Wake an HMI panel's backlight from a PLC event

What turns a blanked panel back on

Three things can light the glass, and only one of them takes its orders from the PLC:

• A touch. It works, and it needs a person standing at a dark machine.
• A longer saver timeout, or the saver off. That only postpones the blanking. The panel still goes dark, and the PLC still has no say in when it lights.
• A backlight event. The Event Manager Database watches its conditions and runs each event's actions when a condition is met; the Backlight entry in the action list turns the backlight OFF or ON. This is the piece that carries a PLC condition.

Panels whose editor carries an Event Manager Database use the names in the steps below. Other editors move the same two pieces, a condition trigger and a backlight action, elsewhere in their event or macro system.

Keep the two jobs separate: the tag says when an operator is needed, and the backlight action restores visibility. Wire the wake to the Backlight entry explicitly; alarm banners and screen changes are other actions with other jobs.

What you need

• The panel's programming software and its project, with the Event Manager Database on the Database tab.
• A PLC tag the panel can read, one that sets exactly when an operator must look at the screen.
• Your plant's normal download path from the editor to the panel.
• About 15 minutes at the bench: at a 1-minute test timeout, three wake cycles fit with room to spare.

Set up the wake event, step by step

1. Pick the tag. Choose the tag that goes true exactly when an operator must look: a start command, a fault, a batch ready. Watch it set in the editor's online monitor while the machine runs. If the panel-to-PLC link is new, run the checks in the operator panel PLC link setup first.
2. Open the event database. In the programming software, open the Event Manager Database on the Database tab.
3. Create the event. Give it the condition tag true. When several conditions should light the screen, create one event per condition.
4. Add the Backlight action. The action list carries alarm banners, messages and email as separate entries, and backlight control is its own entry. Add the Backlight action and set it to turn the backlight ON.
5. Leave the saver on. Set the screen saver or backlight saver timeout to the shift's longest hands-off stretch. The backlight saver timeout setup covers that setting in detail.
6. Download and power-cycle. Save, send the project to the panel by the normal procedure, then power the panel off and on once, so the bench test runs what the panel will actually run on Monday.

Event systems differ in when they act: some fire the moment the condition turns true, others re-run while the condition holds. The editor's help states which style your event uses, and the bench test below makes the panel show you. Write the answer down for maintenance.

Worked example: a start pushbutton on Monday morning

Inputs: the panel blanked at 5:00 pm Friday under its saver timeout, and the first start press of the week lands at 6:00 am Monday (scenario values for a weekend shutdown). The event is configured as above, with the start-command bit as the condition and Backlight ON as the action. The help file's description of the Event Manager Database, events that watch their conditions and run when a condition is met, is what lets the wake cross a weekend.

Rule in words: the dark hours run from the moment the saver blanks the panel to the first moment the condition is true, and the Backlight ON event ends them the instant the condition turns true.

Arithmetic: Friday 5:00 pm to Saturday 5:00 pm is 24 h; to Sunday 5:00 pm is another 24 h, 48 h total; Monday 6:00 am adds 13 h. 24 + 24 + 13 = 61 h.

Result: 61 hours in which the only wake available was a walk to the machine and a touch. Batch counters and messages could refresh the whole time; refreshed content on black glass is still black glass.

Decision: with the event installed, the panel lights the moment the start bit sets at 6:00 am Monday, and the operator reads the screen without touching it. The threshold to check before you rely on it: if the only writer of the wake tag is the panel's own touchscreen, the event can never fire from a dark panel, because a blank touch screen takes no press. Put the condition on something written while the panel sleeps, such as the machine's start chain or a batch request from the PLC. Keep machine start interlocks in the PLC and the safety hardware; a backlight event is a visibility function, and no safety condition should depend on it.

Bench-test the wake before the panel returns to the line

Set the saver timeout to 1 minute for the bench run, so a blank cycle takes a minute instead of a shift, and restore the production value afterwards.

1. Condition false. Leave the tag false, let the panel blank, then set the tag true. The glass should light and the current screen should be readable.
2. Condition retriggered. Clear the tag and set it again while the panel is awake. This catches a transition that never lands or a second condition that never fires.
3. Condition already true. Set the tag true first, then let the panel blank while it holds true. If the panel lights right away, your event re-runs while the condition holds; if it stays dark until the tag pulses off and on, your event acts on the transition. Write down which one yours is.

Pass means glass lit and screen readable. A current number under black glass is a failed test. When the panel stays dark, check in this order: the downloaded project is the one with the event; the tag changes in the online monitor; the action entry is Backlight, set to ON; the condition's address matches the address the PLC writes. Record the tag, the event and the timeout for maintenance, so a dark panel on a Monday reads as a sleeping panel first and a fault second.

Clock schedules, panels that stay lit, and the aisle board

A clock can own sleep and wake too: sleep at 7 pm, light at 7 am, no event required. That setup, and the tests a schedule needs before it becomes the production recovery path, are in Wake an HMI screen from a screen saver on a PLC schedule. The two designs combine: the clock handles the idle hours, the event handles demand.

Panels a walking shift must read with no machine event are the one case for the saver off. A lit backlight spends its rated life in hours whenever it is lit, so reserve that for panels where the reading never waits for a condition.

Recommendation: drive Backlight ON from the tag that means an operator is needed, keep the saver enabled at the shift's idle timeout, and pass all three bench states before the panel goes back on the machine. Leave the backlight on only where a walk-by must see the panel with no event, and put faults the whole aisle should see on a separate andon-style board; our shop-floor signage is built for that job.

Questions