Magnet measurement

Nuclear magnetic resonance is very accurate I think...

Thomas

On Wed, 31 May 2006 13:56:57 -0400, "Ken O"

ya thats what i figured, I am thinking of building one, I found this site

I am finding out that hall effect sensors are very hard to find... its not a hot item.

kenO

Hi, Ken-O. The reason you're having trouble finding the part is that Radio Shack really doesn't carry very much in the way of components these days, and also that the manufacturer is obsoleting the part.

The cross-reference is the Allegro A1321LUA-T. It operates on the same voltages, same pinout, and has the same sensitivity (5mV/G). It's available in stock at Digi-Key for $1.45 USD. And it has a working temperature range from -40C to 150C, so it can be just about as hot an item as you please.

Hope that helps. Book 'em.

Good luck Chris

Ken, generally it's measure using a Gauss meter. Modern instrument uses Hall Effect semiconductors for the purposes.

Harry C.

Ken O wrote:

ya , gauss meter at 500$, a little too steap for me. I thought of building one. looking into it

ken

thats exactly it, thanks a lot, i did go on digikey website, I put hallsensor as a search keyword, and it showed me the another ' apply filter page' i was never successful to get those parts.. ken

go there. your looking at a Gauss meter.

in short, you can use Webers (Wb) as the unit to measure with and that is. 1 weber = the magnetic flux that produces an electromotive force of 1 volt in a 1 turn loop circuit as the flux changes from max to 0 in one second time.

"Ken O"

OK, Ken. Just for reference, if you're having trouble finding a semiconductor, the first thing to do is go to the manufacturer's website, and punch in the part number. Sometimes you get really bad news, but sometimes you get some help. If you'd waited another year to do the project, the part would have been gone, and the recommended cross might not have been so easily found.

Worse comes to worst, you can always email or call the manufacturer's sales engineers. They will recommend a cross (and frequently recommend competitors' parts.

Good luck with your project -- it looks pretty straightforward. Feel free to post again if you get hung up.

Cheers Chris

Really cheap Hall sensors (but SMT package):

Linear Hall sensor, two for $1.00

Here's my list of more. (Old list, so those available from surplus companies have changed.)

For measuring less than a Gauss, here's an interesting circuit:

Sensitive geomagnetic detector

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066 http//staff.washington.edu/wbeaty/

On 2006-05-31, Ken O

Actually I want to do different typr of coils, i need something to compare strenght. So i do not really need the absolute value, but just an indication what works best.

ken

I have quit doing it now but, I have been building a little Guass meter for several years that slotcar (remember those?) racers use to test and match the little magnets in their motors. Yeah, a lot of those guys are very serious about their racing. Anyway, I was able to wholesale it for $150 so you should have no problem building one yourself on the cheap. The units I made used a ratiometric sensor similar to the ones that have been recommended. My earliest versions used opamps to shift and scale the sensor output that fed a panel meter module. The last ones I made used a sigma delta A/D and a PIC driving a standard LCD. Either works just fine. All have used the same sensor built into a traverse probe. The sensor cost me about $13 ea and were never in stock so I always ordered 25 at a time. Whatever sensor you use, make sure it stays linear throughout the range of the field you expect to encounter. Most of those sensors will run out at anywhere from +- 100-2500 Gauss. I don't know if repeatability is all that important to you, but keep an eye on the temperature specs for sensitivity, offset, and linearity.

Mike

On 2006-06-01, Ken O

If by "strength" you mean "lifting strength", then field strength doesn't necessarily tell you everything. A solenoid can have a strong field, but it picks up nothing. The core is important.

The best way is probably an empirical one. Put a block of steel on a scale and note its weight. Attach your magnet to it and lift up. Watch closely and see what the scale reads just as the magnet breaks loose. Subtract this number from the initial weight and this is how much the magnet was lifting. Note that you may get a different amount of lift using the side of a magnet than using the end, too.

Hope this helps.

Don Kansas City

There's a couple of folders of datasheets at these links.