digital proton precession magnetometer

[salman]

i m engineering student.im making a proton precession magnetometer.i m facing problem in my sensor.the sensor is not responnding as desired like taking a magnet close to it does not make any difference in the output of the agnetometer.i have taken idea from DAN HOMEGROWN site about proton precession
anybody having any idea please contact me as soon as possble

[Willy Bayot]

Re: digital proton precession magnetometer

Did you test first your amplification chain?
You probably know that the signal generated by an average sensor is in the order of 1µV lasting a few seconds after cutting the polarization current. There is, to my best knowledge, no way to directly measure this voltage directly at the output of the sensor itself. Thus, you MUST BE SURE that, at least, your pre-amp is working well and that there is NO auto-oscillation of your chain at the base frequency of the filter.
Moreover, the change in precession frequency, even with a magnet close to the sensor, is VERY small. How do you measure its variations to tell that there is none?
The schematic (basic) diagram of Dan is CRUDE. How did you practically implement it?
This principle is a 'differential magnetometer' like the one described in more details by Phil Barnes. This principle supposes that the measuring instruments are your own 'ears' to detect a low frequency amplitude beat signal due to the difference between the frequencies generated by TWO sensors mounted in electrical opposition and separated by one meter or so. It is proven that the human ears can only perceive
such a beat at 1 or 0.5 Hz. This represents a gradient of 10 to 15nT which is already a BIG gradient.

Willy

[FJ]

Re: digital proton precession magnetometer

Hi,
I would be interested in where you have found proof that someone can only perceive 1 or .5 hz difference in frequency? I thought that I could do a lot better than that.
Thanks,
FJ

[Willy Bayot]

Re: digital proton precession magnetometer

Differential mags like the ones of Dan or Phil do not generate a low beat frequency but rather a slow AMPLITUDE beat as a result of the ADDING of the output signals from the two sensors.

Human ears are quite sensitive to frequency variations but not so much to amplitude variations.

To get a real beat frequency, you would need TWO distinct amplification chains with a signal mixing (MULTIPLIER) at their output.

You could easily see this from the FFT results of the WAV file made available on the Web by Phil Barnes and captured at the output of his amplifier in presence of a magnetic target.

Willy