So you also did not work for those people in the 80s during the cold war. But we can't talk about that . LOL
You expose the Martian Dave (a coaxial shows no change).
Cables with unconfined fields, pick up a lot from the environment.
A good instrument that measures R,L,C as a number can be blind as jn says.
It reads voltage/current amplitudes and registers phase angles, fits them to a chosen model and spits out numbers.
Doing cable tests within a large Faraday shield is an option but not for an amateur.
For an unshielded testing environment, we have to consider RF sources within a broad freq spectrum, both the active (most are outside the testing room, some are inside) as well as the passive.
By passive RF sources I mean metal structural members or surfaces acting as RF reflectors. Given an existing RF field, depending on it’s dimensions,
such a passive member can resonate and reradiate. Consider the cumulative effect from many such passive transmitters and their distance from the UUT . This distance too is something to think over.
Using a cvr to watch UUT’s current waveform on a broadband oscilloscope can say a lot.
George
Lucky you ..
Huh ....
Why can you, digitisis is in the head only, because it is digital and digital seems to be bad for hard core audiophiles, glad I'm deaf.
Only in that my questions were rhetorical.
Lenz is the reaction to rate of change of the field. The currents within the conductive surface create currents, those currents are creating fields which are bucking the inducing field. In the copper, it's simply rate of change and conductivity of the copper. In the iron, that is a very different story in that it's permeability is a function of the magnitude of the induced field as well as the polarity of the change of the field. If the absolute value of the inducing field is 500 gauss, and it is rising, there will be one permeability value, if it is dropping, another. It's the hysteresis thing. The bucking currents within the iron are a function of rate as well as permeability. Instead of a shorting ring, I'd first break the iron conductivity normal to the flux path without modifying the permeability along the path. Trivial to do with Micro wire EDM, brass wire maybe 1.5 to 2 mils diameter.
In the end, it's really the only way to examine what the load current is. The beauty of using a cvr of say, 10 millliohms, is that it is not disturbing the system much to get the information, so actual low impedance drivers can be examined on a high impedance line. The challenge with such a low value is the self inductance of the cvr.
jjn
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JN,
So if I am following you correctly are you saying to place a layer of thin copper lets say at the junction of a top plate and a steel cup to break the steel circuit at some point outside of the gap where a normal shorting ring would be placed? I know what an edm machine is so you are talking about a thin electrode wire I think? Could this be a few thousandths of say copper shim material? Would this still have the intended effect of a Faraday ring in reducing eddy currents?
DF96,
So true that random and chaotic are very different things.
So if I am following you correctly are you saying to place a layer of thin copper lets say at the junction of a top plate and a steel cup to break the steel circuit at some point outside of the gap where a normal shorting ring would be placed? I know what an edm machine is so you are talking about a thin electrode wire I think? Could this be a few thousandths of say copper shim material? Would this still have the intended effect of a Faraday ring in reducing eddy currents?
DF96,
So true that random and chaotic are very different things.
A pic:
EDM the pole and plate like the picture. The flux has to travel into the surfaces at the gap, and there are no cuts which introduce permeability of 1 into the mix. The cuts eliminate eddy currents.
Any structure which the flux has to pass through cannot have low permeability. Making the plate or pole out of steel laminations introduces material in the 2 to 3% by volume range, and that 2 or 3 % air or glue heavily compromises the permeability. Lam stacks are anisotropic, permeability normal to the glue surfaces is not 98% of the iron, but easily an order of magnitude down at the least.
This design cuts the eddies, and retains the flux path reluctance where it was supposed to be.
Edit: I doubled the cuts on the outer plate, but really, all you need to do is get the uncut widths at the gap into the 1mm or .5mm range. I've measured stacks with both, and at .5mm, I get very good hf results.
BTW, this concept is patented. I was considering this design as a collaboration with you a while back as I did not find any pre-existing, but eventually I did find the concept (sigh). Not EDM mind you, but segmented iron pieces.
Shorting rings should not be seen by the voice coil assembly.
edit: I added this to my gallery.
Edit v2..Lamination of circles to make the pole piece causes the vc magnetic permeability to cog, so it is unwise to make the pieces out of a lam stack. As the vc moves, the direction it moves must have a smooth magnetic environment.
Edit v3: btw, it is a trivial process to cut everything in the magnetic structure, then vacuum impregnate the structure to hold the pieces together.
Yes. Like dating and marriage..
jn
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When it comes to autos, I feel that the personal opinions here are confusing. I DO know that my associates BMW is more comfortable on long trips than my Acura. And my old, but in good condition, Porsche 944 is VERY uncomfortable on long trips, almost backbreaking. Jack's Mercedes is VERY comfortable for long trips, almost perfect, but the back seat of the Bentley is pretty good too!
John I guess we all have different anatomy and perhaps some would be comfortable in one seat and not in another. You can ask BMW why they offer an optional Recaro seat for the cars if the factory seat is supposed to be so great? I know I am not the only one who thinks the upgraded seats are better on the back.
JN,
Running out but will reply later, that looks like it would be very difficult to produce those wedge shaped sections?
JN,
Running out but will reply later, that looks like it would be very difficult to produce those wedge shaped sections?
I have the optional Recaro seats in a new Cad. CTS-V. Last week I sat in a Bently Continental GT.... the driver seat was a lot better in fit and comfort.
But, I must say that I have driven 1000 miles non-stop (except for gas) and got out of the CTS-V and felt just like I had only gone to the local store.
Moral to the story is ---?
I dont have one... just thought I would get in the spirit of things and go with the flow here.
-Richard
But, I must say that I have driven 1000 miles non-stop (except for gas) and got out of the CTS-V and felt just like I had only gone to the local store.
Moral to the story is ---?
I dont have one... just thought I would get in the spirit of things and go with the flow here.
-Richard
I have no idea what you're talking about...
You expose the Martian Dave (a coaxial shows no change).
I think he enjoyed it too much...
More discussion about Ls measurements for high current cables would not hurt my feelings. Really looking forward to your data.
Dave
No. Trivially easy.
1. Bond the entire magnetic structure.
2. Bond the entire structure to a carrier surface, front of gap at top.
3. EDM horizontally through the center of the pole, down to the carrier surface.
4. Rotate some increment.
5. Repeat cut down to carrier.
After all the cuts are done, each wedge is held in place by the carrier.
While still bonded to the carrier, vacuum impregnate the entire structure. If you want, fill the gap with a material that can be removed at a later date, teflon, or something that will dissolve or melt. Just do not exceed curie.
Or alternatively, don't fill the gap, simply clean it out post processing.
Vacuum impregnation is not that difficult, and if the gaps are 3 to 4 mils, just select an epoxy that has a low viscosity and reasonable pot life. Cycle the vacuum several times, and cure it at atmospheric.
Just de-air it properly first. Remember, you are relying on the impregnation for structural, not for magnetic reasons. It doesn't even matter if you get bubbles, even out to 10-20%. But a good process will get you void free.
You can even put features on the pole and outer plate to aid in placement during impregnation if you don't have a good enough process for bonding to the carrier.
This can even be made as lots of thin wedges that are assembled using a thin paper or glasscloth shim between metal surfaces, with fixturing to hold it concentric to some tolerance. Choose the paper or cloth for a specific thickness, and as long as it's porous, good deal.
Don't go for a matched expansion epoxy, as the filler will make it very difficult to get the epoxy into the gaps. It tends to clump on the ends of the gaps and at the edge of glasscloth. Only use totally unfilled epoxy.
jn
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Oh, btw. I've no idea if it is possible to clear the gaps during the EDM process, as a 1 to 2 tesla magnetic field will prevent the fluid from washing the particles away. I suspect that the only viable ways will be to either EDM pre magnetization, or EDM the steel prior to assembly. The front pole and plate and backplate can be EDM'd and impregnated first, then combined with the magnet later. Many different ways to skin this cat.
jn
jn
Thanks JN for the detailed description. That sounds interesting but sure would be cost prohibitive on a production basis. You said someone has a patent on this methodology? Basically it sounds like a laminated transformer concept with high permeability material such as a stainless steel material.
From my experience, I find the stycast to be the best.
The 2851 is a thermoset compound, requires no mixing, unfortunately it requires cold storage to retain some shelf life. It comes in FT, MT, KT, and GT. these are different in the filler size. FT has the finest alumina powder filler, MT has bigger particles and some of the smaller particles to go interstitial to the larger ones..KT and GT have 3 and 4 sizes of particles respectively. The thermal conductivity is by order, GT best, KT, MT, then FT.
Ft I use for the thinnest layer possible, and when I have to fill small dimensions.
The 2851 is best for electronic components, with a cure at about 90C, followed by a post cure of 150C. The final glass transition temperature is about 117 to 125 C, depending on the year of the datasheet (go figure). It can be stored at room, but I have the people here store it in a freezer...still, we watch the shelf life anyway.
I currently use 2850, which is a two part epoxy. I'm using FT and MT at the moment. the 2850 has three hardener options, 24LV (or 23LV), a room temp cure with a glass transition of about 45C, and catalyst 9 and 11, both better oven cure hardeners, with higher glass transition temps. The room temp cure is best for parts which have a final operating temperature between 77K and 1.8 K.
The best part about using the 24LV is that because the transition temp is so low, I can use a heat gun to do repairs. With the work at 50 or 60 C, the epoxy becomes soft and easily removed. The bad part of the low transition temp, is that it goes soft and it's expansion coefficient goes nuts, 90 to 110 ppm/degree C. Once it's taken that high, it expands and deforms in and out of any cavity, compromising the physical integrity.
OH, almost forgot. The 24 and 23 LV hardener cause the mix viscosity to drop an order of magnitude, where the 9 and 11 do not. It really is weird seeing how thin it gets when 7% by weight hardener is added to the pasty resin. Also, If possible, use a vibration table when potting, as the vibration causes the viscosity to drop, allowing it to flow better. If you intend to use a 10 to 15 mil thick layer between a flat copper plate and it's mounting surface, your best bet is to paint the surfaces, place them, and cure it. Otherwise, you'll get air pockets. Also, de-air if possible. I used 10 mil thick ceramic alumina shims to space the unit from the case bottom.
I will most likely use the 2850 FT for my resistor potting. Not the best if I plan on heating the unit to greater than 50 C, but I don't think I'll be heating a .1 or .01 ohm resistor that much from a rmx 1450 output.
jn
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