By what mechanism does my digital caliper work ?

Question

I bought one of these , and they are amazingly accurate. They say it works by using capacitance. I cannot under stand how it uses capacitance to make such measurements,upto 150 mm !

Answer 1

Pretty good and accurate... only if you take care of temperature!
It is not capacitance, sorry: it would be way too sensitive to YOU! (as your body changes de dielectric of the capacitor). Much more simple: a small roller (wheel) rolls down the slide as you move the head. As it moves, the rotating roller sends pulses to a counter, the "processor" inside counts the pulses... and displays the distance. (That's how you can reset the zero at any place: you just reset the counter to zero where the head is)
These "rollers" are called, in fact, "rotational encoders" (or "shaft encoders").
There are other methods, for more expensive units, such as a ceramic line-up on the side of it, marked with tiny lines: this is the reference. An optical "encoder" does the same as it moves.

Answer 2

It is done with a linear encoder embedded in the head. along the length of the non moving portion you will often see a pattern of ridges, bumps or lines. The encoder "reads" theses lines and calculates how far the head has moved.
this is also how digital readouts on older lathes and mills.

Answer 3

what is the mechanism of digital callipers?

Answer 4

What the F...