To choose an HMI, work back from “what the operator needs to see and press” to screen size, resolution and the way of touch; then confirm which controllers it has to connect to (the ports and the communication method must match); then match the protection rating against the water, chemicals, temperature and outdoor conditions at the installation site; and then look at the screen editing software, memory capacity, logging and maintenance. This article is about industrial HMIs fitted on a machine or control cabinet panel; whole-plant supervisory systems built on industrial PCs are out of scope. It is divided into 4 stages:
Stage ① | Screen and type: size and resolution, touch or keys, mounting height.
Stage ② | Communication and connection: ports, a single brand or several brands, drivers and connection needs.
Stage ③ | Environment and protection: water and chemicals, IP code, temperature, brightness and outdoors.
Stage ④ | Screen programming and maintenance: editing software, tag count and screen count, logging and backup, layering of screens.
This article starts from “you already know the machine needs an operating screen”. Each stage below covers what to do, what public sources say, and what Jiahon can help with; sources, exceptions and this article’s own summary are in the Notes at the end. This is the general case and still depends on the individual case.
Figure 1: The four stages of choosing an HMI — screen and type, communication and connection, environment and protection, screen programming and maintenance (schematic, not to scale).
Stage ①: Screen and type — what the operator needs to see, and how to press
What to do:
Work back from the target application: first write down what the operator needs to see, what to press, and where the operating is done, then choose the screen.
Sort the application first: just replacing buttons and switches; handling data (recipes, trends, records); or supervising a whole system. The third usually needs a full industrial PC and is outside panel-type HMIs.
Size and resolution: a large screen has large touch targets, can be seen from further away and holds more graphics, but cost and mounting space also rise; look at the pixel resolution, which decides the detail of the graphics.
Touch or keys: industry often uses resistive single-point touch, which works with gloves; consumer capacitive multi-touch often fails to sense a gloved finger and is also affected by water. For applications with a lot of data entry, mostly numbers, consider built-in keys, or an external keyboard and mouse.
Mounting height: decide the height of the screen center first; a source mentions about 66 inches (about 1.68 meters, measured from the finished floor to the screen center) as a common target.
What public sources say: A 2019 trade-media selection article (the author is a technical marketing person at a maker) says: selection starts from the needs of the target application, then confirms the options needed; operators usually prefer a larger screen, because touch targets are large, it can be seen from a distance and there is room for graphics, but cost and mounting space also increase; what to compare is the pixel resolution, which decides graphic detail; a screen center at about 66 inches (about 1.68 meters) is a common mounting target; consumer capacitive multi-touch often fails to sense a gloved finger and is also affected by water, while industrial HMIs often use resistive single-point touch, which works with gloves; applications with a lot of data entry may need built-in keys or an external keyboard and mouse (Notes table 1). A 2009 trade-media article (the author is a product manager at a drive and control maker) divides HMIs into three classes: those that replace buttons and switches; those that handle data (recipes, trends, records), for which the article suggests at least a 6-inch color screen and at least 4 MB of memory, plus a flash card; and those that supervise a whole system (functions like SCADA and MES), which need a full industrial PC and several Ethernet ports; touch and keys are about equally durable, the choice mostly depends on user preference, and keys are preferred where there is a lot of numeric entry and gloves are worn. A 2026 distributor knowledge-base article (published by a maker) says the size of full-color TFT displays runs roughly from 3 inches to 21 inches.
What Jiahon can help with:
HMI (Human-Machine Interface): one page lists two panel models: 5.7 inch, QVGA (320×240), 65K colors, 8 MB memory; and 10.4 inch, SVGA (800×600), 65K colors. Both are powered by DC 24 V, and both state dual COM ports plus Ethernet. The touch type and cutout size are not written on the product page; please inquire.
Industrial Touch HMI: 7-inch TFT, resolution written as W320×H240, 32,768 colors, DC 24 V power, panel-embedded. The touch type and cutout size are not written on the product page; please inquire.
Stage ②: Communication and connection — who to connect to, and with what
What to do:
First list the equipment to connect: how many controllers and drives, and what communication port each has; define the connection needs to the controllers before selection.
Ports: Ethernet is the common port for connecting to controller networks; older equipment may still need serial ports (RS232C, RS422/485); one USB type connects peripherals (keyboard, mouse, memory stick, barcode reader) and the other connects a computer to transfer programs without using up an Ethernet port; a model with video output can connect a remote screen.
One brand or several: controllers and an HMI of the same brand have simple support and may share one tag database; mixed brands call for checking how drivers are obtained and updated, their execution speed and the connection method.
Proprietary and general-purpose types: a proprietary type connects just to controllers of the same brand; a general-purpose type needs a driver for that controller. On a mixed-brand site, you can choose an HMI with an OPC UA server function, or use a protocol gateway.
Write the tag count, screen count, number of communication ports and connection distances into one table before asking suppliers (this sentence is this article’s summary).
Figure 2: Three ways an HMI connects to controllers (schematic, not to scale; the ways each device supports differ, so take each device’s written specification as the reference).
What public sources say: The 2019 trade-media article above says: define the connection needs to the PLC network before selection; Ethernet is a common need; serial RS232C and RS422/485 may still be needed; one USB type connects peripherals such as a keyboard, mouse, memory stick and barcode reader, and the other connects the program transfer cable of a computer without using up an Ethernet port; there can be an HDMI output to connect a remote screen so that people can see the screen from a distance. The 2009 article says: a same-brand combination has simple support (just one vendor to find), and the HMI and controller may also share the same tag database; mixed brands call for checking how drivers are obtained and updated, the execution speed of the drivers and the connection method. The 2026 distributor knowledge-base article (published by a maker, with product promotion) says: a proprietary HMI connects just to controllers of the same brand, and a general-purpose one needs a driver for that controller; RS-232 is about 15 meters, RS-485 about 1,200 meters, and Ethernet 100 meters per segment; most HMIs poll the controller every 10 to 100 milliseconds; on a mixed-brand site it recommends choosing an HMI with an OPC UA server function, or using a protocol gateway (Notes table 2).
What Jiahon can help with:
HMI (Human-Machine Interface), Industrial Touch HMI: both pages state dual COM ports plus Ethernet; the Industrial Touch HMI page states that the COM ports are RS232/RS422/RS485. Both pages state support for the communication protocols of mainstream PLCs (the page lists several controller brands) and state that changing the protocol program connects PLCs of different brands. Whether there is a driver for your controller, please give the controller model and Jiahon will check.
The PLC and HMI series page: this is a series page for PLCs, and the same page also lists three touch HMIs: 8.4-inch SVGA (800×600), 10.4-inch (analog resistive touch, supports SDHC cards) and 12.1-inch SVGA (multi-touch); the communication ports listed are USB, Ethernet, RS422/485 and RS232 (depending on the model). Which controller to pair with, please inquire.
The PLC process module series page: this is a series page for PLC process modules, and the same page lists a 15-inch touch HMI with a resolution of 1440×810 and an interface written as PROFINET/Ethernet. For the rest, please inquire.
Stage ③: Environment and protection — what the site will throw at it
What to do:
First look at the environment: whether there is washdown or dripping water, chemicals, vibration, electrical noise, extreme temperature, and whether it is outdoors.
Protection rating: look at the IP code for dust and water; where there is washdown or dripping, also look at enclosure standards such as NEMA 250 or UL 50. The two digits of the IP code speak of solid foreign objects (one digit) and water (the other); oils and chemicals are not discussed by the IP code’s source and have to be confirmed separately (assess with the site’s pollution degree or the safety data sheet).
Be clear which part the stated rating is for: for panel-mount models the product page often writes the rating of the “front panel” (this sentence is this article’s summary; the example is in Jiahon’s product page below).
Compare brightness (in nits), backlight life and operating temperature range together; many ratings are “limited to indoor use”, so outdoors put the unit in a sheltered place or add a sun shade.
Where electrical noise or vibration is heavy, washdown is needed, temperature is extreme or the site is outdoors, a rugged panel, a high IP rating or a sunlight-readable screen may be needed; choose a rugged type from the start so as not to replace it later.
What public sources say: The 2019 trade-media article above says: where there is washdown or dripping, choose a rating that meets NEMA 250 or UL 50; chemical exposure is assessed by the site’s pollution degree or the safety data sheet; many ratings are “limited to indoor use”; outdoors, put the unit in a sheltered place or add a sun shade; display brightness is in nits, and the average backlight life and the operating temperature range should be compared too. The 2009 article says: electrical noise and vibration may call for a rugged panel, washdown may call for a high IP rating, extreme temperature and outdoors call for a sunlight-readable screen, and it advises planning a rugged type from the start to avoid replacement later. A knowledge-base page on a fastener company’s site (no date, no author shown) says: the IP code is IEC 60529, rating the protection of an enclosure against solids and water; the first digit runs from 0 (no protection) to 6 (fully dust tight), and the second digit from 0 (no protection) through dripping, spray, jets and immersion to 9K (close-range high-temperature high-pressure washdown); taking IP65 as an example, 6 is fully dust tight and 5 is water jets from any direction; the page does not discuss oils and chemicals (Notes table 3).
What Jiahon can help with:
Industrial Touch HMI: the product page states a front panel protection of IP65f (dust-proof and waterproof); protection other than the front panel, operating temperature and brightness are not written on the product page; please inquire.
HMI (Human-Machine Interface): the protection rating (front panel and other parts), operating temperature and brightness are not written on the product page; please inquire, take the written specification as the reference, and then compare it with the environment at your site.
Stage ④: Screen programming and maintenance — to last long and be easy to change
What to do:
Editing software: look at how easy it is to pick up (drag and drop, import and export, copy); whether there is offline simulation so that screens can be tested without hardware.
There are three software routes: proprietary, simple and quick to develop, but the program is tied to that brand’s hardware; hardware-independent, which can run on different hardware but may be harder to use and have fewer special functions; and open, fully free, but demanding in development time and software ability.
Runtime functions: static and animated objects, bitmaps, library objects, user permission groups, language switching.
Memory and computing power: tag count and screen count have limits; trends, recipes and built-in calculations take up capacity, so use a conservative estimate.
Logging and backup: an SD card slot can store data logs; remote access can have a web server (view the screen in a browser), FTP (update the program and back up remotely) and e-mail notification.
Layer the screens: ISA-101 divides displays into four levels: an overview of the whole operating area, an overview of a unit or main task, task details, and diagnostics and information.
Supply and support: when changing models, whether the program can be moved within the same brand’s product line, and whether the maker has local support, should be looked at together; some HMIs can also serve as controllers.
Figure 3: The four levels of screens (schematic, not to scale; the level names follow an industry consultancy’s introduction to ISA-101, and for details take the full text of the standard).
What public sources say: The 2019 trade-media article above says: in the setup environment, look at drag-and-drop editing, import and export, and copying, with offline simulation (testing without hardware), and whether the software is free or needs a license; runtime functions include static and animated objects, bitmaps, library objects, permissions for users and access groups, and language switching; tag count and screen count should be checked against the limits the HMI states; trends, recipes and built-in calculations lower performance, so use a conservative estimate; an SD card slot can log data; remote access includes a built-in web server for viewing in a browser, a built-in FTP for remote update and backup, and outgoing e-mail notification; software licensing and warranty should also be compared; for complex or custom needs, it advises getting a sample first, or trying a low-cost simulation mode. The 2009 article says: software is of proprietary type (simple, quick to develop, but tied to one kind of hardware), hardware-independent type (runs on many kinds of hardware, but may be harder to use) and open type (fully free, but long to develop and needing more software engineering ability); some HMIs can also serve as controllers; an expandable product line lets a program be reused between higher and lower HMIs; local support and technical support (phone or e-mail, fees, around the clock or office hours) should be asked about; the author argues for comparing features first and price after. A 2018 article from an industry consultancy introducing ISA-101 says: the standard covers the whole life cycle of an HMI from design, implementation and operation to maintenance, for continuous, batch and discrete processes; it lists four levels of display: an overview of the whole operating area, an overview of one unit operation or main task, task details (including the main control modules), and diagnostics and information screens; HMIs for machines were then under study by a working group and were not within the early scope of the standard (Notes table 4).
What Jiahon can help with:
HMI (Human-Machine Interface), Industrial Touch HMI: the number of tags and screens they can hold, the memory card and backup method, and the editing software and license are not written on the product pages (just the 5.7-inch model states 8 MB of memory); please inquire; whether a program can be moved when changing models, please also inquire.
The PLC and HMI series page: the 12.1-inch HMI on the same page states memory of 57 MB (ROM) and 128 MB (RAM) and an LED backlight life of 60,000 hours; the 10.4-inch model states support for SDHC cards.
When you need to match a type, please prepare five items first: the controller models to connect and their communication ports; the number of tags and screens to display and log; the installation place and environment; whether the operator wears gloves; and whether remote backup is wanted. You are welcome to contact Jiahon.
Further reading: PLC vs HMI: What Is the Difference
Notes: Sources and Exceptions
This is for readers who need to check; skipping it does not affect the practice above. Where your machine specifications, the written specifications of the HMI and the safety standards differ from this article, theirs prevail.
Where each stage comes from
| Source | Where it is used, and where it comes from |
|---|---|
| Source 1 | Stages ① to ④: applications, size and resolution, touch, ports, environment, software functions, logging and remote. A trade-media HMI selection article (June 10, 2019; the author is a technical marketing person at a maker; the page also shows a 2025 modification date) |
| Source 2 | Stages ① to ④: classes, touch and keys, single or mixed brands, rugged types, software routes, vendors and support. A trade-media HMI selection article (March 30, 2009; the author is a product manager at a drive and control maker, older; the page also shows a 2025 modification date) |
| Source 3 | Stages ①②: range of screen sizes, proprietary and general-purpose, distances, polling, mixed brands. A distributor knowledge-base article (May 28, 2026; published by a maker, with product promotion) |
| Source 4 | Stage ④: the four display levels of ISA-101. An industry consultancy’s article introducing ISA-101 (July 25, 2018; just the introduction was read, not the full text of the standard) |
| Source 5 | Stage ③: the IP code. An IP code explanation page on a fastener company’s site (cites IEC 60529; the page has no date and no author shown) |
| Jiahon material | “What Jiahon Can Help With”. From Jiahon product pages |
Table 1 | Screen and type
| Item | Content | Source |
|---|---|---|
| Method | Work back from the target application: first look at the needs of the application, then confirm the options needed | Source 1 |
| Size and resolution | Operators prefer a larger screen (large touch targets, visible from a distance, room for graphics), and cost and space rise too; compare pixel resolution, which decides graphic detail | Source 1 |
| Size of full-color TFT | About 3 to 21 inches | Source 3 |
| Mounting height | Measured from the finished floor to the screen center, about 66 inches (about 1.68 meters) is a common target | Source 1 |
| Touch | Industry often uses resistive single-point, which works with gloves; consumer capacitive multi-touch often fails to sense a gloved finger and is affected by water | Source 1 |
| Keys | With a lot of data entry, consider built-in keys or an external keyboard and mouse; touch and keys are about equally durable, and keys are preferred where there is a lot of numeric entry and gloves are worn | Sources 1, 2 |
| Classes | Replacing buttons and switches; handling data (recipes, trends, records), for which the article suggests at least 6-inch color and at least 4 MB of memory plus a flash card; supervising a whole system, which needs a full industrial PC and several Ethernet ports | Source 2 |
Table 2 | Communication and connection
| Item | Content | Source |
|---|---|---|
| Connection needs | Define the connection needs to the controller network before selection | Source 1 |
| Ports | Ethernet is common; RS232C and RS422/485 may still be needed; one USB type connects peripherals and the other connects a computer for program transfer without using up Ethernet; HDMI output connects a remote screen | Source 1 |
| Single or mixed brands | A single brand has simple support and can share a tag database; mixed brands call for checking how drivers are obtained and updated, execution speed and connection method | Source 2 |
| Proprietary and general-purpose | A proprietary type connects just to controllers of the same brand; a general-purpose type needs a driver for that controller; on a mixed-brand site, an HMI with an OPC UA server function or a protocol gateway is recommended | Source 3 |
| Distance | RS-232 about 15 meters; RS-485 about 1,200 meters; Ethernet 100 meters per segment | Source 3 |
| Polling | Most poll the controller every 10 to 100 milliseconds | Source 3 |
| Reminder | The article closes by saying this is general information and to follow manufacturers’ documents, safety standards and site procedures; it contains product promotion | Source 3 |
Table 3 | Environment and protection
| Item | Content | Source |
|---|---|---|
| Washdown or dripping | Choose a rating that meets NEMA 250 or UL 50 | Source 1 |
| Chemicals | Assess with the site’s pollution degree or the safety data sheet | Source 1 |
| Indoor and outdoor | Many ratings are limited to indoor use; outdoors, put the unit in a sheltered place or add a sun shade | Source 1 |
| Brightness and life | Brightness in nits; also compare average backlight life and operating temperature range; the source gives no numeric threshold | Source 1 |
| Rugged types | Electrical noise and vibration may call for a rugged panel; washdown may call for a high IP rating; extreme temperature and outdoors call for a sunlight-readable screen; plan it from the start | Source 2 |
| IP code | IEC 60529: the first digit is protection against solids, 0 to 6, where 6 is fully dust tight; the second digit is protection against water, 0 to 9K; IP65 is 6 fully dust tight and 5 water jets from any direction; oils and chemicals are not discussed | Source 5 |
Table 4 | Software, functions and screen design
| Item | Content | Source |
|---|---|---|
| Editing and simulation | Drag-and-drop editing, import and export, copy; offline simulation; software free or licensed | Source 1 |
| Software routes | Proprietary (simple, quick, but tied to hardware); hardware-independent (across hardware, but may be harder to use and have fewer special functions); open (fully free, but long to develop and needs more software ability) | Source 2 |
| Runtime functions | Static and animated objects, bitmaps, library objects, user and access group permissions, language switching | Source 1 |
| Capacity | Tag and screen counts to be checked against the stated limits; trends, recipes and built-in calculations lower performance, so use a conservative estimate | Source 1 |
| Logging and remote | SD card slot to log data; built-in web server for viewing in a browser, FTP for remote update and backup, outgoing e-mail notification | Source 1 |
| Vendor side | Software licensing and warranty; some HMIs also serve as controllers; programs reusable within a product line; local and technical support; compare features first and price after | Sources 1, 2 |
| Sampling | For complex or custom needs, get a sample first or try a low-cost simulation mode | Source 1 |
| ISA-101 | Covers the life cycle of design, implementation, operation and maintenance; continuous, batch and discrete processes; four display levels: the whole operating area, a unit or main task, task details, diagnostics and information; HMIs for machines were then studied by a working group and were not in the early scope (2018) | Source 4 |
Standards referenced
The standards cited in this article should be taken in the current edition of each issuing body.
IEC 60529 Degrees of protection provided by enclosures (IP Code) (this article read just an explanation page, not the full text of the standard). Issuing body: IEC (International Electrotechnical Commission).
NEMA 250 enclosure standard (source 1 mentions the number; this article did not read the full text). Issuing body: NEMA (National Electrical Manufacturers Association).
UL 50 enclosure standard (source 1 mentions the number; this article did not read the full text). Issuing body: UL (Underwriters Laboratories).
ISA-101 HMI standard (this article read just an industry consultancy’s introduction, not the full text of the standard). Issuing body: ISA (International Society of Automation).
This is the general case and still depends on the individual case.
Exceptions and limits
What was seen and not seen: this article looked at 2 trade-media selection articles (2019 and 2009, both by maker staff), 1 distributor knowledge-base article (2026, published by a maker), 1 article by an industry consultancy introducing ISA-101 (2018) and 1 IP code explanation page on a fastener company’s site (no date). The full texts of ISA-101, IEC 60529, NEMA 250 and UL 50 were not read, and no data sheet of any Jiahon product was read.
Sources with a standpoint: the authors of sources 1 and 2 are maker staff; source 3 is a knowledge-base article published by a maker, with product promotion. This article takes just general statements and the numbers they themselves write.
Numbers are examples: the range of screen sizes, memory, transmission distances, polling times and mounting height are all examples or rules of thumb from the sources, not selection thresholds. Source 2 is a 2009 article, its memory and screen numbers are very old, and current models have different specifications, so take them just as examples. The distances in source 3 list just RS-232 and RS-485 and do not list RS-422.
Conversion: the conversion between inches and meters was done by this article (1 inch is about 2.54 cm, and 66 inches is about 1.68 meters).
This article’s own summary: “write the tag count, screen count, number of communication ports and connection distances into one table before asking suppliers” in Stage ② is this article’s suggested practice; “be clear which part the stated rating is for” in Stage ③ is this article’s reminder based on product pages that write the rating of the “front panel”; neither is written directly in the sources. The other sentences can be matched to statements in the sources.
Names of standards: NEMA 250 and UL 50 are enclosure standard numbers mentioned in source 1, and this article just writes the numbers, without having read their full texts; for the display levels of ISA-101, source 4’s account is followed.
Scope: this article covers just panel-type industrial HMIs; it does not discuss whole-plant supervision on industrial PCs, HMIs on mobile devices, or price and lead time.
Equipment and products: the figures and wording in “What Jiahon Can Help With” were read from the text of the product pages on October 13, 2026; the product images were not looked at and no specification sheets were read; they were not verified by this article; the specification is as on the product page, and for what the product page does not write, please inquire. The model numbers, series codes and brands on the product pages are not written here; the “also see” and “application scenes” and marketing wording of the product pages are the pages’ own and were not quoted. Which HMIs the site has was found with the site’s product search; a product search is not a stock inquiry, and for stock please inquire.
This article is a summary for the general case, not a restatement of standard clauses, and not an endorsement of any maker, equipment supplier or service provider, nor an assurance for your equipment and process. Please take your machine specifications, the written specifications of the HMI and the safety standards, and your own validation as the reference; this is the general case and still depends on the individual case.