Multi-sensor data fusion technology based on gas detecting system can restrain the excursion and the noise of the sensor and improve the accuracy of the system. Based on the technology mentioned above, the thesis devises an indoor decorating poisonous gas detecting system. The system comprises the data real-time displaying part, the acousto-optic alarm part and the serial port communication part. In addition, the data fusion method based on adaptive weighted is used in the system to improve the accuracy of the system.The thesis deeply analyzes the detection principles of electrochemical formaldehyde, ammonia sensor and semiconductor toluene sensors. Then a system plan is put forward and is implemented. So the analyses for software and hardware design of the system are given. The hardware section consists mainly of three parts. The first part is a series of sensor signal conditioning circuits, including formaldehyde and ammonia sensor conditioning circuit, formaldehyde sensor signal conditioning circuit and temperature- humidity sensor signal conditioning circuit. The second part is the TMS320LF2407A Controller circuit including the gas concentrations acquisition, the temperature- humidity parameters acquisition, the liquid crystal displaying circuit and the acousto-optic alarm and so on. The third part is a position machine communication circuit. The software section consists of two parts. One is the program with C language and assembles language embedding machine. In this part, the performances of the system initialization, the interrupt sampling, the data real-time displaying, the acousto-optic alarm and the data communications are realized. The other is the position machine software based on VB language. It mainly achieves the real-time transmission, the data reservation and the displaying gas concentration.The data fusion method based on adaptive weighted is presented in this thesis. Namely, the mean square error (MSE) and the measurement accuracy of the raw data from these multi-sensors are fused and are estimated accurately. The advantage is no need the prior knowledge of data measurement but only according to the measurement accuracy when we make sure the corresponding weights of the different data. In the light of this method we can calculate and gained the minimum fusion value and then apply it to indoor poisonous gas detecting system to improve the accuracy and robust of the system.In the end, the real experiments show that the system has a steady quality and high accuracy as required. The system is of a bright future.