Are we measureing Guass or Oersted with our home-made DIY magnetometers?

[raygun85]

OK, so I've made my own magnetometer to test the strength of my magnets in pickup making. I can see that this going to be quite useful in the long run for determining lots of variables in my pickup design. There is just one thing I don't understand. I have searched the forums pretty extensively and re-read older threads y'all have contributed to before. However, according to the readings from Magnetic Hold and http://music-electronics-forum.com/t26164/, I'm wondering....

Are we really measuring gauss with our handy-dandy DIY magnetometers? Or are actually measuring oersteds?

Anyone have any thoughts on this? I try to be as scientifically accurate in my research and design of pickups and it would be helpful to know. Because it seems that no matter how we slice the cake, for instance, Alnico V is listed on the websites of many magnetic researchers and manufacturers as being more in the range of 12,000 gauss (12KG); while our handy-dandy DIY magnetometers are giving us readings between 600-800. The information at Magnetic Hold's website seems to indicate that our readings more closely reflect that of oersted than gauss.

Or perhaps we are reading gauss though our mickey-moused readers are incapable of giving us those big kilogauss readings and so we are settling for a relative but otherwise accurate reading?

I'm totally new to all of this so comments are more than welcome. I just want to make sure of what we're actually taking measurements of and what units we should be referencing.

[salvarsan]

Given that Gauss and Oersteds are interconvertible, and that in air vs. vacuum,
the difference between them is 0.37 parts per million, it may not be important.

Within the scope of guitar pickup building, the integrated Hall Effect sensors from Allegro
and Analog Devices have sufficient range (±1500 Gauss) and accuracy (3%).

Greater range and accuracy cost more.

How much do you want to pay?

Tags: B-field, magnetic flux, H-field, magnetizing field, Br, remanent magnetism, Hc, coercivity

[salvarsan]

That 12 kG remanence figure (Br) for Alnico 5 is a limiting value.
You can only make an A5 magnet so long before the field maxes out.

A magnet also has coercivity, Hc, its resistance to demagnetization.
Think of it as a magnetic "stiffness".

Br and Hc determine the magnet's maximum energy, usually expressed as MGOe = mega-gauss x Oersteds x physical constants.

Coercivity values let you estimate how small the magnet can be before it tends to self-DEmagnetize.
This is can be a problem with A2 and A3 pole pieces in old pickups.

[raygun85]

Thanks for the informative and intelligent response. Since my post earlier today, I read some info that basically stated what said about the two units having comparable figures and, basically, being interchangeable. What you mentioned in your second post about the length of an Alnico V and the field maxing out, that is interesting. So, for bar and rod magnets, the measurements are actually much lower than 12KG and our Hall Effect Sensors are giving us accurate measurements? Ok...that makes sense.