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Product Selection and Applied Technology Handbook 2021
Assessing HMI Hardware Options
Assessing HMI Hardware Options The importance of HMIs has grown with the increased connectivity of devices and systems in modern manufacturing. To stay relevant to manufacturer’s needs as industry digitizes further, OEMs have to consider multiple HMI options—from built-in and stand-alone displays to color vs. grayscale and processing speeds.
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he technology in modern human machine interface (HMI) display, controller, and communication hardware provides state-of-the-art multimedia functions. Manufacturers today need these displays to be capable of displaying graphics from multiple sources, such as PLCs, memory sticks, and video cameras. While most HMI technology revolves around the software, the hardware and design features of the HMI are equally critical to ensure a robust and reliable interface. PC-based HMIs are known for using what is referred to as an operator interface. The main difference between these operator interfaces and standard HMI panels is the flexibility of the software for PC-based HMIs. This software can be custom written for a particular application or be used to provide a base level of programming. As a result, PCbased HMIs can offer better selection for your software to display your graphics. PC-based HMIs also tend to be physically bigger, allowing them to host a wider range of components and a wider motherboard. They also require a UPS backup to minimize failures after power loss. A particular advantage of PC-based HMIs is that they allow for the use of C code and .Net blocks, along with the basic HMI/visualization functionality. This makes it possible to provide high-powered decisionmaking at the point of machine control. Whichever option you choose, traditional HMI or PC-based, it should be designed from the ground up for industrial applications, instead of being a modification of a commercial design. While commercial products will be cheaper than their industrial counterparts, they won’t last in industrial applications, and may not even function correctly.
SIZE AND COLOR The first thing to assess about an HMI for an OEM should be its display size. Choices typically range from 4.3 to 15 inches. The bigger the display, the easier it will be to view from a distance, but also the more expensive it will be. Another consideration is the amount of information to be shown on the display. If it will be extensive, this could require a larger display, even if the typical viewing distance will be very close. The next requirement is color or monochrome. Monochrome displays are less expensive, but color provides more options when designing screens. Most suppliers only make monochrome available with smaller display sizes, so the only applications favoring these small monochrome displays will be those with limited amounts of information to be displayed on each screen.
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MEMORY AND PROCESSOR PERFORMANCE Like most computer and controller applications, faster CPUs and more memory are desirable. With a faster CPU—millions of instructions per second—quicker operation and response times are realized. An example is instant response to a button press on an HMI, which is highly desirable. Another good indicator of a fast system is one that will start up within a few seconds, compared to others that can take 15 to 40 seconds to boot up. Projects developed for these fast HMIs will download faster and the screens will update faster as well. In addition to faster scan times, more user memory is also desirable. More screens, more graphics, more data, and more programming are available with larger memory. A good target for internal user memory is 50 MB or more with additional memory needs covered by use of an SD memory card or similar. Many suppliers recommend using an integrated system where the HMI runtime is prepackaged with the hardware. This permits the OEM to be confident the HMI has been tested and will run seamlessly with other hardware systems that provide for connectivity.
CONNECTIVITY Hardware connectivity, such as for remote access and monitoring, are becoming as necessary for manufacturers as the device’s control capabilities. These connections in HMIs include Ethernet, USB, and SD memory-card ports. These ports often enable support for multiple industrial protocols simultaneously, as well as FTP server and email functions. Also be aware that HMIs often need to communicate with other HMIs, PC-based HMIs, other computing platforms, and via the internet. Most HMIs will also need to communicate via USB to PCs and other platforms. Given these considerations, an HMI should have, at a minimum, at least the following ports: • One serial RS-232/422/485; • One Ethernet; • One A-type and one mini-b USB; and an • SD memory card. Some suppliers also recommend that HMI hardware should have Power over Ethernet connectivity.
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