digital calipers

[skmetal7]

I was wondering how a digital caliper/micrometer works. anyone ever have a thought about this? does it work on some kind of varying resistance on the slide? and how does it measure so accuratly without losing its place (of course when there are no metal chips inside, i hate that).

[edo]

I couldn't figure it out either. I picked up some 6" ones from Harbor Freight (recent coupons advertise them for $6.99). I took one apart hoping to adapt it to my router table. I wanted to remote the display and embed it in the top of the table and hook up whatever it used for measuring distance to the router, but I couldn't separate the two parts. The PCB that the LCD display is on has a bunch of small traces along it that contact the sliding the bar. The sliding bar is composite fiber and doesn't have anything special on it.

If anyone knows, I'd still like to figure out how to mount one on my router table.

[Joey]

I bought a digital vernier scale, the type you can bolt onto a machine slide, for example a quill feed. The orientation of the quick reference scale was wrong for what I wanted ie. the graduated ruler 0 to 150 needed to be reversed, so I thought I`d try prise it apart from the slide.
I lifted the scale slightly and noticed there were what seems to be circuitry lines
printed on the underside of the rule scale which is just held in place with a sticky adhesive. I didn`t know if the reader head would screw up having to possibly read back to front, so I never took it off.

[One of Many]

These scales are basically an absolute encoder, but do have incremental capability.

This link should explain it quite well

DC

[edo]

DC - The link was great in explaining how to pull the data, thanks.
But I still don't understand how it reads movement across the PCB traces, or as Joey said, the circuity lines.

[phantomcow2]

I had it explained to me once. I believe it has something to do with inductance
This is a good thing to research

[NC Cams]

The device is purely a digital counter.

If you get hold of a Red Lion counter catalog, they have "counters" that can count stuff and/or be used to make digital scales to record length from turning screws or moving devices.

The thing being "counted" is either an optical reflection or an electronically sensed edge or perhaps a magnetic flux change.

Again, the Red Lion catalog provided me with an explanation that facilitated an understanding of the technical processes involved.

[Al_The_Man]

AFAIK it uses the Inductosyn method, I believe first developed by Farrand.
http://www.ruhle.com/
You don't see the linear machine scales much anymore.
Do a search for inductosyn theory, should show how.
Mitotoyo make a cheap linear DRO read out on this principle.
http://www.ruhle.com/operation.htm
Al.

[One of Many]

Sorry about that. I thought it included comprehensive information I read a long time ago.

One explanation

One Patent

The guts

There are several different encoding formats of this type of scale.


I have interfaced the Digimatic code with the Parallax SX48, but have not worked with the output of these chinese scales yet. The chinese scales seem to pass through continuous data updates for external use. While the Digimatic output must be requested and has a specific embedded data format.

DC

[Al_The_Man]

It apears they adapted the inductosyn method but replaced the inductive coupling method with a capacitive one.
Al.

[skmetal7]

wow this is way more complex than i thought! cool though. thanks for the explanation and links.

[edo]

I too appreciate the links. Who'da thunk there was "stuff" under the ugly Cen-Tech Made in China sticker on the slide bar.