Talk-Polywell.org

The cheapest certifiable gaussmeter ($380) that I have been able to find is at
http://www.trifield.com/gauss_meter.htm

I had been looking at an auction of several high end gaussmeters (without probes) where the probes themselves are an order of magnitude more expensive than the above.

That should be very helpful with field mapping.

A small/low current WB model could be built that could be very helpful in confirming computer codes.

You can easily build your own these days. Check out the Alegro A13xx series of hall sensors. I've used them to map fields fairly well.

drmike wrote:You can easily build your own these days. Check out the Alegro A13xx series of hall sensors. I've used them to map fields fairly well.

Building another device is a side track that I am trying to avoid. I had looked at Analog Devices AD22151 which is a similar sensor but was going to go that route only as a last resort. My main concern is that these devices are made as trigger sensors (detect an edge between two relative voltages). They're not made as absolute measurement devices and have no standardization traceback. In my particular test I need a referenced measurement. They also need a microcontroller to interface to a computer system. I have a number of microcontrollers sitting around with USB interface capability so I was thinking of ordering several AD22151s and lash together a physical stack so that multiple close spaced measurements could be taken. Then I would have a set of relative measurements that might provide some information.

Most Hall sensors are intended for position sensing and have the high hysteresis, but that is a deliberate tweak. I can't remember which one of the Allegro Hall sensors I used, but it was specifically an analog sensor, and nicely linear. It was also quite flat. Without calibration, it should be reasonably accurate just setting it up per the data sheet.

As I recall, it was not quite flat enough ... Richard Hull (fusor.net) gave me a 1 kilogauss calibrator, a permanant magnet device for checking magnetometer probes which had a very uniform field across a narrow gap into which you inserted the probe. The Allegro chip would not quite squeeze in, but might have with just a pinch of sanding. I left the probe calibrator with EMC2.

Our company calibrates magnetometers routinely (down in the <1 gauss range, for compasses). We use a Helmholtz Coil. It is very easy to build one of these at a scale suitable for calibrating gaussmeters, and it is just a matter of putting in enough current. In fact, a truncube magrid is almost the same as a 3-axis Helmholtz coil, except you would turn one magnet's polarity around. The relationship between magnetic field in a Helmholtz coil is a function of turns, amps, and dimensions, and well-documented, the data found readily on-line. If you have a good ammeter and are qualified to build a magrid, you can build a magnetic field calibrator.

Thanks Tom - I like that idea for calibration. Most of the stuff I've done hasn't really needed good calibration. That sounds like a great way to do it.