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In Reply to: RE: Let me repeat this once again since you are having such a hard time. posted by Dan Banquer on July 01, 2010 at 13:05:36
Earth ground is cheaper than a faraday shield and in many applications works just as well.
Try and get a grip on that Steve
It's not my habit to grab a steaming pile of bullshit.
A wire stuck in the ground provides absolutely NO shielding whatsoever.
Good God, Dan, you're sounding just like the quacks and charlatans you used to rail against. You outta team up with Geoff Kait.
se
Follow Ups:
See link below.
d.b.
See my reply to said post.
se
From September 24, 2003:
"There is plenty of science for those of us who dare to open and fully read things like the Belden Master Catalog, or Henry Ott, or Morrison."
Then on July 6, 2005 after both Ott and Morrison disagreed with his preconceived notions with regard to earth ground:
"I think you Ott, and Morrison have some catching up to do with a good portion of the electronics industry."
se
***A wire stuck in the ground provides absolutely NO shielding whatsoever.That wire suddenly turns a piece of metal into a shield.
It also diverts the ESD currents away from the sensitive circuits.
In addition, it bleeds the RF energy off the cable shield, so it would not get rectified by the circuit.
Other than these... yes... just a wire.
Edits: 07/01/10
> > That wire suddenly turns a piece of metal into a shield. < <
Not by itself. *If* that ground wire is connected to the *signal* ground of another component, then you may see some of the shielding effects you are talking about.
But running a wire fifty or a hundred feet to the feeder box and then another fifty or a hundred feet back to the other component is a stupid way to try to provide shielding. The inductance of the connection would be off the charts and there would be virtually no shielding at high frequencies.
Far better to link the two components with as short a length of ground wire as possible. Which is what normally happens when you connect them with an interconnect cable.
No earth ground is required, or even helpful.
Just look at the millions of Japanese receivers with two prong power cords. They seem to work just fine. No hum. No dead bodies.
***Just look at the millions of Japanese receivers with two prong power cords.That may be the key here, Charles. It is all the matter of point of reference. I did not design Japanese receivers... but I spent over 20 years designing super-sensitive world-leading instrumentation that dealt with femtoamps and nanovolts, and at one point was considered a go-to guy in one of HP divisions on subjects of RFI, EMI and ESD. This is not meant to browbeat anyone, but I have had enough of that nonsense. I am truly sorry to see you thrown your hat into this, and I am done with it.
BTW, those Japanese designers, unlike some here, know full well they would be far better off with three-conductor power cords, but they had to compete on cost alone. That they managed to achieve pretty good results with super-low-cost solutions is great credit to them. But they would have done even better with the "right" configuration.
Edits: 07/01/10 07/01/10 07/01/10 07/01/10 07/01/10
That may be the key here, Charles. I did not design Japanese receivers... but I spent over 20 years designing super-sensitive world-leading instrumentation that dealt with femtoamps and nanovolts, and at one point was considered a go-to guy in one of HP divisions on subjects of FRI, EMI and ESD.
Then you should write a book on the subject for all those poor schlubs who wasted their money on Ott's and Morrison's works.
se
***all those poor schlubs who wasted their money on Ott's and Morrison's works.
You obviously are not one of them.
i think it is stated in Ott's book as well. a potential reference is not necessary for a faraday shield but most have holes, slot etc. so it is better off to have a potentail reference and a ground connection is as good as any.
of course it does not solve all problems. i didn't say grounding but a potentail reference. since you have Ott's book handy, i'm sure you can find the relevant paragraph.
Here's something everyone can read:
Ground - A Path for Current Flow
It was written by Ott back in 1986 while he was still with Bell Labs.
Though I'm sure it's full of errors and myths so read it with a grain of salt.
se
All the stuff he writes about was a common engineering knowledge long before the article was written. In 1980 my first assignment at HP was to eliminate the crosstalk an in analytical instrument, between the variable power loads and its electrometer input. I did it by properly separating the ground planes to control the current flow patterns.So yes, a good read... you should try it.
Of course it has nothing to do with the present discussion... too bad you don't even realize that.
Edits: 07/03/10
how about page 199 of Ott' book on the grounding of sheilds.
how about page 199 of Ott' book on the grounding of sheilds.
How about personal communication with Ott directly?
The AC Power/Earth ground system is an array of long conductors, acting as antennas, picking up all kinds of noise. It is also heavily polluted with noisy AC power currents and their harmonics, from the power system and other equipment -- and completely out of your control. The earth is not a low impedance conductor. The resistance between two earthed points is rarely less than a few ohms and typically tens of ohms. The National Electrical Code allows the AC power ground to earth ground connection to have an impedance as high as 25 ohms.
Further:
If you did try to ground your product through a 6' power cord connected to the AC power outlet on the wall and then another 20' of house wiring to the earth ground, the conductors would have so much impedance (inductance) at RF frequencies that they would not keep the equipment at the same potential as the earth at all.
Let's take an example. At 20 nH per inch (typical inductance of a random wire), the twenty six feet of wire would have a total inductance of 6. 24 uH. At 50 MHz that amounts to an impedance of 1,960 ohms. So you see the futility of trying to ground your product to the earth using a wire. Even 6" of wire would have an impedance of 75 ohms at 100 MHz.
Let's look at the situation another way. The 26' of wire is over a wavelength long at 50 MHz, therefore it will act as a good antenna. If RF current flows between your product and the earth on the ground wire, it will radiate. If no RF current flows on the ground wire, you don't need the wire. Hence, at best the ground wire will be useless. At worst the ground wire will be an effective antenna and radiate. Therefore, you would be better off without it.
se
The National Electrical Code allows the AC power ground to earth ground connection to have an impedance as high as 25 ohms.
Many people read that part of the NEC code incorrectly.
NEC actually says if the ground resistance is greater than 25 ohms it shall be augmented by one additional electrode. (NEC 2008, 250.56)
The ground resistance could be 1000 ohms.... If the electrode was one 8ft ground rod then by code at least one more 8ft rod would be need to be driven. Code is satisfied....
Many people read that part of the NEC code incorrectly.
NEC actually says if the ground resistance is greater than 25 ohms it shall be augmented by one additional electrode. (NEC 2008, 250.56)
The ground resistance could be 1000 ohms.... If the electrode was one 8ft ground rod then by code at least one more 8ft rod would be need to be driven. Code is satisfied....
Heheh. Clever.
Though Henry's point remains the same.
se
What he mentions are just a bunch of simple engineering facts everyone knows. Unfortunately he - and you - draw a totally incorrect conclusion from them.
If I were to follow his example and speak of cars, I would tell you they are expensive to buy and maintain, they cost a lot to refill, they break down, they get involved in accidents, they are hot in summer and freeze your ass in winter...
All that is correct, and yet to many of us having that imperfect car is whole lot more preferable to not having it.
Same here. You, OTOH, due to your lack of knowledge, are only able to see one side to the story. So what the impedance is what it is - you are unable of putting it into perspective.
Why don't you spend some time talking to engineers who have done work in that area? I mean - besides Ott. I am not asking you to disregard what he is saying, just to get the whole picture. Then you will learn how to make good use of that imperfect, but so important ground wire.
Why don't you spend some time talking to engineers who have done work in that area? I mean - besides Ott.
I have. I've also discussed this issue with Ralph Morrison.
I am not asking you to disregard what he is saying, just to get the whole picture.
If one can't get the whole picture from two of the world's most widely recognized authorities on the subject, then who exactly is one to get it from?
Certainly not from you or Dan.
Neither of you have brought one shred of illumination to this subject. All you've done is play silly games.
"You're not asking the right question."
"What's the right question?"
"Figure it out."
In my book, that makes you nothing more than a charlatan.
char·la·tan : one making usually showy pretenses to knowledge or ability
se
i think it is stated in Ott's book as well. a potential reference is not necessary for a faraday shield but most have holes, slot etc. so it is better off to have a potentail reference and a ground connection is as good as any.
Well, holes and seams in the shield are a whole other issue and grounding doesn't prevent ingress through holes and seams.
se
And I think since it's been a long time when Victor did that work he is not telling the necessary details about what you do when the frequencies are in microwave territory, the place he worked in. Only digital audio has those frequencies. A linear audio amplifier does not have any appreciable amount but can be susceptible a tiny bit to over 1 GHz noise.
When he says he worked in femto-amps and nano-volts, that's not possible in the audio to FM bands yet, I believe, but maybe. The airwaves are polluted too much to shield it down to femto-amps with grounded coaxial lines. Not on the cabling nor the power cords. I measured about SOTA measurements in 2009 on DC current at drift plus noise less than 5 pico-amps on triaxial, way ahead of coaxial for that. But at 20 GHz, the noise floor is really low and the DC leakage doesn't matter, as in working within the residual noise of the big bang as your noise problem (except in case of other such equipment present at same frequency such as from satellite signals, etc.). The only thing to apply is proper microwave theory for low noise, such as solid "ground planes" and absorption material unique to these frequencies: poly iron for one.
These are not used in audio amps, and thus Victor is bringing up old work that makes for apples to oranges comparisons. A terminated microwave power amp is not a non-terminated audio power amp at all. Even still, antenna for microwave is sent down earth grounded coaxial cable because the dish and LNA are potential lightning targets, not because it needs to be earth grounded for noise. (See those grounding splices in satellite systems on your roof to the home?) But usually the HP/Agilent equipment is all referenced to earth ground for (what else) safety, but also for power strip equipotential setups for low noise on the "ground plug". We did it for both reasons, with the second reason dubious as our SOTA equipment did better and better circuit grounding schemes within each box. Victor exited long before I, and I exited just June, 2009 working on low noise measurements, lower that Victor's equipment was.
Still, the wavelengths are so short that ground wire is silly to think about as a noise conductor except for the low FM frequency areas of the wideband NA's, SA's, sources, etc, and a trickle at 1GHz. It is good for electrostatic issues with the outside world that may damage equipment and sometimes if not perfectly designed, a boost for the noise shielding for reasons akin to holding rabbit ears a certain way to pick up channel 69 1/2. In other words, by black magic not known. So that is not an engineering approach to low noise design where if it just happens to help this time, always do it.
That is my say on the subject. Sorry Dan and Victor. The theory is not there for you wherever you came up with it.
I've been trying to go on the idea of wood amplifiers with three prong circuits and balanced power, isolation transformers and build a closed-circuit common for low noise for all equipment. Then just electrostatically drain any voltage from circuit common to ground with a resistance to ground in one location, eliminating as much as possible noise inducing loop area in the common potential down the chain. The chain matters more for low noise; the grounding issue is just in the way as it is today for performance in my opinion.
In fact, that was my last system block diagram.
-Kurt
***And I think since it's been a long time when Victor did that work he is not telling the necessary details about what you do when the frequencies are in microwave territory, the place he worked in.
This is a perfect example of... how did you put it... ah, yes! Here: "The problem here is a failure of complete communication, pure laziness, and/or forgetfullness."
You can state that, or you can say this is a wonderful example of answering the post without reading it first.
If you will indeed read my posts, it should become clear my work at HP involved DC to low frequencies. There are several key words to that effect.
A failure of communication... you can say it again! :)
No information nor explanation from you, just whining that you're right and you have the credentials. Big deal, so do I. That makes me just as big an authority. So I just cancel your opinion out. Now we have a null.
-Kurt
You wrote several paragraphs that had nothing to do with what I said - perhaps it is time to go back and for a change read before answering?
> > Now we have a null. < <
Not at all. You also have Ralph Morrison and Henry Ott on your side. I think I'd have to give your team the nod....
Not at all. You also have Ralph Morrison and Henry Ott on your side. I think I'd have to give your team the nod....
But according to the other team, Morrison and Ott are just a couple of buffoons.
se
When the statement says "add a wire to the shield floating around in space to earth ground to make this a shield" is only true, and is usually true because of grounding laws, when the system in question being shielded is indeed also earth grounded. Then you form the all important equipotential between shield and equipment.
Trying to use this shield with a handheld DMM floating will do little because the DMM is not referenced to ground in this case. EMI travels right through it magnetically, but some static can be diverted to ground or reflected back if the material is correct, so there is some help. For hum, it can help a tiny bit by absorbing some magnetically if that kind of material is there. But this is the most poor shield if it works at all.
The real solution to shield the handheld, is to reference the shield to the circuit common inside the DMM by a conductor to the DMM, not earth ground. Magnetic shielding is mostly magnetic deflection around the circuit with material like mu metal and soft iron and never needs grounding; it's a different method. EMI at other frequencies require different solutions such as conductors and RF absorbers like ferrite or on up to poly iron.
But in general, the shield is always most effective with solid shielding, close proximity to the shielded components and small for all the wavelengths. And the final thing: a connection to circuit common - not way out in left field with two different high impedance ground connections for min effectiveness.
-Kurt
Please educate me. I have all of Morrison's book plus Ott's. All are the latest edition (last time I looked) with the exception of one of Morrison's. (I forget which one. I think I have four. The one that is not the latest edition is the second latest edition.)
So please point me out to the chapter where it explains how connecting anything to earth ground makes it quieter. Thanks.
That wire suddenly turns a piece of metal into a shield.
No it doesn't.
A piece of metal shields in two ways. One is reflection loss and the other is absorption loss. Reflection loss works by way of reflecting the impinging interference due to impedance mismatch between the material and the wave. Absorption loss works by absorbing the wave energy by way of eddy currents in the material itself.
Neither of which have anything to do with whether or not the piece of metal is connected to a piece of wire stuck in the dirt, but the properties of the material itself.
Reflection loss is most effective when the material has a high conductivity/low resistivity and is most effective at shielding against electric fields. So copper would be more effective than aluminum or steel. Efficacy is only minimally increased with thickness.
Absorption loss is most effective when the material has a high permeability and is most effective at shielding against magnetic fields. So steel would be more effective than copper or aluminum. Efficacy is increased significantly with thickness
If the piece of metal fully encloses the circuit it's shielding, it doesn't need to be tied to any ground to work effectively. If it doesn't fully enclose the circuit, then it should be tied to the CIRCUIT'S ground to prevent it from capacitively coupling noise to the circuit. Tying it to a wire stuck in the ground won't help any.
Holes and seams in the metal will also determine how effective it is, but this doesn't have anything to do with whether or not it's tied to a wire stuck in the ground.
It also diverts the ESD currents away from the sensitive circuits.
It can keep a chassis from accumulating a static charge, but don't know that it would help much with regard to a discharge event. But for the sake of argument I'll grant you that.
In addition, it bleeds the RF energy off the cable shield, so it would not get rectified by the circuit.
From Ralph Morrison:
"At RF, the impedances involved along any path are very high. In fact if you do the classical impedance calculations the impedance are higher than the impedance of free space. All this means is that the grounding wire controls nothing.
The perception of draining noise in one direction is ridiculous."
se
nt
nt
especially when it is obvious that you have no real world application experience, and therefore do not understand real world applications.
Have a nice day;
d.b.
That's what quacks and charlatans like Geoff Kait, Jack Bybee et al. expect people to do. And there was a time that I thought you were above mindless shit like that but apparently I was sadly mistaken. You're no different than they are. Make empty claims, wave your hands, call those who disagree with you closed-minded idiots, etc.
You haven't been able to cite a single authoritative source to support your claims and impugn those who have established themselves as authoritative sources throughout the electronics industry.
So fuck you, Dan. You're just another charlatan as far as I'm concerned.
se
...but you are absolutely right on this one. Don't let them get you down.
...but you are absolutely right on this one. Don't let them get you down.
Thank you, Charles.
Get me down? Naaaaah. You outta know me better than that by now.
se
Could you provide a specific source to substantiate the claims you'd made, particularly with regard to literal earth ground?
I've heard various claims from Dan for years and now from you with regard to literal earth ground. The only two specific sources Dan cited were Ott and Morrison, both of whom have vehemently disagreed with his claims.
If Ott and Morrison are both just a couple of quacks who don't know what they're talking about, then who IS writing authoritatively on the subject of literal earth ground and the seeming magic it supposedly performs?
se
Listen Steve,
I don't wish to make a public mockery of your obvious lack of knowledge in regards to authoritative sources on this matter, however I will provide you with a lead to one of the most critically regarded geniuses of whom I believe Tesla himself once remarked was 'profoundly & flatulently incorrigible"
Reginald P. Balderdash III, B.Sc. A.Ss.H.Ol.E
-Bachelor Of Scientology, Calcutta (Failed)
-Associate of Specialist Sciences Houston Omni Literary Effluence
Now that I have levelled the field, keep it clean... or it simply isn't football, old chap.
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