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Old 16th November 2008, 08:16 PM   #31
poobah is offline poobah  United States
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We all can get stuck "in the box" sometimes... this flux ring can be made from nearly any type of iron (steel)...

We are not worried about any of the issues that drive the use ferrites...

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Old 16th November 2008, 08:42 PM   #32
jcx is offline jcx  United States
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I think this requires some care in materials selection

the application does need low Hc, Br; detecting 2A after multiple cycles to 250 A requires low residual magnitzation - certainly not a high carbon steel property

if transformer steel is OK, then you're back to U_I shapes being readily avalable
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Old 16th November 2008, 08:47 PM   #33
poobah is offline poobah  United States
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good point...

I can't remember what gizmo it was in... but I have seen good ole' mild steel used with H.E. chips...

Any other material with low remanence???

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Old 16th November 2008, 09:57 PM   #34
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poobah, page 31 of the following...
(fig 63) shows an example of what you've described.

That would be pretty dreamy. Just a 3 cent piece of sheet with tabs that could be bent around the conductor.

I still wonder if, all state of the art considered, I'm going to be able to just build a current detection switch of non-contact, non intrusive (split core) design, capable of a two amp threshold ac and dc.

If it is possible to do this, it just stumps me that a version is not available off the shelf at Digikey. A universal non-contact, ac/dc, current detection switch (i just want to know if there is currrent in the line .. no more, no less). This would be available in a three pin unit ready to go. Say 6-24vdc inputs and analog output pin.

I'm dreaming again.
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Old 16th November 2008, 10:52 PM   #35
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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

jcx, thank you very very much for the ideas. This is just the sort of tinkering that I am fond of. I'm often jigging such things with epoxy to get what I need. I'm, at this stage, inclined to think that the gap tolerances we're discussing are a bit beyond my skills with epoxy models. Aren't we talking mere thousandths here for repeatability?

For the love of God. Can someone just point me to a clamp-on AC/CD current switch with a nominal amp threshold?
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Old 17th November 2008, 01:28 AM   #36
anatech is offline anatech  Canada
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Hi jcx,
I really like your U-I clamp idea. An E-I core might even work (from an old transformer, or new core pieces).

Hi bluebeard,
Have a look at the bigger distys. They have hall detection switches in expensive assembilies. They look close to indestructable. They may also have the same idea in a less expensive form. Can't say as I've looked that closely. Buying a Hall switch rather than a linear sensor should make things easier on you.

The Fluke clamp sensors will be a linear type. This adds to your signal conditioning a little. You may find that a single Hall switch may work on it's own. The additional magnetic path only increases sensitivity, so try a sensitive switch first.

Looking at Digikey and searching for a Hall switch (bulk, cut tape) brings us a number of choices that are in stock. Here is a data sheet from Allegro. Just one example of many listed for less than $2.00 . Nifty stuff.

"Just because you can, doesn't mean you should" my Wife
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Old 17th November 2008, 03:51 AM   #37
jcx is offline jcx  United States
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the sim claims Bx changes from 0.95 mT @ 1.2 mm gap to 1.1 mT @ 1 mm gap

absolute accuracy shouldn't be your main goal with a quick hack like this - but I'd guess you can keep reassemby variability < 0.004 inches
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Old 17th November 2008, 07:48 AM   #38
poobah is offline poobah  United States
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Tell ya what...

Remenance IS an issue. JCX has the cool software and brains... how's about a spec on the detection threshold level?

As an example would 2 to 4 amps, including magnetization etc..., work?

... might have been the same datasheet, but Allegro talked about powered iron... or Ni-FE materials for low remenance. One upside to a non ferrite material is more flux... that can also mean that saturation (therefore magnetization) is an issue though...
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Old 17th November 2008, 09:05 AM   #39
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A lot of good educated guesswork here and some useful caveats, but why go looking for trouble when it will come and find you? Solve your problems in the order that they present themselves.

A few simple experiments will put you in a better position to evaluate the economics and decide your future direction, both in terms of your own skills and the inherent difficulty of the task.

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Old 7th April 2013, 10:26 AM   #40
RCruz is offline RCruz  Switzerland
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Can anybody help here ? My 1980's Tangential Tone Arm and my 2010 improvement
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