< Peter Gee > >The other day i say a device that was attached to a lathe that gave a >digital measurement from the tool (ie the position of the tool on the bed) >to another point. *maybe the chuck, but this box had a zero button. >it used a sensor that was waterproof, it was parallel to the bed, and had a >male and female V section that slid over the other. this unit had imperial >and metric modes. > >my question to you all is, how would you make something like this ? >how do you determine a distance to a resolution of a maximum of 1/1000 of an >inch that is waterproof and can live in an environment that is noisy, has >oil/ water, metal shavings, vibration etc. In our machine shop we have optical scales on all the lathes and mills. Mitutoyo makes the versions we have but there are lots of outfits that make these things. These are linear glass scales that work on a vernier and quadrature basis with occasional tics on a fourth channel to give some notion of absolute position. HP has an inexpensive and compact linear scale reader that we've used on some high precision positioning rigs. Great PIC application although there are a number of dedicated chips designed to make sense of this scale output. Cheers, Win Wiencke Image Logic Corporation ImageLogic@ibm.net