Design And Implementation Of Real-Time Database For Domestic Programmable Logic Controller

Domestic PLC(Programmable Logic Controller)strives to quickly respond to the real-time condition of the producing equipment,mainly used in the field of industrial control.In the industrial production process,the emergence of production accidents,abnormal alarm,can be real-time feedback to the monitoring center through real-time database,so that monitoring personnel can make a quick response.Hence the specific application of PLC system scene requires that the entire system needs to have higher real-time performance.This feature of PLC system requires a unified data management platform,but the traditional relational database is difficult to meet the real-time requirements of PLC system transactions.Therefore it is necessary to design and implement the real-time database system which is applied to domestic PLC system,so as to uniformly manage the data and schedule the emergency.The purpose of researching and developing the real-time database in this thesis is to provide an effective data management platform for our data monitoring software,and the main aspects of our design and implementation includes: data acquisition and output,real-time data processing,alarm service and historical data dump.The main contents and results of this thesis can be summarized as follows: 1)Briefly introduce the structure of domestic PLC equipment and data monitoring software,analyze the necessity of real-time database research and development,and the real-time database system features,functions and some useful techniques in the development of the system.On the basis of deep understanding of real-time database architecture and functional characteristics,design its structure.2)Realize the real-time and high-efficiency data acquisition and output,in the real-time data acquisition and output,according to the PLC device data characteristics to design private communication protocol,communicate with the mode of a question and answer in the PLC and real-time database data,meanwhile,design data change forwarding mechanism based on dead zone as the first level data compression in the data compression process.3)Aimed at the real-time requirements of the system,design the special real-time data processing module to uniformly process the collection of real-time data and according to the actual application of PLC data volume design based on shared memory "two input four output" memory data table for data writing.Realize effective real-time alarm function,which a real-time database system must have.This thesis designs alarm judgment mechanism,writes alarm data to real-time alarm table,and regularly reads the alarm information from alarm management module according to the actual situation.4)When storing the historical data,make full use of existing relational database powerful data management capabilities,use My SQL database to store the compressed data.Here using the integrated compression algorithm in the historical data queue data for the second level of data compression,greatly reduce the historical data volume.5)Design a real-time transaction scheduling strategy that conforms to the system characteristics.In consideration of the low concurrency of the current system and as the transactions in the real-time database system are mostly soft real-time transactions,we design the same priority FCFS(First Come First Served)transaction scheduling strategy on top of the static priority,which is conducive to further enhance the real-time property of our system.6)In the process of system test,we mainly test and check the data insertion and query of the used My SQL database in the local My ISAM engine,test the data insertion and query in the memory database,and after that compress the data generated by the PLC for a short time to validate the compression effect.Finally,through the real-time database development of data monitoring software and PLC platform to establish a dual capacity tank test model,and make an initial assessment about the overall performance of the real-time database.Through the real-time database and the host computer data monitoring software are integrated in the dual-capacity water tank test environment based on PLC and a series of tests,which proves the real-time and usability of the real-time database.The entire operating effect and performance have obtained the preliminary expectation.