On Sat, 2007-10-20 at 07:36 -0700, Peter C. Wallace wrote: > SNIP------------------------------------------------------------------> > > Using an oscilloscope, when I probed the power supplies with the spindle > > running, I got about .5 Volts of ripple that had a three stair step up > > and down appearance. Probing the +5 Volt differential signals I got a > > very short 10 Volt spike on the rising edge of each pulse, but otherwise > > they looked well formed. Without the differential boards, the +5 Volt > > encoder pulses had a more drawn out spike on the rising edge and the > > tops varied about a Volt above +5. > > > > The whole idea of the differential boards where to reduce the > > susceptibility of the system to noise, but the boards themselves seem to > > make the effect of the noise worse. > > > > Are your differential inputs terminated? If not, that would account for the > spike... > > CAT5 has 100 Ohm charateristic impedance, so you need a 100 Ohm resistor > across each A /A, B /B, X /X pair. > > > Peter Wallace
Now that you mention it, I recall that the app note in the data-sheet for the RS-422 pair shows an Rt. To learn more, I found: http://www.microesys.com/pdf/TN-422_Signal_Termination.pdf http://www.bb-elec.com/tech_articles/rs422_485_app_note/system_configuration.asp Apparently, there is a fair amount of information available on this, if one is inclined to look for it. I was trouble shooting with the CAT-5 because it was handy, and I guessed that it has noise attenuation properties. The installed cable is about three feet of stranded 22 gauge (that's funny, spell check shows gauge as miss-spelled, are you Brits at it again?) four twisted pair. Each pair has a foil wrap and stranded drain. I don't know its impedance, but I suppose I could start with 200 Ohms and work my way up. The data-sheet indicates that anything lower that 90 Ohms should not be used. I'll give it a try today. My encoder disk problem cropped up again too. I am using a one inch U. S. Digital disk with a .466 inch hole and .500 inch shaft. There doesn't seem to be enough clamping area to keep the disk flat, so I have run the disk up towards the receiver end of the slot, so it rubs slightly in one spot, but works better. It seems that it might be best to buy the disk/hub assembly from USD. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe Bridgeport mill conversion pending Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
