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 ----- 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_W0QQitemZ >>>140200200097QQihZ004QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewItem >>> >>> (7 hours to go, $22.50) >> >>Another couple sets: >> >>http://cgi.ebay.com/INSIDE-MICROMETER-AND-END-MEASURE-SET_W0QQitemZ350017355 >>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_W0QQit >>emZ330206299195QQihZ014QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewItem >> >>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
