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
