I've built a setup for determination of a linear position using an inexpensive slide potentiometer. The accuracy isn't good enough for what I need, and it also is inconsistent (hysteresis). I don't really know where to start with wiring an LVDT to the Arduino; and also I don't really want to spend $300+ on an LVDT. Does anybody have a suggestion for a sensor that will get accuracy of .001", other than an LVDT?
Thanks!
Does anybody have a suggestion for a sensor that will get accuracy of .001"
That's asking a lot. Over what range? 0 to 1"? 0 to 10'? 0 to 3 miles?
You may want to check some of the below post.
Range is only around 1".
.001" for 0-1", that's 1,000 steps. 10 bit A/D has 1023 steps. Cutting it pretty close and downside is worst case Atmel AVR spec for accuracy, non-linearity, etc, spec is +/- 2 LSBs, so it's really a great 8 bit A/D 256 count convertor.
You might want to consider some kind of mechanical coupling (linear to circular, say rack and pinion or friction drive) to a high enough resolution optical quadature encoder. Just count the steps rather then try to measure them, always more accurate in the digital world. That's how those digital micrometers and calipers work.
Lefty
Inexpensive tinkering.
Sorry I didn't provide the whole picture. All I'm doing is measuring linear position, then using that value for a computation (several times a second). Right now I'm using a slide pot with a range of 0-.787" (cost ~$3). It would be fine, except for the hysteresis error. While output should be linear, I'm getting a slight curve as the distance is consistently increasing, and a different curve as the distance is decreasing. Maybe I just need a better quality slide pot, I'm not sure.
Connecting to a digital caliper sounds promising, unless there is a chance I will run into the same problem.
I guess a mechanical gain such as a rack & pinion setup would work, but I would be hard pressed to create something with such tight tolerances on such a smalls scale.
Other alternatives: use a rack-and-pinion setup to drive a rotary encoder, or reflective sensors to measure the passage of a printed strip of alternating black and white bars.
Some old mainframe disk drives used an optical grating, typically created with vacuum deposition on glass, for really precise reading of the head position. You might find some of those in a surplus store somewhere (although it's a long shot).
I've been looking through the forum and there are lots of posts on using digital calipers with the arduino...but, they all seem to run into problem after problem. Has anyone been successful to take that signal and capture a corresponding measurement?
If you use appropriate gearing, you might use a multi turn pot like below.
https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2111880_-1
if the linear movement is SLOOOOWWWWWW and under your own control, then you might
consider converting a servo, like I did.
I used this hack in order to fill & empty a large syringe
(making a model submarine dive and surface)
It worked very well.
you can determine displacement by counting rotations.
just be sure to use limit switches because this thing is strong.
you will need a limit switch for determining the origin anyway.
one whole turn is equivalent to the displacement of an M3 nut over a
threaded rod. but you could also count rotations of other gears, and
increase resolution
http://users.bart.nl/~raalst/kilo/propkolben.html
(sorry, my website graphical design instincts leave to be desired :-[ )
So it looks like my options are either a dial caliper or some sort of mechanical gain for a pot (whether rotary or slide). I've been reading through all the posts on the dial caliper, and still don't see anyone who had complete success...so I'm not confident I would be the one to figure it out.
I'm not sure where to find a tiny rack and pinion setup. I see plenty of servo gearing, but nothing for a linear rack. Any suggestions?
Thanks again!