Steve Blackmore wrote: >On Sun, 16 Aug 2009 12:10:50 -0500, you wrote: > > >>OK, base period is 62.5 us. For safety, we should never have encoder >>counts coming faster than twice that period. >>So, that is 125 us or 8000 Hz. Just to pick round numbers, 3600 RPM is >>60 rev/second, or 16.67 ms. So, we can read no more than 8000 >>counts/second, and need to fit that into .01667 seconds. 8000 * .016667 >>= 133. So, you need a 128 or 100 count/rev encoder. Encoders are >>usually specified as cycles/rev (also written pulses/rev) and that is 4 >>x less than the count rate. So, you need a 25 or 32 cycle/rev encoder! >>That's why people use hardware assist to handle these encoder counting >>chores. >> >> > >Looks like a Mesa card may be a good bet, but... > >$199 + 22.5% import duty + carriage + 15% VAT = a lot :( > > You could get the 7i43 instead, which is $89. It connects to the parallel port, which may limit your servo loop rate eventually, but otherwise it's the same thing as a 5i20. Oh, that and the fact it only has two I/O connectors instead of 3.
- Steve ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
