# What is a Human-Machine Interface (HMI)?

> A human-machine interface (HMI) is the hardware or software through which an operator interacts with an industrial controller or process.

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## Content

It may be a local panel with buttons and indicators, a dedicated operator station, or software that presents process graphics, measurements, equipment states, alarms, trends, and controls. Depending on authorization and design, an HMI can also change set points, operating modes, or commands.

An HMI shapes the operator’s view of the physical process, so both displayed information and control actions require protection. False, delayed, missing, or confusing information can lead to unsafe decisions even if the underlying controller remains functional. HMI design, cybersecurity, alarm management, and operator procedures therefore need to be considered together.

### Key points

- **Define authority:** Separate view-only, routine control, engineering, and administrative functions; use named access and protect high-impact commands or set-point changes.
- **Harden the station:** Minimize software and services, restrict removable media and remote tools, control application changes, and use tested allowlisting or endpoint protection where compatible.
- **Protect the path:** Segment HMI communications, allow only required controllers and services, secure remote sessions, and prevent direct internet or general enterprise access.
- **Preserve trustworthy operation:** Synchronize time, retain useful alarms and events, back up displays and configuration, test recovery, and give operators an alternate method to assess process state.
- **Important limitation:** Securing or restoring the HMI must not obscure alarms, delay essential control, or create unsafe operator workload. An available screen also does not prove that its data is timely or authentic; process indications should be validated for critical decisions.

### Related terms

[Programmable logic controller (PLC)](<https://yellowcube.eu/glossary/programmable-logic-controller/>) · [Supervisory control and data acquisition (SCADA)](<https://yellowcube.eu/glossary/supervisory-control-and-data-acquisition/>) · [Industrial control system (ICS)](<https://yellowcube.eu/glossary/industrial-control-system/>) · [Secure remote access](<https://yellowcube.eu/glossary/secure-remote-access/>) · [Operational technology (OT) security](<https://yellowcube.eu/glossary/operational-technology-security/>)

### Sources

[NIST glossary: Human-Machine Interface](https://csrc.nist.gov/glossary/term/Human_Machine_Interface) · [NIST SP 800-82 Rev. 3: Guide to Operational Technology Security](https://csrc.nist.gov/pubs/sp/800/82/r3/final)

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