Remote Control and Monitoring Protocols for PLC and HMI Systems: A Case Study of MODBUS, WMI and VNC

This electronic document is Programmable Logic Controllers (PLC) are used in Automation systems in a variety of applications. PLC is the control unit of the systems or machines. It collects information from sensors and controls the output ports. PLCs can also be used to communicate between the devices or sensors. In this study, remote control protocols of PLC have been investigated and a remote control and monitoring implementation has been realized by using Windows Management Instrumentation (WMI), RS-485, RS-232, and VNC protocols. A machine has been designed to separate the sprue from the injected plastic. The machine is equipped with GMT brand 396R model PLC, a 7” touch screen Human Machine Interface (HMI) and Variable Frequency Driver (VFD). PLC is remotely controlled through WMI connection from Ethernet port, HMI is monitored and controlled by VNC protocol, VFD is controlled by the PLC through RS-485 and HMI is connected to PLC through RS-232 MODBUS protocol. The advanced communication gave extra flexibility and increased the efficiency while reducing the maintenance cost.