THIN CLIENT HMIs IN
PROCESS AUTOMATION Dr. Marc SeiĂ&#x;ler, Product Portfolio Manager, Pepperl+Fuchs
Virtualisation has become more and more popular in process automation and has opened up more possibilities for how HMI systems can be deployed.
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irtualisation is a technology that stems from the information technology (IT) industry and has become more and more popular in process automation. Virtualisation promises to ease software management while reducing costs. This trend also has an impact on the human machine interaction (HMI) in such systems. Especially in combination with thin client technology, virtualisation provides an easier and cost-efficient way to control process automation systems even in the harshest industrial environments.
What is a thin client? Over the last decade, thin clients have become more and more popular in process automation systems and industrial applications. Especially with the trend to virtualised, centralised automation systems, thin clients represent a powerful and cost-efficient technology enabling the users to access the applications and information that run on centralised hosts (host servers). In contrast to conventional, decentralised automation systems, where usually all data and applications run on powerful PC-based workstations, in centralised automation systems, the data and applications reside on the hosts which are usually servers. A thin
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client only runs the user interface that is required to access the applications on the host (see Figure 1). To do this, a thin client has a minimalistic, usually embedded, operating system (OS) and only provides drivers for the input and output devices (such as mouse, keyboard, touchscreen and monitor) that are connected to the thin client. Additionally, installed communication protocols enable the exchange of the system inputs and outputs between the thin client and host (see Figure 2). All of these remote protocols rely on the same principle. The host generates the user interface (such as GUI and sounds), which is then compressed and sent via an Ethernet-based remote protocol to the thin client. The thin client receives the compressed data, decompresses them and displays them on the screen to the user. User inputs (via keyboard, mouse, touchscreen, etc) are sent in the opposite direction. The thin client captures the physical user inputs and redirects them via the remote protocol to the host. The host decodes the user inputs and delegates them to the hosted operation system and applications. For the applications that run on the host this is transparent, which means that for the applications it looks like the user is interacting locally on the host. Due to today’s high-performance Ethernet infrastructures, the user
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