HMI beep stops on button press: the two causes

Why does the HMI beep stop when a button is pressed?

Because the panel is built that way. With a PLC-commanded beep active, pressing any on-screen button other than a screen-change key, or any function key, silences the tone. The panel maker confirms this as intended behavior, whatever value your logic last wrote to the beep word.

There are two sounds and they have separate controls. The PLC-commanded beep follows the control word: your logic writes 8001H to start it, and the panel sounds it until a write changes the word. The project's help file states that rule plainly: "The BEEP stays on until the bit is turned off." The key click is the panel's own feedback. It follows a different rule that the panel applies with no reference to the word: a press on any on-screen button other than a screen-change key, or on any function key, cuts the active tone. The maker's support desk confirms this as intended, so no ladder edit or address change removes it on this panel family. Work with it: pulse the word so a press costs one tone, and give the alarm an indication no key can reach.

Why did the key-press beeps die when I turned the PLC beep off?

Because the OFF write was a plain zero. On the panel family whose beep word takes the ON value above, the correct OFF word is 8000H. Writing 0000H stops the PLC beep and also takes the panel's own key-click sound down with it.

The observed mapping is consistent. A project that wrote the zero word to end an alarm found every key click gone, including the clicks on a password screen. Changing the OFF write to the correct word ended the tone and brought the clicks back. Whatever the panel does internally, the value you write decides the outcome, so the fix is mechanical: search the program for every constant written to the beep word and make the OFF word printed above the only OFF value. If your panel's help prints different ON and OFF words, run the same test with your values. The key-click check at the end of this page tells you whether your OFF word is the right one.

Which beep stopped, the alarm tone or the key click?

Check which sound disappeared before you touch the project. The two faults have different fixes: a tone that dies on key presses needs a pulse and an independent indicator, while missing key clicks point at a zero write where the logic should have sent the correct OFF word.

Match your symptom to its correction:

• The alarm tone starts, then stops the moment a non-screen-change button or a function key is pressed. Key handling on this panel family. Pulse the word and give the alarm an indicator no key can touch.
• Key clicks went silent everywhere, right after the PLC turned its beep off. A plain zero OFF write is in the logic somewhere. Replace every OFF constant with the correct OFF word.
• The pulsed tone trips on and off unevenly. The ON and OFF writes do not travel over the panel link at identical speed, and fast cycles show it worst. Widen the period; 2.0 seconds cycled more evenly than faster settings.
• The beep never sounds at all. The enable or the address is wrong. Work through the checks below before writing new logic.

What do you check before changing the beep logic?

Confirm the panel link first: the beep enable check box in the project's PLC-panel setup, the control word address one word above that setup's base address, and a safe-state ON test that writes the ON word and makes the panel sound.

1. Open the panel project's PLC-panel setup screen and confirm the beep enable check box is ticked. Note the base address printed there; the beep control word sits one word above it.
2. Match that address against the register your PLC logic writes. A write to the wrong word explains a beep that never starts.
3. With the machine in a safe test state, write the ON word from the PLC and confirm the panel sounds. Test writes on a panel link before you trust them, the same discipline as any operator panel PLC link setup.
4. With the tone active, press a non-screen-change button, then a function key, then a screen-change button, and note which of the three cuts the tone.
5. Write the OFF word, confirm the tone stops, then press a key. A click that follows proves the OFF word is right and the local beep still lives.

How do you pulse the beep so a key press cannot kill it?

AND the alarm bit with a self-resetting 2-second timer. Then use two comparisons on the timer accumulator to write the ON word for the first half and the OFF word for the second, so any key press cuts at most one tone and the next write re-arms it within 2 seconds.

The pattern is a self-resetting timer with two comparisons. The alarm bit runs the timer on a 2.0-second period. One comparison covers the first half of the accumulator and writes the ON word; the other covers the second half and writes the OFF word. The tone becomes beep-beep instead of one held note, and a press that lands during a tone costs you that tone only, because the next ON write is never more than 2.0 seconds away. Expect the two halves to sound slightly unequal: the ON and OFF writes take different times over the link, and 2.0 seconds was the period that cycled most evenly for exactly that reason. The same pulse idea in a different job is in Make an HMI button beep once with a PLC timed pulse.

Worked example: how does a 2-second pulse cycle run the beep word?

A bagging line's reject-jam alarm drives the beep word while operators enter passwords on the same screen: with a 0.1-second time base and a preset of 20, the timer runs 2.0 seconds, the accumulator below 10 writes the ON word for a 1.0-second tone, and 10 to 20 writes the OFF word.

The numbers, step by step. The time base is 0.1 seconds, so a preset of 20 runs 20 × 0.1 s = 2.0 seconds before the timer resets and starts again. The first comparison takes accumulator values 0 to 10 and writes the ON word, holding the tone for 10 × 0.1 s = 1.0 seconds. The second comparison takes 10 to 20 and writes the OFF word, giving 1.0 seconds of silence. The cycle delivers 60 s ÷ 2.0 s = 30 tones a minute, and the worst silence an operator can create with a key press is the 2.0 seconds until the next ON write.

The reject-jam alarm also drives a stack light from its own output, so the fault stays visible through every press, and the password screen still clicks because no rung in the program writes a plain zero. Decision: on this panel family, the correct OFF word for every OFF state, a 2.0-second pulse on the word, and alarm-bit-driven lights keep the alarm working through operator input.

How do you keep the alarm visible when a key press cuts the tone?

Drive a stack light and an external sounder from the alarm bit itself, through a PLC output, so operator input on the panel can never touch them, and use the function-key lights as a second cue the way one project kept a status lamp lit through every press.

Two paths, both fed from the alarm bit. The first is the lighter one: the function-key lights double as the status cue, so when a press cuts the tone, the lamp state still says the alarm is up. Tie those lights to the alarm bit, never to the beep word, or a press will dim the lamp along with the tone. The second is the stronger answer for a loud shop: a PLC output wired to an external sounder and a stack light, sound and light that the panel cannot reach. Wire the output and indicator the way you would for wiring an HMI button and indicator to PLC bits, and size the sounder from its own data sheet and your PLC's output specification; those ratings come from your hardware documents, and no beep-word value affects them.

What do you test after rewriting the beep logic?

Run the full cycle in a safe state: write the ON word and hear the tone, press a non-screen-change button and hear it stop, confirm the next pulse re-arms within 2 seconds, write the OFF word, and finish by pressing a key to prove the key click still sounds.

1. Start the alarm from the PLC and confirm the panel sounds.
2. Press a non-screen-change button: the current tone stops, and the next pulse sounds within 2.0 seconds.
3. Press a screen-change button and confirm the tone keeps running through it.
4. Let the logic write the OFF word and confirm the tone stops and stays stopped.
5. Press any key and listen for the click. A click closes the job: every OFF write is the correct word and the local beep survived the change.

Recommendation: On a panel whose beep word takes the ON and OFF values printed above, make that OFF word the only OFF constant in the program and delete any rung that writes a plain zero. When an alarm has to stay perceptible while operators work the screen, pulse the word on a 2.0-second cycle and hang the stack light and external sounder from the alarm bit through a PLC output, so no key press can take the alarm down with the tone.

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