Automation and IIoT
What is an HMI (human machine interface)?
An HMI is the screen operators use to monitor and control a machine or process. How HMIs work, high performance HMI design under ISA 101, and HMI versus SCADA.
Quick answer
An HMI (human machine interface) is the screen or panel operators use to see what a machine or process is doing and to control it. It displays states, values, trends and alarms from the PLC or SCADA system and accepts commands such as start, stop and setpoint changes.
Updated 30 October 2026. Written by the Ajinkya Technologies engineering team, reviewed by Amey Kadle.
HMI explained
HMIs range from small touch panels on a single machine to control room workstations running SCADA clients. They communicate with PLCs over industrial protocols and present the process as graphics, numbers, trends and alarm lists.
Design matters because operators make decisions under pressure. The ISA 101 standard describes a lifecycle for HMI design and the principles behind what is often called high performance HMI: muted grey backgrounds so abnormal conditions stand out in colour, consistent layouts and navigation, trends that show direction rather than single numbers, and alarm presentation aligned with alarm management practice.
In a connected plant the HMI is also an input point for production data: operators can confirm reasons for stops, enter quality checks, see the current order and work instructions. Done carefully, this gives MES the context machines cannot provide without adding typing work for operators.
Key concepts
- Operator view and control of the process
- Panels on machines, workstations in control rooms
- ISA 101: consistent, high performance design
- Grey backgrounds so abnormal states stand out
- An input point for stop reasons and checks
Questions
What is the difference between HMI and SCADA?
An HMI is the operator interface, sometimes for a single machine. SCADA is the wider system that collects data from many controllers, manages alarms and history, and usually includes HMI clients.
What is a high performance HMI?
An HMI designed to help operators spot abnormal situations quickly: muted colours for normal states, colour reserved for alarms, consistent layouts and trends, as described in ISA 101.
Can the HMI collect downtime reasons?
Yes. Asking for a reason on the HMI when a stop exceeds a threshold is one of the simplest ways to add context to automatically captured downtime.
References
How we help with HMI
We design and build HMI and SCADA screens to ISA 101 principles for plants and system integrators, and add stop reason and quality inputs that feed MES directly.
Interactive 3D demo with simulated data: cut the network and watch the edge store and replay.
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