Tehokas kommunikaatio rajoitetun kaistanleveyden kaukovalvonta sovelluksissa

Serial radio modems are long-standing but usable technology and they are still widely used in data communication in many applications. Slow transmission speed, point-to-point connections and signal attenuation are the negative aspects of serial modems. Old and new radio modem models are still compatible with each other because they have not changed greatly over the years. Radio modems can transfer many transmission protocols therefore user can select the most suitable protocol for the application. The goal of this thesis was to improve the usage of serial radio modems in communication between PLCs. Data transfer speed generally cannot be increased thus only necessary data should be transferred through radio modems. The protocol that was used in this thesis was Modbus RTU which is supported by numerous process control devices. Radio network enables reading and writing data to remote automation systems using Modbus RTU. Every device in the network has to be polled individually and round times of large networks can increase to tens of seconds. The basic idea in improving the communication rate is that every station in the network was read sequentially but stations can jump the queue if needed. This thesis studied how different data should be divided in the communication. It is not necessary to use cyclical data transfer method for all the data and therefore some data could only be transferred when needed. Performance of the communication system was tested using existing remote monitoring system. The new communication system is similar to existing one therefore performance of the new implementation can be verified. The performance of both systems were measured and results have been presented in the last chapter