Monitoreo de variables utilizando un sistema maestro-esclavo con PLC´s Siemens por medio del protocolo Modbus ASCII y transmisión inalámbrica.

Abstract

One of the business units of Siemens Costa Rica takes care of implementing different control systems, like in aqueducts. Such applications are characterized by the considerable distance between storage tanks and water wells; this makes wireless communications a must for telemetry transmissions. For many applications an open protocol is demanded, that’s why this project came to be, to use a wireless communication protocol such as modbus ASCII, to transfer data between PLCs The main objective is to develop a program that can implement the main functions codes of the protocol to guarantee a proper data transfer on a master slave PLC system. It’s also important that the final program can be easily modifiable so it can be used on future projects without having to make many changes. The system was developed by designing each and every routine, first, the master slave communication routine. Then a simple function code was implemented and verified that the slave PLC received it. Afterwards a routine was programmed on the slave so that it allows the slave PLC to acknowledge a query and generate a proper response. This routine was extended to allow the polling of different slaves. Finally the rest of the functions codes were implememented. To verify that the system works, several different telemtrys were implement.