HMI (Human Machine Interface) is the user interface in a manufacturing or process control system. It provides a graphics-based visualization of an industrial control and monitoring system.Previously called an "MMI" (man machine interface), an HMI typically resides in an office-based Windows computer that communicates with a specialized computer in the plant such as a programmable automation controller (PAC), programmable logic controller (PLC) or distributed control system (DCS). By providing information, alerts, commands and other tools, an HMI connects the user with the process being controlled. So the more adapted the tools are to the user, the more appropriately he or she can react. An intuitive, user-friendly HMI can make the difference between an inefficient system and a cost-effective one.
HMI, SCADA & DCS
HMI and SCADA are related to each other inasmuch as one or more HMIs are subsets or components of a SCADA system. Additionally, a DCS or Distributed Control System is very similar to a SCADA system, and may also use one or more HMIs as well. All these components are classes of, or describe parts of, an ICS or Industrial Control System, which is the general description of the Automation. In modern control systems, there is a great deal of overlapping technology and functionality between these two classes of ICSs.