Set the HMI backlight saver timeout on a PLC panel

Why does an LCD HMI panel need a backlight saver at all?

The LCD image itself is immune to the burn-in that drove CRT-era screen savers; the part that ages is the backlight lamp, and the saver's whole job is to cut the hours it stays lit.

On the reference family that lamp is fluorescent; later panel generations use LED bars, and the logic holds either way. The lamp is the wear item, and none of the documentation behind this article quotes a lamp-hour rating for these panels, so size the saver in idle minutes and let the saved hours pile up on your own logs. An image-based saver cannot do this job: it changes what the panel shows and keeps the lamp burning behind the picture, which is the opposite of what an idle panel needs.

Where is the backlight saver setting in the HMI project?

Look in the project or terminal configuration for an item named saver, display saver or backlight; on the reference family it sits under Setup > Project Attributes > General as Display Saver, with a documented inactivity range of 30 to 1500 minutes.

You need the panel's project configuration software on a PC, the project file for that machine, and the usual download path to the panel. Vendors file the setting in different places, so search the settings tree for saver, backlight, display off and idle before you conclude the feature is absent.

1. Open the machine's project in the configuration software.
2. Go to Setup > Project Attributes > General and open the Display Saver item.
3. Enter the inactivity interval in minutes. This family accepts 30 to 1500; another family prints its own limits beside the field, and its range rules.
4. Save and download the project to the panel the way you push any project change.
5. Reopen the saved project and confirm the minutes you entered are the minutes that stuck.

Two details worth stating plainly. The field takes an idle-time threshold in minutes, and when untouched time reaches it, the documented action is to switch the lamp off. The setting offers no dimming level: a half-lit idle screen is a different feature, and this family documents none.

What timeout number should you set?

Set the shortest idle gap your shift pattern regularly leaves untouched: 30 minutes for any panel that sits alone for half an hour or more, and note that the top of the range, 1500 minutes, converts to 25 hours.

The timer counts untouched time and every key press resets it, so the value cannot black out a busy screen. It decides only how long an unattended gap runs before the lamp drops. Read your shift pattern against it:

• Panel touched at least every 30 minutes while the cell runs: set 30 minutes. The shift never sees the dark state.
• Idle gaps of an hour or more between checks: 30 minutes still holds, and everything past half an hour of the gap is dark.
• Idle days between campaigns: step up toward 1500 minutes, which is 25 hours and holds one full idle day. A weekend outlasts the cap, so a holiday shutdown still wants the panel powered down with the cell.

One trap worth naming: some terminals carry a second idle timeout that governs the programming or remote connection between PC and panel, usually filed under a dashboard or terminal-settings page. Changing that one adjusts the link and leaves the lamp alone, and if the timeout you are chasing acts on a session, tracing a robot pendant screen timeout gives the order to check such timers in.

Recommendation: set the lamp saver to 30 minutes whenever the cell sits unattended for stretches of half an hour or more, raise it toward 60 minutes only if operators report the dark return as a nuisance, and leave any connection or login timeout at whatever your site's IT rules already assign.

Is a full-screen bitmap a screen saver?

No: a bitmap is an ordinary project object, and on the reference family static bitmaps, dynamic bitmaps and bitmap buttons are all allowed but none of them may overlap another object, so a full-screen image is lit artwork, not a timed saver.

Two consequences follow. A bitmap sized to the whole screen collides with every pushbutton or readout on that screen, so artwork that fills the display needs a screen of its own or free space sized to fit. And whatever the bitmap shows, the lamp stays lit behind it, so it buys no idle relief at all. If you want artwork while the panel is in use, size it to free area, walk every control on that screen for overlap, and review the finished layout before the download. If you want something visible at idle, a logo or shift notes, that is a content wish and it costs the lamp hours you are cutting; a separate offline signage screen beside the cell carries that material on its own lamp, and our display range is where to compare sizes. So: bitmaps for active-screen artwork, Display Saver for idle.

Worked example: how many lamp hours does a 30 minute saver save?

Take a cell that runs one 8-hour day shift, waits through the other 16 hours of each working day, and gets the 30 minute saver: the lamp stays lit for 0.5 hours of the idle gap and dark for 15.5 hours, which is 96.9 percent of the gap.

The arithmetic, step by step:

• Idle window per working day: 24 h total minus the 8 h shift leaves 16 h.
• Lamp lit inside that window: the first 0.5 h, up to the 30 minute threshold, then off. Dark time: 16 h less 0.5 h is 15.5 h.
• Share of the idle window dark: 15.5 ÷ 16 = 0.969, so 96.9 percent.
• Over a planning year of about 250 working days: 15.5 h × 250 days = 3,875 lamp hours a year the lamp no longer burns.
• Cross-check the cap: at 1500 minutes the threshold is 25 h, longer than the whole 16 h gap, so a maxed-out saver would never fire on this pattern. The cap fits equipment idle for a day or more between uses.

Decision for this cell: 30 minutes. The same arithmetic moves linearly with the shift pattern: a two-shift cell with an 8 h overnight gap burns 0.5 h of it, and the yearly figure becomes (8 h − 0.5 h) × 250 days = 1,875 lamp hours.

How do you prove the saver works before sign-off?

Run one complete idle cycle on the real panel: download the project, leave it untouched for the interval plus about 5 minutes, confirm the lamp drops, then operate the panel the way the machine's operators do and confirm the working screen is back and usable.

Run the test with the production screen layout in place, because a layout that looks right while the panel is awake says nothing about the idle transition. Note the time of your last touch, wait the interval plus the margin, and check the state. Then use the same input the operators use every shift and confirm the working screen returns and responds.

Log three lines for the handover: the interval in minutes, the date the cycle passed, and the input that woke it. The next person who meets a dark panel at shift start then reads it as configured behavior.

If the requirement runs the other way, the PLC forcing the screen awake on a schedule for an event or a shift start, that is a separate mechanism with its own register work, covered in Wake an HMI screen from screen saver on a PLC schedule.

Why is the screen still faintly visible when the lamp is off?

The liquid crystal image holds its pattern when the backlight drops out, so a healthy panel shows a very dim picture in a dark cell; seeing that faint image after the interval is the sign the project is running and only the lamp is off.

Use it as the look-alive check during the idle test: a faint image at the expected minute means the saver did its work. A screen with no faint image at all points to a different fault, a panel that lost its project or its power, and a panel that loses its project after a power cycle walks through that check.

Contrast adjustment is a legitimate display control, and operators reach for it when the dim idle picture annoys them. It changes how visible the idle picture is and is a separate control from the saver, so keep it out of the saver decision.

What changes on a Windows panel PC?

A Windows panel PC splits the job in two: the display-off timer lives in the power plan, and the session lock is the security policy Interactive logon: Machine inactivity limit, which accepts 0 to 599,940 seconds, and 599,940 ÷ 3600 is 166.65 hours.

The policy locks the interactive session after the configured number of idle seconds, and your site's security rules usually own that number, so match them. The power plan's display-off timer is the lamp saver's equivalent. For a panel PC that operators touch about once an hour, a 15 to 30 minute display-off timer keeps idle lamp time down without locking anyone out mid-task, and the session lock rides on the site's own figure.

Decision: session lock to the site security figure, display-off timer to the shortest idle gap operators accept, and read the unit on each field before you type, because the HMI field counted minutes while the Windows policy counts seconds.

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