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
