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
