End users expect intuitive user interfaces, and product designers respond by incorporating these interfaces into more products. For industrial automation , touchscreen HMIs are a mature technology and a valuable complement to many machine and process automation applications, extending the functionality of switches, buttons, and lights on control panels. While familiar, it's crucial to carefully evaluate each HMI use case to ensure the right product is selected for the specific application requirements.
First, examine the required HMI functionality and attempt to initially select the devices and software that meet the needs. A more reliable approach is to examine specific application requirements and then work backward to confirm that the necessary options have been chosen.
The environmental conditions of the target application need to be assessed because the HMI must be physically installed in a feasible area. Most options are straightforward, but some are not.
In some environments, if the HMI is vulnerable to being submerged in water or directly sprayed with water, it needs to meet the protection rating requirements of standards such as NEMA 250 or UL 50 for electrical equipment. Cleaning chemicals, process chemicals, or other airborne contaminants can also affect the HMI . The level of contamination at the site or material safety data sheets can help define the expected environmental conditions. Customer specifications, local installation regulations, or preferences may necessitate meeting certain ratings or certification standards.
Another key issue is whether to place the HMI indoors or outdoors. NEMA and UL ratings are often limited to "indoor use only." Even the brightest HMIs outdoors are still susceptible to direct sunlight, which can cause heat problems. Users should consider placing outdoor HMIs in more protected areas or equipping them with sunshades.
Ensure that the HMI environment level is suitable for the application, and that the physical specifications are also appropriate.
HMIs typically contain sensitive display elements and backlights, and may have stricter requirements for operating temperature ranges compared to other automation components. Display brightness and average backlight lifespan should be carefully evaluated. Brightness represents the display's visibility. A constantly lit backlight indicates how long the device can be used.
HMI physical display size and interface
Choosing the right display size often requires a balance. Most operators want the largest possible display size, especially when they need to select touch links, and even when the application is simply for viewing, such as when they need to observe the monitor from a distance, a larger monitor is better. Larger displays provide programmers with more space to develop graphics. A variety of HMI hardware product lines in different sizes can help users learn to use a system across multiple different models.
The software should be easy to use for creating basic graphics, enabling remote connections, data logging, and security.
However, larger HMIs often mean higher costs and may require valuable control panel installation space. The monitor's installation height should meet the working needs of most employees; a common practice is approximately 66 inches from the ground to the monitor.
In addition to various physical display sizes, most HMIs offer multiple color options, and users can compare resolutions in pixels, which determines the level of detail in the graphics display. For certain applications with specific needs, especially those involving data input, users may prefer to use an onboard physical keypad or an external keyboard and mouse. Most designers, following current trends, choose to use touchscreens.
It's important to note that many consumer touch devices tend to use capacitive multi-touch. This technology is generally unaffected by gloved fingers and water, but it can respond to multiple concurrent touches or gestures. On the other hand, industrial HMIs typically employ resistive single-touch technology. Resistive touchscreens can respond to gloved fingers, can only correctly respond to one touch at a time, and are unaffected by external contaminants, making them the preferred choice for industrial applications.
Create a checklist
The configuration environment, runtime functionality, and remote access of HMI software should be evaluated. Programmers typically spend a significant amount of time configuring the HMI environment. For end users, it is important to obtain a software license or confirm whether the software is free. Typical users are interested in the software's ease of use, drag-and-drop editing, click-to-create-object functionality, and whether the most frequently used objects are predefined.
Programmers want to know if the software has good import/export support, database tools, efficient copying methods, and a built-in simulation or testing environment so users can perform proof-of-concept checks and program verification without actual hardware. Programmers use configuration software to create tags that communicate with the PLC and other devices, develop graphics linking to these tags, and configure other built-in HMI functions. The 10 most important functions for user operation are:
●Basic objects: Used to draw static graphics, such as pipes and devices;
●Static library objects: such as water tanks, containers, and silos;
● Bitmap function: Allows users to import their own images;
● Animated objects: buttons, number displays, and bar charts;
● Pre-configured library objects: More complex objects, such as proportional-integral-derivative (PID) panels;
● Advanced objects: including trend, recipe, and alert displays;
●Security: Ability to define users and access groups and assign permissions to objects;
●Language switching: Useful for manufacturers selling equipment internationally;
●Alarm: Indicates discrete and analog alarm conditions;
●Data logging: Used to support offline trend analysis.
Even if the HMI specifications provide the appropriate functionality, users should be aware that actual implementation may not always go as expected. For users requiring a specific look and feel, it is best to conduct a simple comparison of several HMI configurations, list the necessary features, and obtain the configuration software to test them.
Before selecting an advanced application, it may be necessary to investigate the specific details of the HMI. Special attention may be needed on how the HMI handles floating-point labels and any related mathematics or calculations. Logic is typically executed internally within the PLC; information is displayed on the HMI. Some HMIs offer onboard logic, trigger evaluation, execution functions, and event manager capabilities. These features facilitate more granular display and can participate as part of the machine logic. If complex functionality is required, pre-test each function.
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