# Measuring magnets



## Patom (Jan 13, 2007)

Hi guys,
I've been lurking around here for a long while. Probably longer than most.You guys are a excellent source of info.

I've hit a sort of cross roads. 
I found this project, used it and am wondering if it has any value. 

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p030.shtml

Tell me what you think. Can this actually work to match magnets?

Thanks,
Tom


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## SwamperGene (Dec 1, 2003)

Yes, in fact BRP sells a Magnet Matcher that is similarly designed.

It's another example of "relative" matching, where you don't get a true gauss reading, you simply comparing mags against a set reference. I've been doing it using my pocket scale, a steel slide bar out of an old scanner, and legos (lol), and it gives me the same results using a batch I did with the Magnet Matcher.


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## 1976Cordoba (Sep 20, 2000)

Patom said:


> http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p030.shtml
> 
> Thanks,
> Tom


Welcome, officially then, Tom! :wave:

And there were just too many words at that link for me, so maybe someone else can add their input. Sorry! :freak:


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## Patom (Jan 13, 2007)

I admit I didn't read all of them until I built it and it didn't work!!


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## Patom (Jan 13, 2007)

Thanks Gene for the reply. 

I found the magnet matcher after I built this and wondered if it was the same technology.


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## tjetracer (Mar 20, 2003)

The BRP Magnet macther is the same technology with some advances. The design in question uses a 5mV/G sensor which maxes out well below the strength of most ceramic magnets. You can measure basic tjet mags but above that you will saturate the sensor. It won't be able to do JL magnets. You will need to put a spacer in front of it to increase the range. The reading range will also be low since the sensor will only outout a small DC voltage. An amplifier is needed to increase the range for better use. One last thing is that the output reading will center around 2.55 volts so all plus or minus reading will have to be subtracted from that value to show the true strength of the magnet. Get the calculator out. The BRP magnet matcher goes down to below 1mV/G and has all the features I mentioned above. I made sure I made it that way.
Thanks
Jerry
Bowman Racing Products


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## T-Jet Racer (Nov 16, 2006)

This is a great article, I also read somewhere that you can take your reed switch, glue it onto a ruler, hook up you ohm meter and slide the magnet up the ruler till it picks the switch. see where it was on the ruler then match it with the next one by the distance till it made up the reed switch. probably not as good as this device though...


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## SwamperGene (Dec 1, 2003)

T-Jet Racer said:


> This is a great article, I also read somewhere that you can take your reed switch, glue it onto a ruler, hook up you ohm meter and slide the magnet up the ruler till it picks the switch. see where it was on the ruler then match it with the next one by the distance till it made up the reed switch. probably not as good as this device though...


 
LOL I was just gonna post that, I tried that idea after seeing a gizmo that used a plastic ruler and compass. I simply used a reed switch with a multimeter set to audible continuity test. Slide the mag til it beeps. You can do it on a piece of paper for that matter, marking the "stop" position on the paper for each test. The only problem I had was that any tiny change in angle of the mag can make a big difference in the reed's response. It'd work great though if a jig was made up to keep the mag precisely oriented to the reed. The only other problem is that reed reaction varies with temperature, so any matches made should be confirmed at the same time as opposed to marking them and putting them aside.


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## Patom (Jan 13, 2007)

More honesty:
I have four kids and spring is science fair season. Like any good slot car enthusiast, I always look for ways to expand the hobby.(obsession?) 
I saw the magnet matcher somewhere on the bay and already have the BRP site bookmarked. 
Thanks again guys,
Tom


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## oldraceral (Dec 1, 2005)

Here's another article on the same subject.
http://my.execpc.com/~rhoadley/magmeter.htm
I made a simple jig out of an old tjet chassis fastened to a small block of wood. Attached the voltage regulator to the back of the chassis and glued the Hall effect device into the middle of the chassis, approximately at the armature shaft hole. With everything mounted solidly, it's easy to put a magnet into the chassis, get a reading, calculate the strength, mark the magnet and do the next one. If you set up a little assembly line it's very quick.
The most important thing is as tjetracer said, if you place the magnets too close they will saturate the device and all read the same. (Learned from experience, that's why I built the little jig.)
I've also been trying 440X2 motor mags and traction mags in this. It does work, but a purpose-built jig will give more consistant readings.
My local Radio Shack had to order the parts, but they are rather inexpensive.


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## T-Jet Racer (Nov 16, 2006)

oldraceral said:


> Here's another article on the same subject.
> http://my.execpc.com/~rhoadley/magmeter.htm
> I made a simple jig out of an old tjet chassis fastened to a small block of wood. Attached the voltage regulator to the back of the chassis and glued the Hall effect device into the middle of the chassis, approximately at the armature shaft hole. With everything mounted solidly, it's easy to put a magnet into the chassis, get a reading, calculate the strength, mark the magnet and do the next one. If you set up a little assembly line it's very quick.
> The most important thing is as tjetracer said, if you place the magnets too close they will saturate the device and all read the same. (Learned from experience, that's why I built the little jig.)
> ...



thats a great idea using a bad chassis as a jig to hold the magnet at a fixed position. It will keep all the measurements at the identical distance everytime.

:thumbsup:


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## Hornet (Dec 1, 2005)

A bolt and some washers works good,a small container filled with steal shot,will also do a good job,and they're simple:woohoo:


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