Calibrating the gradiometer to measure weak magnetic field

[manav_singal]

Hi,

I had built Fluxgate Magnetometer based on Carl's article.

http://www.geotech1.com/pages/mag/pr.../fmx1/fmx1.pdf

I ordered the parts from Fat Quarters Software and received the complete package. I assembled the complete equipment based on specification provided and the equipment is working in terms of detecting weak magnetic fields with two sensors oriented in same direction with 18" apart in a plastic enclosure. I am not using the feedback point of Fluxgate sensors.

The main challenge I am facing is to calibrate the VCO output ranging from around 250 Hz to 1124 Hz range as I don't have any reference field.

The oscilloscope (VCO output) doesn't show any frequency beyond this range in case of no field or high field near a static magnet.

I intend to measure the field in micro Tesla range and calibrate the output of VCO into a display to measure the oscillating magnetic field intensity around a circular coil with multiple turns and measure the gradient based on distance from dipole moment.

Please help in providing some pointers and your prompt reply would be highly appreciated.

Thanks,

Manav Singal

[Krzysztof]

Hi!
1. Do you have anything at all on the output FGM3?
2. Note that the FGM3 are not calibrated! It is a generator of magnetoiduktive MI. Everyone is different.
3. At the output of IC1 have digitally the size differential frequency (8bit).
4. See the discussion of fmx1 in the magnetometer. search for the order to get out of IC1.
5. In General, fmx1 is an indicator of the difference of the magnetic field, there is a measure of the!
6. Do not give FGM3 around a strong magnet, do not want to have bad surprises!
7. Adjusting VCO is difficult and has a small input voltage range.
8. To measure small magnetic fields, measurement using frequency two FGM3 (one under the conditions of constant-for example in the Helmholtz).
The sensitivity of the FGM3 is of the order of 10nT-this is not a lot.
Best regards Chris.

[manav_singal]

Thanks for reply. I am looking for how to calibrate magnetic Flux strength with respect to VCO output frequency. I am able to get minimum 10 Hz(with almost no magnetic field around) and maximum 400 Hz (near a electromagnetic coil) delta frequency between two sensors with AC voltage given to electromagnetic coil. My question is what is magnetic flux correspond to 400 Hz and 10 Hz of VCO output. please let me know.

[Krzysztof]

Hi.
See post #2 point 2, 5.
It is not for calibration! It's just an indicator!
Sorry for my bad English; good read!
Best regards. Chris.

[Krzysztof]

Manav_signal
Point 2 #2. Note that the FGM3 are not calibrated! It is a generator of magnetoiduktive MI. Everyone is different.
See the description of the FGM3 (frequency distribution).
Take a similar graph with zero field by Helmholtz coil. Then by adding current (mA) to Helmholtz coil current you have requested for calibration.
It applies only and exclusively each piece separately FGM3.
It cannot be used in a simple differential system (FMX1)!
This can be done in pure digital system, knowing the characteristics of the microprocessor is a convert.
Only it will be professional-no DIY.
Best regards Chris.