In brief
An HMI (human-machine interface) is the operator interface of a machine, usually a touch panel, through which operators monitor and control processes.
Contents
What is HMI?
An HMI connects people and machines: it displays states, measured values, alarms and recipes and accepts inputs, such as setpoints or start and stop commands. In practice, the term is mostly used for operator panels connected to the PLC via a communication interface. Larger plants are additionally operated via control systems or visualisation software on PCs.
Designs range from text displays with keys through touch panels with various screen sizes to panel PCs with a full operating system. Key parameters are display size and resolution, mode of operation, interfaces, supply voltage, mounting cut-out, front-side degree of protection and the configuration software used, including its version. Panels with a higher front-side degree of protection and stainless steel frames are used in areas subject to washdown.
Typical faults are failed backlighting, unresponsive touch surfaces, damaged front membranes and memory errors. When replacing a panel, the project matters as much as the hardware: without a backed-up project file or compatible firmware, a new panel often cannot be commissioned. Discontinued panels frequently require migration of the visualisation.
In practice: maintenance and procurement
For every operator panel, back up the current project file, software version and firmware, ideally on a memory card as well. For an enquiry, the manufacturer part number, display size, interfaces and mounting cut-out are needed so that a successor model fits mechanically and electrically.
Synonyms and abbreviations: operator panel · human-machine interface · touch panel · operator interface terminal · HMI panel
Frequently asked questions
What is the difference between an HMI and a PLC?
The PLC runs the control program and switches drives, valves and other actuators. The HMI is only the operator interface: it displays data from the PLC and transmits operator inputs to it. If the HMI fails, the machine may continue to run, depending on the programming, but can hardly be operated.
What needs to be considered when replacing an operator panel?
Important are an up-to-date backup of the project, the matching version of the configuration software and compatible firmware on the replacement device. With a successor model, the mounting cut-out, interfaces and screen resolution must be checked, as otherwise screens may shift or communication with the controller may fail.
What information is needed to replace an HMI?
Needed are the manufacturer part number from the nameplate, display size, mode of operation, interfaces to the controller, supply voltage, mounting cut-out and firmware version. It is also helpful to state which software and version were used to create the project, so that transfer of the visualisation can be checked.