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Re: [TekScopes] Re: Why is Mu Metal used?
And this applies above power line frequencies.
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I have personal experience with this on the 7834 oscilloscope which uses a switching power supply. This particular 7834 has a geometry issue and one of the tests I did was to operate it without the mu metal shield in place. The result was that the display on the CRT was so smeared as to be unusable and barely even recognizable. Some oscilloscopes do get away with just using a metal shield. On Sat, 20 Feb 2016 20:55:01 +0100, you wrote:
Ahh ok, now THAT makes sense and tells me a lot + gives me some |
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Re: Why is Mu Metal used?
¿ªÔÆÌåÓýIt¡¯s used to keep magnetic fields out of the path the electrons travel in the CRT. Copper foil will shield electric fields, and to some extent will shield AC or changing fields. Mu metal channels or attracts the magnetic fields into itself more effectively than air or vacuum due to it¡¯s higher permeability. ?It¡¯s permeability is tens of thousands of times that of steel. ?
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Re: Why is Mu Metal used?
On 2/20/2016 3:36 PM, `Richard Knoppow dickburk@... [hp_agilent_equipment] wrote:
Hello-- One more thing about MuMetal: in practice, you're supposed to reanneal the shield if you make major structural modifications, such as cutting away a portion of, or bending the shield. Otherwise, the shield's permeability decreases. You can supplement the shield by adding a second (steel) shield between the Mu-metal shield and an offending magnetic-field source. This may not always be practical. 73-- Brad AA1IP |
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Re: eBay buyer protections are poor
>The key is to use the 3" semi-hard foam (the kind that you can compress
with significant force but it will always return back to its original
shape and size, its usually pink or white, comes with new TV's etc) and
use a bunch of tape to tape this all the way around the perimiter of the
front of the unit, [snip]
This is excellent packing advice, and this is exactly why stuff like new TVs are also packed this way: engineers have researched the issue and come up with this stuff, since a lot of big things like this are shipped directly to peoples' homes these days. The problem, however, is that while *you* obviously take the time to ship stuff properly like this, you can't count on some random idiot on Ebay to do so.? So, buyer beware: don't bid until you make sure the seller is going to pack it properly.? Don't just buy something for $$$ from some random person, have them ship it internationally, and then bitch and whine about how Americans are all morons who can't pack things when it arrives damaged. |
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Re: Why is Mu Metal used?
¿ªÔÆÌåÓý?? Mu metal is a shield for magnetic fields. It has extremely high permeability, the ability to conduct magnetic fields the Greek letter Mu u is the symbol for permeability.?? See: for more. ??? Now, if you take a magnet and a piece of soft iron the magnet will attract the iron. If you place even a fairly thick sheet of conductor, like copper or aluminum, between the two the magnet will still attract the iron with little or no reduction in strength.? Now if you place a sheet of Mu metal between the attraction will be much reduced depending on the thickness of the Mu metal and its exact type.? The use of Mu metal shields around CRTs and transformers prevents the effects of either static or alternating magnetic fields. These can distort or modulate the beam in the CRT or induce hum in a transformer or allow the transformer to induce a field in some other device. ?? Good conductors like a thick copper shorted winding of either wire or ribbon, are used in power transformers to eliminate eddy currents in the core but this is different than magnetic shielding. On 2/20/2016 10:48 AM, 'cheater00 .'
cheater00@... [hp_agilent_equipment] wrote:
Hi guys, Why is Mu Metal used to shield CRTs in scopes, rather than just grounded copper foil? I never understood the precise reason for that. Thanks ------------------------------------ Posted by: "cheater00 ." ------------------------------------ ------------------------------------ Yahoo Groups Links <*> To visit your group on the web, go to: <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: (Yahoo! ID required) <*> To change settings via email: hp_agilent_equipment-digest@... hp_agilent_equipment-fullfeatured@... <*> To unsubscribe from this group, send an email to: hp_agilent_equipment-unsubscribe@... <*> Your use of Yahoo Groups is subject to: -- Richard Knoppow dickburk@... WB6KBL |
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Re: [TekScopes] Re: Why is Mu Metal used?
Ahh ok, now THAT makes sense and tells me a lot + gives me some
keywords to follow up on. Thank you very much! On Sat, Feb 20, 2016 at 8:27 PM, kmec@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
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Re: [TekScopes] Re: Why is Mu Metal used?
¿ªÔÆÌåÓýThe skin depth for copper at 60 Hz is large enough that significant field
energy can penetrate through material thin enough to be practical, resulting in
interference. Mu metal (iron that has been annealed (degaussed) in a reducing
atmosphere, usually hydrogen)) acts to divert magnetic field lines around the
shielded object without add any remanent field of its own. I am sure others
can/will add more.
?
73
Jeff Kruth
WA3ZKR
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In a message dated 2/20/2016 2:10:54 P.M. Eastern Standard Time,
hp_agilent_equipment@... writes:
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Re: eBay buyer protections are poor
I disagree.? I have bought Agilent ESG-DP, 8341B, 8753ES, 4395A, E4440A, Tek CSA8000, R+S misc, and various heavier advantest equipment in the past year or so.? The key is to use the 3" semi-hard foam (the kind that you can compress with significant force but it will always return back to its original shape and size, its usually pink or white, comes with new TV's etc) and use a bunch of tape to tape this all the way around the perimiter of the front of the unit, SECURELY tape it with a lot of tape to keep it from moving at all, then put a flat piece across the faceplate, and fill in any gap between this 2nd piece and the faceplate with paper wrapping, then SECURELY tape this all together and to the body of the unit.? Then stuff the box with paper (or something else that won't migrate and won't compress significantly) so that the rest of the box supports the body of the unit (and there isn't significant force on the front foam from the weight of the unit).? Anywhere there are any BNC/SMA/etc connectors, you must put 3" of the foam mentioned above.
The problem is with the kickers in the fedex/UPS distribution centers. The boxes rapidly move down conveyers and are scanned, and when they reach the appropriate split/chute, this little wall kicks out *BAM!* and throws it down the other path.? The problem is that with heavy packages, it takes significant force to get the package moving and there will be significant momentary force exerted on wherever it gets kicked.? This will momentarily compress that part of the package.? Packaging that migrates or yields will get compressed and no longer protect after a kick or two.? I have seen BNC connectors punched through 4 layers of cardboard from these kickers, faceplates broken, etc, so I always provide very specific packing instructions to private sellers, and the materials needed are usually cheap if you give them a few different options. All of? the equipment that I have received damaged was damaged because it was packed in material that yields (compresses but does not return) - such as 1-2" styrofoam (no good for faceplates and most corners, only good for flat sides with no protrusions!!); Bubble wrap (shameful), etc.? The key is to use this foam that takes significant force to compress, can be compressed to about 1/2 its original thickness by significant force, but always returns to original size.? It's the same foam that TV's usually come packed in, computers, new test equipment, etc. Protect the corners, use very secure taping to make sure the foam WILL NOT move, protect any surface with protruding connectors, and if you really care about the back corners (I often do not as I rarely see damage on rear corners unless they have protruding pillars like advantest and R+S) then use the same foam on those as well. |
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Re: [TekScopes] Re: Why is Mu Metal used?
Jack Mcmullen
Another reason, the CRT beam is most?susceptible to magnetic fields as seen in the television deflection yoke scanning the beam. A sufficient magnetic field close to the CRT will deflect or modulate the beam even slightly causing poor focus trace quality inaccuracy
Jack KG6INX
-----Original Message-----
From: 'cheater00 .' cheater00@... [hp_agilent_equipment] To: TekScopes ; hp_agilent_equipment Sent: Sat, Feb 20, 2016 11:02 am Subject: [hp_agilent_equipment] Re: [TekScopes] Re: Why is Mu Metal used? ?
I understand a changing magnetic field would induce a current in the
copper foil, and so the magnetic field would effectively be "used up" by the copper foil, though. Why is copper shielding not effective against 60 Hz? That's not DC after all. Thanks a lot I'm only learning about EM theory On Sat, Feb 20, 2016 at 7:57 PM, snapdiode@... [TekScopes] <TekScopes@...> wrote: > grounded copper foil would do precisely zero against a dc field > > Mu-metal - Wikipedia, the free encyclopedia > > > > > > > > Mu-metal - Wikipedia, the free encyclopedia Mu-metal is a nickel¨Ciron soft magnetic alloy with very high permeability suitable for shielding sensitive electronic equipment against static or low-frequen... > > > > > > > > View on en.wikipedi... > > Preview by Yahoo > > > > > > > > > > Permeability (electromagnetism) - Wikipedia, the free encyclopedia > > > > > > > > Permeability (electromagnetism) - Wikip... In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, it is the degree of... > > > > > > > > View on en.wikipedi... > > Preview by Yahoo > > > > > > > > > > > > > > ------------------------------------ > Posted by: snapdiode@... > ------------------------------------ > > > ------------------------------------ > > Yahoo Groups Links > > > |
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Re: [TekScopes] Re: Why is Mu Metal used?
On 2/20/2016 2:06 PM, Jack Mcmullen forjack842@... [hp_agilent_equipment] wrote:
Hello-- ...And Mew Metal shielding will keep cats out of transmitters....<g>. 73-- Brad AA1IP |
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Re: [TekScopes] Re: Why is Mu Metal used?
I know they're different Jack, I'm asking how. CheersOn Sat, Feb 20, 2016 at 8:06 PM, Jack Mcmullen forjack842@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
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Re: [TekScopes] Re: Why is Mu Metal used?
Jack Mcmullen
You're comparing apples and oranges. 60hz Magnetic fields are what MU-metal are best at filtering out. Copper screen is best for shielding RF electric fields as radiated from antennae.
Jack KG6INX ?
-----Original Message-----
From: 'cheater00 .' cheater00@... [hp_agilent_equipment] To: TekScopes ; hp_agilent_equipment Sent: Sat, Feb 20, 2016 11:02 am Subject: [hp_agilent_equipment] Re: [TekScopes] Re: Why is Mu Metal used? ?
I understand a changing magnetic field would induce a current in the
copper foil, and so the magnetic field would effectively be "used up" by the copper foil, though. Why is copper shielding not effective against 60 Hz? That's not DC after all. Thanks a lot I'm only learning about EM theory On Sat, Feb 20, 2016 at 7:57 PM, snapdiode@... [TekScopes] <TekScopes@...> wrote: > grounded copper foil would do precisely zero against a dc field > > Mu-metal - Wikipedia, the free encyclopedia > > > > > > > > Mu-metal - Wikipedia, the free encyclopedia Mu-metal is a nickel¨Ciron soft magnetic alloy with very high permeability suitable for shielding sensitive electronic equipment against static or low-frequen... > > > > > > > > View on en.wikipedi... > > Preview by Yahoo > > > > > > > > > > Permeability (electromagnetism) - Wikipedia, the free encyclopedia > > > > > > > > Permeability (electromagnetism) - Wikip... In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, it is the degree of... > > > > > > > > View on en.wikipedi... > > Preview by Yahoo > > > > > > > > > > > > > > ------------------------------------ > Posted by: snapdiode@... > ------------------------------------ > > > ------------------------------------ > > Yahoo Groups Links > > > |
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Re: [TekScopes] Re: Why is Mu Metal used?
I understand a changing magnetic field would induce a current in the
copper foil, and so the magnetic field would effectively be "used up" by the copper foil, though. Why is copper shielding not effective against 60 Hz? That's not DC after all. Thanks a lot I'm only learning about EM theory On Sat, Feb 20, 2016 at 7:57 PM, snapdiode@... [TekScopes] <TekScopes@...> wrote: grounded copper foil would do precisely zero against a dc field |
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Re: Why is Mu Metal used?
Jack Mcmullen
The Mu-Metal exhibits ?a shield against 60hz transformer magnetic fields commonly known to induce beam distortion.
-----Original Message-----
From: 'cheater00 .' cheater00@... [hp_agilent_equipment] To: TekScopes ; hp_agilent_equipment Sent: Sat, Feb 20, 2016 10:49 am Subject: [hp_agilent_equipment] Why is Mu Metal used? ?
Hi guys,
Why is Mu Metal used to shield CRTs in scopes, rather than just grounded copper foil? I never understood the precise reason for that. Thanks |
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Hp 70900B ROMs
Hi everyone, |
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Re: eBay buyer protections are poor
In the past I've very successfully shipped test equipment. Unfortunately, to pack it right takes strong boxes and good packing materials and these aren't always available for free. The extra size and weight also adds shipping cost. Ebay kind of demands immediate shipment so I found I was paying a lot for materials and nobody was willing to pay. A company which receives gear would have a lot of materials to ship with, but not an individual. I pretty much stopped selling on ebay but would consider it if a buyer would pay to have a local pack-and-ship that I dropped off an item at do the work (haha, good luck with that!).
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I think that large, high end test equipment is close to unshippable by the general population. To think otherwise means you're taking a gamble, so bid accordingly, as they say. Peter On 2/20/2016 10:55 AM, daniel@... [hp_agilent_equipment] wrote:
The next bit, about buying from US sellers to avoid the hassle is just not true.So out of a country of 310 million people, you managed to find a few people who have no clue how to pack stuff. Big surprise. That's what you get for buying from people who aren't professional packers and shippers. Buy from people who are professionals and you probably won't have that problem. But you're probably not going to find professionals selling old test equipment, so we're really talking about different things. |
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Re: eBay buyer protections are poor
Sellers frequently give no choice, they ship how they want to ship and you pay the cost.
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The pricing formulas are different at USPS, UPS and FedEx which means that for any particular package, depending on density, weight and distance, one or the other might be more competitive. I have found at times USPS was the least costly option, at other times they were the most expensive. USPS seems cheapest for international and paperwork and customs is smoother and cheaper too. This is all in a constant state of flux, pricing changing all the time, so you have to keep checking all options for just about every shipment. Peter On 2/20/2016 10:53 AM, daniel@... [hp_agilent_equipment] wrote:
Sure, I got a few dodgy items, but when you are buying 100 resistors for$2.95 including shipping, what do you expect? |
David Hess
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