An HMI is used for three primary roles: replacing push-buttons, data handling, and system supervision.
- The push-button replacer function takes the place of LEDs, On/ Off buttons, switches or any mechanical device that performs a control function. The elimination of these mechanical devices is possible because the HMI can provide a visual representation of all these devices on its LCD screen, while performing all the same functions.
- Data handling is used in applications that require constant feedback and monitoring. HMI's that serve as data handlers come equipped with large capacity memories.
- The last of the three HMI types is referred to as the system supervisor because it works with SCADA (Supervisory Control And Data Acquisition) and MES (Manufacturing Execution System) to display information. These are centralized or distributed control systems that monitor and control entire sites or complexes of large sub-systems spread out over large areas. An HMI is usually linked to the SCADA system's databases and software programs to provide real-time trending, diagnostic data, and management information.