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Old 14th November 2008, 11:17 PM   #21
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thank you anatech - more things to keep in mind. I'll pass along whatever comes about just in case anyone else finds this of interest.

It's not really audio related; but then again, when I consider it within the realm of current sensing apparatuses, a paper cone connected to a wound bobbin within a magnetic field isn't really too far removed! No wonder I drew so much constructive comment.
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Old 15th November 2008, 03:50 AM   #22
poobah is offline poobah  United States
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You know bluebeard,

Unless you're going build a zillion of these... for your own reasons... I would really look into a FLUKE current clamp... everything you need... already DONE. It shouldn't be that hard then to figure out the signal etc... plenty of geeks around here to design an interface amp (gain and offset)...

If you must go through the agony of building your own, there are toroids that will slip right over a MIG/TIG torch without an "opening mechanism... just a thought...





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Old 15th November 2008, 02:58 PM   #23
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Not a zillion, but I hope to make a couple of dozen. You're right about the Fluke route (one of the more ironic company names eh?). They were even among the places I emailed for information along the way. The clamp is a couple of hundred dollars. There are in fact a few other ac/dc Hall Effect sensors/switches out there that are somewhat less than that. Unless I can make this for less than 15usd in parts, it just wouldn't be a practical avenue for me to take in this project. I'd have to find some other way of sensing current in the wire, or arc at the torch.
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Old 15th November 2008, 05:20 PM   #24
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Maybe this is of help: http://www.lem.com/docs/products/FHS%2040-P%20SP600.pdf

No need for a ferrite core then. Simply make a PCB that you can attach to the high current busbar. Mechanical stability is mandatory.
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Old 15th November 2008, 05:57 PM   #25
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http://content.honeywell.com/sensing...862_1_EN_w.pdf
http://sensing.honeywell.com/index.c...=1&catId=79839 Click on current sensors -> current sensors
http://sensing.honeywell.com/index.c...s_id/79957.htm
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Old 15th November 2008, 06:02 PM   #26
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I have experience from current sensors at work and 300 A types. Price approx.10-15 USD
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Old 15th November 2008, 08:21 PM   #27
jcx is offline jcx  United States
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for a clamp on concentrator no cutting is needed if you use U-I core, can adjust the gap to standardize sensitivity when setting it up

10x10mm core opening 2-D field sim:

Click the image to open in full size.

I get ~ 1 mT in the air gap with the 1mm offset I bar, 2 A current, u_r 100, but I'm no expert with this software

2-D ignores fringing field from Z axis truncation so field values might be lower, although grinding a taper could more than make up the leakage if your concentrator is much wider in the Z direction than the sensor element

remember you need low hysterisis magnetic material, and sensor

sensor sensitivity, hysterisis and Vos tempco can limit your low current resolution

ground/polished faces aren't really important when you have 1mm+ intentional air gap dimensions to fit sensor body

Student QuickField (free, <256 mesh nodes)

http://quickfield.com/
Attached Files
File Type: zip ui_conc.zip (8.0 KB, 7 views)
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Old 16th November 2008, 04:46 PM   #28
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Here's a decent representative page of what I've found out there commercially.
http://www.bbautomacao.com/home_Open...d_Windows.html

Interesting particularly since the split core devices only begin at the 100amp sensitivity range. Below that, and into the milliamps, are the solid core. The prices on these are pretty reasonable as well. I see pages like this and it lures me into deeper and deeper google rabbit holes in the hope that I'll find my holy grail.

But I worry that perhaps the absence of lower current split core versions may indicate that the core consists of some form of non separable windings around the core. Maybe this can't be done?


While a lot of people have told me this might be difficult to do, nobody so far has strictly disabused me of the idea.

jcx, isn't the U I core merely another iteration of a split toroid (functionally). I'd prefer the split core ferrite since I can get them with nylon housings hinged and snapped (I suppose the U I cores can be similarly purchased, but is there any advantage to them over the 'C' cores?
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Old 16th November 2008, 06:53 PM   #29
jcx is offline jcx  United States
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I'd rather not have to fixture and grind brittle 1/2 round shapes when I can buy the U-I pieces

the sensing gap can be easily adjusted by sliding the I bar

the offset square corners give a natural wedge for higher flux concentration

one possibility:
glue a hall sensor on the end of the I bar, with the hall element aligned/centered on the corner/edge where my field plot shows the greatest flux concentration
then put the I bar + sensor (wired to the sensor cable) in a "boat", coat the U legs with mold release and adjust the assembly while monitoring the sensor output with a reference current thru the window
fill the boat with epoxy and let it cure, encapsulating the I bar and hall sensor, and a little way up the U legs
now you have custom pockets to assure perfect alignment when you remove the U legs from the hardened epoxy - and have standardized the sensor sensitivity
a nylon cable tie around the whole should be able to hold the U core in place when reassembled around your welding cable
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Old 16th November 2008, 07:26 PM   #30
jcx is offline jcx  United States
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another U-I geometry, higher concetration factor, maybe unrealistly thin gap?

Click the image to open in full size.
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