A PLC is the controller that executes machine logic, while an HMI is the screen an operator uses to view and adjust that logic by interacting with the display. The PLC makes the decisions and drives the outputs, and the HMI displays status, alarms and setpoints for human oversight. Here are the roles of PLC and HMI equipment, and how they interact:
- PLC function: The programmable logic controller reads inputs, runs the program and switches outputs in real operation, with no screen required to function. The PLC is from an easy-to-source manufacturer such as those on your shop floor.
- HMI function: The human machine interface gives operators a window into the controller, showing run states, fault messages and adjustable parameters. The display has hardwired buttons in the event of screen failure.
- Data exchange: The HMI reads and writes PLC tags over a protocol such as ethernet/IP or PROFINET, so a setpoint changed on screen reaches the controller.
- The ethernet industrial protocol adapts data exchange to facilitate communication between components, such as sensors.
- PROFINET is a process field network that is the leading standard in industrial automation and controls.
If the HMI goes offline, then a well-programmed PLC keeps running the process, because the control logic does not live on the screen. It is stored on the network and cloud backup system, which Adgo Controls programs all components onto. The PLC runs the logic and the HMI is how your operators see and steer it, so the two are designed together. If the operator interface is your focus, our HMI integration work covers that side of the system.
