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Thanks, The emissions come from both enclosure A and B......slightly more from B than A.In one of those I recommended to determine which of your systems (A or B) causes the emission, reply #9 in [1].
Hi
Page 30 of this
says...
Filters that must provide significant levels of attenuation at frequencies above 100MHz, must employ shielding techniques as well. They will not be able to achieve the required performance otherwise.
Is this true?
Why does this common mode choke purport to be able to provide attenuation above 100MHz….
Wurth 744841414
…it doesn’t have shielding
Hi,
We have got to pass radiated EMC (30MHz to 1GHz), but in a “real” situation where what we cannot afford “proper” RF EMC techniques…and in truth…”real” EMC techniques just wouldn’t be mandated, or realistic.
Our setup is as attached.
The following doc calls for a “RF Reference plane” for use with EMC filtering and shielding….
…That sinks us from the start. We have two panels, whose metal enclosure is earthed, but that earth comes from the earth wire in the long 3-core power cord…..so that connection is so high Z to RF that its NOT a connection at all. So we have no RF reference plane!!!…and our metal chassis is basically floating at RF !!!
So straight away no official EMC literature is of any help to us!!!
Does anyone have an “EMC guide for real-life, cost constrained situations” document, instead of these “perfect EMC” guides which tell how to do EMC for super-expensive medical devices or military devices with RF gasketted connectors etc? I’ve read tons of them and they are no use.
I mean, Feedthrough capacitors, etc etc aren’t much use without an RF reference plane.
Take the blue cable between the two enclosures in the attached.
What are the options?...........
(a)…Two core cable unscreened?
(b)…Three core cable with third connector connected to chassis at each end?
(c)…Two core cable with screen…screen left floating…it may as well float…both our chassis’s are already floating at RF?
(d)…Two core cable with screen connected to chassis at “A”?
(e)…Two core cable with screen connected to chassis at “B”?
…and what if we just don’t bother connecting our chassis’s (A and B) to earth at all?....after all, the power cord earth connection is NOT a connection at RF…its too high Z. And then what should we connect our Y capacitors to?....there is no Earth. How are the common mode chokes working at all?
No EMC literature discusses these real options. Do you know the real answers?
Thanks, we did this, we found that there is signficant emissions coming out of Box A.Your best bet for the moment would be to split the system into 2 and deal with Box 1 first using a resistive load at the load.
Having screened cable (screen connected to chassis A and B) significantly improved emissions, when compare to non-screened 2 core cable being used between A and B. Academic EMC theory would tell us that this would not be the case, but it was...showing how inapplicable is modern academic EMC theory to this case.My advice would be to forget screened cables etc for the moment as thats going to add further cost and probably still not address your problem.
Thanks...everything in our system is going to radiate, because there is no "RF reference plane", and having one would be impractically costly. Nothing is earthed, due to the unavoidably high Z of the earth cable in the mains cable to the product. We have no "ground"...and no EMC tutorials address our case.An ungrounded screened cable will still radiate.
I agree that modern academic EMC theory calls for that...but it is impractically expensive. We have no "ground plane"...having one would be impractically expensive.Box 1 would need to be screwed down onto the ground plane using a low impedance bond for EMI
Box A on its own has passed conducted emissions. We are now doing radiated emissions.With the conducted data you can address the conducted emissions first.
Thanks, we did this, we found that there is signficant emissions coming out of Box A.
We also disconnected A from the mains, and put a 12V battery in A, and used that to power B....it gave slightly more emissions than the "resistive load" case above.
Thanks, Box A is an established unit that passes conducted and radiated when used on its own (with no cable coming out of it as we are doing now).hats a good start, Stay on Box A with a resistive load for a while. Don't jump around doing what if scenario's, address box A emissions first for both the power lines and the output side. You will need to address both prior to moving to looking at box B.
Thanks, Box A is an established unit that passes conducted and radiated when used on its own (with no cable coming out of it as we are doing now).
We now want to have Box B connected to it as shown, but this is causing the radiated emissions problems to rear its ugly head.
We simply cannot make significant changes to Box A...its an established unit used in many products. About the most we could do to A is add a common mode choke to the cable as it leaves A to go to B.
Box B is the new bit, and this is where we need to concentrate our efforts because its too expensive to go making too many changes to box A.
Thanks, i thought problems above 10MHz were always Common Mode?
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