What Our Machine Does NOT Measure
It’s important to understand what the texture analyzer can tell us, and what it can’t. It cannot measure actuation point, pretravel, some aspects of the rebound, nor switch lifetime.
Actuation point is one of the more misunderstood switch metrics. For example, with a tactile switch, you’ll see a bump in the force curve; it stands to reason that the bump is the actuation point, right? But those are unrelated; the tactile bump is caused by a part of the switch mechanism that might not be the same part as the one responsible for registering a keypress. In the vast majority of keyboard switches, the part that causes the tactile bump and the part that facilitates actuation are not one and the same, and as a result they don’t generally coincide 100%. Actuation may happen at virtually any point in the key travel, technically. You can see that here:
This brings us to another important clarification regarding the actuation point: There’s a difference between when the switch actuates (triggers a digital event) and when a character appears on your monitor. This process requires a longer explanation, but in a nutshell, when you press a key, at some point the switch actuates; it sends a digital signal across the PCB and into the MCU; then it goes from the MCU, across another path on the PCB, to the USB bus; and from there the signal flows through the keyboard cable and into the computer, where it’s processed and tells the computer to produce the character on the screen.
All of this happens extremely fast - but there is a certain amount of lag. A texture analyzer is incapable of such a measurement; to do so requires measuring electrical signals, and it would also require precise knowledge of where in the key travel the switch sends the electrical signal. Therefore, we cannot measure the actuation point using a texture analyzer.
If we cannot precisely determine the actuation point, then we cannot accurately measure pretravel, because the pretravel ends at the actuation point.
Further, the texture analyzer cannot measure switch lifetime. We stated earlier in this article why the switch lifetime claims from switch manufacturers are mostly pointless marketing spin. (In short: The vast majority of users will never reach 50 million keypresses in the time they own and use a keyboard, so whether a switch is rated for 50 million, 60 million, or 80 millions presses is meaningless in real life.) In any case, testing those claims is an impossible task for a texture analyzer like the one we use. It requires an incredibly expensive piece of factory equipment that presses all the keys on a keyboard fast enough and over a long enough period of time to measure any claims about switch lifetime.
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