This is what I meant about relative vs. absolute. Relative can be very good.
Think of a relative sensor as if it were a dial indicator. That is how these work. Like a dial, they are good for many things, but useless for other things. The linearity spec tells you how the error changes with distance. Unlike a dial indicator they have more error when the distance is greater. If I told you the error is 1% per inch then you would expect really good results at distances of 0.01 inch but you'd expect 100% error at 100 inches. (of course you'd never see that because they don't see 100 inches.) On Mon, Mar 7, 2022 at 12:36 PM Thaddeus Waldner <thadw...@gmail.com> wrote: > Acuity sells what I need brand new for $1000. > Keyence appears to be a much more common brand, given by the number of > eBay items. > These are not time-of-flight devices; they work instead by measuring the > position of an angled laser spot on the target. > > I’m looking at the Keyence IA-065. The working range of 2.17" - 4.13” > would work for my application. I’m a bit puzzled by the “linearity" spec on > the data sheet. It reads as follows: > +- 0.1% of F.S (F.S.=+-10 mm 0.39”, 55 to 75mm 2.17 to 2.95”) > > I read that as within the range of 55mm to 75mm, the linearity will be > within 0.2% of that range, which comes to 0.04mm or about 0.0016”. Is my > logic and math correct? > > Second question, what is the simplest (and cheapest!) way to get this > analog voltage into LinuxCNC. I do have a couple of 24-bit I2C devices on > hand (ADS1220). Is this workable without writing a driver or something like > that? > > > > > On Mar 7, 2022, at 2:01 PM, gene heskett <ghesk...@shentel.net> wrote: > > > > On Monday, 7 March 2022 12:44:21 EST Thaddeus Waldner wrote: > >> Hi, > >> > >> I’m looking for a laser distance sensor with about 1-3 thousandths > >> resolution and about a 5-10” working range. I wouldn’t mind buying a > >> used unit. > > > > 1. I didn't know they came in that high a resolution w/o needing a > quorum > > of the US Senate to authorize the payment, then signed by the President. > > > > If you want to know why, calculate the time difference of that 3 > > thousandths of an inch increment, remembering that it has to travel out, > > and back to the measuring device, equal to C/2 in speed. You will I > > suspect will come up with a very small fraction of a picosecond. > > > > Interferometry can measure that change, but the mod function to detect > > the individual null and count it has to start at zero, or a known micron > > sized distance before it can count the nulls passing by as it moves from > > zip distance, back to your point of interest at a 12" max range. Moving > > slow enough to count, will take a 2048 bit counter and several days. > > > > Technically, we can do it but you'll need a couple of dump trucks full > of > > gold to finance one neasurement. We can't yet buy a calibrated answer in > > 10 milliseconds for a $500 bill. Someday? Maybe, but it may take a new > > method to be invented. > > > >> Does anyone here know of some brands/ models to check out? > >> > >> Google has pointed me at some Acuity products but I wondered if there > >> were other options besides that. > >> > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > Cheers, Gene Heskett. > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author, 1940) > > If we desire respect for the law, we must first make the law respectable. > > - Louis D. Brandeis > > > > > > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
