I am trying to understand the meaning of 'Trip force' of keypad dome on these pages, and this, and this.

Example: Trip Force: 14.1 oz. [400g]

Does it mean that when I put a mass of 400g on this dome then it will be depressed?

On another website this parameter has a different name 'operating force' and is given in units of gram-force (gf).

Does these 2 websites show same parameter with different names and units or these are different?


See the plot below: (Source https://www.snaptron.com/quality/test-procedures/)

As you gradually push down on the dome, increasing the force that you apply, the switch will begin to displace - at a certain point, $F_{MAX}$, the dome will 'pop' inside out - it is bi-stable, and this is what causes the 'click' and tactile feedback that you feel. After this snap, it takes a lower force to hold the switch down that it took to push it down in the first place.

The 'reverse snap', when the switch pops back to its original shape happens when you remove force from the switch, and reach as low as $F_{RMIN}$.

To answer your question directly, the "Trip Force" will correspond to $F_{MAX}$ on this plot, and any sites that only list the force with units of grammes (a unit of mass, not force), will mean $\text{gf}$. This is simply a typo/error/simplification on their part.

enter image description here

  • $\begingroup$ Newtons comes to mind as the SI unit... $\endgroup$
    – Solar Mike
    Nov 10 '20 at 12:44
  • $\begingroup$ So if the website says the 'Trip force' is 400 gF, does it mean that when I will put a mass of (approx) 400 grams on the dome switch then it will push-down the dome button? $\endgroup$
    – scico111
    Nov 10 '20 at 12:48
  • $\begingroup$ @scico111 - yes it means exactly that. But once pressed, you don't need to keep 400gf on the button for it to remain held down, as you might for a "non clicky" type of button. $\endgroup$ Nov 10 '20 at 20:36
  • $\begingroup$ @JonathanRSwift If I need a higher 'trip force', let us say 800 gf, but I have domes of 400 gf available then if I use two domes under a key (one dome on top of the other) then will it give me approximately same effect as a dome of 800 gf? Assume that a 800 gf dome is not available in the same size as the track size on the PCB. $\endgroup$
    – scico111
    Nov 12 '20 at 6:36

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