Embedded HMIs excel in automation applications

Delivering the right human-machine interface (HMI) experience is critical whenever people need to interact with automation.

By Bill Dehner August 5, 2020


Learning Objectives

  • Industrial PCs (IPCs) are used by many on the plant floor, but embedded HMIs can do many of the same things.
  • Embedded HMIs are seen as the best technical choice for local displays out on the factory floor; industrial PC (IPC)-based HMIs may be perceived as a better fit for larger applications.

The ways we interact with our phones, vehicles, and automation systems have been generalized as human-machine interfaces (HMIs). Using a car, for example, HMIs have progressed over the years from mechanical (manual transmission stick shift), to electrical (headlight switch), to digital (touchscreen navigation controls). Digital systems appear to be the highest evolution of the HMI, and there are a few ways to implement these types of interfaces.

For today’s industrial automation systems, users generally have two options for digital HMIs installed on the plant floor. They can select dedicated HMIs, also known as embedded HMIs, built for purpose. Or, they can choose standard or industrial PCs (IPCs) running more general operating systems (OSs) and IPC-based HMI applications.

Because PCs are so common, many might think an IPC solution is the best choice because embedded HMIs were less capable than IPC-based HMIs. However, embedded HMIs can perform nearly all the same functions of an IPC HMI, with a lower net operating cost, smaller form factor and easier maintainability. Following are some points to consider when deciding between an embedded or an IPC-based HMI.

HMI evolution

The first automation HMIs were simple and physical pilot devices such as pushbuttons, switches, lights and needle gauges. These allowed operators to initiate inputs to automation systems and obtain output indications of status. Some devices, such as selector switches, provided input and output capability. Many users appreciated the immediate response and tactile feedback of these panel-mounted devices serving as human-machine interfaces.

Digital HMIs were a great advance. Users could pack a far greater density of controls and indicators into one interface display, taking up only a modest footprint. The configuration could be updated via software and it was far easier than reworking and rewiring a physical control panel (Figure 1).

Early digital HMIs were mission-specific embedded systems only capable of the specific and limited operations technology (OT) tasks they were designed to perform, making them highly efficient and lightweight from a computing standpoint.

As PCs – and later IPCs and then mobile devices – became available with general-purpose information technology (IT) operating systems (OSs), suppliers created HMI software to run on these systems. IPC-based HMIs quickly overtook embedded HMIs in performance, capabilities, and look-and-feel. However, these features came at a price.

Reasons to use IPC-based HMIs

PCs and their ruggedized IPC counterparts gained functionality and lowered costs due to mass commercial adoption. Major benefits of PCs employed as HMIs include:

  • Rapidly updated high-performance processors
  • Generous memory
  • Large storage
  • Numerous wired and wireless connectivity options
  • Repairable component-based designs
  • Capability to host higher-level functionality software, such as databases and analytics
  • OT personnel could choose from many HMI software packages
  • Improved integration with IT systems.

So what is not to love about the comprehensive flexibility of an IPC-based HMI? In most cases, especially for mid-sized equipment or smaller machines, the overall lifecycle cost for using an IPC HMI exceeds an embedded HMI’s cost. In many situations, IPCs are too feature-rich for an industrial HMI’s job, driving up costs and complexity.

Complications manifest themselves in hardware, OS and software management.

PC-based hardware is modular and economical, but not well suited to the rigors of industrial use. IPCs are built for the target environment, but this specialization means the hardware is more expensive than office-grade PCs.

Another part of the problem is the operating system, which users must carefully manage and update. While embedded HMIs are not immune from the need for performance and security updates, PC-based platforms are much more vulnerable and therefore must be constantly updated to maintain cybersecurity.

A benefit of IPC HMIs is users can choose from dozens of HMI applications, suites and related software products like historians, reporting packages and more. Users can create their own custom-coded applications. However, the diversity of software options places a burden on the end user to confirm interoperability, keep up on licensing costs and requirements and update the software. An IPC can form the basis for an attractive HMI. It may run for years as it was installed, but it is more likely to require ongoing support and updates.

Users also must consider their display needs. Many IPCs are standalone boxes needing a separate panel-mount display. While this means users can mix and match the exact parts they want, it creates more effort on the installation side. Maintaining a consistent panel cutout size for the display is a great concern for future maintainability of any HMI.

For these and other reasons, those considering an IPC HMI should look at embedded HMI options.

Embedded HMIs as the “just right” choice for functionality

The size of the application in terms of tag count and number of displays needed can be a major factor when determining the best type of HMI. For many types of equipment and processes that are mid-size and below, an embedded HMI offers the right level of functionality.

While embedded HMIs may use some commercially-based computing elements, their hardware design is tailored for the role with accommodations for the temperature and other environmental factors associated with industrial applications. Instead of using a resource-hungry general-purpose OS, an embedded OS only needs to host the HMI functionality, which requires much less processing power and memory.

Embedded HMIs are often ready to work right out of the box. Their all-in-one touch screen form factor is easy to work with, presents fewer points of failure than an IPC-based HMI assembly, and lends itself to maintaining a spare on the shelf. They can be quickly deployed, whether for a new project or replacing a unit for an existing system (Figure 2).

Embedded HMIs also can make good economic sense from several standpoints:

  • Dedicated, and sometimes free, PC-based software development environments are easier to set up
  • Runtime software included
  • Complete product pricing typically less than an IPC plus software licensing
  • Compact and robust design is better for installation and maintenance
  • Standalone configurations are less likely to need system updates
  • Faster to replace an entire unit than for an IPC-based solution.

HMI platforms used to compete based on detailed feature sets. Today’s HMIs are quite mature, and there is a lot of crossover between IPC-based and embedded HMIs when it comes to basic functionality. Both types can:

  • Communicate with many types of target devices
  • Support a variety of industrial protocols
  • Are configured with tags
  • Provide a rich variety of graphical objects
  • Offer animation options.

In some cases, that maturity has led to simplification. For instance, extensive animation associated with older HMI designs has fallen out of favor, replaced to a large extent by a simplified high-performance HMI design principles most HMIs can accomplish.

Embedded HMIs are seen as the best technical choice for local displays out on the factory floor, whereas more powerful IPC-based HMIs may be perceived as a better fit for larger applications, such as supervisory systems. Both types of HMIs can communicate with one or more controllers, although most often embedded HMIs are used to connect with just one local controller.

Making the remote connection with an HMI

Remote connectivity is another technical consideration when selecting an HMI platform. There will likely always be a need for some sort of local and control room HMIs. However, developments with mobile device hardware, wireless networking, lightweight communication protocols, cloud connectivity, and the security offered by virtual private networking (VPN) mean many end users are trending toward the use of mobile HMIs.

IPC-based and embedded HMIs can support mobile, and when doing so neither needs a local display. This can be termed as running “headless.” Many IPCs are already headless if a monitor is not plugged into them, and some embedded HMIs are now available in headless configurations. Alternately, a headless embedded HMI can be used to drive a separate touchscreen or large-format display, just like an IPC (Figure 3).

When slightly less can be more with HMIs

There is no doubt IPC-based HMI platforms are very capable. For complicated control scenarios, large systems, and advanced automation tasks such as historization, database management, extensive recipe handling and the like, an IPC HMI is likely the preferred solution. Users can mix and match a wide variety of hardware and software products and configure them as needed.

However, it is also clear today’s embedded HMI platforms provide comprehensive functionality, often approaching an IPC HMI. They feature all the most common HMI visualization functions, and also deliver other services like data, event, and alarm logging. Embedded HMIs are built for installation in harsh field conditions, and provide an easily configured, quickly deployed, and readily maintained platform.

More advanced features such as built-in, cloud-connected remote connectivity make embedded HMIs even more attractive for many applications.

Even in this age of powerful PC platforms, designers should carefully consider the required features for the next industrial human-machine interface application, and review the initial and sustaining costs, to determine if an embedded HMI is the best fit for the next project.

Bill Dehner, technical marketing manager, AutomationDirect. Edited by Chris Vavra, associate editor,  Control Engineering, CFE Media, cvavra@cfemedia.com.


Keywords: Human-machine interface, HMI, embedded PC


What benefits could embedded HMIs bring to your plant floor?

Author Bio: Bill Dehner has spent the majority of his 14-year engineering career designing and installing industrial control systems for the oil and gas, power and package handling industries. He has a BSEE with an associate degree in avionics from the USAF and is currently working for AutomationDirect as a technical marketing engineer.