Measuring the field strength of a permanent magnet

I want to measure the strength of a magnetic field, or more accurately get an idea of how the strength drops with distance away from a neodymium magnet. I picked up a TM192 meter second hand quite cheaply ( https://www.test-meter.co.uk/tenmars-tm-192-triaxial-magnetic-field-meter#product-tabs-navigation ) but it doesn’t seem to do this. If I wobble a magnet in front of it the reading shoots up but if it is static I get virtually no reading. I presume I have the wrong sort of meter, or is it faulty? What sort of meter do I need, or any particular model, ideally cheap.

just for interest, or a specific work-science reason?

https://www.npl.co.uk/electronic-magnetic-materials/magnetics

The TM-192 gauss meter is capable of measuring electromagnetic fields of extra low frequencies (ELF) from 30Hz up to 2000Hz. The TM-192 measures the electromagnetic field radiation intensity produced from a range of equipment including:

The meter you have bough only measures alternating fields (think AC), not static ones (DC) like you will see from your permanent magnet; at least while it is static relative to the meter.

So you would need to find a new meter, that can measure static (DC) levels if you want to measure a fixed magnet.

Possibly something like this if you’re after a budget one:

https://www.aliexpress.com/item/1005005955357382.html

I’m relying on stuff in my head from decades ago here but:

The TM-192 gauss meter is capable of measuring electromagnetic fields of extra low frequencies (ELF) from 30Hz up to 2000Hz

That’s why the magnet creates a reading when you move it but not when static. Static is basically 0hz.

You can still use the meter though if you just need relative measurements rather than absolute. Possibly. If you can standardise how you move the magnet in speed etc (to give you a frequency), then you can measure the reading as you move it away (in distance) then move the magnet horizontally to generate a frequency.

The frequency will be low but the meter is measuring something, as you say, so if at 3cm, say, the reading is consistent, this approach could work.

If you want the actual Gauss measurement, it won’t work.

Edit: There are apps that might work.

https://play.google.com/store/apps/details?id=com.keuwl.gaussmeter

Thanks all. Looks like I need a different meter. All the cheap ones seem to have a resolution of 1 Gauss. Even going up to a few hundred pounds (which I don’t want to do) doesn’t improve it much. The one I have goes to 0.01 mGauss. Quite a difference, although obviously mine doesn’t work for this application.

I really need actual values was hoping for 10 mGauss accuracy

Lazy way: stick a couple of washers onto some sensitive scales and then measure the force exerted by your magnet at different distances.

or more accurately get an idea of how the strength drops with distance away from a neodymium magnet

I’d hazard a guess as ‘inversely with the square of the distance’. That old inverse square law malarkey.

one way to measure it would be to use a nearby wire with a fixed AC current flowing through it and determine the change in deviation of that wire compared with its distance from the magnet

1 gauss is not much so i think you’ll need good kit. But this is west i know

I teach a level physics. You can find a field strength between cheap ceramic magnets quite easily. Put the magnets in a yoke on a balance. Zero the balance. Pass a straight wire between the magnets parallel to the face. Use the balance to measure the force when you pass a known current through the eye

F=BIL

L is the length of wire. The trouble is l estimateas the field drops off beyond the end of the magnet

One magnet makes this problem worse. The further you get from the magnet the wider the field

The problem with using force in steel is that magnetises the steel in a non linear way.

I always enjoyed science at school, and I have a sort of understanding of what’s being discussed here, it’s when numbers start getting involved that brain cells start squeaking and running out of my ears! 🤪

For fun/interest there’s an app for phones (Android, not sure if there’s an iphone version) called ‘physics toolbox’ that allows you to see the output of the various sensors directly, including the magetometer.

I’m not sure how useful it’ll be to the OP but it’s interesting to be able to see the output fron the accelerometers in 3 axis, the mic, the lightmeter, the wifi strength, GPS data (I was surprised to see my phone tracking Russian and Chinese sats), etc.