On Sunday 27 January 2008, Kenneth Lerman wrote: >At 1080 feet per second, one wavlength of sound at 50 KHz is 1/50 foot or >about 1/4 inch. I think you want way more resolution than that. > >Ken
I had in mind one of the 200 khz+ models, Ken. Furinstance, 200 khz gives .067" per wavelength according to kcalc using Massa's formula's and converting to inches, and a quadrature phase detector can surely break that down to one or 2 degree increments. 2 degrees would give us .0003" accuracy that wouldn't be subject to cyclic errors in the screws and such. For my little mill, that is, as an ex bro-in-law used to say, "close enough for the girls I go with". Heck just having a known zero point every 0.067" would beat the pants off the dial indicators I have. There is also some even higher frequency stuff out there. I've sent for P&A on the 420khz devices from the link in my reply below. And google turned up one that claims megahertz plus stuff. That's probably out due to air attenuation factors but TBT I haven't looked. This is something I may be able to knock up a breadboard proof of concept model that I'd never take a picture of, else somebody would pull my tinkers license, in a price range I can afford. If it shows promise even if my breadboard model has trouble nailing jelly to a tree cuz its not very rigid, well... Ya never know, but I do like to think out loud. Others picking holes in my theory are always welcome to comment. :-) The sheer cost of a laser src pure enough to do this prices it well out of my range, and I suspect out of range for anybody but GM & Toy. I *think* this is doable in a 3.2 USD price range. >----- Original Message ----- >From: "Gene Heskett" <[EMAIL PROTECTED]> >To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >Sent: Sunday, January 27, 2008 3:03 PM >Subject: Re: [Emc-users] Ball screws + error compensation > >> On Sunday 27 January 2008, John Kasunich wrote: >>>John Kasunich wrote: >>>> For measurements every inch, you can often find jig-borer micrometer >>>> sets on ebay or other surplus places, often mis-listed as inside mics >>>> like this one: >>>> >>>> http://cgi.ebay.com/PRATT-WHITNEY-10-PIECE-INSIDE-MICROMETER-SET_W0QQite >>>>mZ >>>> 140200200097QQihZ004QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewIte >>>>m >>>> >>>> (7 hours to go, $22.50) >>> >>>Another couple sets: >>> >>>http://cgi.ebay.com/INSIDE-MICROMETER-AND-END-MEASURE-SET_W0QQitemZ3500173 >>>55 826QQihZ022QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewItem >>> >>>Missing a few parts, makes it less interesting to most buyers, but it >>>has three 12" standards, so it can do 1" to 51" in steps of 1". No bids >>>so far, with less than one day to go, and an asking price of $20. >>> >>>http://cgi.ebay.com/PRATT-WHITNEY-11-PIECE-INSIDE-MICROMETER-SET-0001_W0QQ >>>it >>> emZ330206299195QQihZ014QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewI >>>tem >>> >>>This set is complete, has 3 bids ($10.50) so far, and will probably go >>>up a bit. >>> >>>There are a few more as well. >>> >>>Even cheaper would be a set that is missing the micrometer head. >>>However, they'll be harder to find because they're more likely to be >>>mis-listed as something else. Perhaps search for Pratt & Whitney or >>>Lufkin, since the rods are usually marked with the makers name. >>> >>>Like anything, its possible that the rods are worn and no longer >>>accurate. You can do some testing, by comparing for instance a 12" rod >>>to another 12" rod, or to the sum of a 6" and two 3", etc. In general >>>though, people tended to use those things gently. >>> >>>Regards, >>> >>>John Kasunich >> >> Interesting John. But the whole idea has threads about interferometer >> based >> methods going around in my head, and the thought of the single frequency >> coherence required to make that work keeps backing away from the >> relatively >> expensive he-neon lasers that still require some filters to achieve a >> reasonable facsimile of single frequency output, plus the fact that the >> accuracy level with an IR source is 10x overkill for this, and thinking in >> terms of ultrasound in the 50khz plus ranges. >> >> First, single frequency is easily achieved, and second, given a phase >> detector, wouldn't the accuracy be more than sufficient for uses such as >> this >> over distance ranges up to say 4 feet? Speed of sound in air vs pressure >> and >> temp would need to be taken into account, but what other problems might >> there >> be? I have in mind a peizo mic on both ends, one carried by the table and >> the other fixed, with the table mounted one being the mover, and the >> stationary one being the pickup and detector driver. >> >> Can anyone throw a wrench into this and debunk the basic idea? The >> medical >> field is awash with suitable transducers I believe. >> >> At <http://parsonicscorp.com/ultrasonics.html> is one that operates at: >> Model Number 42005 >> Frequency kHz 420 >> Capacitance pf 650 >> Insertion Loss db at range listed -80 8" >> Maximum Drive Volts p-p 150 >> Rise Time Microseconds 100 >> Temperature Range Degrees F 0 - 135 >> Beam Angle Total -6bd Pulse Echo Mode Degrees 6 >> Bandwidth -6 db in kHz 20 >> Power Input at rated Voltage Watts RMS 4 >> Typical Range* 3" - 18" >> Housing Material ABS >> Transmission Window ABS >> >> For longer distances than 18" additional gain would be needed in the path >> of >> the one used for a microphone, but a quadrature detector should be able to >> count ok. Side shielding for ambient noise control might be in order some >> some environments due to the 20 khz bandwidth spec, but I can't see any >> reason it couldn't work at least as accurately as any mechanical method >> could. One would want to scope the output and adjust the driver >> oscillator >> to center it on the individual pairs most sensitive frequency which would >> help in the ambient noise cases. This is however, well above the shops >> local >> crickets I'd bet... >> >> I'll email them for a quote just for grins & giggles. >> >> -- >> Cheers, Gene >> "There are four boxes to be used in defense of liberty: >> soap, ballot, jury, and ammo. Please use in that order." >> -Ed Howdershelt (Author) >> We are what we are. >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by: Microsoft >> Defy all challenges. Microsoft(R) Visual Studio 2008. >> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > >------------------------------------------------------------------------- >This SF.net email is sponsored by: Microsoft >Defy all challenges. Microsoft(R) Visual Studio 2008. >http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The scum also rises. -- Dr. Hunter S. Thompson ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. 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