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- Опубліковано 4 жов 2024
- A demonstration of near-field magnetic interference and how to shield it.
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"25KHz is quite high frequency"... Tell that to The Signal Path lol
Yeah, he'd call that "DC". Did you see the crazy 500GHz or 1THz os-silly-scopes he was playing with in some episodes? I think he had some crazy light/laser source to look at. My mind breaks when thinking about something cycling a billion times a sec. Hang on - so MHz is a million, GHz is a billion, so THz is a trillion! Bloody hell. And to sample that properly you have to go beyond that by quite a bit. Black magic. (EDIT: or time-interleaved madness)
@@WillArtie just don't even try to look the prices for the equipments he uses
@@michelfeinstein yeah I know! $400 or there about was a big purchase for me when I got a Rigol DS1054Z!
I come from an industry were 2KHz was considered high frequency.
@@EEVblog I'm all power supplies and audio DJ, (as in your initials.. not a music dj...) so I'm with ya there. Edit: you mean sonor/deep sea stuff?
Somewhat related - railways that use "axle counter" train detection systems often make use of a form of magnetic sensing where a tx and rx coil are placed on either side of a rail and nominally there is a certain minimum magnetic flux linking the two coils. When a train wheel passes over the rail (directly between the rx and tx coils), due to the wheel being of a high permeability material (steel) the flux is rerouted through the wheel structure and the field at the rx coil is much lower - hence a train wheel has passed. This saves on older mechanical parts that physcially switch as a train passes as these fail more often + it's a right side fail safe system as if the tx coil loses power, the field will diminish at the rx coil and will seem as though a train is there rather than failing to detect any trains passing.
Some railways also have a low voltage AC signal (15V or so) between the two rails which gets shorted/pulled down if a train passes. Same idea - if the voltage source dies, it will seem like there is a train there as a failsafe.
I have seen a YT vid a few years ago where a UA-camr charged his phone using that energy, probably not good for the operation of the railway... :D
@@TheRailroad99 Yeah they're called track circuits - they started out being simple DC applied to the two running rails over long sections called "blocks" and each block would be separated with special "insulated rail joints". These days some high speed tracks are circuited using high frequency AC track circuits that don't even require insulated joints while still being able to have isolation between different blocks - this can be done with clever high frequency techniques.
@@ThomasMoody a big problem with DC was galvanic corrosion on the ?negative? rail. AC does not have this issue.
Interesting that modern railways don't need insulators between block sections anymore - didn't know that!
I've seen this before. I was a service engineer for an electron microscope company. I had a customer who had to spend $200k USD on room prep because they decided to put a TEM and SEM next to where the 13KV building supply came in. Just what you want next to sensitive equipment. With fully welded walls of thick Al and vibration mitigation, the room was AMAZING. Except for low frequency magnetic field fluctuations. I could tell in the image when the elevator half way across the building away moved.
Another technique that's useful for very low frequency/DC magnetic fields is active magnetic shielding via Helmholtz coils. Completely impractical for compact applications but does create a controlled environment when testing out sensitive things like magnetometers.
this makes me remember the ciba geigi experiment/patent. i gigantic kondensator with hoigh dc volltage to create a field that shields from outer side. or so. oh my english ;)
@@Raketenclub Worked on 'MagnaVoid' - Microvitec CRT monitors with built in active magnetic cancellation back in the day, for industrial applications - built a big perspex Helmoltz coil demo rig with 2 monitors stacked on top of each-other, one with and one without the system to take to trade shows... ah, what fun!
Thanks for another informative video Dave. I love the way you can make "dry" sound like a "fun adventure".
Love the excellent visual explanation, nothing makes a better experiment than seeing the measurements take place on the instrument in near real time
This is fascinating. Thank you.
You need one 'o them there "cow shields" made of "moo metal.
So I better swap my tin foil hat for a copper hat to stop the government from mind reading 🤣😂😆😉👍
Video sponsored by the global asociation of copper foil producers 😉👍🤣
You need a combination of mumetal and steel. Ned Kelly was ahead of his time.
That's videos I expect from you .... great! Short, explanatory and so useful.
Really good demonstration about the importance of the proper shielding!
Though the CRT is shielded on the sides, the front is glass with a mask. The H field can easily be transmitted through the front of the CRT. At the very end of the video you held the aluminum box higher and the effect was much lower. Putting the Al, Cu & steel sheets in between completely covered the glass front of the CRT that was not shielded.
...so you're saying that we need transparent Aluminium for the front...?
I hear all of the “preppers” saying that to save your electronics, during a solar storm or a nuclear blast, that a microwave oven is shielded enough to stop the EMP. Could you make a video explaining if this actually works or not?
There is a dedicated chip that detects EMP's and gives trigger output. It's designed to shut down system before the pulse hits.
@@EEVblog Oh that is interesting, can you make a video of it or a short description?
Lassi Kinnunen That is what I figured. I am not as smart as Dave, on this subject, but I love learning, plus I figured it could be a good subject for a few good laughs. I have some friends that keep pre-paid phones and laptops, in an old microwave in the garage, just for that purpose. I do not know wether to believe it, or to laugh at them.
@@EEVblog The trigger output is sent via Tachyons?
Preppers & EMP ... whiffs of audiofoolery
Love how it's 2020 and we have a black and white printout of a youtube video haha
I'm old school.
Kurosawa Mode for UA-cam.
great vid - I have one of those DSA's and I ended up making a simple remote control for it so I could start the averaging (plus a couple of other things) as I moved things away from it
I've triggered them remotely in various test setups over the years.
@@EEVblog glad I'm not the only one, given the price of the thing, I was sweating bullets when I did it.
as an aside, this is one of the things I like about your channel, in all the years that I've watched it, you've never turned into one of those guys who act like they're too good to talk to the audience.
*Dave:* 25kh is quite high frequency
*Shahriar has left the chat*
The all new Trojan copper shield, reduces probe sensitivity
It's free on Epic Games store for a few more hours.
Trojan. Precision you want. Protection you trust.
I am a audio tech, got a desperate call at 5AM there was noise everywhere in the mixing console. I tried to talk through it but was forced to go in at 5am. The Studer 24 track machine has Mumetal shields on the head guard. There was an CRT computer monitor sitting on the meter bridge a couple feed from the machine. The assistant had forgotten to flip up the head shield when loading the tape. I was not happy and knew what the noise was as soon as I saw the test box sitting in front of the CRT in this video.
The basic thing you need for H-field shielding is a good magnetic conductor. Mu-metal is one example.
Thanks! I learn lots with your videos! 😊
Hm. Bet you could do a whole video or a whole series of videos on shielding. You could even try to answer the age-old questions: Do I ground my shielded cable's shield at one end or both? If at one end, which end?
The rabbit hole is quite deep.
@@EEVblog Yes, but deep rabbit holes are the most fun and somewhat of a specialty of yours. And knowing how far to go down them to achieve a practical if not necessarily perfect engineering solution is often difficult. In any case, I really enjoy your quick afterthought follow-up videos - and all your others, too.
What about mu-metal shielding?
I mean actually testing it.
But yeah this was actually what I was yelling at my screen with last video.
Again a nice video Dave. You're on a roll lately 👍🏻👍🏻
I didn't have any. Steel does the same job for this video.
Your videos are always very interesting. Thumbs up!
I guessed "too close to the monitor" last time. Yay
Cos I happened to be using a 100 gain in a Die-cast box myself in the last audio project. For an old 70's phono cartridge pre-amp. You can't trust those boxes to do the biz. I ended up created a shielded, potted solution - in a box.
I often found 15.625 Khz in many older classical music. disc albums on sale, they came from CRT TV and can be annoying to listen.
Not necessarily from broadcast TV receivers. There was a period, as mixing desks were starting to get computerised features, that they actually built a CRT right into the console!
Early PC stuff--put the CRT monitor on top of the floppy drives creates interesting effects. The drive head amps get the EM field from the CRT deflection circuits and the video goes wobbly from the magnetic field in the drive spindle motor. Add a steel hood over the drives and you can read and write disks, but the display still goes a little wobbly from the very low frequency of the motor magnetics.
But most computer cases were made of steel sheet. I never had such issue with the old machines.
@@laharl2k In the 1970s, high-density foam, vacuformed or injection molded plastic was very popular for microcomputer cases. I can cite numerous examples.
@@tubastuff
So i guess you are talking about something like an amiga or a comodore then?
At most all i've seen or have is from the late 80s, and they where all XT/AT.
@@laharl2k My personal experience was with a Durango F-85 (ca. 1977). High-density foam case sprayed with zinc on the interior to deal with RFI per FCC part 15.
@@tubastuff
Oh that i never even knew existed and yeah its quite obvious that that tiny CRT being so close to the floppies could cause some trouble. I was thining more like crt in the middle, not directly on top of the floppies, thats really bad design.
Why don't you use [Pause] button on your analyzer when you want to show averaging results for a period of time when display was closed?
It's Dave
Very informative video. Thanks!
The skin-depth for aluminium at 25kHz is 0.5mm. If you take a thicker material (and not a zinc alloy but conductive aluminium) then a 3mm sheet shall block M-fields almost completely. Warning - a "cut-line" - i.e. where the lid closes on the box - compromises the integrity of the shield. (this is why the copper "strip board" perf-board does not shield at all at 8:19 ). Most magnetic shielding can be done without mu-metal, just with good design and some thought. Mu-metal or other high-permeability ferromagnetic metals have potential to fail too, if slapped-on without careful thought.
Watching a video of a printed screenshot of a filmed piece of paper. Inception!
Thanks, learned something more.
Will Copper coloured paint help?, Asking for a friend.
Great demonstration of our 'Noisy surroundings'.
Thanks for sharing.
You can get conductive nickel screening paint.
@@EEVblog interesting, thanks. Have a great weekend.
For a free high permeability steel for making your own near-field magnetic shield, breaking open a discarded microwave oven, the big transformer inside contans laminations of silicon-steel which are high permeability. An edge grinder can easily remove the two strip welds that hold it together, and the laminations are relatively thin sheets that are also relatively soft and can be cut with sheet metal snippers and then hammered flat on an anvil. If you recycled and put a big transformer into one of your projects, it might benefit from this kind of shielding from the near-field magnetic radiation. HTH.
i have heard that for low frequencies, mains frequency, one can use Laminated Copper around 6" thick or more for shielding. Based on this video, I wonder if laminated mild steel would be more effective. This is how one would shield their homes from power distribution lines near their homes. Of course, if one is planning on trying this, you will need to dramatically increase your foundation footing and foundation. Same for roof rafters. Same for walls.
If you're putting that much copper up, you don't need more wall!
Skin depth of Cu at 25kHz is 400um+, and 1oz is around 35um so you wouldn't expect much effect from such a thin layer.
The wonders of Black Magic and RF at a cool 25kHz - neat.
You could also try sintered ferrite sheets such as Würth FSFS 357003 or Kemet EFX
Of course the simplest & easiest solution is to not put your super-sensitive instrument next to a bloody CRT. ;)
Interresting...
Good deal. Reminds me I can still move forward on the spiral conical antenna instructable since I left off with only the "form." Excellent referenced video for sure. Makes me wondering what newer high magnetic permeability materials can do, to improve performance of the older systems. en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials
Same thinking goes with...., I think it's the OLED's are the quietest... though, mainly thinking upgrading the sources of noise, RFI, EMI, etc. in the systems for a modern upgrade to the old boys. Would be nice if silver foil was more commonly available. I guess that's what's used to line the mil/intel grade boxes. Plasmonic resonance frequency is one of those newer buzz words to me... though is more to do with electric effects and I guess somehow with magnetic... though the magnetic world is another beast. Just like polarization. Tables with polarization related to electric characteristics don't seem so common... same with the magnetic characteristics. Great demo! Thanks for sharing! Good fun.
oh man, why don't you say this earlier ... i got such problems :-D thx great info
At my job I have to do testing for ingress into a coaxial cable network. Sometimes it doesn't matter if the meter is connected to anything or not it will fail in certain areas of town. Bad shielding on the meter. If I put the meter inside my vehicle's steel center console, I can get my test to "pass".
Would have loved to see a CRT next to a LCD both doing the same measurements
Do you have any nickel silver (also sometimes called German silver) to try it with? Most of the shielded enclosures I've seen in devices use nickel silver.
quite interesting
Dave has the added problem of needing to get his test equipment and the device he's testing in the same shot.
Most people would have the analyzer about an arm's length away.
Although it's not relevant to this 25KHz testing, you said "If" there were low frequency fields of around 100Hz present.
Surely there actually was, due to the vertical deflection coils of the CRT?
Many guitarists use coper tape inside the guitars 1/4" output jack partition, the jack socket is mounted to a plate that lifts off,and a small compartment is behind. The jacks sockets are very usually unbalanced so they try to quieten the noise with copper. So should they be using a mix of metals to prevent noise and many layers of metal tape? 1khz and below is very important.
You'd have the know the exact problem source, but yeah, MuMetal might be worthwhile.
Dave, you are the nearest electronic Genius I know. I'm seeking an answer or the path to find the answer to this question: "Is there a frequency range, through which an internet type packet communication could be passed through the power grid? " Even pulse DC?
Thinking there might be a way to utilize the power grid to communicate information long distances to the boonies where there are few other communication methods. Any thoughts where I could beneficially pursue a meaningful answer. Thanks Dave.
Powerline Ethernet exists. For long distance, there's DSL. Not sure what you're getting at here.
Data over AC has been done.
Its not seemed to perform well.
For the boonies satellite and microwave work better.
Ethernet over power lines is a thing, you can buy commercial products for your home. Long range sucks arse because a single wire is a horrible transmission line, and EMC would be a huge problem. I'm not even sure how those home device get approval for that.
Answers, Answers, Answers. Thanks so much, you guys. Dave, you and your following are RESIDENT COLLECTIVE GENIUSES . Profound ... Thank you.
@@EEVblog Those ethernet over powerline devices wipe out the whole HF band. They should be illegal.
So 25kHz is the frequency the CRTs magnetic field is operating at, what's happening at 50 and 75? Harmonics?
Great vid!
It seems to be more spatially related to the 3.5” disc drive, right?
So that means that those old game consoles that had big copper sheets in them (e.g. the Sega CDX) were for protecting the electronics from CRTs! I’ve always wondered why they looked engineered to withstand the apocalypse.
Was that a tenacious d reference there? Dave? Are you also a man of culture?
I am indeed highly cultured.
@@EEVblog Expected no less from master senpai!
@@TrickyNekro BTW, the government totally sucks.
@@EEVblog Ssshhh now, they are listening!
@@EEVblog "BTW, the government totally sucks." just change $=1 to $=0
Quick test to know if a metal has high permeability is to see if a magnet sticks to it. Sticks = high permeability
Why EMF in Low Field is higher than in Low field
Fun and Interesting
If you connect Ch1 to the Source output on the 35660 you will probably see the same. You probably have to zoom in at 24.665 kHz with 1 kHz span. The shielding between the CRT and the signal generator is not that great in this instrument.
Isn't that pink bubble wrap mildly conductive? I.e. anti-static? Is it OK to wrap a bare circuit board with it?
It's ok. It does neither conduct nor protect from ESD. Quite useless
Need some transparent aluminum?
Any ideas for a probe to sniff around an enclosure for EMF? ie efficacy of screening / protection.
I hope to understand your words in the Arabic language Honestly, I hope the translation system gets excited and learns from you. I cannot express my gratitude to you
What would have happened if you would put a copper enclosure inside an ferromagnetic enclosure? Edit: I should have waited till the end before posting a comment.
WHY are you using an antique 30+ year old CRT signal analyzer, when you have modern LCD wide-bandwidth spectrum analyzer ?
Spectrum Analysers don't do down to DC.
Dude, it’s the pink bubble wrap !
what about a faraday cage?
Can anyone tell me if the sheild needs to be grounded or isoilated and what would the affects be in either case?
9:15 nice. You've invented a movement sensor based on EMI 😅
Qorax IIRC, this is the principle by which many traffic light detectors work. The presence of the car disrupts the field, signaling to the traffic light to change its sequence.
@@codydowling1120 Ah I thought it were just capacitive coupling sensors, like those old school touch buttons that used to be on 70s design home appliances.
What if the shields in this video were grounded? Would that help at all?
I showed that, they are mains earth grounded.
Something I've noticed...... Most people pronounce the letter H as "aych"......... and some pronounce it "haych". Dave is the latter.
You've just discovered language can differ with country.
"aich" is the standard UK English pronunciation of the letter. I have always found it kind of amusing that "dropping your Hs" is a sign of social class, except when it comes to pronouncing the name of the letter, when the inverse is true. And then you get the weird London hypercorrection of people inserting H at the beginning of words when there isn't one.
Hello this is Thomas does anyone talk about HP power source
Thought you had ground beef in there by the thumbnail
can you teardown ram or storage of smartphone ?
Look up Branch Engineering channel on UA-cam.
For magnets you want bismuth shielding.
Where can I buy this device?
I thought it was raw meat in the box from the thumbnail 🥫
A steel/iron sheet ideally mu metal as you mention while I write this comment will be best
Unless you have an intense field and then you want both.
Dave, what effect does gamma radiation have on a capacitors dielectric?
not one good for its longevity.
Id say it would cause it to break down
@@jhoughjr1 if so, how is space travel possible?
Hm, how about that. I always thought shielding didn't work unless it was grounded...
is this the basic of faraday cage?
can you do a video on faraday cage?
Faraday cage is for an electric field.
You HAVE to do a deep dive on the new ATX 12vo PSU standard it's a fucking dumpster fire in my opinion.
OK i don't mean to be that guy, but when I post this there is 1 thumbs down.
I must know what is wrong with this video? i mean its in focus, informative, has audio, to the point, has some experiments...
What is wrong with this video that it deserves a thumbs down?
At some point it legit can just be a missclick with very low sample rates.
Serial haters. Every UA-camr of any size gets them. They thumbs down the video within a minute of the release.
And still counts as engagement from the POV of the algorithm, iirc, so joke's on them.
From the preview I thought you had a steak in there
I never get why aluminium foil is so effective at shielding RFID, since RFID is basically only the magnetic field.
Much higher frequency
@@userPrehistoricman Yes but the distance is still not nearly in the same order of magnitude as the wavelength.
I need a analog used but working oscilloscope . I am a poor guy I couldn't afford even 50 dollars .So can you please send me some link of oscilloscope which is under 20 dollars including shipping because I am in India
Try using screws on the lid and shield the gap between the lid and the case.
FYI, UA-cam suspended sending email notifications to all subscribers.
"This is just a tribute" - Did you just made a Tenacious D reference?
"hach"
MVVblog is better