HMI alarm background color resets on screen change: fix with blink

Why the color drops back on the next screen

Three behaviors sit behind the symptom, and each one is checkable on the panel:

• The alarm's condition is a PLC bit. It stays true no matter which screen is open, so the loss of color says nothing about the process; it is a display issue.
• With the alarm steady, the panel applies the alarm color once, when the condition first turns on. Opening another screen repaints the background with that screen's default, and nothing reapplies the alarm color, so the panel falls back to green. Toggling the switch off and on paints the screen you are standing on; the next navigation drops it again.
• With blink enabled, the alarm reapplies its color on every blink cycle. A screen change can repaint the background between cycles, but the next cycle brings the orange straight back.

Symptoms and what each points to

• Background turns orange when the toggle turns the bit on, then returns to green after you open another screen, with the bit still true. The alarm is steady, so nothing repaints the color after navigation.
• Background holds orange across screens once blink is enabled. That is the fix working: every blink cycle reapplies the color.
• The panel flashes between two colors while the bit is on. The two blink colors differ. That is a visible alarm, useful when the operator must act now, and distracting for a flag that stays on for hours.
• Toggling the switch off and on restores the color on the current screen only. The alarm painted the screen you are on, and the next screen change will drop it again.
• The background never changes at all. Check the bit in the PLC first, then check that the alarm's condition addresses that bit and that the project was transferred to the panel.

The fix: enable blink and set both blink colors the same

The change lives in the alarm's own configuration in the panel's project software, in the alarm that currently drives the background color. The panel's documentation names the backlight color field and its blink option; use the names your software prints, because menus differ between panel families.

1. Open the alarm that turns the background orange and confirm its condition addresses the PLC bit that marks the force or override.
2. Turn on the alarm's blink option for the backlight color.
3. Set both blink colors to the same value. Orange is a common override color; use the one your machine's convention assigns.
4. Transfer the project to the panel the way you normally do, then run the test in the section below.

With the two colors equal, each blink cycle paints the same orange twice, so the eye reads a steady color. The cycle time is the panel's own, and the documentation for the panel in question does not publish a figure; you do not need it, because the color comes back on every cycle either way. If you do want a flashing alarm, set the two colors different and the blink becomes a visible call for attention. If you also want the PLC itself to shift the backlight color outside the alarm system, changing an HMI backlight color from a PLC covers that separate path.

Example: one force bit, four screens and a 4-hour override

The setup: a 3-inch color touch HMI running a four-screen project, with a force or override flag on one PLC bit set from a toggle on the panel. The whole background should read orange while the bit is on, and the override lasts 4 hours of a shift. Default background: green.

The rule in words: a steady alarm paints once and loses the paint at the first screen change; a blinking alarm repaints on every cycle, so it survives navigation.

The arithmetic:

• Screens to survive: 4 screens, so walking from the first to the last is 3 screen changes, each one a repaint. A steady alarm reapplies its color 0 of those 3 times, so the indication dies one change into the walk.
• With blink on, the color is reapplied on every cycle. 4 h = 240 min, so the panel repaints orange on every cycle for the full 240 min the bit is on.
• Visible flashing: each cycle has 2 blink phases, and both phases show orange, so 2 phases with 0 color difference gives 0 perceptible flashes.

Result: the panel reads orange on all four screens for the whole 240 min while the bit stays true. The decision the example produces: an indication that must outlive navigation needs blink enabled and the two colors matched; blink off means the color is gone at the first screen change.

Test before the panel goes back into service

Run the same sequence that showed the fault, with the bit held true:

1. Turn the toggle on and confirm the bit reads true in the PLC, on the PLC side, not by the screen color.
2. Confirm the background goes orange on the screen you are on.
3. Walk to each of the other screens without turning the bit off, and confirm orange on every one.
4. Turn the toggle off and confirm the color drops back the way the alarm's clear behavior is configured. If the panel stays orange with the bit off, fix the clear path before the panel carries a live flag.
5. Power-cycle the panel with the bit still on and check the color again on every screen.

Keep the color as an operator aid. Commission it against the actual bit state, and leave machine safety functions in the PLC logic and the hardware interlocks; a screen color has no place in a safety function.

If the color still will not hold

Work down this list before touching PLC logic:

• Confirm the project with blink enabled was actually transferred to the panel; a saved project leaves the panel running the old one until you download it.
• Confirm the alarm you edited is the alarm that drives the background, and that a second alarm or a screen-level background setting is not competing for the same color.
• Confirm the alarm's condition addresses the bit you think it addresses; watch the bit in the PLC while you toggle.
• An alarm that shows on some screens but misses others is a different fault; HMI alarm priority will not carry an alarm to every screen covers that side.
• If the color and the bit still disagree, stop using the color as the operator signal, capture the project, the bit state and the screen sequence, and take it to the panel maker's official support channel.

To color a single object instead of the whole panel, changing a numeric display color from an alarm tag covers object-level colors driven by the same alarm condition.

The decision

Recommendation: whenever an alarm-driven background color must stay visible across screen changes, enable that alarm's blink option and set both of its blink colors to the same value, orange in the worked example above. Keep the two colors different only when you want a flashing alarm the operator must act on. If the color still drops back with the bit true, check the project transfer, the alarm assignment and the screen-level background settings in that order, and leave the PLC bit logic alone; the bit was never the problem.

Questions