Br versus actual measurements

[evansste]

I've bought neodymium magnets, from a particular source, over the course of several years. I often need the strongest magnets that I can get my hands on, so I've always ordered N52 neodymium magnets. Most of my magnets are 2" x 2" x 1" rectangular magnets, which are magnetized through the 1" thickness. I have a gauss meter and have measured the B field of these magnets by placing the probe on the surface of the magnets. I usually get a measurement of around 4200 to 4500 gauss. Is this what I should expect for N52 magnets of this size with these dimensions?

The last magnet which I ordered, looks the same, and has the expected 4500 gauss measurement. However, the box, which it came in, has N42 printed on the side. Has my supplier been scamming me all of this time by selling me N42 magnets, yet claiming they are N52?

I've decided to post this question in this forum because I need the experience of someone who works with these types of magnets. Should I expect a 4500 gauss measurement from an N52 magnet that is 2" x 2" x 1", or does this seem more like the measurement of an N42?

I recognize that the Br, for a magnetic material, will always be much higher than what you can measure on the surface of a magnet. So a Br chart doesn't help me. The experience of someone who works with magnets, and is familiar with these types of measurements, would be very helpful.

Thanks so much for your time, and for any input that anyone is willing to give.

 

[MagMike]

The numbers seem about right for N52, but it'll depend on the construction of the gaussmeter probe you are using.

See if you can locate the location of the Hall sensor inside your probe and use that value as the Z position in the following online calculator:

http://www.dextermag.com/resource-center/magnetic-field-calculators/field-calculations-for-rectangle

I'd recommend using 14.2kG for the Br value.

If it is a critical application and you have serious doubts, you can send a sample to an independent lab for testing.

 

[EdStainless]

If you really want to measure the working field why not use a Helmhotz coil and a flux meter, that would be more representative as it would be the entire magnet being measured.
But either of these measurements is at the open circuit slope. Someone would need to measure them in a permiameter to measure the actual Br.
Then again, since in application you are working at some slope below Br perhaps open circuit is better.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[prex]

I get quite lower values for N42 magnets (4"x4"x1"), so you should be OK.

prex
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[evansste]

Thanks so much, to all of you, for your input. It has all been extremely valuable.

I just wanted to make sure that I'm not being ripped off, and you guys have given me more than enough information to determine that I'm not.

prex, your insight concerning your measurements for a 4"x4"x1" N42 is very helpful since I have no N42 magnets, of a similar size, for which to compare. So that was very helpful.

The gaussmeter, that I'm using, is very simple. I have no trouble finding the Hall sensor since I can actually see the shape of it at the tip of the probe. Based on the calculator that MagMike suggested, my magnets seem to be in good shape.

EdStainless, I hadn't even heard of some of the equipment that you mentioned. It's great to know that such equipment exists should I require more precise measurements. Thanks for the information.

I'm really glad I came to this forum. It has been very helpful to receive input from people who actually work with magnets, and have a good understanding of them. Thanks again to all of you, and it's great to know that my magnet supplier continues to be reputable.

Steven Evans

http://www.BoolEngine.com

 

[MagBen]

As long as you place your Hall prob at the same location (note you will get a higher reading on the concers) and parallel against the surface of magnet, it is unlikely you got a similar reading (4500Gs) from N42 vs N52. There is a considerable difference in Br betwen N42 and N52, and therefore, you will get a considerable different readings with your guess meter. Using the formula Mike offered, and estimating the Hall sensor gap to the surface, the calculated value should pretty much match what you measured.