The Gaussmeter Project
A while ago, a member of the ATIS Stationary Engine List, Ed Stoller and I began discussing the design of a low-cost Gauss Meter kit for engine folks. A Gauss meter is used to tell the strength of magnets and it could be used to test magneto magnets for strength.
What we ended up was an inexpensive meter kit that Ed can supply. It consists of a printed circuit board and all the components (except a 9 to 12 Volt battery) and your digital meter to make the meter work.
To measure a magnet, the sensor (supplied in the kit) is held away from the magnet and the voltage is noted (usually around 2.5V). Now, put the sensor against the magnet and move it until the voltage is at it’s highest (for the South pole) or at it’s lowest (for the North pole).
Subtract the voltage you measured without the magnet from the voltage you got with the magnet and divide by 0.0013 and the result is the strength of the magnet in Gauss.
You can get more information by emailing Ed Stoller at: edstoller@earthlink.net
The meter isn’t linear above about 800 Gauss but will read with reduced accuracy to nearly 1,400 Gauss. This range should be fine for testing old magnets. If the range turns out to not be high enough, a friend can design a little Mu Metal shield to go over the sensor to reduce the sensitivity by a known amount. We’ll check into that later if we have to.
Here’s a picture of the fancy meter I made using the kit Ed
supplies plus some parts I had in my junkpile.
My meter measures South pole magnets only and I made a scale for the
meter so it reads directly in Gauss.
Accuracy isn’t traceable to the National Bureau of Standards but it will
be fine for most applications.
The actual Hall Effect sensor is the little square black thingy at the end of the cable.
The little adjustment to the right of the switch is to set the electrical zero of the meter (“0 Gauss”).
To test the battery, flip the switch down and the meter will read 700 Gauss or more for a good battery.
To test a magnet, hold the probe next to the magnet, flip the switch up and find the strongest reading.
Here's a simplified schematic of my Gaussmeter minus the voltage regulator and on/off switch
August 19, 2003
Ed Stoller writes:
I have been playing with my Magnet Meter and have some observations.
The sensor in the Magnet Meter is specified to be linear over the range from - 800 Gauss ( North ) to + 800 Gauss ( South), that is from .5 to 4.5 Volts output. The sensor output is in saturation from 0 to .030 Volts (North) and from 4.97 to 5 Volts(South) . The question is what happens above 800 Gauss until it really saturates ?
To answer the question, I set up an Electro magnet with a variable DC power supply to see if the Electro magnet was linear with respect to current and to map the magnetic field to both extremes. The data was collected at 2 milli amp increments form 15 to 60 milli amps in both directions and put into a spread sheet (Excel). The spread sheet made it easy to convert the output Volts to Gauss and make a graph.
The graph clearly indicates the Electro magnet was linear to 800 Gauss and well beyond, to 960 Gauss. So what does this mean?
Keep in mind that once the sensor is in saturation, you really can't tell it by varying the magnetic field, By looking at the graph and picking the last point that was still in the linear region, I conclude that the measurements are valid any where from .2 Volts to 4.9 Volts. Your Magnet Meter should work fine up to 960 Gauss vice the advertised 800.
Have fun,
ED
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Lyle Nelson has made his version of the gauss meter. Here are a couple of picturesof his creation. He used the housing from a felt pen and a telephone cord.
If enough guys make meters for themselves, I will publish a database of magnet strengths for various magnetos here so other guys can use their meter to see if their magnets are up to par.
Comments are appreciated. You can send them to either:
Ed Stoller: edstoller@earthlink.net
or me: edurand@mchsi.com
Have fun!
Elden