Thanks for all the info Bruce! I suspect you are right that it is radiated noise. I should probably start with the outbound motor wire from the VFD. It is about 5 ft. long and not shielded. There are also a couple other cables I can shield as well that current aren’t. -Tom
> On May 11, 2015, at 10:05 PM, Bruce Layne <linux...@thinkingdevices.com> > wrote: > > I'm sorry to hear that the Rasmi filter didn't help your noise > problems. I bought four of them, and I've installed the first one but > am 1-3 days away from finally installing that electrical panel and > testing the electronics. > > Without the Rasmi filter, my CNC router has some noise on the VGA > monitor. Sometimes it's barely noticeable, and sometimes it causes a > lot of screen flicker. It's VFD frequency (spindle speed) specific. > Occasionally, it will blank the screen, which makes controlling the CNC > router "interesting". I tried clamp on ferrite toroids on the VGA and > monitor power cables and that helped a little. The big problem is the > way I ran several feet of the monitor cables adjacent to the spindle > motor cable. I knew better, but hoped the motor cable shielding would > be sufficient. I bought better quality double shielded VGA cable but > haven't tried that yet. I should rerun the spindle motor cable far away > from any data cables. > > The Rasmi filter is used to filter conducted noise. It attenuates the > electrical noise that might be conducted on the incoming power lines. > The Rasmi filter does nothing to attenuate radiated noise that's > broadcast by the VFD and the spindle motor cable. This type of noise is > analogous to a radio signal that's transmitted through the air, as > opposed to being conducted on wires. I suspect radiated noise might be > a lot of your problem. The spindle motor cable is a transmitting > antenna. All of those other wires in the panel are receiving antennas. > > Good wiring practices can help, as you've already mentioned. I route > power cables in one wireway and data cables in other wireways. It's a > nonlinear world, so when a data cable needs to cross a power cable, have > them cross at 90 degree angles and don't run them adjacent to each > other. Use shielded cable. Shielded spindle motor cable will help > prevent the VFD from transmitting radiated noise. Shielded cable for > sensitive data signals will help prevent them from receiving the > radiated noise signals. Shielding the noise source and the sensitive > signals fights the noise at both ends. Keep as much distance as > possible between high current lines (particularly the spindle motor > cable between the VFD and spindle motor as it has some high frequency > switching noise that radiates very well). Distance is your friend. The > electromagnetic coupling is in inverse proportion to the square of the > distance between the receiver and transmitter. Twice as close results > in four times the noise. Four times as close gets you sixteen times as > much noise. Shielded twisted pair for data cables (like Cat5 ethernet > cable) is particularly noise immune because the shield blocks a lot of > the radiated noise, and the noise that makes it through is greatly > attenuated by twisting the cable which greatly reduces the common mode > noise in those lines. Ground the cable shield at one end only. > Usually, the shield is terminated at the source. In the case of the > spindle motor cable, I'd ground the shield in the electrical panel next > to the VFD. For most applications, I like a star grounding > configuration where all of the grounds terminate at one common grounding > post. Scrape off any paint and use a star washer to bite into the metal > and tighten it enough to make a good gas proof electrical connection > that won't corrode in a year or so and cause a high impedance path to > ground. A single ground point prevents current loops, where there is a > current flowing between two or more ground points. In some special > circumstances, you might have better results with a power ground and a > data ground, or an analog ground and a digital ground. With two > completely separate ground systems, the low voltage electronics won't be > subjected to a few volts of ground float noise from a noisy power device > like a VFD. If the two subsystems need to have a common reference > voltage, the two ground systems can be connected by a resistor > (typically 1K to 100K) and/or an RF choke to allow the common voltages > of both subsystems to float to the same voltage while attenuating AC noise. > > Pretty panel wiring is usually less noisy, particularly where radiated > noise is concerned. > > I hope that helps. > > Good luck slaying the noise gremlins. ------------------------------------------------------------------------------ One dashboard for servers and applications across Physical-Virtual-Cloud Widest out-of-the-box monitoring support with 50+ applications Performance metrics, stats and reports that give you Actionable Insights Deep dive visibility with transaction tracing using APM Insight. http://ad.doubleclick.net/ddm/clk/290420510;117567292;y _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
