HMI enclosures for panel PCs and touch displays

Three ways to house a display

Panel PCs and HMIs are built to be mounted in a panel: the bezel and its gasket seal the front, and the electronics sit behind the panel, protected by whatever encloses them. There are three common ways to provide that panel and that protection:

• In the door of a control enclosure. The display becomes the operator face of a larger enclosure that also holds power supplies, I/O and terminals. On a NEMA4 Enclosure wall-mount enclosure with the panel PC configuration, the door is laser-cut to the exact panel opening of the IMD panel PC you choose, deburred and fitted with mounting studs before it ships.
• In an HMI enclosure. A slim shell built around one display, for a screen on an arm, a stand or a machine frame. Ours are 304 stainless, cut for one IMD panel PC from 7 in to 23.8 in, or for an IMD touch monitor with an IMD mini PC on a bracket behind it, with a gasketed rear cover, a VESA 100 rear and an optional operator strip.
• In a custom enclosure. When a display shares a housing with other devices, or the size is unusual, a custom enclosure is drawn around the layout.

The door option suits a display that is part of a control panel. The HMI enclosure suits a display that has to be where the operator stands, away from the control panel, with only network and power cables between them.

The display opening and the front seal

A panel PC seals against the front of the panel with its own gasket, clamped by clips or studs from behind. Three numbers from the device's installation manual decide whether it seals:

• Cutout size and tolerance. HMI manuals typically give the cutout with a tight, one-sided tolerance, for example +1 / -0 mm, or +0.5 / -0 mm on some models. Too small and the unit will not fit; too large and the gasket may not cover the edge.
• Panel thickness range. Clips work over a stated range, for example 1.6 to 5 mm in one HMI manual. A thin panel can also warp under clamping, and one manual warns that a thin installation wall may need strengthening.
• Clamp torque. One maker specifies 2.3 to 2.6 N·m on the clip screws "to provide a proper seal", and warns that the gasket is a compression seal, so sealing compounds must not be used.

The front rating of an HMI applies only as installed: one manual states that its front rating applies "on the front panel when properly installed in an enclosure". Gaskets age, and HMI makers recommend replacing them on a schedule; one says at least once a year. The cutouts and HMI windows guide has more on cutouts for other HMIs. For our HMI enclosures and panel PC doors, the opening is cut for the specific IMD panel PC, so the cutout matches that unit.

What IP65 at the front means

An IP65 code under IEC 60529 has two parts. The first digit 6 means dust-tight: no ingress of dust. The second digit 5 means protected against water jets: the IPX5 test uses a 6.3 mm nozzle delivering 12.5 L/min from 2.5 to 3 m. IPX6, the "powerful jets" level of an IP66 enclosure, uses a 12.5 mm nozzle at 100 L/min. So an IP65-type front takes a hose rinse, but it is a lighter test than the one a NEMA 4X-type / IP66 enclosure body is rated to.

In washdown areas that means:

• Rinse the screen and bezel; do not aim a hose or lance straight at the edge of the display seal.
• Hot, high-pressure washdown at close range is a different test (IPX9 or IP69K), which neither the display seal nor the enclosure is rated for. See washdown enclosures for food and beverage.
• The finished assembly is rated by its weakest part. NEMA's rule is that a field-installed assembly's rating is limited by the least severe rating of its components, so every gland and opening on the housing needs at least the same rating.

The IP rating chart explains every digit and how IP codes relate to NEMA types.

VESA mount or panel mount?

A panel-mount display seals into a panel, and the panel needs something to hold it. A VESA mount is the other half of that problem: a standard hole pattern on the back that lets a display or housing go on an arm, a pedestal, a yoke or a wall bracket.

The VESA Flat Display Mounting Interface standard (FDMI, often called the VESA mount) has parts by display size. Part D covers flat displays from 12 in to 22.9 in diagonal weighing up to 14 kg (30.8 lb). Its center mounts are the familiar square patterns: 100 x 100 mm (MIS-D 100) and 75 x 75 mm (MIS-D 75, for displays up to 8 kg), fixed with M4 machine screws. Larger displays move to Part E (23 in to 30.9 in, up to 22.7 kg, six-hole interfaces) and Part F (31 in to 90 in, multi-hole interfaces).

Our HMI enclosures have a VESA 100 rear, so the whole sealed housing, display included, goes on an arm or bracket made for that pattern. Two checks before you order the arm:

• Weight. Rate the arm for the housing plus the display, not the display alone, and keep within the VESA part's limit.
• Cable route. Arms that tilt and swivel need a cable loop that does not pull on the glands at the end of travel.

As with any type-rated enclosure, fix the housing by its external mounting points; NEMA notes that many type-rated enclosures need a mounting means external to the electrical cavity. See the enclosure mounting guide.

Heat from the PC

A panel PC, or a touch monitor with a mini PC behind it, is a heat source inside a sealed box. With no air exchange, the heat leaves through the walls, and enclosure thermal guides use the relation heat dissipated = k x A x temperature rise, with k about 3.7 W/m²K for stainless steel. As an illustration of the scale: a housing with 0.2 m² of exposed surface, held to a 15 °C rise, sheds about 11 W. Slim HMI housings have little surface, so this is the check that matters.

• Compare the PC's power draw with what the housing can shed, and keep the inside within the PC's rated operating temperature from its datasheet.
• One enclosure maker's thermal guide notes that the reliability of electronic components is cut in half for every 18 °F (10 °C) above about 72-75 °F, so a few degrees matter.
• Do not add a fan that exchanges outside air: it breaks the seal unless it carries the same rating.

If the numbers do not work, choose a lower-power PC, move the PC into the main control enclosure and run only the display to the operator, or go to a larger enclosure. The enclosure heat calculation guide has the full method.

Sun, glare and viewing height

Outdoors and under skylights, the sun adds heat and washes out the screen. One enclosure maker's thermal guide puts peak solar load at about 97 W/ft² over much of the United States, and its tests showed a sun shield cutting the temperature rise by 25% (top only) to 56% (wall-mount shield). Shade the display where you can, with a canopy, a hood or simply by orientation; if you need a hood on a custom housing, ask in your quote request; whether we can build it is confirmed on the quoted drawing.

Indoors, glare is mostly about placement. OSHA's computer workstation guidance is to place the screen so its top line is at or below eye level, and perpendicular to windows. On an arm, that means setting the pivot height for the operators who will actually stand there, and angling the screen away from windows and bright overhead lights.

Cable entry and service

Every cable into the housing (power, Ethernet, USB, a barcode scanner) passes through an opening that has to keep the seal. Use cable glands rated at least to the housing, sized to each cable's diameter, and bring them in from below where you can, so water runs off the entries rather than into them. Leave a service loop inside so the rear cover can come off without pulling on connectors, and use connectors with strain relief.

Keep the number of entries small: every extra opening is another seal to maintain. A single network cable and a power cable are often enough when the PC runs the HMI software. For thread types, hole sizes and gland torques, see the cutouts and cable glands guide.

Choosing the display and the housing

Start from the display. The HMI enclosure page filters by the IMD panel PC each housing is configured for, from 7 in to 23.8 in. If you are still choosing the computer, compare industrial panel PCs by screen size, power draw and rated operating temperature, then pick the housing cut for that model. For a display in a control panel door, choose a wall-mount enclosure with the panel PC configuration. For anything else, such as two displays, a display with a row of pushbuttons, or a different HMI, send us its cutout drawing with a custom quote request; the custom enclosure specification guide lists what to include.

Frequently asked questions

Sources

1. VESA, Flat Display Mounting Interface (FDMI) Overview (Parts B to F, size and weight ranges)
2. Wikipedia, "Flat Display Mounting Interface" (MIS-D 75 and 100 patterns, weights, M4 screws; from VESA FDMI v1 rev 1)
3. IEC 60529 Ed. 2.2, Degrees of protection provided by enclosures (IP Code): IP6X, IPX5 and IPX6 test conditions
4. NEMA, "NEMA FAQs: Enclosures" (Q15 weakest link, Q16 external mounting)
5. Pro-face GP4000 series hardware manual (cutout tolerance, panel thickness, warping, gasket replacement, front rating)
6. Rockwell Automation, PanelView 5510 / Plus 7 stainless installation (clip torque, compression gasket)
7. Hammond Manufacturing, heating selection (k for stainless steel)
8. nVent HOFFMAN, Spec-00488, thermal management (reliability, solar load, sun shields)
9. nVent HOFFMAN, Spec-01113, wall-mount sun shield test
10. OSHA eTool, Computer Workstations: Monitors (top line at or below eye level, perpendicular to window)