Hi all, Despite all the horror stories I've had pretty good luck with shielded or unshieled CAT5 for encoders. Indeed, I would not ground both ends of an encoder cable. The Mazak uses a system where the braid on signal cables is stripped off for about 2" and they are all clamped to a common ground in one place and left open at both ends.
Just my experience or good luck. :-) Dave On May 14, 2009, at 3:16 PM, Gary P. Fiber wrote: > Gene Heskett wrote: >> On Thursday 14 May 2009, [email protected] wrote: >> >>> Hi >>> I want to ask about shielding of cable. >>> I am building bigger machine and for my new machine I need extend my >>> encoder cable. My encoder cable has DB 15 connector. >>> I do not want to cut cable and re-solder all 15 wires. I want to use >>> pre-made cable that already has male female connectors so I can >>> use them >>> as an extension cord. >>> First, can I do that? >>> Are there any problems with using extension cable (10 ft) for >>> encoder >>> signals? >>> >> >> With adequate shielding I think you can. >> >> >>> Second question, that extension cable has aluminum wrapping >>> around wires. >>> >> >> ALU wires=Oops. mylar/alu foil=good but see next question. >> >> >>> That cable does not have shielding like woven wire mesh around >>> aluminum >>> wrapping. >>> >> >> Does it have a 'drain wire' that is about 22 or 24 gauge equ in >> stranded wire >> that can be brought out and tied (soldered) to the appropriate >> ground point? >> >> At frequencies we deal with, it can be as much as 60db quieter >> than an >> equivalent 98% braid covered cable. (That in math terms, is about >> 1 million >> times quieter, and is because the mylar foil is a 100+ % coverage, >> not the >> braids 98% at best, and is often 90% or less in cheap cable) This >> drain wire >> should be electrically bonded (soldered) to the DB15 shell on both >> ends, >> likewise your existing cable you want to re-use should also show >> continuity >> from end shell to end shell. I'd scrape it just to see the >> shielding before >> I'd use it. No shielding, nope.. >> >> Whether you tie that drain wire and the machine end of the DB15 >> shell to the >> machine depends on how the encoder is covered. If it is in a >> metallic housing >> that is not grounded to the machine, then connect the encoder >> housing to the >> DB15 shell at the machine end. This would be the ideal situation, >> but if the >> encoders housing is metallic, and grounded to the machine, you may >> have to >> opto isolate the encoder signals to get truly clean A-B-Z sigs. An >> oscilloscope will tell that tale. Or take more heroic measures to >> shield the >> spindle motor power & keep its noise under control if that is the >> primary >> noise src. >> >> >>> So, do those woven wire mesh around aluminum wrapping important? >>> >> >> Yes, unless they too are alu (test by soldering, if it won't, its >> alu), which >> would be somewhat less useful than those belly appendages on a >> boar hog. You >> should find another brand of cable where that is tinned copper & >> solderable. >> The alu oxide, forms in .001 second or less when alu is exposed to >> the oxygen >> in the air, is a very very good insulator, and that is not what >> you want >> wrapped around that foil supplying its ground. >> >> >>> Will noise pass through single aluminum wrapping? >>> >> >> With the 'drain wire' well grounded, the isolation will be >> somewhere in the >> range of 100-110 db. 120 with good terminations. Std braid only >> covered coax >> is in the range of 55-65 DB, and the FCC forced the cable >> companies to replace >> all that 20+ years ago because it leaked so bad. Those cable >> operators that >> drug their feet had a dead giveaway, visible to any savvy tech, >> the channels >> on their system that had local broadcasters on them were unusable >> because we >> also leaked _into_ their systems. The cable folks were hard to >> convince >> locally, particularly when they needed the channel we were on for >> the last 25 >> years, then discovered they could not get rid of the ghosts. We >> just as >> firmly replied that it was NOT our problem and that they should >> tighten up >> their systems to meet the FCC leakage specs, and it came home to >> roost about a >> year later when the FCC truck came to town and wrote them up a >> citation for >> every stop the truck made. Lets just say that Pandora's box was >> full. Some >> viewer called them I guess, it sure wasn't us. >> >> Yes, I'm a retired broadcast engineer with a 1st phone from 1962, >> and have >> been a C.E.T. since 1972. :) >> >> >>> For the spindle I am using 2.5 hp router. Not many electric power >>> tools >>> around. >>> That spindle and 3 servomotors. >>> >>> Thanks >>> aram >>> >> >> > I am curious wouldn't you be concerned with creation of a ground loop > when grounding the "drain" wire at both ends? Or will the servo motors > ignore a ground loop? > > During my railroad days working on Defective Equipment Detectors in > the > 1980's, most of my shielded cable was grounded to the rack but not at > the Bolometer end. The circuits for the infra red sensors were real > high > impedance so any noise at all would translate to false train stops at > the recorder. > > Here's something you'll appreciate, Once in a trip into Illinois we > had > to move a detector readout location . I think we ran 16 and 18 KHz > line > overlay carrier and shot that 105 miles down # 6 solid copper, 600 > balanced dispatcher line. In that 105 Miles we lost 10db checked on > a HP > 3551 transmission test set and a Harmon Selective voltmeter.. At one > point we got so much AC off the lines due to overhead power running > parallel we had to install 60 Hz drains on the open wire line. > > Oh ya I am just getting my little PC Router set up using EMC2 and a > Shuttle computer. The mechanics for the router / engraver was made by > Paul Jones. Have his PCB spindle too. I am using Probotix motors and > drivers. Huge table 5.5 inches by 5.5 inches :) 3 inch Z axis > travel. I > have to measure the X and Y axis travel yet to set up the stepper conf > but it does move and will simulate the snowflake example in EMC2 until > it hits the ends of the travel. The router should be just right for me > for now since I don't make to large of circuit boards. I want to use > gEDA and PCB for the circuit design but may use Eagle and PCB-GCcode. > > Gary Fiber K8IZ > > 2nd Phone 1979, FCC converted to a GROL in 1984 with Ship Radar > Endorsement since 1987. > > > > > > ---------------------------------------------------------------------- > -------- > Crystal Reports - New Free Runtime and 30 Day Trial > Check out the new simplified licensing option that enables > unlimited royalty-free distribution of the report engine > for externally facing server and web deployment. > http://p.sf.net/sfu/businessobjects > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Crystal Reports - New Free Runtime and 30 Day Trial Check out the new simplified licensing option that enables unlimited royalty-free distribution of the report engine for externally facing server and web deployment. http://p.sf.net/sfu/businessobjects _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
