Updating software on dozens of operator PCs spread across a plant is slow, risky and easy to get wrong. Central servers with lightweight clients change that, so one update reaches every screen and the hardware on the floor stays simple.
Operator screens no longer need a full SCADA installation on every PC. Web and terminal server clients run the application centrally and simply display it on rugged, low maintenance hardware.
What Is a Thin Client HMI?
A thin client HMI is an operator display that runs little or no local SCADA software and instead shows screens served by a central server, through a web browser or a remote desktop session. It keeps the job of a normal human machine interface while moving the heavy work to the server room.
A thick client, by contrast, has the full runtime installed locally. Each thick client must be patched, licensed and backed up on its own.
Automation.com reports that thin clients used in pharmaceutical plants must meet IP66 for washdown. ARISTA workstations described there use 316L stainless steel housings suited to cleanrooms.
Client Types Compared
Screens render in any modern browser.
RDP session runs the HMI on a server.
Firmware only device with no local OS.
Full runtime installed on a PC.
Many modern platforms now include an HTML5 client as standard. The shift is part of the wider move described in 4 generations of SCADA architecture.
How the Architecture Works
The data side works exactly as in any SCADA system. Only the presentation layer changes.
6 Essential Thin Client HMI Benefits
Screen design still matters on every client type. Follow ISA 101 HMI design practices so pages load fast and stay readable.
Security Essentials
Every client is a network endpoint, so encrypt traffic with TLS and require individual user logins. Our guide to SCADA network security covers zones and firewalls.
Give remote and management users read only views where possible. Apply the principles of zero trust for OT networks and secure remote access.
| Control | Purpose | Example |
|---|---|---|
| TLS encryption | Protect data in transit | HTTPS for web clients |
| User roles | Limit who can write | Operator vs viewer |
| Read only views | Safe remote monitoring | Management dashboards |
| Session timeout | Close idle sessions | Logout after 15 minutes |
Server Sizing Formula
Sized RAM = Required RAM × (1 + Headroom ÷ 100)
Example:
Base 8 GB, 20 clients, 0.5 GB per session
Required = 8 + 20 × 0.5 = 18 GB
With 25 percent headroom, about 22.5 GB
Base and per session figures here are example assumptions. Always use the sizing numbers published by your SCADA vendor.
Thin Client Server Calculator
A single server is a single point of failure for every screen. Plan a standby server using SCADA redundancy architecture.
- One place to update and patch.
- Cheaper, longer lasting field hardware.
- Easy remote viewing in a browser.
- Consistent screens on every station.
- Needs a reliable plant network.
- Server failure affects all clients.
- Some graphics run slower in browsers.
- More network endpoints to secure.
Where They Fit Best
Compare vendor offerings in our list of HMI system manufacturers. Enterprise level planning ideas are shared in enterprise SCADA tips.
Yokogawa FAST TOOLS Specification
Publishing HMI Screens to a Browser
Thin Client HMI FAQ
Related Articles
- What Is HMI
- SCADA HMI Screen Design
- SCADA Network Security
- SCADA Redundancy Architecture
- 4 Generations of SCADA Architecture
External References
- FAST TOOLS General Specification, Yokogawa
- Web Based SCADA HMI Clients Support Remote Service, Automation.com
- Thin Client, Wikipedia
What We Learn Today
- A thin client HMI displays screens served from a central server.
- HTML5 and terminal server clients simplify updates and hardware.
- TLS, user roles and redundant servers keep it secure and available.