Research On Reliability Evaluation Of Ammonia-nitrogen Water Automatic Monitor

Water quality monitor is an important instrument for monitoring water quality, its reliability has a very significant effect on monitoring water quality. During the period of product design, domestic water quality monitor instruments focused on meeting the functional requirements, lacking of research on reliability evaluation. This dissertation was based on ammonia-nitrogen water quality monitor as study object, including methods of rapid reliability test for water quality monitors and design of reliability test system. The finished work of this dissertation as followed:(1) This dissertation studied on ammonia-nitrogen water quality monitor for its work principle, structure and work conditions; analyzed the factors which would influence water quality monitor and the failure mechanisms of water quality monitor, these factors include temperature, humidity, voltage and current; established the reliability block diagram of ammonia-nitrogen water quality monitor.(2) This article proposed that the failure distribution of ammonia-nitrogen water quality monitor is consistent with the Weibull distribution, and given the reliability indices of Weibull distribution; put forward the reliability analysis method based on field failure data; analyzed accelerating model, degenerating model, degenerating data conversion method and false failure life corresponds to life distribution; proposed stepping method for reliability analysis of accelerated degradation data.(3) Chosen temperature as accelerating stress, the failure criteria for relative error is greater than 10%, designed the accelerated degradation testing program of stepping method for water quality monitor reliability analysis; according to testing program, set up a hardware platform for the reliability test system of ammonia-nitrogen water quality monitor.(4) This system used MFC framework and Microsoft SQL Server2008 to develop the reliability test software system of ammonia-nitrogen water quality monitor. The software has two parts, includes stepping accelerated degradation testing and reliability data analysis. Stepping accelerated degradation testing module via a serial port to communicate with ammonia-nitrogen water quality monitor, so that can realize the purpose of real time monitoring, data display, data storage and data export; reliability data analysis software is used to analyze field failure data, which has the functions of data import, data display, data processing, graphics display and so on.(5) This dissertation used specialized software MATLAB to deal with testing degradation data, and got the expectancy life of water quality monitors is 22191.74 h, median life is 21662.98 h, characteristic life is 25018.87h; used reliability analysis software to handle field failure data, and acquired the expectancy life of water quality monitors is 21095.5h, median life is 21354.11 h, characteristic life is 22869.73 h. Finally, compared results of processed data, which proved that the design of stepping accelerated degradation testing and reliability testing system can evaluate the reliability level of ammonia-nitrogen water quality monitor fast and effectively.