fluxgate magnetometer

Try

Speake & Co Llanfapley

or

Autonnic Components

Fluxgating seems to be a British speciality.

Buy my design from Honeywell Sensors Division >:-} ...Jim Thompson

Might use that in the autopilot (ardupilot Pixhawk) 3-axis digital compass Honeywell HMC5883L but I don't think it can work for geomagnetics :D

cheers, Jamie

I meant to say geomagnetics for mineralogy applications

My very rough idea so far is to put the magnetometer at the wing tip of an electric brushless motor powered fixed wing UAV, and then for the sensitive magnetic field sampling, cut the electrical power to the main electronics (brushless motor etc) for a short sample window and glide during each sample! Rough idea..

Is that actually a fluxgate? I recall the Honeywell being different physics.

You remember incorrectly. ...Jim Thompson

Got a link to a product?

The HMC100x series is not fluxgate technology. It's a strange magnetoresistive thing that needs big periodic "strap driver" reset pulses to cancel drift. I was considering them for a project, but they are way too weird.

You may be out of luck here. A windmilling electric motor will still have magnetic fields that IMHO will override the local variations of the geomagnetic field.

On a sunny day (Fri, 21 Nov 2014 17:06:28 -0800) it happened Jamie M wrote in :

What about the permanent magnets? Fluxgates are affected by any iron in the vicinity, even more so by any magnets, You can easily make your own, and find out:

Maybe use a shunt motor, so when you measure the field, turn off the magnetizing field to the rotor and freewheel the stator windings

Cheers

Klaus

Most brushless speed controllers have the option to brake the motor by shorting its windings. This brake system is very effective and can easily stop the propeller even at cruising speed.

yeah, but how do you turn off the permanent magnets?

Using an internal combustion engine seems a whole lot simpler, eg: those glow-plug motors have no magnets at all.

a towed glider may be another option.

Perhaps a magnetic reluctance motor, all though there may be some remaining magnetization of the rotor that can influence the measurement

Regards

Klaus

think 'gradiometer' as in, put one sensor away from 'noise' source and put the other closer to the 'noise' source. To some degree the two sensors will be in the field you WANT to measure, a 'uniform' field. But the noise source field will be dropping at the rate of inverse cube [hoepfully] so you can remove some of its effects.

In geologic surveys, the sensors require pretty sensitive sensors that measure down to the earth's magnetic field noise floor. After all the rule of thumb is that 1 ton of iron shifts the field 1 gamma at 100 feet [from memory, but think that's about right, I have a list of magnetic field SHIFT vs MATERIAL vs DISTANCE]

a gamma is a nT, earth's field is around 50,000nT a ton of iron is a lot of metal at a distance, so you see the problem with performing a geologic survey 'carrying' your sensor around. I remember hearing about most airborne geologic surveys are performed by trailling the sensor out on a wire troling out the back of the airplane extending beaucoup distance away from the plane's fuselage. Used in the C ?? airplane for submarine searches. I remember the military seeking solutions to problems that used such a sensor, either containing stabilizing methodology, or advanced DSP algorithms to remove 'flutter' of the sensor as it was dragged along at flight speed.

Not sure but I think most readily available fluxgate sensors have a noise floor too high to do a geologic survey, The technology can only be used as a great compass. Oil industry uses SQUIDs for field exploration. [Note: I designed a portable, 18 inch diameter magnetic field measuring system with a noise floor about 1/10th earth's noise floor so it was capable of replacing SQUIDs in field exploration at a much lower cost, WITHOUT need for being super cooled or getting easily saturating from AC mains.]

One technology you did NOT mention is GMR sensors: They're small 'point' sensors [easy to make a gradiometer] and their noise floor can get down low [not as low as possible, but low] Forget about any attempt to use Hall Effect. They're current hogs and noisey.

NVE Corporation (800) GMR-7141 (800) 467-7141

are they GMR sensors?

did you contact NVE Corporation (800) GMR-7141 (800) 467-7141

very knowledgeable people.

The Honeywell sensors are some sort of magnetoresistive thing:

definitely not fluxgates.

Ask Jim for details of how the Honeywell things actually work. He surely remembers.

Most brushless speed controllers have the option to brake the motor by shorting its windings. This brake system is very effective and can easily stop the propeller even at cruising speed.