HMIs and IPCs may look the same, but they have fundamental differences in capacity, performance, and flexibility. Both have their pros and cons, and both are still viable for use in automation systems.
Today, many industrial applications use industrial PCs (IPCs) and human-machine interfaces (HMIs) to acquire, process, store, or display data. If the presence of both in factories is quite common, the design of an IPC or HMI is often indistinguishable from each other. Most likely, you won’t even be able to tell them apart at first glance. Many users even call an IPC HMI, adding to the potential confusion.
However, there are technical differences between the two that go beyond their outward physical appearance. These differences include the feature set, connectivity, levels of flexibility to modify or add functionality to the system, and last but not least, overall performance.
This white paper explores the main differences between HMIs and IPCs and points out what criteria you should consider before equipping a new machine with one or the other.
First, let’s take a look at the operator panel HMIs. HMIs are pieces of hardware specially designed to communicate through a communication protocol to a programmable logic controller (PLC).
You can think of them as a monitor for the PLC, but there are other use cases. Older HMIs used serial communication protocols like MODBUS RTU, PROFIBUS, or DeviceNet. On newer HMIs, it is more than likely that the main communication interface will be an RJ45 Ethernet port that talks about protocols like MODBUS TCP, EtherNet/IP, Profi net, or OPC DA/UA, just to name a few.
HMIs are often proprietary in that they are designed to work flawlessly only with certain PLCs and devices from the same vendor. Third-party connectivity can be a challenge, depending on how well or poorly a given communications driver is integrated into the HMI firmware. It is certainly not a given that all PLC models and/or communication protocols are seamlessly supported in the required HMI design software.
Also, traditional HMIs are generally only supported by manufacturer-specific HMI design software. This locks users into a single manufacturer. While a captive audience is certainly good for the manufacturer, it may not be as advantageous for the user.
Also, the multitude of HMI design software packages available on the market are typically not compatible with each other. This means that you cannot transfer HMI visualization projects from Vendor A to Vendor B. If you want to move your HMI project, you will usually have to re-create your visualization application from scratch. That, in turn, increases development cost and time; Not to mention that it complicates the support aspect after the implementation of the automation system.
HMIs often cover small screen sizes from about 4 to 12 inches, but some manufacturers also offer larger screen sizes such as 18.5-inch widescreen units. Traditional HMIs mainly use the older resistive touch technology that only allows one-touch operation. If you like gesture control like swipe or pinch zoom or multi-touch capabilities, you should look at HMIs that feature a capacitive touch screen.
Keep in mind that the more features you add to an HMI, the closer you get to the feature set and price of an IPC. In this case, the cost advantage of an HMI over the industrial PC decreases to a point where it would be better to change the display concept to an IPC-based system.
Traditional HMIs are specially designed pieces of hardware that have a small footprint, closed operating system. The downside is that you cannot install any software on them, as the manufacturer locked the operating system at the factory and usually only provides a Runtime for the display software.
The advantage is that you cannot introduce viruses or malware into a closed HMI as easily. Plus, they don’t require a formal shutdown like a traditional PC. We will see more about this when we take a look at the IPCs below.
HMIs also often use slower processors, as they don’t need much “reserve” to accommodate other tasks or software packages. The HMI manufacturer needs to balance manufacturing costs against required performance and as such must find an acceptable compromise in their hardware design to get the job done.
Some newer open HMIs, such as the HTML5 web panel, attempt to further blur the line between HMIs and IPCs as they no longer rely on specific communication protocols or PLC models
They use the open HTML5 protocol and simply connect to a web server via an IP address, much like a web browser on a computer would connect to a website. This allows the connection of these web panels not only to a PLC, but also to other devices with an integrated web server. An example would be a configuration or diagnostic page on an IIoT-enabled AC drive.
Factory computers are nothing new anymore, and many can completely replace a traditional PLC and HMI. One of the benefits of an IPC: It can serve multiple purposes within a system, so an IPC device can act as a logic controller, data concentrator, and/or operator display interface all in one piece. This lowers costs and increases performance and capacity.
IPCs have more processing power, more system memory (RAM), and usually much more mass storage space. Their greatest advantage is also their greatest potential disadvantage: They have an open operating system. The current operating system of choice for the factory is Windows 10 IoT, which is the industrial version of Windows 10. While it may seem like the home or office version of Windows 10, it removes some of the components not normally needed in the office. factory, such as games, the Microsoft store, or Cortana.
Windows 10 IoT therefore has the advantage of having a smaller footprint for the operating system, allowing it to fit smaller and lower-priced mass storage devices. This is an important aspect, as industrial applications often require more robust, but also more expensive, solid-state mass storage devices.
The IoT version also offers other conveniences. You can obtain a pre-license from the IPC manufacturer, which eliminates the need to connect the IPC to the Internet to complete the Windows registration process. Another advantage of the IoT version is that it gives the user full control over updates or permanently turn them off completely.
Older IPC systems can still run Windows 7; however, this is not recommended for new systems because the Windows 7 operating system no longer receives updates, patches, or security fixes from Microsoft. This would make such systems vulnerable to malware or ransomware if left connected to the Internet without proper precautions such as additional hardware firewalls.
As with any open operating system, you can install any type of software from any type of vendor on an IPC. Again, this can pose security risks if malware or a virus were to reach an IPC via a USB stick or the Internet. Therefore, there must be good software and hardware protection, which must be regularly reviewed and updated.
IPCs use higher performing CPUs (think Intel Core i-series) and more RAM. IPCs typically feature larger screen sizes than traditional HMIs. Larger screens allow more data to be displayed at the same time, or can make it easier for the operator to view the data. Numerous interfaces such as dual Ethernet ports, multiple USB and/or serial ports allow connection of more hardware and help future-proof applications more easily compared to a traditional HMI.
You usually don’t have to rewrite your software much when upgrading or changing your IPC hardware, since they all use a common Windows-based operating system. Obviously, changes to screen size, resolution, or aspect ratio should be taken into account as they can affect how data is displayed on the screen.
With the advent of portable devices like tablets, you may be asking yourself, “Why do I need an HMI or IPC on my machine?” While an IPC tablet is ideal for personal use, it is not industrial grade and, due to its mobile nature, could easily be lost or stolen.
While some analytical data could certainly be displayed via the cloud, any critical machine data must be displayed on a dedicated, industrial-grade HMI or IPC that is permanently installed and in full view of the operator. This increases machine uptime and is also a safety feature to protect the machine and its operator. However, tablets and other mobile devices can be used in addition to the fixed HMI / IPC, e.g. eg for remote operation.
Industrial hardware, be it HMI or IPC, is also designed for harsher environments and offers more mechanical protection against shock, vibration or extreme temperatures.
Conclusion: a place for both
HMIs and IPCs may look the same, but they have fundamental differences in capacity, performance, and flexibility. Both have their pros and cons, and both are still viable for use in automation systems. In the end, weighing the specific needs of each application, based on factors such as performance, cost, size, and feature set, will determine which is the best option.