In the beginning most embedded HMI applications were dedicated to handle a particular task in a single piece of equipment. A typical embedded HMI would be used to replace pushbuttons, indicating lights, analog meters, and thumbwheels on an operating panel for a simple machine. It would communicate with the machine's controller, often a Programmable Logic Controller (PLC), via a low-speed serial communications link, and there would be no communications to other devices, controllers, or computers.

Programming of these basic embedded HMIs was done on a PC, with the compiled program downloaded to the HMI via serial communications. The embedded HMI used a proprietary Operating System (OS) and hardware, which kept costs high. Once programmed, an embedded HMI couldn't be modified or changed without reprogramming at the PC, shutting down the HMI, and loading the new program.

Despite these high costs and limitations, embedded HMIs still offered a huge improvement over existing hard-wired operator interface solutions in terms of flexibility, performance, and cost.

The most significant savings resulted from the elimination of PLC inputs and outputs to and from all of the operator interface devices. With hard-wired panel-mounted operator interface devices, every pushbutton needed a corresponding discrete PLC input, every light was driven by a discrete PLC output, every meter required an analog PLC output, and every thumbwheel and potentiometer was wired to an analog PLC input. This was not only very expensive up front, but was a nightmare to change.

With a hard-wired operator interface, a simple addition of an indicating light requires drilling a hole in the enclosure front panel, installing the light and its nameplate, wiring the light back to a PLC output, and reprogramming the PLC. This assumes adequate front panel space and a spare PLC output. By contrast, the task of reprogramming the HMI and the PLC to add an extra indicating symbol is relatively simple.

For machines and other applications requiring a large number of pushbuttons, lights, meters, and thumbwheels or potentiometer – all with corresponding PLC I/O – an embedded HMI provided substantial cost savings. In addition, the embedded HMI might also have been capable of providing some advanced features such as trends and graphs, allowing it to replace a chart recorder.

HMI evolution

To evolve from isolated, basic machine operator interfaces to advanced systems, embedded HMIs took advantage of the same technological changes that have driven the evolution of SCADA systems, namely PCs and Windows OSs.

In the early 1990s, PCs were introduced into factories and plants, typically hosting SCADA and similar software in control rooms. Later in the decade, industrial PCs were introduced, allowing advanced HMI applications to migrate to the plant floor.

After some initial reluctance in the market, primarily due to the poor real-time performance and frequent reboots of Windows, these PC-based advanced HMIs became the de facto standard, which sounded the death knell for the proprietary SCADA and other advanced HMI systems.

The next revolution was in the related areas of bandwidth and networking. Huge increases in bandwidth as a result of the expansion of Ethernet capabilities allowed systems to be easily linked together, ending islands of automation.

The introduction of networking standards such as TCP/IP along with the increasingly open PC-based SCADA architectures enabled plant floor information to be accessed by a growing number of remote devices, such as laptops and office PCs.

After the introduction of PC-based SCADA, the launch of the Microsoft Windows CE OS platform enabled developers to offer many of the tools and functionality found in a PC-based SCADA system to a wide variety of smaller capacity remote devices. As a result, many vendors competed to build low-cost platforms, driving down hardware prices.

At the same time, the Internet paved the way for information exchange among a wider range of hardware platforms, including embedded HMIs, PLCs, and SCADA systems. Embedded and advanced HMI software packages began offering remote access capabilities, first from browsers and then from apps. This wasn't simply a convenience factor, as giving operators and managers the ability to view information from anywhere helped plants to run more efficiently with less manpower.

By adopting Windows CE and its embedded Windows successors as standard OSs, embedded HMI came to look and function more like advanced PC- and Windows-based HMI software packages. For many users, embedded HMI was now more than good enough for their applications, allowing them to switch from PC-based HMI. This resulted in huge cost savings, as everything associated with embedded HMI was much less expensive, including the programming software, runtime licenses, annual software maintenance fees, and the target platform.

With PC-based HMI in an industrial setting, an industrial PC was required along with a monitor. With embedded HMI, a single industrially hardened platform filled the same role, and at a dramatically lower cost. Modern embedded HMI software can reside on embedded platforms with limited processing power, memory, and other hardware resources – but still provide advanced features such as user-friendly graphic interfaces, remote access and real-time reporting, and trending of key performance indicators.

Remote access and user-friendly interfaces

Engineers and operators expect the same ease of use and functionality they get from their personal devices to be present in their work environments, specifically in terms of HMIs. Today's smartphones and tablets set user expectations for wireless connectivity, graphical interfaces, and exceptional mobility, so it's no surprise consumer electronics are becoming a major force for industrial HMI. In fact, many businesses are cutting costs by enacting "Bring Your Own Device" (BYOD) policies, allowing production personnel to use their own smartphones and tablets as mobile HMIs.

HMI users now call for unifying the operator interface experience across all devices. They expect HMI software – whether embedded or PC-based – to deliver the same dashboard experiences across multiple hardware types, from embedded HMI screens to smartphones and tablets, regardless of the OS.

In response, some embedded HMI packages are now offering these features. These software solutions enable applications to be created for embedded HMI devices that can be accessed from PCs, other embedded HMIs, smartphones, and tablets.

By providing HTML5 support, these HMI solutions facilitate access to the main HMI screens, but are properly sized for each device that supports the HTML5 standard. The HTML5 standard is ushering in the end of users suffering slow Internet browser downloads or months-long waits for an app to be created for their particular device, as it allows embedded HMI software vendors to quickly roll out apps to virtually any smartphone or tablet. HTML5 support will become a requirement as BYOD policies become more common, as workers use a multitude of devices on the job and demand the superior performance of apps as compared to browsers.

Not only must data be presented in the same way across devices to improve worker efficiency, it must also be easy to access and manipulate. While multi-touch technology might seem like another "me too" feature, it actually helps users execute commands as much as three times faster than with traditional single touch screens.

With more and more handheld devices being used to retrieve information, users need a familiar and quick method for interacting with data. Multi-touch delivers the familiar functionality of smartphones and tablets to industrial applications such as scrolling, zooming, object rotation, and drill down. Instead of wasting precious minutes during an emergency using dropdown menus and commands to move between screens, multi-touch users are able to locate the necessary information, then zoom into the problem area and make changes in seconds (Figure 1).

The future is upon us

HMI advances have broadened the range of industrial automation interface devices, and it's possible it might one day be replaced with a new term, such as visualization, as applications become more integrated. Perhaps this is even more likely when discussing embedded HMIs.

The days of isolated, expensive, and proprietary HMIs with limited functionality accessible only to a user in front of a machine are rapidly ending. Today's embedded HMI applications instead offer many of the features of SCADA and other advanced HMI systems, but at much more attractive price points, particularly for plant-floor applications that require industrially hardened platforms.

While operators will still be needed on the plant floor in some situations, the spread of remote HMI devices communicating to local controllers and HMIs will greatly increase worker mobility and productivity. This future won't replace the need for humans, but will instead greatly increase their reach across multiple plants and plant areas, allowing them to rapidly apply their expertise as needed to improve operations.

Marcia Gadbois is Vice President of InduSoft, Invensys.

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