I'd like to find/build a simple/affordable gaussmeter that can measure at least 10,000 G.

Thread Starter

Darkstar

Joined Sep 3, 2010
117
I've seen the simple circuits for Hall effect gaussmeters that can measure refrigerator magnets.(such as http://www.coolmagnetman.com/magmeter.htm) but I'm starting at about 3000 Gauss and going up possibly over 10,000 Gauss (maybe near 20K) using industrial permanent ceramic and metal magnets and condensing the field. If it was calibrated that would be nice, but I would settle for something that can give relative measurements, The metal magnet I started with I measured at 6,500 Gauss 40 years ago. I have no idea how much it has decreased over the years. I have some very large ceramic magnets in the 28 to 80 pound range. Their field strength is unknown. Their weight and the large field area makes working with them dangerous. Sometimes it takes all my strength to just slide one magnet across another. I have been able to add and condense the fields of the ceramics and use them to increase the strength of the metal magnet a small amount. I can already do multiple demonstrations seen on YouTube in which people use Neodymium magnets. Mine have a weak surface field, but it's compensated for by the large area, up to 70 sq. in. It is slow going and involves a lot of guesswork and trial and error to find the best arrangement that will produce the strongest additive field. With a real time measuring device I could condense months of work into a few days. I guess I can assume that if it was possible to fiddle with the simple, weak field circuit to allow measurement of strong fields, someone would have done it by now. This project is not worth spending hundreds of dollars for a meter I may use for only a few days. Even the metal available is too expensive. I found a company that sells pure iron (about the least fancy material) and their smallest piece of rod available was 3-4 feet x 1.25'' diam and cost $4072.00. So I can't even use anything better than steel found in hardware stores

Nevertheless, I've done quite well in general. I've slowed a stack of thin aluminum sheets taped into a stack 3/4'' thick in a gap about 1.25'' wide. Narrowing the gap to about 0.03'' increases the field density greatly. With the narrow gap, my aluminum sheets (1'' wide x 0.025'' thick x 8'' long) will free-fall at less than 1''/second. I'm trying to get all I can out of the materials I have without resorting to using Neodymium (which I've shown I don't need anyway.) The best method I've found of measuring relative increase or decrease in lifting capacity of my metal magnets has been to put playing cards between the magnet and a metal weight. If the magnets got stronger they will lift the weight with more cards between the magnet and weight, and vice versa. The magnet poles are separated enough to measure them individually. My best measurement is usually about 77 cards between one magnet pole and a metal weight of 402 grams (just a convenient weight.) I keep trying to improve on these figures.

I saw in an email an article about a sensor called "Magnetoresistance in Magnetic Field Sensors: Applications for TMR Sensors" so I wondered if this was something I could use? Another idea I had, which would be crude, would be to measure voltage drop, or something, of a low voltage AC current in a small coil which I could place where I wanted to make a measurement. It might be able to give relative differences in field strength I think and let me know if I'm setting things up better or worse than other times.

Thanks.
 

Alec_t

Joined Sep 17, 2013
10,746
If all you need is a comparative measurement, you could make a simple sensor by suspending a steel nut on a thread. To do the measurement, (1) Place a reference magnet a known distance A from an origin point vertically below the sensor suspension point and note the thread's angular displacement. (2) Remove the reference magnet. (3) Place the magnet under test at sufficient distance B from the origin point to give an identical angular displacement. The square of B/A should then give the ratio of the strengths of the two magnets (I think :) ).
 

ebeowulf17

Joined Aug 12, 2014
3,055
What I've done when measuring strong magnetic fields was make a jig to hold the magnet a fixed, repeatable distance from the sensor.

I've experimented quite a bit with the Honeywell SS495 and the Hamlin 55100-AP, and had good results with both. Neither sensor will get you to 10,000 Gauss, but field strength measurements are always given in terms of Gauss at a specified distance, so just choose a distance that covers the range of magnetic field strengths you're looking for. In my case, I measured at around 17mm spacing. The magnets I was checking were:

Strong neodymium magnets block N42 , stronger than N40, N38 and N35

Br Max: 13200 gauss

Neodymium magnets Block N42 1" x 0.25" x 0.25" Thick Rare Earth Magnet
http://www.magnet4less.com/product_info.php?products_id=35
 

Thread Starter

Darkstar

Joined Sep 3, 2010
117
@ Alec_t & ebeowulf17
Both your suggestions have the same problems: 1. They are not specific enough. 2. my magnets are huge by normal standards so the surrounding field can completely enclose any smaller local variations within the overall field. I've tried using a compass but it will reverse up to 5 feet away. Up close it is held immobile. That's what would happen if I brought your designs too close. They would measure a distant field but get too close and the exponentially increasing field suddenly jumps. I need to know the surface field density where I want to connect the magnet I'm trying to make stronger. The only way to make one stronger is to put it into a stronger field so I have to know where that contact point is. So far using playing cards has been the best way to quantitatively measure the strength, but I can't pick up 100 lbs of magnet in one hand, hold the cards in the other to see if it will lift my weight. It has its limitations. Two other things hindering me are that I don't have good, high permeability metal, and I don't have a shop to shape it so that it concentrates the field. While it's true magnetic fields prefer to travel in ferrous metals rather than in air, their strength does peter out over distance and most steel I can find isn't made pure enough so it weakens the field a lot. I tried using metal bars to guide the field to a place where I could attach my test magnet. That worked a little at best. Air gaps between metal or metal and magnet are like high resistance points in a circuit. Good surface contact is best. Overall, I've tried about 80 different configurations of magnets and metal. In some cases putting metal over a pole face can "collect" field lines there for me to tap off. At other times it's best to leave the cover plate off and let the magnets touch directly. I try to use the original yokes when possible since these were expensive magnets and would have come with good metal, but these yokes are over 1/2'' thick. One weighs 28 lbs. It can be tricky to position them where they need to be. Without knowing if I'm attaching the magnets to the point of highest field density, all I can do it put it together, leave it for a week then take it apart and hope the strength has gone up and not down. That takes up a lot of time. There are some similarities to electric circuits, such as the field lines following a path of least resistance. But they don't have a start and end like electric charges. Even people in the business don't understand how to calculate everything and they admit to using fudge factors when making magnets with specific field shapes.

Buying a Neodymium would take the fun out of it. As I said I can do the same demonstrations but on a larger scale with weaker magnets. I'll bet there are a lot of kids who don't know what they can do with ordinary magnets if they arrange them correctly.

To give you an idea what this looks like, I'll try to upload a photo of a design that looks like it should work, doesn't do well. In this design there is a long central ceramic magnet (31 lbs, 14'' x 5''x 2.25'', it's half of a much larger unit.) There are 2 ceramic plates on each side (4'' x 7'' x.625'', total 28 lbs.) The silver bars on the sides were supposed to pick up field lines from a large area of the ceramic magnets additive fields and guide the field lines to the small working poles on the legs of a C magnet attached at the end. The bases of the legs touch so no yoke is needed between them (less resistance)
81-3-, Top View.jpg
 

ebeowulf17

Joined Aug 12, 2014
3,055
@ Alec_t & ebeowulf17
Both your suggestions have the same problems: 1. They are not specific enough. 2. my magnets are huge by normal standards so the surrounding field can completely enclose any smaller local variations within the overall field. I've tried using a compass but it will reverse up to 5 feet away. Up close it is held immobile. That's what would happen if I brought your designs too close. They would measure a distant field but get too close and the exponentially increasing field suddenly jumps. I need to know the surface field density where I want to connect the magnet I'm trying to make stronger. The only way to make one stronger is to put it into a stronger field so I have to know where that contact point is. So far using playing cards has been the best way to quantitatively measure the strength, but I can't pick up 100 lbs of magnet in one hand, hold the cards in the other to see if it will lift my weight. It has its limitations. Two other things hindering me are that I don't have good, high permeability metal, and I don't have a shop to shape it so that it concentrates the field. While it's true magnetic fields prefer to travel in ferrous metals rather than in air, their strength does peter out over distance and most steel I can find isn't made pure enough so it weakens the field a lot. I tried using metal bars to guide the field to a place where I could attach my test magnet. That worked a little at best. Air gaps between metal or metal and magnet are like high resistance points in a circuit. Good surface contact is best. Overall, I've tried about 80 different configurations of magnets and metal. In some cases putting metal over a pole face can "collect" field lines there for me to tap off. At other times it's best to leave the cover plate off and let the magnets touch directly. I try to use the original yokes when possible since these were expensive magnets and would have come with good metal, but these yokes are over 1/2'' thick. One weighs 28 lbs. It can be tricky to position them where they need to be. Without knowing if I'm attaching the magnets to the point of highest field density, all I can do it put it together, leave it for a week then take it apart and hope the strength has gone up and not down. That takes up a lot of time. There are some similarities to electric circuits, such as the field lines following a path of least resistance. But they don't have a start and end like electric charges. Even people in the business don't understand how to calculate everything and they admit to using fudge factors when making magnets with specific field shapes.

Buying a Neodymium would take the fun out of it. As I said I can do the same demonstrations but on a larger scale with weaker magnets. I'll bet there are a lot of kids who don't know what they can do with ordinary magnets if they arrange them correctly.

To give you an idea what this looks like, I'll try to upload a photo of a design that looks like it should work, doesn't do well. In this design there is a long central ceramic magnet (31 lbs, 14'' x 5''x 2.25'', it's half of a much larger unit.) There are 2 ceramic plates on each side (4'' x 7'' x.625'', total 28 lbs.) The silver bars on the sides were supposed to pick up field lines from a large area of the ceramic magnets additive fields and guide the field lines to the small working poles on the legs of a C magnet attached at the end. The bases of the legs touch so no yoke is needed between them (less resistance)
View attachment 161153
Just to be clear, the problem is that you need to move the sensor around, very close to the magnet, looking for subtle changes in the field at various positions? You're not just looking to measure changes in overall strength of the whole magnet / assembly, but instead wanting to identify certain key points on the magnet / assembly?
 
Ever thought of making your own probe? I've done Hall effect measurements, so why not use the material as the sensor. The length should be larger than the width. Over the length, you supply a current and over the width you measure a differential voltage. Gold wires were actually attached using silver paint.

What I actually did, was made a holder using a microscope slide with copper foil with an adhesive. I made 5 contacts. On certain materials, I sed a 10 turn potentiometer that could null the other contact. The center tap, was the V contact.

Pogo probes in my holder would make contacts to the copper.

https://order.universitywafer.com/default.aspx?cat=Silicon sells doped wafers.

Home cutting could be an issue. I used a diamond water lubercated saw at work.

There is this wierd low melting point stuff that can be used to attach things. It dissolves in Acetone. It was used to mount samples to the water saw and my sample holder.
 

Thread Starter

Darkstar

Joined Sep 3, 2010
117
Just to be clear, the problem is that you need to move the sensor around, very close to the magnet, looking for subtle changes in the field at various positions? You're not just looking to measure changes in overall strength of the whole magnet / assembly, but instead wanting to identify certain key points on the magnet / assembly?
That's correct. I need to connect to the points with highest field density if I want to increase the strength of the black C magnet legs.
 

Thread Starter

Darkstar

Joined Sep 3, 2010
117

Thread Starter

Darkstar

Joined Sep 3, 2010
117
Ever thought of making your own probe? I've done Hall effect measurements, so why not use the material as the sensor. The length should be larger than the width. Over the length, you supply a current and over the width you measure a differential voltage. Gold wires were actually attached using silver paint.

What I actually did, was made a holder using a microscope slide with copper foil with an adhesive. I made 5 contacts. On certain materials, I sed a 10 turn potentiometer that could null the other contact. The center tap, was the V contact.

Pogo probes in my holder would make contacts to the copper.

https://order.universitywafer.com/default.aspx?cat=Silicon sells doped wafers.

Home cutting could be an issue. I used a diamond water lubercated saw at work.

There is this wierd low melting point stuff that can be used to attach things. It dissolves in Acetone. It was used to mount samples to the water saw and my sample holder.
Oddly enough, I used to be in the electronics industry making microscopic circuits including Hall devices. I have gold wire, silver paint, metal alloys that are liquid just above room temp and wet both glass and plastic, even silicon and gallium arsenide wafers, but not doped. So I should be able to make my own probe. I would need to follow your circuit though. However, considering the above price of a foreign made probe, which would be calibrated, and my lack of fancy electronic measuring equipment, I would choose the calibrated probe. Thanks.
 
However, considering the above price of a foreign made probe, which would be calibrated, and my lack of fancy electronic measuring equipment, I would choose the calibrated probe. Thanks.
So would I. The magnet we used was a 30 killo-gauss electro-magnet.

We lacked the fancy equipment too like the Hall card from Keithley. We improvised. We had two old electrometers that had an analog out. These did a measurement to ground to each side. Then a DVM to subtract them. Instrumentation all depends on the resitivity. So, for the low resistivity stuff, I used a potentiometer to null at the sample. We always had to "borrow" equipment from other set-ups to do the measurements.

We also had a manual current source.

I did hall measurements on Zn3P2 wafers that I synthesized and I did some thin film measurements on CuInSe2. I designed the holders for both. We also had a cryo-chamber for the samples too.
 
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