Fitting a whole A4 page onto a small HMI shrinks 10 pt capitals to under 1 mm, which no one can read at a machine. Crop the page to its text column, split it across three screens at step boundaries, and paginate with next and previous buttons: on a 7-inch 800 x 480 panel the same line lands near 3.3 mm and reads from about half a metre.
A page of maintenance text becomes unreadable when it is fitted onto a small HMI screen whole. The fix is arithmetic. The capitals of a 10 pt line drop to 0.45 mm on a 4.3-inch 480 x 272 panel when the whole A4 page is fitted. They come back to about 2.3 mm on a 7-inch 800 x 480 panel once the page is cropped to its text column and split across three screens. This page works the numbers first, then builds the screens: three cropped images, one screen each, with fixed next and previous buttons. An operator reads the procedure page by page, in order, at a position that stays put.
Why the fitted page shrinks
HMI design software draws each project screen at the physical size of the target panel. When you change the target HMI device, the design software raises a screen scaling choice for the screens in the project; your software's help names the exact prompt. That is the mechanism to work with: a bitmap placed to fill the screen is shown with exactly the panel's pixels, and the panel's pixel count is fixed by the hardware. An A4 page exported at 300 dpi is 2480 x 3508 px, from 210 mm and 297 mm at 300 dots per inch. Fitted whole onto a 7-inch 800 x 480 panel it displays at 339 x 480 px, a scale of 480 ÷ 3508 = 0.137. No export setting changes that, because the panel still has only 480 rows of pixels to show the page in. The recovery comes from showing less page per screen.
Worked example: one A4 procedure page on two panel sizes
The source is a one-page A4 procedure with 25 mm side margins, so the text column is 160 mm wide, and body text at 10 pt. Exported at 300 dpi it is 2480 x 3508 px; the column crop is 160 ÷ 25.4 × 300 = 1890 px wide; three crops are 3508 ÷ 3 = 1169 px tall, with the cuts moved so no step straddles a boundary. Two rules turn pixels into decisions:
- 10 pt is 10 ÷ 72 in = 41.7 px tall at 300 dpi, and capitals are about 70 percent of point size in most text fonts, so about 29 px.
- The FHWA legibility planning figure allows 30 ft of viewing distance per inch of capital letter height; the cautious form, 20 ft per inch, serves fast reading. Panel pitch comes from the datasheet active area: a 7-inch 800 x 480 panel is about 152 mm wide, so 152 ÷ 800 ≈ 0.19 mm per pixel; a 4.3-inch 480 x 272 panel is about 95 mm wide, about 0.2 mm per pixel.
Carrying the 7-inch three-crop case through: scale = 480 ÷ 1169 = 0.411 (the height limits before the 800 ÷ 1890 = 0.423 width does); capitals = 29 × 0.411 = 11.9 px = 11.9 × 0.19 mm = 2.26 mm; distance = 2.26 mm = 0.089 in × 30 ft/in = 2.7 ft = 0.82 m.
| Presentation | 7-inch, 800 x 480 | 4.3-inch, 480 x 272 |
|---|---|---|
| Whole page fitted | 0.76 mm capitals, readable to 0.27 m | 0.45 mm capitals, readable to 0.16 m |
| Three text-column crops | 2.3 mm capitals on a 3.3 mm line, readable to 0.82 m | 1.4 mm capitals, readable to 0.49 m |
| 1:1 crops at panel width | 5.5 mm capitals, readable to 2.0 m, 8 screens per page | 5.8 mm capitals, 13 screens per page |
Distances use the 30 ft per inch figure; at the safer 20 ft per inch, multiply each by 0.67.
The decision: on a 7-inch panel, build the three column crops. Capitals of 2.3 mm read from about 0.55 m at the cautious figure, a normal position in front of a machine-mounted panel, and the whole page costs three taps. On a 4.3-inch panel, no split of the full page passes 1.4 mm capitals, so type the steps as text objects and reserve 1:1 image crops for short cards such as a lockout card.
Build the paginated screens
What you need
- The procedure as a PDF or printout, with its document number and revision
- The panel datasheet line with resolution and active area, for the pitch
- An image editor that crops by pixel count
- The design software's screen-change object and static text object
Steps
- Mark the page breaks at step boundaries. Keep every caution on the same screen as the step it qualifies, and never let a break fall between a warning and the action it guards.
- Crop the side margins off to the text column and convert the width to pixels as mm ÷ 25.4 × 300. A 160 mm column is 1890 px at 300 dpi.
- Split the column into three crops of about 1169 px, moved so no step straddles a cut. The crops need not be equal.
- Export each crop in an image format the panel accepts, BMP or PNG on most.
- Create one screen per crop, name each screen after its page label, and order the screens in reading order.
- Place each crop to fill the screen.
- Put next and previous screen-change touch areas in the same spot on every screen, along the right edge, at least about 15 mm across, larger with gloves. Keep the labels to one line, because on many HMI systems a button label will not take a line break.
- Add a static text label on every screen, such as "Page 2 of 3, Torque check", and a Home control on every screen. Add the entry control on the project's main screen so the procedure opens without menu walking.
Why pagination beats a scrolling text object
Some HMI product lines include a static text object that scrolls on its own. If the operator cannot start, stop and step the motion, the line being read drifts and sits somewhere else each time the reader looks back. A ticker can behave that way; a procedure cannot. An operator with a torque wrench on step 6 needs step 6 to stay put, then a deliberate tap for step 7. Test the text object on your panel model before building on it; when it cannot hold position, paginate.
How to check it worked
- Read check: stand where the operator stands, about 0.5 m from a machine-mounted panel, and read every screen. A screen that fails gets cut in two; never shrink the text further.
- Navigation check: walk entry, next, next, next, home. The last screen needs a deliberate Next behavior, and Back on page 1 goes home or does nothing, by design.
- Glove check: work every button in the gloves actually worn at the machine.
- Hand-off check: hand a technician the panel at the entry screen and ask for one step from the middle. They should reach and read it without help.
- Revision check: compare every screen against the source document, then record the document number and revision on the first screen in a small text object. When the controlled document changes revision, update the screens before the procedure is next used; an on-panel procedure older than the paper one is a hazard.
When to type the steps instead
Typing wins when any of these hold: the panel is 480 x 272 or smaller; the source text is 8 pt or smaller; the whole procedure fits in about 20 lines. Text objects are editable, they survive a change of panel size, and they read well on any pitch. The paginated pages also travel: the same three crops run on a wireless HMI on the maintenance cart, which brings the procedure to the machine instead of sending the technician to the panel. Notices meant for the whole plant, shift targets and safety recalls, belong on a dedicated shop-floor notice board, not on the machine's HMI.
Recommendation: crop the page to its text column, split it into three screens at step boundaries, and paginate with fixed next and previous screen-change buttons whenever the panel is 7 inches, 800 x 480, or larger and the source text is 10 pt. On a 480 x 272 panel, or with source text of 8 pt or less, type the steps into text objects instead, one step group per screen, and keep 1:1 image crops for short cards. Keep the paper PDF as the controlled source and show its revision on the first screen.
Questions
Does exporting the page at a higher dpi fix the small text?
No. Export dpi only sets how many pixels the crop file contains. Once the crop is placed to fill the screen, the panel shows it with its own fixed pixel count, about 800 x 480 on a 7-inch panel, so a 600 dpi export looks the same as the same crop at 300 dpi. Crop to the text column instead; that is what lifts the display scale from 0.14 to about 0.41 on a 7-inch panel.
Why not split the page into more screens?
With a 160 mm text column on a 7-inch 800 x 480 panel, three screens give a display scale of 0.41 and 2.3 mm capitals. Four or six screens still give about 0.42, because the column width, from 800 ÷ 1890 px, now limits the fit. Extra splits only add taps. To get past 2.3 mm capitals, crop the column narrower or use 1:1 columns about 68 mm wide.
What if the source document prints at 8 pt?
Run the same arithmetic. 8 pt capitals are about 23 px tall at 300 dpi, and after the 0.41 scale of a three-crop page on a 7-inch panel they land near 1.8 mm, which reads only within about half a metre at best. Retype those steps as panel text, or move them to 1:1 crops at panel width.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.