Guest
Show Posts
951
General Mach Discussion / Re: Shield grounded at one end only
« on: February 07, 2014, 09:38:44 AM »
I think sometimes it pretty much boils down to some twisted form of black magic. I think it has a lot to do with the location of the component generating the noise. Envision a control cabinet with nothing but low voltage/current components like a PC and BOBs. Leaving that you have a few control wires going to a VFD. I would likely start by breaking convention and grounding the shield at the VFD end only. Most I have seen in industrial controls suggest grounding the control end only but I view that as a suggested starting point. If that doesn't work, try grounding both ends. If that doesn't work try grounding only the end opposite of the controller. Sometimes floating the ground of a power supply helps, others it causes a real mess. I think it boils down to the fact that we simply do not know enough about EMF. Some of it can be extremely difficult to measure and it is hard to analyze data you do not have. EMF is like a fire. Try to contain it as close to the source as possible because it is going to do everything it can to spread to everything in sight.
Most of the time you can narrow it down to the source of the problem pretty quick. Other times it takes for ever and others you never do. The ones that just blow my mind is when you have a machine all wired up and tested and maybe even run for extended periods of time with no issues. Pick it up and move and now noise is a serious problem. Everything I know to measure are dang near identical. Dedicated ground rods megged to within a few ohms of one another. Same wiring, same routing, same input power, same type building, same kind of lighting, relative humidity........ every thing I can think of. Obviously I'm missing something but what? The only thing I can come up with is that it is simply located at a different spot on this molten Iron core rock we call earth. Could drive a man mad. Most of the time the solution is to fiddle with the shields again. I just find things like this bizarre to say the least and anywhere from humbling right up to embarrassing.
If any of you guys have seen similar and actually narrowed it down and could put your finger on it how about share it. Or share the most bizarre source of noise you have found and the solution.
Brett
Most of the time you can narrow it down to the source of the problem pretty quick. Other times it takes for ever and others you never do. The ones that just blow my mind is when you have a machine all wired up and tested and maybe even run for extended periods of time with no issues. Pick it up and move and now noise is a serious problem. Everything I know to measure are dang near identical. Dedicated ground rods megged to within a few ohms of one another. Same wiring, same routing, same input power, same type building, same kind of lighting, relative humidity........ every thing I can think of. Obviously I'm missing something but what? The only thing I can come up with is that it is simply located at a different spot on this molten Iron core rock we call earth. Could drive a man mad. Most of the time the solution is to fiddle with the shields again. I just find things like this bizarre to say the least and anywhere from humbling right up to embarrassing.
If any of you guys have seen similar and actually narrowed it down and could put your finger on it how about share it. Or share the most bizarre source of noise you have found and the solution.Brett
Cure all is right. A little bit of that stuff and absolutely nothing matters. I think you should label it Magic Eraser. 