HMIs & Operator Displays

HMI is the acronym for Human Machine Interface which, simply put, is an interface between a user and a machine. HMI is a term specific to manufacturing and process control systems. An HMI provides a visual representation of the status of a control system with real-time data acquisition. 

HMI's can also act as the centralized control unit for manufacturing lines as they are usually equipped with non-volatile memory containing data recipes, can execute event logging and event triggering, and can provide video feed for status monitoring. For a manufacturing line to be integrated with an HMI, it must first be connected to a Programmable Logic Controller (PLC) or Motion Controller. It is the PLC/Motion Controller that takes the information from the machine sensors and converts it into Boolean algebra to communicate with the HMI.

The greatest advantage of an HMI is its user-friendliness and ability to personalize its graphical interface. An HMI can fully support complex applications with multiple screens and several routines running concurrently. Every HMI comes with different features; some may play sound, play video, or even have remote access control. The selection of an HMI should be optimized for a customer's specific application taking into consideration the capabilities of the typical user, as well as the environmental conditions such as noise, lighting, dust, vision, etc.

An HMI is used for three primary roles: replacing push-buttons, data handling, and system supervision.

  1. 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.
  2. 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.
  3. 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.