Differential drive is always the best solution, look at Ethernet. It can push 100 megabit over a kilometer using unshielded cable.
But single ended signals can be noise resistant if the wire uses resistive termination. The opto-isolator is proving resistive termination. On Wed, Oct 13, 2021 at 6:43 PM John Dammeyer <[email protected]> wrote: > Hi Chris, > When I developed my ELS for 1PPR one of the criteria was that the index > vane or slot had to be wide enough so that it would generate a pulse at > least about 5 or so 50uS ticks wide and at least again that wide for the > non index period. That the tick count would then be at least about 500 uS > per rev. That's a frequency of 2000 Hz in minutes 120,000 RPM. Very > unlikely an old surplus lathe can run that fast. > > A lathe like a small Unimat DB-200 could run 8100 RPM which is a 135 RPS > or a period of about 7.4mS. If the index pulse slot is 250uS the non index > pulse time is 0.00715mS or about 143 ticks. So it's pretty easy to expect > the index pulse to be active for 3 ticks or 150uS. Most noise is much > larger than that. > > For a system where there are spurious index pulses or noise, and the > HPCL2631 solution I proposed wasn't possible, I'd be tempted to add a > 1-shot pulse extender right at the encoder to create a longer index pulse. > Once again debouncing that in software (or hardware with a counter that > verifies low for X clocks) creates a reliable index. > > Since Peter's encoder had push pull outputs and a drive capability of at > least 10mA it made sense to go high speed optical. If it wasn't and had > simple TTL output then I'd have suggested adding high speed differential > drivers like the AM26LS31CN which has 4 channels. See attached schematic. > > A differential receiver at the other end and using twisted pair 100Ohm > impedance wire with 100 ohm resistors at both ends creates a nice balanced > transmission line more immune to interference. > > John Dammeyer > > > > -----Original Message----- > > From: Chris Albertson [mailto:[email protected]] > > Sent: October-13-21 6:10 PM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] Fwd: Fwd: Rogue Index Pulses > > > > You are right, but under all conditions, the resistor connecting the wire > > to ground through a diode has lower impedance than the same wire > terminated > > at a transistor gate as was the case before. The proof is that it works > > now. > > > > The other thing was thinking is that it should be simple to use software > to > > filter out a ghost pulse from an encoder. After all, we know that it can > > only happen once per revolution. We could look at the counter that > racks > > A/B quadrature pulses and know it is is time for an index. Software > > could do this even with no configuration by spinning the shaft. In fact > > verifying that the index pulse always happens at the expected time is a > > great why to error-check that no counts were dropped or added. It would > > be a great self-dignostic. > > > > On Wed, Oct 13, 2021 at 4:11 PM John Dammeyer <[email protected]> > > wrote: > > > > > To fair we need to use the word low resistance path to ground. The > > > impedance of the wiring at 300kHz where electrical noise might exist > from a > > > VFD may be considerably higher. > > > > > > Think of the basic electronics of an inductor and capacitor in > parallel. > > > At DC the resistance and impedance is the coil resistance to ground. > At > > > ultra high frequencies the reactance of the capacitor is likely so low > that > > > it's also a short circuit to ground. And in-between somewhere at some > > > frequency the pair are in resonance and the 'impendance' can be very > high. > > > > > > The wire from the encoder to the electronics has inductance, > especially if > > > coiled up and there is capacitance per foot/meter rating on various > > > cables. It may or may not be important depending on the noise > frequency. > > > > > > John Dammeyer > > > > > > > -----Original Message----- > > > > From: Chris Albertson [mailto:[email protected]] > > > > Sent: October-13-21 3:51 PM > > > > To: [email protected]; Enhanced Machine Controller (EMC) > > > > Subject: Re: [Emc-users] Fwd: Fwd: Rogue Index Pulses > > > > > > > > Then this proves the cause. The isolators provide a low impedance > path > > > to > > > > ground. It is just current-limiting resistor and a forward-biased > diode. > > > > With this low impedance to ground there is no way for EMI to cause > the > > > > voltage on the wire to raise. > > > > > > > > On Wed, Oct 13, 2021 at 1:40 PM Peter Hodgson < > > > [email protected]> > > > > wrote: > > > > > > > > > > > > > > Well............! > > > > > > > > > > A quick update for those that are interested. > > > > > > > > > > The HPCL2631's won the postal race and arrived in the mail today. > > > > > > > > > > I made up a little 'interface' board to mount them on with the pull > > > ups, > > > > > caps, etc. and fitted that board this evenening. > > > > > > > > > > After an initial check on the index pulse I ran my G76 program (in > air) > > > > > for the M47 x 3.0 thread, that as giving me so much trouble, whilst > > > > > watching Halscope for the encoder index and I didn't see one ghost > > > > > pulse. I did see one that was missing over the 7 mins but I don't > think > > > > > a missing pulse is going to give me as much trouble as ghost pulse > and > > > > > anyway that could have been a software glitch. > > > > > > > > > > Too late to cut metal now but I will tomorrow. > > > > > > > > > > Looking good though! > > > > > > > > > > Pete > > > > > > > > > > > > > > > > > > > > On 13/10/2021 19:12, John Dammeyer wrote: > > > > > > I'll agree with Andy here. I have a dual trace older digital > scope > > > and > > > > > a 4 trace digital that can even decode CAN, SPI and I2C > messaging. I > > > > > bought a small Digilant PC development kit version for $400 or so > to > > > get > > > > > UART decoding for a PAN-TILT system that was misbehaving. The add > on > > > > > module for the scope to do that was $1200 so a no brainer. Haven't > > > used it > > > > > since we solved the serial port issues 3 years ago. > > > > > > > > > > > > But my 4 trace I use all the time. The 2 trace has spent time > out in > > > > > the shop by the mill but was useless for determining what the > issue was > > > > > with the out of spec DC servo that only lost steps in one > direction and > > > > > never the other. The G-54 zero crept in one direction resulting > in the > > > > > center drill peck holes being in one place and then a bit later the > > > drill > > > > > bit for those holes not lining up. > > > > > > > > > > > > In a noisy shop environment just getting the scope to see real > data > > > as > > > > > opposed to the noise it picks up may be impossible. I saw that at > a > > > > > Siemen's plant in Regensberg Germany back in the early 90's. We > > > scoped a > > > > > CAN bus and could barely see the signal on the differential pair > yet > > > the > > > > > system operated flawlessly. Just couldn't find the right ground or > > > > > whatever... > > > > > > > > > > > > So the money spent on a scope may not be worth anything. > > > > > > > > > > > > John > > > > > > > > > > > > > > > > > >> -----Original Message----- > > > > > >> From: andy pugh [mailto:[email protected]] > > > > > >> Sent: October-13-21 3:22 AM > > > > > >> To:[email protected]; Enhanced Machine Controller (EMC) > > > > > >> Subject: Re: [Emc-users] Fwd: Rogue Index Pulses > > > > > >> > > > > > >> On Wed, 13 Oct 2021 at 11:13, Peter Hodgson< > > > [email protected]> > > > > > wrote: > > > > > >> > > > > > >>> I'm watching a couple of Oscilloscopes on eBay so might take > the > > > > > plunge. > > > > > >> I am going to go against the consensus and suggest that if you > don't > > > > > >> already have an oscilloscope, and don't know how to use one, > then > > > you > > > > > >> might not find it much help. > > > > > >> > > > > > >> I certainly got nowhere trying to use one to track down false > > > > > >> triggering of limit switches. And I have owned a 'scope for > decades > > > > > >> (though not used it more than a few times a year) > > > > > >> > > > > > >> -- > > > > > >> atp > > > > > >> "A motorcycle is a bicycle with a pandemonium attachment and is > > > > > >> designed for the especial use of mechanical geniuses, > daredevils and > > > > > >> lunatics." > > > > > >> ? George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > >> > > > > > >> > > > > > >> _______________________________________________ > > > > > >> Emc-users mailing list > > > > > >> [email protected] > > > > > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > _______________________________________________ > > > > > > Emc-users mailing list > > > > > > [email protected] > > > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > _______________________________________________ > > > > > Emc-users mailing list > > > > > [email protected] > > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > > > > > > > > -- > > > > > > > > Chris Albertson > > > > Redondo Beach, California > > > > > > > > _______________________________________________ > > > > Emc-users mailing list > > > > [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
