Grounding. Power ground must be separated from small signal ground. The VFD also generate a common mode voltage and unless a common mode inductor is added to increase common mode impedance there will be a high frequency current flowing thru the protected earth wire which in combination with the protected earth cable impedance at high frequency will make it bounce around. I know about two paths for the common mode voltage: capcitance inside the VFD to protected earth and between motor cables and protected earth.
Nicklas Karlsson On Mon, 11 May 2015 21:00:39 -0400 Tom Easterday <tom-...@bgp.nu> wrote: > Early on we made a decision to put our VFD into the same cabinet as the rest > of the electronics on a lathe retrofit - I originally had two separate > cabinets, one for power with vfd and one for electronics. This was to save > space and bring the size of the cabinet on the machine down to a more > reasonable size so it might fit through doors, etc. In retrospect, perhaps > that was a bad idea. But here we are trying to address VFD induced noise > problems. The cabinet is shown in a picture here: > https://www.flickr.com/photos/37438950@N00/17219261571/in/album-72157651167328249/ > > <https://www.flickr.com/photos/37438950@N00/17219261571/in/album-72157651167328249/> > There is actually more wiring completed now then what is shown in the > picture but you get the idea. > > After having read about folks often using Rasmi input power filters to solve > noise issues I purchased one from ebay and installed it today. It didn’t > help, and may have actually made the problem worse. I installed it very > close to the VFD input power terminals as recommended. > > When I run the spindle motor on it’s lowest RPM I hear a high pitched whine > (at the motor) and strange things begin to happen in Axis. Windows pop up, > perhaps a homing window, perhaps a touch off, perhaps Axis switches to MDI > mode, sometimes it turns the machine off, sometimes it turns the machine off > but the spindle keeps moving! Sometimes the VFD shuts off and displays "oL > 1” on the screen. > > So now I want to understand how this noise is getting into the PC. I first > thought it was because the keyboard, mouse, and video cables ran past the VFD > in the cabinet and noise was being induced on the keyboard cable. So in > trying to isolate where the issue was I disconnected those cables and ran > them far away from the VFD. No help.. I then wondered if it was coming in > the AC power to the PC, so I rerouted the PC power to a completely different > outlet outside of the cabinet. No help. I then rerouted the network and > video cables to get those away from the VFD, no help again. Even with the > door open (as you see in the picture) I have noise. The only thing > connecting the PC to the rest of the system is the parallel cable which is > about 12” long that connects to the Mesa 7i85s card (and again, that is at > the other end of my cabinet from the VFD). Today I borrowed a friend’s > 0-1Ghz spectrum analyzer to see if I can find the source/frequency of the > noise and/or where it might be getting to the PC. I will start playing with > that tomorrow. > > I am wondering if anyone has any ideas of where i can look, or what I can do? > -Tom > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ 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
