Feature: HMI
The standalone controller Even in today’s ever-more-connected world, there are still cases where process plant operators either can’t or don’t want to connect to external systems and devices. A typical example would be where an older or more basic PLC-style device is used within a machine or process line; see Figure 1. It is still necessary for operators and engineers to interact with the system, but the underlying PLCs do not support wide-area cloud connectivity. In these cases, an HMI of appropriate size and capability
can be used as a standalone controller, providing an interface that ranges from simple mimic panels and virtual pushbutton control of a single machine, to a sophisticated visualisation, historian and alarm package for an entire production line or distributed process, offering a mix of pushbutton and recipe- based control options. Te HMI effectively becomes a single- screen, self-contained SCADA system, providing a cost-effective option where a multi-screen setup is not required.
The graphical endpoint In this case, the HMI panel is considered as a visualisation package for an industrial PC or similar, which provides the edge intelligence for the machine, line, or process; see Figure 3. Here, an edge device enables site intelligence, typically
acting as a gateway, providing data enrichment, aggregation and filtration, leading to actionable insights, which are then conveyed to the enterprise. It may also host user applications designed to manipulate the local data in order to layer control and management strategies on top of the devices connected to it. In these cases, the HMI may simply be a touchscreen display
18 July/August 2024
www.electronicsworld.co.uk
HMINavi’s high levels of functionality provided by the no-code configuration environment can save significant development time and cost when creating a system
driven by visualisation soſtware running on the edge device, but more typically will provide functionality very similar to a standalone controller. Indeed, in many cases, the HMI operates independently of the edge device, interfacing directly to the underlying process to recover its data.
The HMI as a gateway Te concept of using an HMI device as a system gateway is a good solution. Architecturally, the gateway is a point at which data converges from lower order devices, and this is obviously also true of any HMI deployment point. By providing mechanisms for porting applications on the HMI hardware directly, users can handle the device protocol and data recovery capabilities of the HMI system themselves, potentially saving them a lot of development effort. And, using HMI soſtware like Advantech’s HMINavi interfacing to the
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