Data Acquisition System With MODBUS Protocol

Abstract

The prime objective of any modern instrumentation and control system is to establish communication between instruments and controller-located at distance apart from the field in the control room. Adding to that controller located at control room, must communicate with the control devices, which act upon a given process. In this project, a data acquisition system is developed with the use of MODBUS protocol for limited MODBUS function support. The communication system designed can be seen as a miniature version of the systems adopted in the modern industrial control system. The MODBUS master GUI is designed in the LabVIEW. Two MODBUS slave devices are designed using PIC18F4550 microcontroller. A multi-point communication system is created using RS-485 standard bus topology to connect the master and both the slaves. Real time data acquired by the slaves using ADC channels are then monitored by the master, using MODBUS query response cycle. Validation of the master and slaves are carried out by the Modbus Poll and Modbus slave simulator respectively. This validation test confirms their interoperability and compatibility with MODBUS supported devices other than those developed in this project.