[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.

[One of Many]

I'm not sure Al. The capacitive design has its limitations for environmental conditions. The Patent I posted was from 1986, so some improvements have been made. The early digital calipers really sucked. Every time I picked them up, they were auto off'd so you would need to close them to recalibrate and turn them back on. Moving them too fast was a huge problem too.

Mitutoyo made them reliable and affordable. The accuracy is still +/- 1 or 2 counts, which could be an issue on a machine tool DRO.

I do get a chuckle out of some folks claiming to read their calipers to the nearest 1/2 thou. Reading it and trusting it are a whole lot different!

I would not trust any digital caliper with .0005 resolution below .002 precision fits. It can be even worse(and poor practice) when taking an ID measurement with one set of jaws and an OD measurement with the other and foolishly expect precision fits.

Much wiser if you MUST use calipers, to use telescoping gages on ID's and the like to measure over and retain the same reference scale using the same jaws. Periodically taking a measurment on a known standard on both pairs of jaws will keep that trust in check.

DC

[phantomcow2]

I'm not sure Al. The capacitive design has its limitations for environmental conditions. The Patent I posted was from 1986, so some improvements have been made. The early digital calipers really sucked. Every time I picked them up, they were auto off'd so you would need to close them to recalibrate and turn them back on. Moving them too fast was a huge problem too.

Mitutoyo made them reliable and affordable. The accuracy is still +/- 1 or 2 counts, which could be an issue on a machine tool DRO.

I do get a chuckle out of some folks claiming to read their calipers to the nearest 1/2 thou. Reading it and trusting it are a whole lot different!

I would not trust any digital caliper with .0005 resolution below .002 precision fits. It can be even worse(and poor practice) when taking an ID measurement with one set of jaws and an OD measurement with the other and foolishly expect precision fits.

Much wiser if you MUST use calipers, to use telescoping gages on ID's and the like to measure over and retain the same reference scale using the same jaws. Periodically taking a measurment on a known standard on both pairs of jaws will keep that trust in check.

DC

I would have agreed with you a month ago, especially on the inside-outside measurement. Since getting my Mitutoyo coolant proof calipers though, I have been blown away. When I got it, I took measurements of bore gages to test the ID measuring and some size blocks for outside measurements. When I tested with a .5" block, it LCD read .5000"
When I tested with a .4999" block, the LCD read .4995". The fact that it was able to detect even the .0001" is damn impressive. I had my boss try it out as well, he got the same. My old Chinese calipers never did that.

[phantomcow2]

That said, if I was getting two parts to a precision fit, I would use a micrometer.

[kentavv]

I am installing some of the Chinese scales on a mill. Is it OK to cut them to length or will that destroy them? Is there any special consideration that must be taken when cutting them? Any chance anyone knows where I might be able to get a cable to attach to the scale at a right angle?

Thanks.

[Willbird]

I also have to say that every set of modern Mitutoyo I have checked to a calibrated ring gauge was DEAD on :-).


I have owned Mitutoyo since the early brown/tan colored ones that kind of sucked,

best buy for the $$ of any precision tool I know of

Bill