On Thursday 30 November 2017 08:54:57 Peter C. Wallace wrote: > On Wed, 29 Nov 2017, Gene Heskett wrote: > > Date: Wed, 29 Nov 2017 23:41:51 -0500 > > From: Gene Heskett <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > <[email protected]> > > To: [email protected] > > Subject: Re: [Emc-users] omron encoders > > > > On Wednesday 29 November 2017 22:42:11 Chris Albertson wrote: > >> So the spindle spins about up to about 3,000 RPM. That is 50 rev. > >> per second. You have a 1,000 line encoder so that is 50,000 lines > >> per second on each channel. You should seeing a 50 KHz square > >> wave on both A and B channels. I don't understand the 1.8 MHz > >> reference. > > > > Theres some ringing on the edges that my fauncy digital scope may be > > counting. But your math is wrong, the way its hooked up its a > > 1000*7161.17=761,170 line/rev, * 3000=38,058,500 hz. I do believe > > thats a bit much for a 5i25 to process. > > If the encoder is on the motor, whats the maximum motor RPM? > > If its 3000 RPM (50 RPS) the maximum output frequency is 50 KHz > (50 RPS *1000 lines) or a 200 KHz quadrature counting rate. > > This means the pulse width will be approximately 10 usec at 3000 RPM. > > For filter setting, to accomodate deviation from perfect square wave > signals, its a good rule of thumb to set the input filter so its time > constant is about 1/2 of the input pulse width at full speed = 5 usec. > So for example you could set the encoder sample rate to 3 MHz and > enable the encoder filter (15 counts) this would be 5 usec. > > Note that most quadrature encoders output frequencies are limited to > 500 KHz or less due to optical sensor bandwidth. > > > As far as count rate limits go, the 5I25 can have a encoder sample > rate of 33 MHz, and with the filter off (3 counts) this means it will > recognize input pulses longer than 90 ns so could theoretically read > quadrature count rates up to about 20 MHz but I dont think there are > any quadrature encoders that fast... > That thought has entered my mind too Peter. Looking at one leg of the output with the motor wide open, its about a 3.5 volt peak to peak signal, which would be dc centered at 1.75 volts, aka a good signal to feed a ttl circuit input with. Its much like a sawtooth in that its rc shaped, and would reach about 4.5 volts p-p at 10% of that speed, beginning to look like a square wave. But this bob seems to be cmos based as its buffered outputs are close to rail to rail. Which means its trigger level of 2.5 volts is translating that into something that while it has square edges, is not a 50% duty square wave. 15 to 20% at best.
One thing I haven't done is to look at the index coming from the spindle encoder to see what its top revs are, and then look at the unused index from the motor encoder to see what its top revs are, and compare that to see if the figures I got from some hal counters are within 1% or so. To verify: I have the scale correct when position is incremented by exactly 1.0000 at each index from the spindle, correct? So verify that, make the differential receivers, and play with the sample clock and filter settings are on todays agenda. If the day, or I, is long enough. :) But first, take care of my lady, who was still sleeping when I put the coffee pot in the microwave. Thanks Peter, for clarifying that. [...] Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
